Chemical Coordination and Integration in Class 11 Biology Free Study Material in PDF

UNIT 1 - NERVOUS SYSTEM I
UNIT 2 - NERVOUS SYSTEM II
UNIT 3 - NERVOUS SYSTEM III
UNIT 4 - ENDOCRINE SYSTEM I
UNIT 5 - ENDOCRINE SYSTEM II
HUMAN PHYSIOLOGY: NEURAL CONTROL AND
COORDINATION, CHEMICAL CONTROL AND
INTEGRATION

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1.1 INTRODUCTION TO THE NERVOUS SYSTEM
The nervous system is specialized for communication of information from one part of the body to
another. The nervous system communicates quickly using neurons, the specialized cells of the
nervous system. Neurons can convey and process information using electrical and chemical signals.
Ultimately, neural communication helps coordinate body activities and ensures we maintain
homeostasis.
The general functions of the nervous system are listed below:
 The nervous system detects changes in our internal and external environment (stimuli) using
specific neurons or specialized cells communicating with neurons called sensory receptors.
 Sensory receptors transform stimuli into electrical signals that our nervous system can
understand. Sensory neurons transmit the electrical signals from the periphery to the central
nervous system (Brain and spinal cord).
 The central nervous system (brain and spinal cord) processes incoming sensory information
to generate “appropriate” responses and also to give us the perception of the stimulus.
 The central nervous system sends commands (electrical signals passed along neurons) out
to the target tissues to produce the response.
Cranial nerves
Peripheral
nervous
system
Brain
Central
nervous
system
Spinal
cord
Spinal nerves
Autonomic nervous
system ganglia
The nervous system consists of two major divisions:
1. The central nervous system (CNS) consists of the brain and the spinal cord, which are
enclosed in the skull and vertebral column, respectively.
2. The peripheral nervous system (PNS) consists of all the neural tissue outside of the brain
and spinal cord. The PNS includes the cranial nerves and spinal nerves, sensory receptors
and ganglia (cell bodies (somas) of neurons that lie outside the CNS). The nerves connect all
other part of the body with the CNS.
UNIT 1 - NERVOUS TISSUE I

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The peripheral nervous system has several subdivisions. It is first divided based on function into
sensory (afferent) and motor (efferent) divisions. Each of these is further subdivided into somatic
and autonomic (visceral) divisions.
The includes
the brain and the spinal cord. which are
enclosed in the skull and vertebral column,
respectively. The CNS is connected to all
other parts of the body by the PNS nerves.
central nervous system (CNS) The of sensory
information, sometimes with higher cognitive
functions to become a conscious perception, may
then lead to either a conscious or subconscious
motor response
central integration
Peripheral Nervous system
peripheral nervous system (PNS)
The
consists of all neural tissue outside of the
brain and spinal cord. The PNS includes
the cranial nerves and spinal nerves,
sensory receptors and ganglia (cell
bodies of neurons that lie outside the
CNS). The PNS brings sensory
information to the CNS or carries motor
output from the CNS to initiate a reaction.
The of the PNS contains
nerves carrying sensory information into the
CNS. The sensory neurons in the sensory or
mixed nerves are also called afferents.
sensory division
The , more commonly
called the autonomic nervous system, controls
the action of cardiac muscle, smooth muscle,
and glands. The responses in these targets
are usually involuntary. Body processes
controlled by the autonomic nervous system
include the contractions of the stomach and
other digestive organs, the heart rate, and
contractions of blood vessels to control blood
pressure and flow though the body.
visceral motor division
The of the PNS contains nerves carrying
information out of the CNS to target organs. The motor
neurons in the motor of mixed nerves are also called efferents.
motor division
The
controls
the voluntary action
of the skeletal
muscles in the body.
The responses in
these targets are
usually voluntary.
somatic motor
division
Includes
The or conduct
signats predominantly from organs contained in the
thoracic and abdominopelvic cavities (ex. heart, lungs,
intestines. bladder, etc). Visceral receptors detect
chunges in the chemical environment of body fluids and
state of internal organs, such as pressure and stretch.
visceral autonomic sensory receptors
The contains neurons located in the
walls of the digestive tract. Some scientists view the
enteric nervous system as a completely independent part
of the nervous system akin to the CNS and PNS since it
can function independently to generate gland secretion
and some aspects of motility and is anatomically discrete.
Other scientists classify the enteric nervous system as a
subdivision of the motor arm of the PNS because it
innervates the same type of effectors (muscles and
glands) the scheme we will use here.
enteric division
Receptors can be neurons, cells of specialized
structures. They monitor and detect changes
to the body`s internal or external environment.
Skeletal muscle
The
are widely distributed
throughout body tissues. They
are located in, and sense
information from the structures
of the skin, muscles, and joints
(including the related structures
of tendons and ligaments).
These somatic senses include
gustation, olfaction, hearing,
equilibrium and vision.
somatic sensory
receptors
The of
are
found in specialized
organs localized in the
head. These special
senses include smell,
taste, sight, hearing
and equilibrium.
receptors
special senses
The
mobilizes body
systems during activity
(‘flight or fight’). It
controls functions that
speed up the heart and
increase energy usage
during emergencies or
times of stress.
sympathetic
division
The
promotes ‘housekeeping’
functions (‘rest and digest’). It
controls functions that have the
opposite effect to reduce heart
rate and decrease overall
energy usage when the body is
returning to normal after an
emergency or during normal
functioning.
parasympathetic division
Start
Effectors are muscles or glands. that respond to moto
nerve impulses.
4
3
2
1
5

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The nerves that comprise the peripheral nervous system can be divided into two divisions based on
whether information is travelling into the CNS or information is leaving the CNS. The sensory
division of the PNS contains nerves carrying sensory information into the CNS. These sensory
nerves are also called afferents (carrying toward). The motor division contains nerves carrying
information out of the CNS to target organs. These motor nerves are also called efferent (carrying
away).
The sensory (afferent) division of the PNS has two subdivisions. The somatic sensory division
conducts signals from receptors located in the skeletal muscles and skin. The visceral or autonomic
sensory division conducts signals predominantly from organs contained in the thoracic and
abdominopelvic cavities (eg. heart, lungs, intestine, bladder etc).
The motor (efferent) division of the PNS is also subdivided into somatic and visceral divisions. The
somatic motor division controls the voluntary actions of the skeletal muscles in the body. The
visceral motor division, more commonly called the autonomic nervous system, controls the
action of cardiac muscle, smooth muscle and glands. The responses in these targets are usually
involuntary.
The autonomic nervous system (ANS) is further subdivided into the sympathetic divisions and the
parasympathetic division. Generally, the sympathetic division is involved in getting the body ready
to respond to a physical challenge or an emotional threat, classified historically as the “fight or flight”
division of the ANS. The parasympathetic division functions in opposition to the sympathetic nervous
system. It is responsible for “rest and digest” activities, and is involved in salivation, digestion,
urination and defecation.
1.2 NERVOUS TISSUE
Salient features
 Originates from the ectoderm.
 Specialized for receiving stimuli, transmit message (conductivity) and coordination by which
two or more organs interact and complement the functions of one another.
 Divided into neurons (nerves) and neuroglia.
1.2.1 Neurons
Neurons are considered the simplest functional unit of nervous tissue. They are long lived (most live
for your entire life), electrically active cells that consume a lot of energy. Neurons are capable of
responding to stimulation, conducting electrical signals, and secreting chemicals that allow them to
communicate with other cells. They cannot usually regenerate if damaged since most neurons do
not retain the ability to divide, as centriole is absent or immaturely present.
Neurons have anatomically and functionally distinct regions for receiving, integrating and sending
information from one part of the body to another.

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Neurofibril
Nucleus of
Schwann cell
Myelin sheath
Neurilemma of
Schwann cell
Axon or axis
cylinder
Axolemma
Node of Ranvier
Telodendria
Cytoplasm
Cell body or
perikaryon
Axon hillock
Dendrites
Axon collateral
Axon or axis
cylinder
Myelin sheath
of schwann cell
Nucleus of
schwann cell
Node of
Ranvier
Neurilemma of
schwann cell
A. Components of neurons
A typical neuron, like that shown above, has two distinct processes or cytoplasmic extensions on
either side of a soma (cell body). On one side of the soma are short, tapering processes called
dendrites (greek denderon – tree). Most neurons have many, highly branched dendrites, although
they may have as few as one. Dendrites receive information from other neurons and transfer it to
the cell body. The greater the number of dendrites, the more information the neuron can collect to
use during decision making.
The soma (cell body) is the region of the neuron that integrates all the incoming information from
the dendrites. The cell body is somewhat spherical in shape and for humans, typically ranges in size
from 5 to 100 microns in diameter. The some contains the neuron’s nucleus and housekeeping
organelles (eg. mitochondria, lysosomes, golgi complex, rough endoplasmic reticulum, etc). The
soma is the only site in a neuron that can synthesize proteins, neurotransmitters, or materials needed
for cell maintenance and repair. ER and ribosome form granules like structure called Nissl’s granules
or Tigroid body, it is here the proteins are actually synthesized in soma. Neurofibrils found in the
cytoplasm help in internal conduction in the soma.

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Axoplasm of axon contains only neurofibrils and mitochondria, no Nissl’s granules. Axon is covered
by axolemma. The terminal end of axon is branched in button shape branches called telodendria.
More mitochondria are found in the telodendria which synthesize acetylcholine (Ach, stored in the
vesicles) with the help of choline acetyl transferase enzyme. Axon is covered by a layer of
phospholipids (sphingomyelin) which is called as medulla or myelin sheath. Medulla is covered by
thin cell membrane, called as neurilemma composed of schwann cells. These schwann cells take
part in the deposition of myelin sheath (myelinogenesis) which acts as an insulator and prevents
leakage of ions.
The axon functions like a cable, relaying electrical signals away from the cell body towards other
neurons or cells (eg. muscles, glands). Axons are also called nerve fibers. The axon has three
regions. As it emerges from the cell body, the axon forms a structure called the axon hillock, a
tapered region that contains the initial segment, or trigger zone, where propagating electrical
signals called action potentials are initiated or generated. The next part of the axon is the longest,
typically a single, thin (.5 to 3 microns), almost constant diameter process that extends to a target.
Axons can be long, short or in between.
Myelinogenesis in the peripheral nervous system (PNS)
In the peripheral nerves, myelinogenesis begins with the deposition of myelin sheath in concentric
layer around the axon by schwann cells. Myelin sheath is discontinuous around the axon. These
interruptions where axon is uncovered by myelin sheath are called nodes of Ranvier.
Myelinogenesis in the central nervous system (CNS)
Neurilemma or schwann cells are not present therefore myelinogenesis process occurs with the
help of oligodendrocytes (neuroglia). Neurons in which myelin sheath is present, are called
medullated or myelinated neurons. In some nerve cells myelin sheath is absent, called as non
mdedullated or non myelinated neurons.
The axon may travel to its target as a single fiber, but some axons form branches called collaterals,
so that they can interact with not just one, but many target cells. The third region of the axon is found
when it reaches its target. Here the axon branches extensively forming the synaptic terminals
(terminal arborization). Each branch ends with a small swelling called a synaptic knob, which
contains vesicles filled with chemical messengers (neurotransmitters) that conduct the signal to
the next cell.
TARGET POINTS
Axon Dendron
Always single One or more
Has neurofibrils but no Nissl’s granules Has both
Long sized process Small sized
Nerve impulse travels away from the cell Nerve impulse travels towards the cell body
body (centrifugal) (centripetal)

