The nervous system has four main functions: 1. Gathering sensory input from receptors 2. Integrating information in the central nervous system 3. Initiating motor responses via muscles or glands 4. Maintaining homeostasis through detection and response to internal and external changes. The nervous system is divided into the central nervous system (brain and spinal cord) and peripheral nervous system (nerves and ganglia). The central nervous system processes information while the peripheral nervous system connects to sensory receptors and muscles/glands. Neurons are the basic functional units that receive stimuli, conduct signals, and transmit to other neurons or tissues.

1. FUNCTIONS OF THE NERVOUS SYSTEM
1. Sensory input— gathering information
• Sensory receptors monitor changes,
called stimuli, occurring inside and
outside the body.
2. Integrating Information
• Nervous system processes and
interprets sensory input and decides
whether action is needed
3. Motor output
• A response, or effect, activates
muscles or glands
4. Maintaining Homeostasis
• The nervous system plays an
important role in maintaining
homeostasis. This function depends on
the nervous system’s ability to detect,
interpret, and respond to changes in
internal and external conditions.
5.Establishing and maintaining mental activity
• The brain is the center of mental
activity, including consciousness,
memory, and thinking.
DIVISIONS OF NS
Central Nervous System
• Brain - Part of the CNS that is located
in the skull and contains about 85
billion neurons
• Spinal Cord - Connected to the brain
through the Foramen Magnum of the
occipital bone and is encircled by the
bones of the vertebral column.
Peripheral Nervous System
• Nerve and ganglia
A. Sensory Division
Afferent (toward) division; conducts action
potentials from sensory receptors to the CNS
• Sensory neurons – neurons that
transmit action potentials from the
periphery to the CNS
→ Somatic Sensory Fibers – carry info
from stimuli coming from the skin,
skeletal, muscles, joints
→ Visceral Sensory Fibers – transmits
impulses coming from the visceral
organs
B. Motor Division
Efferent (away) division; conducts action
potentials from the CNS to effector organs
• Motor neurons – neurons that
transmit action potentials from the
CNS toward the periphery
→ Somatic Motor Nervous System /
Voluntary – transmits action
potentials form the CNS to the skeletal
muscles
→ Autonomic Motor Nervous System /
Involuntary – transmits action
potentials from the CNS to cardiac,
smooth muscles and glands
➢ Sympathetic – fight-or-flight system
➢ Parasympathetic – resting and
digesting system
→ Enteric Nervous System – unique
subdivision; both sensory and motor
neurons contained within the digestive
tract.
CELLS OF THE NERVOUS SYSTEM
Neurons
• Also called nerve cells
• Receive stimuli, conduct action
potentials, transmit signals
Cell body (Soma) – contains a