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B. Types of neurons
(i) Functional classification
Functional classification of neurons is based on the direction of information flow along axons relative
to the CNS. Based on this criterion, there are 3 types of neurons: sensory neurons, interneurons,
and motor neurons.
Sensory (afferent) neurons are specialized for detection of sensory information (eg. light, pressure,
vibration, temperature, chemicals etc). They transduce physical and chemical stimuli into electrical
signals and transfer this information from the periphery towards the central nervous system for
processing. In many cases, sensory neurons have their dendrites, soma and a part of their axon
residing outside the CNS with axon terminals forming connections (synapses) with other neurons
within the CNS.
Interneurons (association neurons) are located entirely within the central nervous system (with
the dendrites, soma and axons of the cell all residing within the CNS). Interneurons are also referred
to as association neurons, in part because they are sandwiched between sensory and motor neurons
where they integrate and distribute sensory information and coordinate motor output. Interneurons
account for 90% of all neurons of the CNS and therefore are the most numerous neurons in the
body. Almost all interneurons are multipolar.
Motor (efferent) neurons carry impulses or motor commands away from the central nervous system
to effectors/ target organs (eg. muscles and glands). Most motor neuronshave dendrites and cell bodies
in the CNS and axons that exit the CNS to form peripheral nerves that travel to effectors (targets).
Posterior root
ganglion
Cell body
of sensory
neuron
Afferent
(input)
transmission
Spinal cord
Dendrites
Sensory neuron
Efferent
(output)
transmission
Motor neuron
Axon
Interneuron
Input
Output
Effectors
(muscles and
glands)
Receptors
Associative area: The cerebral cortex contains motor area, sensory area and large area (regions)
called associative area responsible for complex function like inter sensory association, memory and
communication.
(ii) Structural classification
The structural classification of neurons is based on the number of processes that extend from the
soma. There are 4 basic neuronal structures like those shown in the figure below though there are
many subtle variations on each theme.

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Bipolar neurons have a single dendrite extending from one side of the cell body and a single axon
extending from the other side. Bipolar neurons are small cells, typically extending for less than 30
microns from dendrite to axon terminal. There are not many true bipolar cells in the body. A few
examples are found in the special sense organs for vision and olfaction (smell).
Unipolar or pseudounipolar neurons have a single process that emanates from the cell body. The
single process has dendrites on one end and the rest of the process is an axon. Most sensory neurons
of the peripheral nervous system are unipolar neurons. The dendrites are located in the periphery,
where stimuli are detected. The sensory information travels on the dendrite towards the soma (usually
located ganglia just outside the CNS). The axon stretches into the CNS at the spinal cord.
Multipolar neurons have two or more dendrites on one side and a single axon on the other side of
the soma. Multipolar neurons are the most common neurons in the CNS. One example are motor
neurons which have dendrites and somas located in the spinal cord and axons that leave the CNS
to innervate skeletal muscles.
Anaxonic neurons are small, stellate (star shaped) cells with processes that all look alike with no
apparent axon. Anaxonic neurons can be found in the central nervous system, the retina, and in the
adrenal medulla. Their functions are not well understood.
Apolar/ nonpolar neuron: No definite Dendron/ axon. Cell process are either
absent or if present are not differentiated in axon and dendrons. Nerve impulse
radiates in all directions. eg. hydra, amacrine cells of retina, horizontal neuron cell.
Motor neuron
Dendrites
Pyramidal neuron
Dendrites
Purkinje cell
Axon Axon
Multipolar neurons
Bipolar neurons
Retinal neuron Olfactory neuron
Unipolar neuron
(touch and pain sensory neuron)
Dendrites
Axon
Dendrites Axon
Anaxonic neuron
(Amacrine cell)
Dendrites
Apolar neuron

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1.2.2 Glial cells
Most neurons are surrounded by glial cells (neuroglia), the other cell type found in the nervous
tissue. Glial cells are the supportive cells of the nervous system and are 10 times more numerous
than neurons. The most well defined role for neuroglia is to provide structure to the delicate nervous
tissue. They fill the space between neurons, serving as mortar or “glue” and thus hold nervous
tissue together. Unlike neurons, glial cells retain the ability to divide throughout one’s lifetime. When
neurons are injured, neuroglia are stimulated to divide and form glial scars. Glial cells have different
shapes and sizes and their processes are indistinguishable in contrast to the distinct axon and
dendrites found in neurons.
There are 6 types of glial cells, 4 types are found in the CNS and 2 types in the PNS. The CNS
neuroglia are: astrocytes; oligodendrocytes; microglia and ependymal cells. The 2 types of
glial cell found only in the peripheral nervous system (PNS) are satellite cells and schwann cells.
Glial cells
are found in
Peripheral nervous system Central nervous system
Contains
Satellite
cells
Schwann
cells
Contains
Oligodendrocytes
Microglia (modified
immune cells) Astrocytes Ependymal cells
Myelin sheaths
Form Form
Scavengers
act as
Substrates for
ATP production
Blood-brain
barrier
Neurotrophic
factors
K , water,
neurotransmittets
+
Source of
neural
stem cells
Barriers
between
compartments
Support
cell bodies
Neurotrophic
factors
Provide
Secrete Help form Secrete Take up Create
A. CNS glial cells
Astrocytes are star shaped neuroglia and are the most numerous cells in the central nervous
system. They make up half of all cells in the brain. Astrocytes provide a structurally supportive
framework for neurons with their processes wrapping most non synaptic regions of neurons in gray
matter and covering the entire outer surface of the brain to form the glial pia (connective tissue
meninx) interface. Astrocytes help form the protective blood brain barrier by encircling CNS capillary

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endothelial cells and stimulating the cells to form tight junctions. They help to maintain the
concentration of chemicals in the extracellular space and remove excess signaling molecules.
Astrocytes also react to neural tissue damage by forming scar tissue in the damaged space.
Oligodendrocytes are glial cells of the CNS that wrap and insulate axons and give the CNS white
matter its characteristic glossy, white appearance. Oligodendrocytes have a large soma with up to
15 processes. The processes reach out to axons of nearby neurons and wrap around them (like
wrapping tape around a pencil) forming a high resistance sheath called myelin. Myelin insulates a
small region of the axon (prevents ions from leaking out into the extracellular fluid), which facilitates
signal propagation down the axon towards the synaptic terminal. A single oligodendrocytes process
will wrap axons of numerous different neurons. Processes from many different oligodendrocytes
contribute to the myelin sheath of a single neuron’s axon.
Microglia are small highly mobile, phagocytic neuroglia that protect nervous tissue pathogen infection,
remove debris and waste, and may play a role in remodeling of the synapse that occurs during
development and with learning. About 10 – 15% of CNS glial cells are microglia. Microglia are
derived from monocytes and thus are more closely related to white blood cells than to the other glial
cells. Since cells of the immune system cannot penetrate the blood brain barrier, microglia serve as
brain macrophages, destroying foreign invaders, promoting inflammation and destroying cancer
cells and cells infected with virus. Clusters of microglia in nervous tissue provide pathologists with
evidence of recent injury.
Ependymal cells are cuboidal shaped glial cells that are joined together to form a continuous sheet
lining the fluid-filled ventricles and central canal of the brain and spinal cord. Ependymal cells produce
and secrete cerebrospinal fluid (CSF), the fluid that bathes the tissues of the CNS. The basal side
of the cell has rootlets that anchor the cells to the underlying tissue. The apical surface is marked by
cilia, which helps circulate the CSF.
B. PNS glial cells
The remaining two glial cells, schwann cells and satellite cells, are found solely in the peripheral
nervous system.
Schwann cells are analogous in function to oligodendrocytes (found in the CNS). They insulate the
axons of peripheral nerves in one of two ways. A schwann cell can wind its way round and round the
axon (up to 100 times), while squeezing its cytoplasm out of the way (much like a toothpaste tube
could be wrapped around a pencil), forming a myelin sheath. Like myelinating a single fiber in the
CNS, which requires many oligodendrocytes, a complete myelin sheath in the PNS requires many
schwann cells. Schwann cells can also envelop PNS axons without forming a myelin sheath. Instead
of wrapping a single axon many times, the schwann cell forms an envelope around a bundle of
unmyelinated axons.
Additionally, schwann cells can also assist in the regeneration of a damaged peripheral nerve. If a
peripheral nerve is damaged, it may regenerate if its soma is undamaged and the neurilemma (the
plasma membrane of the schwann cell) enveloping it is intact.

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Satellite cells are found surrounding neural somas in peripheral ganglia (collections of cell bodies
located outside the CNS). Satellite cells resemble CNS astrocytes and are thought to have similar
functions, providing structural support and regulating the chemical environment.
Axons: white and Grey matter
Neuronal axons in the CNS and PNS can be devoid of a glial cell wrap (unmyelinated) or they can
be discontinuously wrapped by glial cells along their entire length (myelinated). In a myelinated
axon, the bare regions where the sheath is interrupted are called Nodes of Ranvier. The myelinated
segments between consecutive nodes of Ranvier are called internodes. The myelin sheath changes
the appearance of axons as well as their electrical properties. Myelinated axons appear white when
viewed by the naked eye in contrast to areas where neuronal cell bodies are concentrated which
appear gray.
1.3 NEUROPHYSIOLOGY
Neurons produce electrical signals as a way of conveying information from one place in the body to
another place very quickly, at speeds up to 100 meters/second (200 miles per hour). These rapidly
travelling electrical signals allow you to perceive sensory stimuli, like the sound of a passing fire
truck blasting its siren. Electrical signals, travelling in different neural pathways, coordinate motor
responses that allow you to move your car out of the way of the fire truck, withdraw your hand from
a dangerously hot pan, and rhythmically contract your diaphragm to breathe. Electrical signals arise
as a result of movement of ions back and forth across the cell membrane of neurons. As ions move
down their electrochemical gradients, they carry their charge with them, creating very miniscule but
physiologically important electrical currents. These ionic currents flowing across membranes are
the basis for the propagating electrical signals that underlie all nervous system functions.
A. Cell membrane voltage
All living, eukaryotic cells have a transmembrane potential (a difference in charges between the
intracellular and extracellular fluid). While the cell is at rest (i.e. unstimulated), the transmembrane
potential is stable and is called the resting membrane potential (RMP). Right at the cell membrane,
there is a little excess negative charge on the inside of the cell membrane and a little excess of
positive charge on the outside. Because separation of charges creates a voltage, a very small probe
on a voltmeter can be used to measure the voltage across the cell membrane. By convention the
voltage outside the cell is set to zero. In a typical cell, the voltage recorded across the membrane is
between – 60 and -90 millivolts (-.06 to -.09 volts) with the negative sign indicating that the inside of
the cell is negative with respect to the outside. Some cells have the ability to transiently alter their
transmembrane potential (excitable cells), while others do not (non-excitable cells).
Non-excitable cells (eg. intestinal epithelial cells) have a stable and unchanging RMP. Excitable
cells, like neuronsand muscle, have a membrane potential that can fluctuate under certain conditions,
with each fluctuation representing a signal produced by the cell. These fluctuations may be small and
local to a region of a cell membrane (often called local or graded potentials) or larger in magnitude

and travel along the length of the cell. These latter potentials, called action potentials, always lead to
some response by the cells. In a neuron, action potentials lead to neurotransmitter release.
B. Neuron resting membrane potential
Ionic composition of the ECF versus the ICF
Ions are not evenly distributed between the inside and the outside of a cell. Sodium is nearly 10
times more concentrated outside the cell than inside. Conversely, potassium is nearly 30 times
more concentrated inside the cell than outside. The uneven distribution of ion leads to concentration
gradients across the cell membrane. Given the opportunity, ions will move down their concentration
gradient (i.e from an area where they are highly concentrated to an area where they are less
concentrated). So, given the chance, sodium ions would move into the cell and potassium ions
would move out of the cell based on their respective concentration gradients.
However, the cell membrane is not freely permeable to ions. Ions cannot freely cross the plasma
membrane because of its structure. The lipid core of the cell membrane is hydrophobic and does
not allow charged molecules to pass through it. Rather the cell membrane is selectively permeable,
meaning it allows certain ions to pass. You know that the ions do not pass directly through the cell
membrane, but rather pass through ion channels. The membrane is permeable to a specific ion if
there are open channels for that ion. Recall that ion channels open and close based on the presence
of electrical or chemical stimuli. Voltage-gated channels open at specific membrane potentials and
are either inactivated (while the stimulus persists) or close when the membrane potential changes.
Ligand-gated channels open when they bind chemicals and close when the chemical is no longer
bound.
At rest, the cell membrane is most permeable to potassium because there are more open potassium
channels at the resting membrane potential than channels for any other ion. As a result, potassium
“leaks” out of the resting cell. The resting membrane is less permeable to sodium, and at rest, a
small amount of sodium “leaks” into the cell.
If these were the only things happening in the resting cell, the resting membrane potential would not
be stable, but rather the net movement of potassium ions would cause the membrane potential to
change. Ions move not only based on their individual concentration gradients, but they also move
based on charge attraction and repulsion. Ions move away from like charges (eg. sodium and
potassium ions move away from each other) and move towards opposite charges (eg. potassium
ions would move toward chloride ions). The net movement of a particular ion is influenced by its
Ion Extracellular fluid (mM) Intracellular fluid (mM)
K+
5 150
Na+
145 15
Cl-
108 10
Ca2+
1 0.0001

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electrochemical gradient (the balance of its concentration gradient and any charge attraction or
repulsion).
One final factor also plays a role in determining the RMP. The sodium potassium pump operates
continually in living cells. At maximum capacity, it pumps 3 sodium ions out of the cell and 2 potassium
ions into the cell, and hydrolyzes 1 ATP to provide the energy for the ion transport.
Sodium
Extracellular space
Potassium
K
+
Na
+
ATP
ADP Pi
Intracellular space
Concentration
+
–
Na
+
+ –
K
+
The sodium potassium pump transports 3 Na to the ECF and 2 K to the ICF
+ +
Cell membrane
The sodium potassium pump is electrogenic (there are an uneven number of charges transported
into and out of the cell resulting in a net charge associated with each exchange cycle). Since 3
sodium ions leave the cell and only 2 potassium ions enter the cell, there is a net negative charge on
the inside of the cell due to the sodium potassium pump.
C. Neuron electrical response
This ion movement produces a change in the membrane voltage around the area of the open channels.
These local shifts in membrane potential are called local (or graded) potentials. Local potentials have
the following characteristics.
They are graded, which means the change in membrane voltage that occurs is proportional to the
size of the stimulus. A stronger stimulus can open more ion channels. A stimulus that lasts for a long
time can either open more ion channels or keep channels open for a longer time. In either case, more
ions are able to cross the cell membrane, which produces a larger change in membrane voltage.
They are decremental, meaning that the signal grows weaker as it moves farther from the site of
stimulation. Ion channels are opened at the site of stimulation and that is where ions move across the
cell membrane. As a result, there isa high concentration of ionsright around the ion channels. Once the
ions cross the membrane, they diffuse away from the channel and there are fewer and fewer ions as
they move away from the open channels. Fewer ionsresults in a smaller change in membrane potential.
They are reversible. If the stimulus comes to an end, the ion channels close and resting membrane
potential is re- established before the signal travels very far.

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They can either excite the cell or inhibit the cell depending on what type of ion channel is opened.
If the stimulus opens a sodium channel, sodium ions enter the cell and deporlarizes (make the
memebrane potential less negative) the membrane around the open channels. If the stimulus opens
a chloride channel, chloride ions enter the cell and make the local membrane potential more negative
than the RMP (hyperpolarizes the cell). Depolarization excites the cell and makes it more likely to
send a signal to other cells. Hyperpolarization inhibits the cell and makes it less likely to send a
signal to other cells.
A stimulus can also affect potassium channels. If the stimulus causes potassium channels to open,
the effect will be hyperpolarization of that area of cell membrane. Potassium leaves the cell through
the open channels, which removes positive charges from the ICF making the inside of the cell more
negative. If the stimulus closes potassium channels, the membrane will depolarize around the closed
channels because fewer potassium ions are leaving the cell.
Neurons generally receive multiple stimuli at the same time – some may be excitatory and others
inhibitory. The overall response of the neuron will depend on the net effect of all the stimuli. In some
cases, the neuron will produce a signal that will travel to other cells. In other cases, no signal will be
sent from the neuron.
D. Action potentials
If there is adequate excitatory stimulation of a neuron, a signal called an action potential is generated.
An action potential is a transient and marked shift in membrane potential that occurs when voltage-
gated ion channels in the membrane open. A series of action potentials can rapidly carry information
from the neural soma along the axon to the axon terminal. A sufficient number of voltage-gated
channels must be present in the cell membrane to initiate an action potential. The dendrites and
most of the soma lack enough voltage gated ion channels for this. However, at the trigger zone,
where the soma interfaces with the axon, there is a high concentration of voltage-gated channels.
To create an action potential in a neuron, an excitatory local potential must reach the trigger zone
and depolarize (a shift in membrane potential making it less negative or even positive) it to the
threshold voltage needed to open the ion channels.
Two types of voltage-gated channel are responsible for the propagating action potentials in most
neurons- a fast Na+
channel (a voltage gated Na+
channel that opens quickly when stimulated) and
a slow K+
channel (a voltage gated K+
channel that opens slowly when stimulated). Let’s take a
closer look at the specific events of an action potential.
Excitatory local potentials reach the trigger zone and depolarize it. If the local potentials depolarize
the membrane to threshold (the membrane voltage at which the voltage gated channels are stimulated
to open), these voltage gated channels begin to open. The fast Na+
channel opens quickly, increasing
the permeability of the membrane to Na+
that flows into the cell down its electrochemical gradient
leading to further depolarization. This causes more fast Na+
channels to open, further depolarizing
the membrane. As the membrane potential reaches 0 mV, the fast Na+
channels become “inactivated”.
A second gate that works like a timer closes the channel. By the time all the fast Na+
channels are
inactivated the membrane voltage has reached its peak.

16
As the fast Na+
channels are being inactivated, the slow K+
channels are finally opening. This increases
the permeability of the membrane to K+
. Potassium ions leave the cell moving down their
electrochemical gradient, and the efflux of positive charge causes the membrane voltage to return
toward the resting membrane potential (repolarization).
Slow K+
channels stay open longer than fast Na+
channels, so more K+
leaves the cell than Na+
entered. The removal of excess potassium ions causes the membrane potential to become more
negative than the resting membrane potential. When this happens, we say the membrane is
hyperpolarized.
Na gates start
opening and some
Na enter into the
axon (K gates are closed)
+
+
+
NEURON INTERIOR
Resting potential;
maintainted by
pump, and permeable
for ions by diffusion
Na -K
K
+ +
+
Na
K
K
+
+
+
gates closed:
gates open, and
more outflux or
Efflux
Many Na
K gates are closed)
+
+
+
Action potential
gates open
and more Na influx.
(
Overshoot
+ ++ ++ ++ +
+ ++ ++ ++ +
2 Na+
+ ++ ++ ++ +
+ ++ ++ ++ +
1
K
+
+ ++ ++ ++ +
+ ++ ++ ++ +
K+
Na+
+ + + ++
+ +
+ + + ++
+ +
Na
+
+ 50
+ 40
+ 30
+ 20
0
- 20
- 40
- 60
- 70
- 80
0 1 2 3 4 5 6 7
Milli seconds
Hyperpolarisation
{
Threshold
level
Depolarisation
Repolarisation
4
3
Membrane
potential
(mv)
E. Action potential refractory period
The duration of time that the membrane is hyperpolarized following an action potential is termed its
refractory period. The refractory period is an interval of time during which that part of the membrane
cannot be excited ( to produce another action potential) or requires a larger than normal stimulus to
be excited. The refractory period is divided into two parts based on whether or not the membrane
can be stimulated to produce an action potential. During the absolute refractory period, the
membrane cannot be stimulated to produce another action potential regardless of the strength of
the stimulus. During the relative refractory period, the membrane can be stimulated to produce
an action potential, but a stronger than normal stimulus is required.

17
The absolute refractory period lasts from the beginning of the action potential (when the membrane
reaches the threshold voltage) until the fast Na+
channels reset to their resting state. As long as the
Na+
channels are open or inactivated, a new action potential cannot be generated.
The relative refractory period continues from the end of the absolute refractory period until the
membrane is no longer hyperpolarized (returns to the resting membrane potential). During
hyperpolarization, slow K+
channels are still open, but are in the process of closing. In order to
stimulate an action potential during this time, a very strong stimulus is needed to overcome the
effect of potassium flowing out of the cell and depolarize the cell.
Previously, we considered the characteristics of local potentials. They are graded, decremental,
reversible, and can either excite or inhibit the membrane. In contrast, action potentials are all or
none, nondecremental, irreversible and always excitatory.
Action potentials within a particular cell are all identical regardless of stimulus strength. If the
membrane at the trigger zone reaches the threshold voltage or a voltage above the threshold, a
maximal action potential will be generated. If the threshold voltage is not attained, no action potential
is generated (no signal is propagated). In this way, action potentials are all-or-none-a cell either fires
a full action potentials or no action potential at all.
The action potential at the axon terminal looks exactly like the action potential that was initially
generated at the trigger zone. Since the signal does not change as it travels the length of the axon
it is non-decremental. It should be noted that the action potential at the axon terminal is not the
same one that originated at the trigger zone, Rather, a series of identical action potentials are
generated as the signal travels toward the axon terminal.
If the membrane reaches threshold, an action potential will be initiated and the signal will be
propagated down the entire axon. Once the events are set in motion there is no stopping them. The
process is irreversible.
In contrast to local potentials, which can either excite or inhibit the membrane, action potentials are
all excitatory (cause an initial depolarization of the membrane).
F. Synapses
A synapse is the structure that allows a neuron to pass an electrical or chemical signal to another
cell.
The cell that delivers the signal to the synapse is the presynaptic cell. The cell that will receive the
signal once it crosses the synapse is the postsynaptic cell. Since most neural pathways contain
several neurons, a postsynaptic neuron at one synapse may become the presynaptic neuron for
another cell downstream.
A presynaptic neuron can form one of three types of synapses with a postsynaptic neuron. The most
common type of synapse is an axodendritic synapse, where the axon of the presynaptic neuron
synapses with a dendrite of the postsynaptic neuron. If the presynaptic neuron synapses with the
soma of the postsynaptic neuron it is called an axosomatic synapse, and if it synapses with the axon

18
of the postsynaptic cell it is an axoaxonic synapse. Although our illustration shows a single synapse,
neurons typically have many (even 10,000 or more) synapses.
There are two types of synapses found in your body: electrical and chemical. Electrical synapses
allow the direct passage of ions and signaling molecules from cell to cell. In contrast, chemical
synapses do not pass the signal directly from the presynaptic cell to the postsynaptic cell. In a
chemical synapse, an action potential in the presynaptic neuron leads to the release of a chemical
messenger called a neurotransmitter. The neurotransmitter then diffuses across the synapse and
binds to receptors on the postsynaptic cell. Binding of the neurotransmitter leads to the production
of an electrical signal in the postsynaptic cell.
Why does the body have two types of synapses? Each type of synapse has functional advantages
and disadvantages. An electrical synapse passes the signal very quickly, which allows groups of
cells to act in unison. A chemical synapse takes much longer to transmit the signal from one cell to
the next; however, chemical synapses allow neurons to integrate information from multiple presynaptic
neurons, determining whether or not the postsynaptic cell will continue to propagate the signal.
Neurons respond differently based on information transmitted by multiple chemical synapses.
Electrical synapses transmit action potentials via the direct flow of electrical current at Gap
junctions. Gap junctions are formed when two adjacent cells have transmembrane pores that
align. The membranes of the two cells are linked together and the aligned pores form a passage
between the cells. Consequently, several types of molecules and ions are allowed to pass between
the cells. Due to the direct flow of ions and molecules from one cell to another, electrical synapses
allow bidirectional flow of information between cells. Gap junctions are crucial to the functioning of
the cardiac myocytes and smooth muscles.
Closed Open
Connexon
Connexin monomer
Plasma membranes
Intercellular space
2-4 nm space
Hydrophilic channel
Structure of an electrical synapse (gap junction)
Chemical synapses comprise most of the synapses in your body. In a chemical synapse, a synaptic
gap or cleft separates the pre- and the postsynaptic cells. An action potential propagated to the
axon terminal results in the secretion of chemical messengers, called neurotransmitters, from the

19
axon terminals. The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptor
on the cell membrane of the postsynaptic cell. Binding of neurotransmitter ot the receptor proteins
on the postsynaptic cell leads to a transient change in the postsynaptic cells membrane potential.
Microtubule
Cytoplasm
Mitochondrion
Presynaptic
neuron Synaptic vesicle
Presynaptic
neuron
Ions flow through
gap junction channels
Neurotransmitter released
Gap
junction
Postsynaptic
neuron
Postsynaptic
neuron
Presynaptic
membrane
Synaptic
vesicle fusing Presynaptic membrane
Postsynaptic
membrane Gap junction channels
Synaptic
cleft
Postsynaptic
neurotransmitter
receptor
Ions flow through
postsynaptic
channels
Postsynaptic
membrane
Structure of a chemical synapse
The process of synaptic transmission at a chemical synapse between two neurons follows these steps:
 An action potential, propagating along the axon of a presynaptic neuron, arrives at the axon
terminal.
 The depolarization of the axolemma (the plasma membrane of the axon) at the axon terminal
opens Ca2+
channels and Ca2+
diffuses into the axon terminal.
 Ca2+
bind with calmodulin, the ubiquitous intracellular calcium receptor, causing the synaptic
vesicles to migrate and to fuse with the presynaptic membrane.
 The neurotransmitter is released into the synaptic cleft by the process of exocytosis.
 The neurotransmitter diffuses across the synaptic cleft and binds with receptors on the
postsynaptic membrane.
 Binding of the neurotransmitters to the postsynaptic receptors causes a response in the
postsynaptic cell,
 The response can be of two kinds:

20
1. A neurotransmitter may bind to a receptor that is associated with a specific ion channel
which, when opened, allows for diffusion of an ion through the channel. If Na+
channels
are opened, Na+
rapidly diffuses into the postsynaptic cell and depolarizes the membrane
towards the threshold for an action potential. If K+
channels are opened, K+
diffuses out of
the cell, depressing the membrane polarity below its resting potential (hyperpolarization).
If Cl-
channels are opened, Cl-
moves into the cell leading to hyperpolarization.
2. The neurotransmitter may bind to a transmembrane receptor protein, causing it to activate
a G protein on the inside surface of the postsynaptic membrane. A cascade of events
leads to the appearance of a second messenger (calcium ion, cyclic AMP (cAMP), or IP3
)
in the cell. Second messengers can have diverse effect on the cell ranging from opening
an ion channel to changing cell metabolism to initiating transcription of new proteins.
TARGET POINTS
 When the AP develops in presynaptic membrane. It becomes permeable for Ca++
. Ca++
enters
in and vesicles burst due to the stimulation and release neurotransmitters (Ach) in synaptic
cleft. Ach reaches the post synaptic membrane via synaptic cleft and bind to receptors. It
develops excitatory post synaptic potential (EPSP). EPSP develop due to opening of Na+
gated channels. Cholinesterase enzyme is found in the postsynaptic membrane. This enzyme
decomposes the Ach into choline and acetate.
 Neuro-inhibitory transmitter (GABA) binds with postsynaptic membrane to open the Cl-
gated
channels and hyperpolarization of neuron occurs. Now the potential is called inhibitory post
synaptic potential (IPSP) and further nerve conduction is blocked.
 In human brain more than 100 billion neurons are present.
 Each neuron connects with 25,000 other cells.
 Glycine is neuro-inhibitory hormone present in spinal cord.
 Glutamate is an excitatory amino acid.
 Physiological properties of nerve fibers are detected by cathode ray oscilloscope.
Stimulates impulse at synapse
Eg. acetyl choline (Ach),
nor-epinephrine or
nor-adrenaline or sympathetin
Neurotransmitters Neurohumors Neurohormones
or or
Stimulatory Inhibitory
Inhibit impulse at synapse
Eg. GABA (Gamma Amino
Butyric Acid), dopamine, glycine

21
 The velocity of nerve impulse is 5 to 50 times faster in myelinated nerve fibers than in non
myelinated nerve-fibers.
 In mammals, the speed of nerve impulse is 100 – 130 m/sec (maximum). In frog, the speed of
nerve impulse is 30 m/sec. in reptiles the speed is 15 – 35 m/sec.
 Acetylcholinesterase enzyme helps in the dissociation of acetylcholine.
 In the form of inhibitory neurohormones. GABA (gamma amino butyric acid) is present.
 Acetylcholine is synthesized by the mitochondria.
 For the conduction of nerve impulses, Na+
is necessary.
 The marking of brain waves is done through E.E.G i.e. electro encephalo gram.
 Curare: A drug which blocks acetylcholine on skeletal muscles to be used by a surgeon for
keeping the muscle relaxed during operation.

22
1. A motor nerve carries impulses from
a) Cranial nerves to effectors
b) Effectors to cranial nerves
c) Effectors to central nervous system
d) Central nervous system to effectors
2. Clusters of neuron cell bodies embedded
in the white matter of the brain are referred
to as
a) Nuclei b) Gyri
c) Sulci d) Ganglia
3. Which part of nervous system is activated
under stress?
a) Autonomous nervous system
b) Parasympathetic nervous system
c) Sympathetic nervous system
d) Spinal cord
4. A nerve conveying impulses from a tissue
to nerve center is
a) Afferent b) Efferent
c) Mixed d) None of these
5. The nerves are made up exclusively from
the
a) Dendrons b) Axons
c) Nodes of Ranvier d) Nissl’s body
6. Certain kinds of stimuli produce responses
without conscious thinking. They are
a) Reflex b) Conditioning
c) Synapse d) None of these
7. Transmission of nerve impulse at synapses
is a
a) Biological process
b) Physical process
c) Chemical process
d) Mechanical process
Simple Questions
8. The functional connection between two
neurons is called
a) Synapse b) Synapsis
c) Chiasma d) Chiasmata
9. A polarized neuron is the one that is
a) Conducting stimulus
b) At resting potential
c) Having action potential
d) None of these
10. Which one does not involve brain?
a) Spinal reflex b) Cerebral reflex
c) Cranial reflex d) Voluntary reflex
11. Speed of impulse on nerves in mammals is
a) 1 m/s b) 100 m/s
c) 1000 m/s d) None of these
12. Four healthy people in their twenties got
involved in injuries resulting in damage and
death of a few cells of the following. Which
of the cells are least likely to be replaced by
new cells?
a) Osteocytes
b) Malpighian layer of the skin
c) Liver cells
d) Neurons
13. GABA (gama amino butyric acid) is a
a) Inhibitory neurohormone
b) Transmittory neurohormone
c) Anti-coagulant
d) None
14. _____ prevent the spreading of impulses
within the neighbouring fibers
a) Nodes of Ranvier
b) Synapse
c) Medullary sheaths
d) None of these

23
15. Synaptic delay is the time taken between
the
a) Actual reception of a stimulus and its
perception
b) Reception of a stimulus and the resultant
sensory reaction
c) Release of a neurotransmitter from one
neuron and stimulation of the next
neuron
d) Conduction of nerve impulse across a
neuron
16. Energy transformation during nerve
conduction is chemical to
a) Radiant b) Mechanical
c) Electrical d) Osmotic
17. In a man, abducens nerve is injured. Which
one of the following functions will be
affected?
a) Movement of the eye ball
b) Swallowing
c) Movement of the tongue
d) Movement of the neck
18. Nerve impulses are inherited by nerve fibers
only when the membrane shall become
more permeable to
a) Adrenaline
b) Phosphorus
c) Sodium ions
d) Potassium ions
19. Schwann cells are present where
a) Nerve is covered with myelin sheath
b) Neurilemma and myelin sheath are
discontinuous
c) Myelin sheath is discontinuous
d) Neurilemma is discontinuous
20. Depolarization of axolemma during nerve
conduction takes place because of
a) Equal amount of Na+
and K+
move out
across axolemma
b) Na+
move inside
c) More Na+
outside
d) None
21. Axoplasm is found in
a) Out of nerve fiber
b) Inside nerve fiber
c) Around the nucleus of smooth muscle
fiber
d) Around the nucleus of neuron
22. Neurons producing hormone like
substances are
a) Neurosecretory
b) Sensory
c) Motor
d) Both (a) and (b)
23. Non-myelinated axons differ from
myelinated in that they
a) Are more excitable
b) Lacks nodes of Ranvier
c) Are not capable of regeneration
d) Are not associated with schwann cells
24. Afferent nerve fibers carry impulses from
a) Effector organs to CNS
b) Receptors to CNS
c) CNS to receptors
d) CNS to muscles
25. The one way or unidirectional transmission
of nerve cells is due to
a) Synapses
b) Myelin sheath
c) Membrane polarity
d) Interneurons

24
26. Acetylcholinesterase enzyme splits
acetylcholine into
a) Acetone and choline
b) Acetic acid and choline
c) Amino acid and choline
d) Aspartic acid and acetylcholine
27. Action potential of a nerve cell is generated
by
a) Na+
b) K+
c) Ca++
d) Cl–
28. Resting potential of a nerve is: (in milli volt)
a) + 70 b) + 30
c) – 30 d) – 70
29. Presynaptic membrane is part of
a) Dendron b) Axon Hillock
c) Telodendria d) Soma
30. Nerve fibers are surrounded by an insulating
fatty layer called
a) Adipose sheath b) Myelin sheath
c) Hyaline sheath d) Peritoneum
31. Which one of the following does not act as
a neurotransmitter?
a) Norepinephrine
b) Cortisone
c) Acetylcholine
d) Epinephrine
32. The autonomic nervous system is
responsible for which function (s)?
a) Motor
b) Sensory
c) Motor and sensory
d) None of these
33. The accompanied diagram shows the
structure of neuron. Identify A to E
E
Axon
terminal
D
Myelin
sheath
Axon
C
Nucleus
B
Nissl’s
granules
A
A B C D E
a Nerve Cyton or Schwann Node of Synaptic
fibre cell body cell ranvier knob
b Dend- Cyton or Schwann Node of Synaptic
rites cell body cell ranvier knob
c Dend- Nerve Schwann Node of Synaptic
rites cell cell ranvier knob
d Dend- Cyton or Nerve Node of Synaptic
rites cell body cell ranvier knob
1. Post ganglionic sympathetic cholinergic
innervation seen in
a) Heart
b) Stomach
c) Sweat glands
d) Intestine
Difficult Questions
2. Which system relays information from CNS
a) Somatic neural system
b) Autonomic neural system
c) Peripheral neural system
d) All of these

25
3. Pick out the incorrect statement?
a) Myelinated nerve fibers are found in
spinal and cranial nerve
b) Unmyelinated nerve fiber is enclosed by
a schwann cells
c) In resting stage the axonal membrane
is comparatively more permeable to
potassium ion and nearly impermeable
to sodium ions
d) Axolemma is more permeable to
negatively charged protein present in the
axoplasm
4. When a neuron is in resting state i.e. not
conducting any impulse, the axonal
membrane is
a) Equally permeable to both Na+
and K+
ions
b) Impermeable to both Na+
and K+
ions
c) Comparatively more permeable to K+
ions and nearly impermeable to Na+
ions
d) Comparatively more permeable to Na+
ions and nearly impermeable to K+
ions
5. Saltatory conduction is superior to
uninterrupted conduction because of
a) Less energy required
b) More speed
c) Less Na+
/K+
pump
d) All of the above
6. If dorsal nerve of spinal cord is broken down
then its effect is
a) No impulse is transmitted
b) Impulse is transmitted but slowly
c) Impulse is transmitted fast
d) No effect on impulse
7. An action potential in the nerve fibers is
produced when positive and negative
charges on the outside and the inside of the
axon membrane are reversed, because
a) More K+
enters the axon as compared
to sodium ions leaving it
b) More Na+
enters the axon as compared
to K+
leaving it
c) All K+
leaving the axon
d) All Na+
enters the axon
8. Alzheimer’s disease in humans is
associated with deficiency of
a) Dopamine
b) Glutamic acid
c) Acetylcholine
d) Gamma amino butyric acid (GABA)
9. Which of the following diagram illustrates
the distribution of Na+
and K+
ions in a
section of non myelinated axon which is at
resting potential?
Na high
+
+ + +
– – –
– – –
K high
+
a)
Na high
+
+ + +
– – –
– – –
K low
+
b)
Na low
+
+ + +
– – –
– – –
K high
+
c)
Na low
+
+ + +
– – –
– – –
K low
+
d)
+ + +
+ + +
10. During recovery, nerve fiber becomes
a) Positively charged on outside and
negatively charged on inside
b) Positively charged on both outside and
inside
c) Negatively charged on outside and
positively charged on inside
d) Negatively charged on both outside and
inside

26
11. Which of the following cranial nerves of
human are mixed in nature
a) Vagus and trigeminal
b) Optic and vagus
c) Auditory and olfactory
d) Trochlear and vagus
12. During the transmission of nerve impulse
through a nerve fiber, the potential on the
inner side of the plasma membrane has
which type of electric charge?
a) First positive, then negative and continue
to be negative
b) First negative, then positive and continue
to be positive
c) First positive, then negative and again
back to positive
d) First negative, then positive and again
back to negative
13. Pacinian corpuscles occur in the skin of
certain part of body in mammals are
a) Pain receptor
b) Naked tactile receptors
c) Gland type
d) Encapsulated tactile receptors
14. Neuropeptides are
a) Neurotransmitter chemicals
b) Neuroglia
c) Products of the choroid plexuses
d) Nutrients for brain tissue
15. These processes occurs during
repolarization of nerve fibers
A) Open Na+
channel
B) Closed Na+
channel
C) Closed K+
channel
D) Open K+
channel
a) (B) and (D) b) (A) and (C)
c) (B) and (C) d) (A) and (B)
16. Unidirectional transmission of a nerve
impulse through synapse fiber is due to
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
17. Unipolar nerve cells can be traced in
a) Spinal ganglion cells
b) Retina cell
c) Motor neurons of spinal cord
d) Vertebrate embryo
18. Sympathetic nervous system is also known
as
a) Cranial b) Craniosacral
c) Thoracolumbar d) None of these
19. Which of the following is dominant
intracellular anion?
a) Potassium b) Chloride
c) Phosphate d) Calcium
20. When the axons membrane is positively
charged outside and negatively charged
inside, then the condition is known as
a) Action potential
b) Resting potential
c) Active potential
d) Differential potential
21. When nerve fibers are stimulated the inside
of the membrane becomes
a) Filled with acetylcholine
b) Negatively charged
c) Positively charged
d) Neutral

27
22. Pre ganglionic sympathetic fibers are
a) Andrenergic b) Cholinergic
c) Hypergonic d) Synergic
23. During synaptic transmission of nerve
impulse neurotransmitter (P) is released
from synaptic vesicles by the action of ions
(Q). Choose the correct P and Q
a) P - acetylcholine, Q - Ca2+
b) P - acetylcholine, Q - Na+
c) P - GABA, Q - Na+
d) P - Cholinesterase, Q - Ca2+
24. Which nerve is purely motor?
a) Abducens b) Trigeminal
c) Olfactory d) Vagus
25. Unidirectional transmission of a nerve
impulse through nerve fiber is due to the
fact that
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
26. Ventral root of spinal nerve is composed of
somatic
a) Motor and visceral sensory fibers
b) Sensory and visceral sensory fibers
c) Motor and visceral motor fibers
d) Sensory and visceral motor fibers
27. One of the examples of the action of the
autonomous nervous system is
a) Knee jerk response
b) Pupillary reflex
c) Swallowing of food
d) Peristalsis of the intestines
28. Trigeminal is
a) Motor in nature
b) Sensory
c) Mixed
d) All of these
29. If myelin sheath is continue in myelinated
nerve fiber than what will happen in neuronal
conduction
a) Velocity is increased
b) Conduction is slow
c) Conduction is stopped
d) No effect
30. Sympathetic nerves in mammals develop
from
a) Sacral region
b) Cervical region
c) Thoracic-lumbar region
d) 3rd
, 7th
, 9th
, 10th
cranial nerves
31. During refractory period
a) Nerve transmits impulse very slowly
b) Nerve cannot transmit impulse
c) Nerve transmits impulses very rapidly
d) None of the above

28
ANSWER KEYS
Simple Questions
1.d 2.a 3.c 4.a 5.b 6.a 7.c 8.a 9.b 10.a 11.b 12.d
13.a 14.c 15.c 16.c 17.a 18.c 19.a 20.b 21.b 22.a 23.b 24.b
25.a 26.b 27a 28.d 29.c 30.b 31.b 32.c 33.d
Difficult Questions
1.c 2.c 3.b 4.c 5.d 6.a 7.b 8.c 9.a 10.a 11.a 12.d
13.b 14.a 15.a 16.d 17.a 18.c 19.c 20.b 21.c 22.b 23.a 24.a
25.d 26.c 27.d 28.d 29.c 30.c 31.b

29
1. Which of the following statements is false
about the electrical synapse?
I) At electrical synapses, the membranes
of pre and post synaptic neurons are in
very close proximity.
II) Electrical current can flow directly from
one neuron into the other across the
synapses.
III) Transmission of an impulse across
electrical synapses is very similar to
impulse conduction along single axon.
IV)Electrical synapses pass electrical signal
between cells with the use of Ach.
V) Electrical synapses are fast.
VI)Electrical synapses are rare in our
system.
a) I and II b) Only II
c) Only IV d) Only V
2. Five events in the transmission of nerve
impulse across the synapse are given below
A) Opening of specific ion channels allows
the entry of ions, a new action potential
is generated in the post synaptic neuron.
B) Neurotransmitter binds to the receptor
on post-synaptic membrane.
C) Synaptic vesicle fuses with pre-synaptic
membrane, neurotransmitter releases
into synaptic cleft.
D) Depolarization of presynaptic
membrane.
E) Arrival of action potential at axon
terminal.
In which sequence to the events occur?
a) E  D  C  B  A
b) A  B  C  D  E
c) A  B  D  C  E
d) E  D  C  A  B
DPP - 1
3. Which role of neuron regarding different
kinds of stimuli is absent?
a) Detect b) Receive
c) Transmit d) Protect
4. During repolarization of nerve
a) K+
gates close and Na+
gates open.
b) Na+
channels are closed and K+
channels are opened
c) Both gates remain open
d) Both K+
and Na+
gates are closed
5. Synaptic vesicles are found in
a) Presynaptic neuron
b) Postsynaptic neuron
c) Synaptic cleft
d) None of these
6. When a neuron is not conducting any
impulse i.e. resting, the axonal membrane
is
a) Comparatively more permeable to K+
and impermeable (nearly impermeable)
to Na+
b) Impermeable to negatively charged
proteins present in the axoplasm
c) (a) and (b) both
d) More permeable to Na+
ions than K+
ion
7. Which one of the following statements is
correct?
a) Neither hormones control neural activity
nor the neuron control endocrine activity
b) Endocrine glandsregulate neural activity,
but not vice versa
c) Neurons regulate endocrine activity, but
not vice versa
d) Endocrine glandsregulate neural activity,
and nervous system regulates endocrine
glands

30
8. Which of the statement is false regarding
synapse?
a) Synapse is formed by 2 membrane first
pre-synaptic membrane of synaptic knob
and second post synaptic membrane of
dendrite
b) Synaptic membrane always be
separated by a gap called synaptic cleft
c) Electrical synapse in very similar to
impulse conduction along a single axon
d) In chemical synapse, neurotransmitter
is released and either excitatory or
inhibitory potential is generated on post
synaptic membrane
9. Synapse is bringing together of two
a) Venules b) Veins
c) Arteries d) Neurons
10. Node of Ranvier occurs where
a) Nerve is covered with myelin sheath
b) Neurilemma is discontinuous
c) Neurilemma and myelin sheath are
discontinuous
d) Myelin sheath is discontinuous

31
2.1 CENTRAL NERVOUS SYSTEM
It includes the brain and the spinal cord. It develops from neural tube in intrauterine life (I.U.L).
Anterior part of neural tube develops into brain while caudal part of neural tube develops into spinal
cord. Brain’s approximately 70 – 80% part of brain develops in 2 years of age and complete
development is achieved in 6 years of age and spinal cord develops completely in 4 to 5 years of
age.
2.1.1 Brain
It is situated in cranial box which is made up of 1 frontal bone, 2 parietal bones, 2 temporal bone, 1
occipital bone. The weight of brain of a adult man is 1400 gm and of female is 1250 gm.
A. Brain meninges:
Brain is covered by three membranes of connective tissue termed as meninges or menix.
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Skin of scalp
Periosteum
Bone of skull
Periosteal
Meningeal
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Meninges
UNIT 2 - NERVOUS SYSTEM II
Endosteal
Duramater



Meningeal
Arachnoid
Piamater
Cerebral cortex
Cranial venous sinus
Arachnoid villi
Subdural
space
Subarachnoid
space
Meningeal layer

32
(i) Durameter: The first and the outermost membrane, thick, very strong and non-elastic. It is
made up of collagen fibers and attached with the innermost surface of the cranium. It is
double layered: outer endosteal layer which is closely attached with inner most surface of
cranium and no space is found between skull and durameter (no epidural space). Inner
meningeal layer is related with the other meninges of brain. Both layers are vascular and
generally fused with each other, but at some places these are separated from one another
and form a sinus called cranial venous sinus. These sinuses are filled with venous blood.
(ii) Arachnoid: It is middle, thin and delicate membrane, made up of connective tissue, found
only in mammals. It is non-vascular layer. In front of cranial venous sinus, it becomes folded,
these folds called Arachnoid villi. These villi reabsorb the cerebrospinal fluid (CSF) from
sub arachnoid space and pour it into cranial venous sinuses.
(iii) Piameter: It is innermost, thin and transparent membrane, made up of connective tissue.
Dense network of blood capillaries are found in it. It is firmly adhered to the brain. Piameter
and arachnoid layer at some places fuse together to form leptomeninges. Piameter merges
into sulci of brain and densely adhere to it. At some places it directly merges in the brain and
called telachoroidea which form the choroid plexus in the ventricle of brain.
TARGET POINTS
 Subdural space: Space between durameter and arachnoid that is filled with serous fluid.
 Subarachnoid space: Space between arachnoid and piameter is filled with CSF. Cranial nerves
also pass through this space.
 Meningitis: Any inflammation of menix that may be caused by viruses, bacteria or protozoa.
 In the brain of frog only 2 meninges are present. Arachnoid is absent while in rabbit, man and
mammals – 3 meninges are present.
 Increase in the amount of cerebro spinal fluid is a diseased condition termed as the
hydrocephalus.
 Piameter is the most vascular and conducting and provides nutrition.
 Around the brain of fishes, only one menix is found called “menix primitive”.
B. Cerebrospinal fluid (CSF):
 Clear and alkaline in nature just like lymph.
 Has protein (albumin, globulin), glucose, cholesterol, urea, bicarbonates, sulphates and
chlorides of Na, K. Protein and cholesterol concentration is lesser than plasma and Cl-
concentration is higher than plasma.
 In a healthy man, in 24 hours, 500 ml of CSF is formed and absorbed by arachnoid villi. At a
time total volume of CSF is 150 ml.
 CSF is present in ventricle of brain, subarachnoid space of brain and spinal cord.

33
 Formation: Mainly in choroid
plexus of lateral ventricles,
minor quantity is formed in IIIrd
ventricle and IVth
ventricle.
 Collection of CSF for any
investigation is done by lumbar
puncture (LP). It is done at L3
–
L4
region. Spinal anesthesia is
also given by L.P.
CSF flow through the ventricles
Superior sagittal sinus
Choroid plexus
Interventricular foramen
Third ventricle
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
Arachnoid granulation
Subarachnoid space
Meningeal dura mater
Right lateral ventricle
Functions of CSF:
 Protection of brain: Acts as shock absorbing medium and works as cushion.
 It provides buoyancy to the brain, so net weight of the brain is reduced from about 1.4 kg to
about 0.18 kg.
 Excretion of waste products.
 Endocrine medium for brain to transport hormones to different areas of the brain.
C. Brain divisions
Ependymal
cells
Capillary
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
Cavity of
ventricle
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and bone
(Na , CI, Mg, etc.)
+
Section
of choroid
plexus
Cerebrospinal fluid (CSF) - choroid plexus
Fore brain Cerebrum, diencephalon.
Mid brain Optic lobes and crura cerebri.
Hind brain Pons, Cerebellum, medulla.

34
During embryonic stage, brain develops from three hollow vesicles:
Forebrain develops form prosencephalon
Mid brain develops from mesencephalon
Hind brain develops from rhombencephalon
Rhinencephalon (Olfactory lobe)
Telencephalon (Cerebrum)
Diencephalon
Metencephalon
(Pons, Cerebellum)
Myelencephalon
(Medulla oblongata (M.O.))
C.a. Fore brain
(i) Cerebrum
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Parietal operculum
Frontal operculum
Orbital operculum
Insula
(island
of Reil)
Short gyri
Central sulcus
Limen
Long gyrus
Circular sulcus
Temporal operculum
 First and most developed part of brain. Makes 2/3 part of total brain.
 Consists of two cerebral hemispheres on the dorsal surface. A longitudinal groove (median
fissure) is present between two cerebral hemispheres. Both the cerebral hemispheres are
partially connected with each other by curved thick nerve fibers called corpus callosum.
 Corpus callosum is the largest commissure of brain. It is the exclusive feature of mammals.
 Curved thick band of white nerve fiber are situated between two cerebral hemispheres in the
median fissure.
 Anterior truncated part of corpus callosum is called Genu while posterior truncated part is
called splenium.
 An oblique band is formed by body of corpus callosum and it goes towards Genu called
fornix.

35
 A small cavity is developed among body of callosum, Genu and fornix called as Vth
ventricle
or pseudocoel. This ventricle is covered by a thin membrane called as septum lucidum.
 Each cerebral hemisphere is divided into 5 lobes – Anterior, middle, posterior, lateral and
insula lobes.
– Anterior lobe is also called frontal lobe (largest lobe).
– Middle lobe is also called parietal lobe.
– Central sulcus separates frontal lobe from parietal lobe.
– Lateral lobe or temporal lobe is separated from frontal lobe and parietal lobe by incomplete
sulcus called lateral sulcus.
– Posterior lobe is called occipital lobe, it is separated from parietal lobe by a sulcus called
parieto occipital sulcus.
 In right handed person, left hemisphere is dominant while in left handed person right
hemisphere is dominant.
 Many ridges (gyri) and grooves (sulci) are found on dorsal surface of cerebral hemisphere.
These cover the 2/3 part of cerebrum. Gyri and sulci are more developed in human being
thus, humans are most intelligent living beings.
Septum pellucidum
Head of caudate nucleus
Internal capsule
(anterior limb)
Corpus callosum
(genu)
Anterior hom
(lateral ventricle)
Amygdala
Hippocampus
Fornix
Corpus callosum
(splenium
Foramen
of monro
Putamen
Internal capsule
(genu)
Globus
pallidus
Internal capsule
(posterior limb)
Third ventricle
Thalamus
Tail of caudate nucleus
Transverse section of brain

36
Cingulate gyrus
Interthalamic
adhesion
Septum pellucidum
Corpus callosum
Lateral ventricle
Anterior commissure
Optic nerve and chiasma
Pituitary gland
Mammillary body
Uncum
Pons
Medulla oblongata
Fourth ventricle
Cerebellum
Inferior colliculus
Superior colliculus
Pineal body
Calcarine sulcus
Parietooccipital sulcus
Thalamus
Choroid plexus
Fornix
Central sulcus
Sagittal section of brain
(ii) Diencephalon
 Small and posterior part of fore brain, covered by cerebrum.
 It consists of thalamus, hypothalamus, epithalamus and metathalamus.
 Thalamus forms the upper lateral walls of Diencephalon (80% part). It is the gate keeper of
brain and acts as a relay center. It receives all sensory impulses from all body parts and
these impulses are send to the cerebral cortex.
 Hypothalamus forms the lower or ventral part of Diencephalon. A cross like structure is found
on anterior surface called optic chiasma. Corpus mammillare / Corpus albicans/
mammillary body is found on the posterior part. It is a character of mammalian brain.
 Epithalamus – Forms the roof of diencephalon. Pineal body (Epiphysis cerebri) is found in
epithalamus.
 Metathalamus consists of medial geniculate body and lateral geniculate body. It is located
in the floor of Diencephalon.
C.b. Mid brain
 Small and contracted part of brain.
 Anterior part contains two longitudinal myelinated nerve fibers peduncles called cerebral
peduncles/ crus cerebri / crura cerebri.

37
 Posterior part has four spherical projections called colliculus or optic lobes. Four colliculus
are collectively called as corpora quadrigemina (2 upper and 2 lower).
 Only 2 colliculus or optic lobes are found in mid brain of frog called as corpora bigemina.
Cerebral aqueduct
Tectum
Tegmentum (reticular formation)
Superior colliculus
PAG
CN III
Medial lemniscus
Substantia nigra
Pars compacta
Cerebral peduncle
Occipito, parieto,
temporopontine fibers
Corticospinal fibers
Corticobulbar fibers
Frontopontine fibers
Root fibers
of CN III
Ventral tegmental
area
Crus cerebri
Spinothalamic and
trigeminothalamic tracts
Red nucleus
Transverse section of midbrain
C.c. Hind brain
(i) Pons (Pons varolii)
 Small spherical projection situated below the midbrain and on the upper side of medulla
oblongata.
 Consists of many transverse and longitudinal nerve fibers. Transverse nerve fibers connect
with cerebellum (lateral lobes of cerebellum) while longitudinal fibers connect cerebrum to
M.O.
(ii) Cerebellum
 Made up of 3 lobes [2 lateral lobes and 1 vermis (divided in 9 segments)].
 Both lateral lobes are enlarged and spherical in shape, thus also called cerebellar hemisphere.
Due to this reason, regulation and coordination of voluntary muscle is more developed as
compared to other animals.
 Three cerebellar peduncles are formed; superior cerebellar peduncle is attached with mid
brain. Middle cerebellar peduncle is attached with pons and inferior cerebellar peduncle
is attached with M.O.
(iii) Medulla oblongata (M.O): Posterior part of brain, tubular and cylindrical in shape.

38
TARGET POINTS
 Mid brain, pons and medulla are situated in one axis and called as brain stem.
 The sensory and associated areas determine the shape, color, sound, taste and smell of
any object.
 Motor area regulates muscular contraction.
 Broca’s area: it is known as motor speech area. It is present in the lateral part of the frontal
lobe of the cerebrum. This area translates the written words into speech. If Broca’s area
gets destroyed the animal is unable to speak.
 The temporal lobes of cerebrum regulate the mechanism of hearing.
 Cerebrum is the center of following:
– Intelligence – Experience
– Emotion – Knowledge
– Will power – Voluntary control
– Memory – Laughing and weeping
– Consciousness – Defecation and micturition
 Diencephalon is the center of carbohydrate metabolism and fat metabolism.
 Cerebellum is made up of three layers and in the middle brain lobes of flask shaped cells called
the “Purkinje cells” are found.
D. Internal structure of brain
 One pair of olfactory lobes are small spherical and solid in human brain. No ventricle is found
in it. Both olfactory lobes are separate with each other and embedded into the ventral surface
of both frontal lobes of cerebral hemispheres. Olfactory center is situated in the temporal
lobe.
Optic chiasma
Olfactory lobe
VENTRAL VIEW OF BRAIN
Lateral geniculate
body
Medial geniculate
body
Olfactory centre
Temporal lobe
Olfactory tract
Frontal lobe
Paracoel or
Lateral ventricle
Third ventricle
or diocoel
Cerebral queduct
or aqueduct of
sylvius or Iter
Fourth ventricle
Cerebrum
Diencephalon
Midbrain
Pons
Cerebellum
Medulla
oblongata
L.S. OF BRAIN
Interventricular
foramen or
foramen of
monro

39
 Except mid brain, cerebellum, pons and olfactory lobes complete brain is internally hollow.
 Its cavity is lined by ependymal epithelium (ciliated columnar epithelium). Cavities of brain
are known as ventricles, filled with cerebrospinal fluid (C.S.F).
 In humans, 1st
and 2nd
ventricles are considered as paracoel or lateral ventricles.
 On the posterior side, both paracoel combine with each other and open into cavity of
Diencephalon through an aperture known as Foramen of Monro.
 Cavity of diencephalon is known as 3rd
ventricle or diocoel.
 Atent shaped space or cavity present between anterior pons, medulla and posterior cerebellum
is called 4th
ventricle.
 3rd
and 4th
ventricles are connected with each other through a hollow tube known as Iter of
Aqueduct of sylvius.
 4th
ventricle continues in the metacoel and metacoel continues in the cavity of spinal cord
called neurocoel or central canal.
 One aperture is found on dorsal surface of metacoel known as foramen of magendie.
 Two apertures are found on lateral sides of metacoel known as Foramen of Luschka [1-1].
 CSF of brain comes out from the foramen of Magendie and Luschka and is poured into sub
arachnoid space.
TARGET POINTS
 In rabbit, cavity of olfactory lobe is hollow called as 1st
ventricle or rhinocoel. Both rhinocoel
continue in cavity of cerebral hemisphere, known as 2nd
ventricle or paracoel or lateral ventricle.
 The optic lobes of frog are hollow and in them optocoel cavity is found. 2 optic lobes are
present. These are hollow and termed as corpora bigemina. In mammals, 4 solid optic lobes
are present.
 The valve of vieussens joins the optic lobes with the cerebellum.
E. Histology of brain
 On dorsal surface of cerebral hemisphere, gray matter becomes more thick and is known as
cerebral cortex/ Neopallium/ pallium.
W
G
Cerebrum
Diencephalon
Cerebellum
1 G
W
Spinal cord
Brain stem
2
G - Gray matter
W - White matte

40
 Outer part of cerebellum is made up of gray matter while inner part is of white matter. White
matter projects outside and forms a branched tree like structure known as Arbor Vitae.
 Coroid plexus: Telachoroidea (Piameter which is merged in ventricle) + blood capillaries +
ependymal epithelium.
 Site: Two major plexuses in lateral ventricles; 2 minor plexuses in 3rd
ventricle while 1 minor
plexus in 4th
ventricle.
 Function: Formation of CSF by secretion of plasma.
 Sometimes (congenitally or infection) aqueduct becomes blocked leading to improper
circulation of CSF and intra cranial pressure increases, head becomes enlarged, this condition
is called hydrocephalus.
 Circulation: From the ventricles, CSF comes into subarachnoid space through foramen of
Magendie and Foramen of Luschka. In sub arachnoid space, CSF is absorbed by arachnoid
villi which pour it into cranial venous sinus. From venous sinus CSF enters in blood circulation.
Choroid plexus Lateral ventricle Foramen of monro Diocoel Aqueduct
IV Ventricle
th
Metacoel
Foramen of megendie and
foramenof luschka
Arachnoid
space
Arachnoid
villi
Cranial
venous sinus
Blood
circulation
F. Limbic system:
 It is visible like a wish bone, tuning fork or liplike.
 Limbic lobe (area of temporal lobe) + hippocampus + hypothalamus including septum + part
of thalamus + mammalary bodies + amygdaloid complex.
 Functions of limbic system
– Behavior, emotion, rage and anger (hypothalamus, amygdaloid body)
– Recent memory and short term memory converts into long term memory. (hippocampal
lobe)
– Food habit (hypothalamus)
– Sexual behavior (hypothalamus)
– Olfaction (hippocampal lobe and limbic lobe)
Name of area Location Relation or analysis
Prefrontal cortex Frontal lobe Seat of intelligence, knowledge, creative
ideas, ability to abstract, memory (organ of mind).
Premotor area Frontal lobe Written center
Associated movement of eye, head and body
Control complex movement of jaw, tongue,
pharynx, larynx.

41
Limbic association area
Premotor cortex
Primary motor cortex
Central sulcus
Primary somatosensory cortex
Parietal lobe
Somatosensory
association cortex
Parieto-occipital
sulcus
Occipital lobe
Visual
association area
Primary visual
cortex
Calcarine
sulcus
Parahippocampal gyrus
Uncus
Primary
olfactory
cortex
Temporal
lobe
Olfactory bulb
Olfactory tract
Fornix
Orbitofrontal cortex
Processes emotions
related to personal
and social interactions
Cingulate gyrus
Prefrontal cortex
Frontal eye field
Frontal eye field
Functional areas of cerebral cortex
Motor area Frontal lobe Analysis of all type of voluntary muscle
Frontal eye field Frontal lobe Responsible for conjugate movement of eye.
Opening and closing of eye lid.
Broca’s area Frontal lobe Analysis for speak if injury to this region
In right handed personIn Present of left side inability to speak (aphasia) even though
left handed person Present of right side muscle concerned are not paralyzed
(motor speech area)
Auditory area Temporal Analysis for sound
Olfactory Temporal or Analysis for smell
hippocampal gyrus
Wernicke’s area (sensory Temporal Analysis for language
area of speech) Sensory analysis for speech
Gustatory area Parietal Analysis for taste
Somesthetic area Parietal Analysis for touch, pressure, pain, knowledge
about position in space taking in information
from environment etc.
Angular gyrus Parietal Sensory analysis for writing
Occipital area Occipital Analysis for vision

42
TARGET POINTS
 Association area responsible for complex functions like inter sensory association, memory and
communications.
 Reticular activating system: It is special sensory fibers which is situated in brain stem and
further go in to thalamus. It is related with consciousness, alertness and awakening. Therefore
it is also called gate keeper of consciousness.
G. Functions of brain
 Olfactory lobe: It is supposed to be the center of smelling power. Its size is small in mammals
comparatively because most of its parts become a part of cerebrum (including olfactory tract)
some animals like sharks and dogs have well developed olfactory lobes.
 Cerebral hemispheres: Controls and regulates different parts of brain. This is the center of
conscious senses, will power, voluntary movements, knowledge, memory, speech and thinking,
reasoning etc. different sense organs send impulses here, and analysis and coordination of
impulses is done then messages are transferred according to the reactions through voluntary
muscles. All the voluntary actions are controlled by cerebral hemispheres.
 Diencephalon: Pineal body, situated in the epithalamus, controlsthe sexual maturity of animal.
 Thalamus – Act as relay center for sensory stimulation. In lower animals, cerebral cortex is
not developed and thalamus acts as sensory center. It is related with RAS and also act as
limbic part.
 Functions of hypothalamus: Thermoregulation, behavior and emotion, endocrine control,
biological clock system and ANS control.
 Centers of animal feelings/ emotions like sleep, anger, (libido), hate, love, affection, and
temperature control pain, hunger, thirst and satisfaction in the hypothalamus.
 Optic chiasma found in the hypothalamus carry optic impulses received from eyes to the
cerebral hemispheres. Animal becomes blind if this part is destroyed by chance.
 Metathalamus: It is related with MGB and LGB: MGB is related with hearing and LGB related
with vision. Nerve fibers of concerning place go through metathalamus.
 Mid brain: Four optic lobes or colliculus present, superior optic lobes are the main centers of
pupillary light reflexes inferior optic lobes are related with acoustic (sound) reflex action.
Crura cerebri controls the muscles of limbs.
 Cerebellum: Impulses are received from different voluntary muscles, joints and controlling
of their movements. When alcohol is consumed in excess, the cerebellum gets affected; as
a result one cannot maintain balance and walking in disturbed.
Thus it is related with fine and skillful voluntary movement and also related with body
balance, equilibrium, posture and tone.
 Pons regulates the breathing reaction through pneumotaxic center.

43
 Medulla oblongata: Controls all the involuntary activities of the body eg. Heart beats,
respiration, metabolism, secretory actions of different cells rate of engulfing food etc. it acts
as conduction path for all impulses between spinal cord and remaining portions of brain. It is
also concerned with reflex – sneezing reflex, salivation reflex, coughing reflex, swallowing
reflex, vomiting reflex, yawning reflex.
H. Basal nuclei / Basal ganglia: Situated in the wall of cerebral hemisphere. Corpus striatum
(caudate nucleus + (putamen globus pallidus) lentiform nucleus) + amygdaloid + claustrum.
Cleft for internal capsule
Caudate
nucleus
Levels of
sections
above
Lentiform nucleus
(globus pallidus medial
to putamen)
Amygdaloid body Tail of caudate nucleus
Lateral geniculate body
Medial geniculate body
Pulvinar
A
B
Thalamus
Body
Head
A
B
Interrelationship of thalamus, lentiform nucleus, caudate nucleus, and amygdaloid body
 Functions:
– Maintains muscle tone.
– Regulates automatic associated movement like swinging of arms during walking.
– In lower animals, when cerebral cortex is not developed basal nuclei acts as motor center.
– Lesion in basal nuclei leads to parkinsonism (rigidity, tremor at rest, mask like face)
– Regulate stereotypic movements; related to initiation and termination of movements.
2.1.2 Spinal cord
A. Anatomy
 Medulla oblongata comes out from foramen of magnum and continues in neural canal of
vertebral column, the continued part of MO is known as spinal cord. It extends from base of
skull to lower vertebra of lumbar (L1
). Its upper part is wide while lower most part is narrow
known as conus medullaris.

44
 Conus medullaris is present upto L1
vertebra.
Terminal part of conus medullaris extends in the
form of thread like structure made up of fibrous
connective tissue called filum terminale.
 Filum terminale is non-nervous part.
 Metacoel also continues in spinal cord where it
is known as neurocoel or central canal.
 Spinal cord is also covered by durameter,
arachnoid and piameter. Anarrow space is found
between vertebra and durameter known as
epidural space.
 Length of spinal cord is 45 cm, length of filum
terminale is 20 cm and weight of spinal cord is
approximately 35 gm.
B. Internal structure
 The outer part of spinal cord is of white matter while inner part is gray matter.
 On the dorso lateral and ventro lateral surface of spinal cord, the gray matter (butter fly like)
projects outside and forms the one pair dorsal and ventral horns.
 Due to formation of dorsal and ventral horns, white matter is divided into 4 segments and is
known as funiculus or white column.
 Dorsal and ventral horns continue in a tube like (bundle of nerve fibers) structure known as
root of dorsal and ventral horn. In root of dorsal horn, ganglia is present called dorsal root
ganglia. Both root are combined with each other at the place of intervertebral foramen.

Vertebra
Medulla
Conus medullaris
Dural sheath
Filum terminale
Coccyx
Level of
lumbar
puncture
C1
L1
L3
L4
S2



Ventral horn
Lateral horn
Transverse section of spinal cord
Dorsal root ganglie
Dorsal Horn
Interneuron
Anterior median fissure
Motor fibre
Ramus ventralis
Ramus
communicans
(form ANS)
Ramus dorsalis
Intervertebral foramen (IVF)
Sensory nerve fibre
Posterior median septum
Neurocoel
Mixed nerve
Mixed nerve
Grey matter
White matter
S
M

45
 Sensory neurons are found in dorsal root ganglia (pseudounipolar) and near to inter vertebral
foramen, its axon extend and gets embedded into gray matter of spinal cord and sensory
nerve fiber come from ganglia and make synapse with ventral root neuron.
 Motor neurons are found in the ventral root. Cyton is found in ventral horn while its dendrons
are embedded into gray matter of spinal cord where they make synapse with axon of sensory
neuron.
 Axon of motor neuron extends up to intervertebral foramen.
 Both sensory and motor nerve fibers combinely come out from intervertebral foramen and
form spinal nerve.
 In some part, lateral horns are also found. Lateral horn cells are found in these horns. There
nerve fibers come through ventral root and further come into intervertebral foramen. These
fibers called Ramus communicans. Ramus communicans forms ANS.
 The group of spinal nerve at the terminal end (L1
) of spinal cord from tail like structure called
cauda equina (horse tail).
 Spinal nerve and its branches are mixed type except Ramus communicans.
C. Functions:
 Acts as bridge between brain and organs of the body.
 Provides relay path for the impulses coming from brain.
 Regulates and conducts the reflex action.
TARGET POINTS
REFLEX ACTION
 “Marshal Hall” first observed the reflex actions.
 Reflex actions are spontaneous, automatic and involuntary. These are mechanical responses
produced by specific stimulating receptors.
 Reflex actions are completed very quickly as compared to normal actions and have no adverse
effect.
 Reflex actions are of two types:
A. Cranial reflex: These actions are completed by brain. No urgency is required for these
actions. These are slow actions e.g. watering of mouth to see good food.
B. Spinal reflex: These actions are completed by spinal cord. Urgency is required for these
actions. These are very fast actions e.g. Displacement of the leg at the time of pinching by
any needle.
 Classification of reflex actions on the basis of previous experiences:

46
A. Conditioned reflex: Previous experience is required to complete these actions. E.g.
swimming, cycling, dancing, singing etc. These actions are studied first by Evan Pavlov on
dog. Initially these actions are voluntary at the time of learning and after perfection, these
become involuntary.
B. Unconditioned reflex: These actions do not require previous experience e.g. sneezing,
coughing, yawning, sexual behavior for opposite sex partner, migration in birds etc.
REFLEX ARCH:
 The path of completion of reflex action is called reflex arch.
 Sensory fibers carry sensory impulses in the gray matter. These sensory impulses are converted
now into motor impulses and reach up to muscles. These muscles show reflex actions for
motor impulses obtained from motor neurons. Reflex arch is of two types:
A. Monosynaptic: There is a direct synapse (relation) found between sensory and motor
neurons, thus nerve impulse travels through only one synapse. E.g. Stretch reflex.
B. Polysynaptic: There are one or more small neurons found in between the sensory and
motor neurons. These small neurons are called connector neuron or inter neurons or
internuncial neurons e.g. withdrawal reflex. Nerve impulse will have to travel through more
than one synapse in this reflex arch.
To brain
6 Primary afferent
neuron stimulates
inhibitory interneuron
7 Interneuron inhibits
alpha motor neuron
to flexor muscle
5 Alpha motor neuron
stimulates extensor
muscle to contract
3 Primary afferent
neuron excited
4 Primary afferent
neuron stimulates
alpha motor neuron
to extensor muscle
2 Muscle spindle
stimulated
Extensor muscle
stretched
1
Flexor muscle
(antagonist) relaxes
8
Stretch reflex

47
2 Sensory neuron
activates multiple
interneurons
3 Ipsilateral motor
neurons to flexor
excited
5 Contralateral
motor neurons
to extensor
excited
4 Ipsilateral
flexor contracts
1 Stepping on
glass stimulates
pain receptors
in right foot
Withdrawal of right leg
(flexor reflex)
Extension of left leg
(crossed extension reflex)
6
Withdrawal reflex
2.2 PERIPHERAL NERVOUS SYSTEM
All the nerves arising from brain and spinal cord are included in peripheral nervous system. Nerves
arising from brain are called cranial nerves, and nerves coming out of spinal cords are called
spinal nerves. 12 pairs of cranial nerves are found in reptiles, birds and mammals but amphibians
and fishes have only 10 pairs of cranial nerves.
In human, I, II, and VIII cranial nerves out of 12 pairs of total cranial nerves are pure sensory in
nature. III, IV, VI, XI, and XII cranial nerves are motor nerves and V, VII, IX and X cranial nerves are
mixed types of nerves. Fibers of autonomous nervous system are found in III, VII, IX and X cranial
nerves.
Knee jerk reflex Withdrawal reflex
No involvement of any interneurons. Role of interneuron is important.
It is an example of monosynaptic reflex. It is an example of polysynaptic reflex.

48
TARGET POINTS
 Longest cranial nerve is vagus nerve.
 Largest cranial nerve is trigeminal nerve.
 Smallest cranial nerve is abducens cranial nerve.
 Thinnest cranial nerve is trochlear/ pathetic.
 Trigeminal nerve is also called “ the dentist nerve” because the dentists desensitizes this nerve
with some anesthetic before pulling out the troubling tooth.
 Important nuclei related with cranial nerves:
E danger westpal nucleus occulomoto nerve.
Gasserian ganglion  trigeminal nerve.
Semilunar ganglion
Nervus intermedium  facial nerve
Geniculate ganglion.
2.2.1 Human cranial nerves
No. Name Origin Distribution Nature Function
I Olfactory Olfactory Enters olfactory lobes. Sensory Smell
epithelium Extends to temporal lobe.
II Optic Retina Leads to occipital lobe. Sensory Sight
III Oculomotor Mid brain Four eye muscles Motor Movement of
eyeball
IV Trochlear Mid brain Superior oblique eye muscle. Motor Movement of
(pathetic) eyeball
V Trigeminal Pons – Mixed
(dentist nerve) –
(i) Opthalmic Skin of nose, upper eyelids, Sensory Sensory supply
forehead, scalp, conjunctiva, to concerning
lachrymal gland. part
(ii) Maxillary – Mucous membrane of cheeks and Sensory –
upper lip and lower eyelid.
(iii) Mandibular – Lower jaw, lower lip, pinna. Mixed Muscle of
Mastication
VI Abducens Pons Lateral rectus eye muscle. Motor Movement of
eyeball

49
Olfactory
nerve
Oculomotor
nerve
Trochlear nerve
Abducens
nerve
Vestibulocochlear
nerves
Hypoglossal
nerves
Accessory
nerves
Optic nerve
Cranial nerves
2.2.2 Spinal nerves
 In rabbit, there are 37 pairs while in frog there are 9 or 10 pairs. Humans have only 31
pairs of spinal nerves. Caudal spinal nerves are absent because human is a tailless animal
and only 1 pair coccygeal nerve are present.
 Each spinal nerve is mixed type and arises from the roots of the horns of gray matter of the
spinal cord.
VII Facial Pons Face, neck, taste buds, salivary Mixed Taste (ant. 2/3
gland. part of tongue)
facial expression,
saliva secretion
VIII Auditory Pons Internal ear Sensory
(i) Cochlear -------- -------- -------- Hearing and
(ii)Vestibular -------- -------- -------- equilibrium
IX Glossopha- Medulla Muscles and mucus
ryngeal membrane of pharyx and tongue. Mixed Taste (post. 1/3
part of tongue),
saliva secretion
X Vagus Medulla Larynx, lungs, heart, stomach, Mixed Visceral
(pneumo- intestine. sensations and
gastric) movements
XI Accessory Medulla Muscles of pharynx, larynx Motor Movement of
spinal pharynx, larynx
XII Hypoglossal Medulla Muscles of tongue Motor Movement of
tongue

50
 In dorsal root only afferent or sensory fibers and in ventral root efferent or motor fibers are
found.
 Both the roots after moving for distance in the spinal cord of vertebrates combine with each
other and come out from the inter vertebral foramen in the form of spinal nerves.
 As soon as the spinal nerves comes out of the inter vertebral foramen they divide into 3
branches:
Ramus dorsalis
Ramus ventralis
Ramus communicans
Somatic nerve
A.N.S
Sympathetic nervous system
Parasympathetic nervous system
Spinal nerves of rabbit
2.2.3 Autonomic nervous system
The autonomic nervous system is a part of the peripheral nervous system which controls activities
inside the body that are normally involuntary, such as heart beat, peristalsis, sweating etc. It consists
of motor neuron passing to the smooth muscle of internal organs. Smooth muscles are involuntary
muscles. Most of the activities of the autonomic nervous system is controlled within the spinal cord
or brain by reflexes known as visceral reflexes and does not involve the conscious control of higher
centers of the brain.
Overall control of the autonomic nervous system is maintained, however by centers in the medulla
(a part of the hind brain) and hypothalamus. These receive and integrate sensory information and
coordinate this with information from other parts of the nervous system to produce the appropriate
response.
ANS plays an important role in maintaining the constant internal environment (homeostasis). ANS is
composed of two types of neurons, a preganglionic neuron (myelinated) which leaves the central
nervous system in the ventral root before synapsing several postganglionic neurons (non myelinated)
leading to effector (concerning organs).
Cervical spinal nerves 8 Pairs -I To -VIII
Thoracic spinal nerves 12 airs -IX To -XX
Lumbar spinal nerves 7 pairs -XXI To -XXVII
(in human – 21 to 25 (5 pair)]
Sacral spinal nerves 4 pairs -XXVIII To -XXXI
(in human – 26 to 30 (5 pairs)]
Caudal spinal nerves 5 pairs -XXXII To -XXXVII
(in human- 1 pair coccygeal nerve)

51
Mechanism sites of ANS: Involuntary muscles, exocrine glands, blood vessels, skin (pilomotor
muscles, blood vessels, sweat glands).
There are two divisions of ANS: The sympathetic (SNS) and the parasympathetic (PNS) –
A. Sympathetic system is related with such visceral reactions, which increases the protection of
body in adverse atmospheric conditions along with calorie consumption (causes loss of energy).
B.Parasympathetic system is related with those reactions in which energy is conserved.
In this way, autonomic nervous system controls the activities of visceral organs double sided i.e.
antagonistic to each other.
Anatomical difference between SNS and PNS
Physiological difference between SNS and PNS
Sympathetic nervous system Parasympathetic nervous system
Thoracico lumbar outflow (T1
to L3
) (Ramus Cranio sacral outflow (cranial nerves) 3, 7, 9,
communicans of T1
to L3
) 10 and sacral’s ramus communicans 2, 3, 4.
Just lateral to vertebral column sympathetic Ganglia are situated separately either near the
trunks are there on both sides (each made up organ or surface of organ.
of 22 ganglia) (rabbit = 18 ganglia)
Preganglionic nerve fibers (Ramus communicans Preganglionic nerve fibers are longer than
of spinal nerves) are smaller than post ganglionic postganglionic nerve fibers.
nerve fibers (arises from sympathetic trunk or
ganglia to organs)
Preganglionic nerve fibers are cholinergic Both pre and post ganglionic nerve fibers are
(filled with acetylcholine) and post ganglionic cholinergic.
nerve fibers are adrenergic (filled with
noradrenaline) except sweat gland which have
cholinergic postganglionic nerve fibers.
Preganglionic nerve fibers are made up of white
ramus communicans and postganglionic nerve
fibers are made up of gray ramus communicans.
Visceral organs Sympathetic nervous Parasympathetic nervous
system system
Secretion Acetylcholine + sympathetin Only acetylcholine
Iris of eye Dilates pupils Constricts pupils
Tear glands or Stimulates secretion of lachrymal Inhibits secretion of lachrymal
lachrymal glands glands glands

52
TARGET POINTS
Heart Increases the rate of cardiac Inhibits the rate of cardiac
contraction i.e. accelerates heart beat contraction i.e. retards heart beat
Secretion of adrenal Stimulates adrenal secretion Inhibits adrenal secretion
glands
Salivary secretion Inhibits the secretion of salivary and Stimulates the secretion of
digestive glands. salivary and digestive glands.
Blood vessels Constricts cutaneous blood vessels, Dilates all blood vessels
which causes increased blood pressure decreasing blood pressure.
but dilates blood vessels of brain,
lungs, heart, and striated muscle.
Increases RBC count in blood.
Lungs, trachea and Dilates trachea bronchi and lungs for Constricts these organs during
bronchi easy breathing. normal breathing.
Alimentary canal Inhibits peristalsis of alimentary canal Stimulates peristalsis of
alimentary canal
Digestive glands Inhibits the secretion of these glands Stimulates the secretion of these
glands
Sweat glands Stimulates secretion of sweat Inhibits secretion of sweat
Arrector pilli Stimulates contraction of these muscles Relaxes arrector pilli muscles
muscles of skin, causing goose flesh
Urinary bladder Relaxes the muscles of urinary bladder Contracts the muscles for
ejaculation of urine (micturition).
Anal sphincter Closes anus by contracting anal Relaxes anal sphincter and opens
sphincters the anus (defecation)
External ganglia Ejaculation Erection
Basal metabolic rate Accelerates BMR Retards BMR.
Comparative account of nervous system in rabbit and human
Characters Rabbit Human
Olfactory lobe
Position Attached distinctly to anterior Attached indistinctly as part of cerebral
end of cerebrum hemisphere embedded in frontal lobe
Shape and size Small, elongated Small, occur as olfactory bulb
Rhinocoel Present Absent and solid lobe

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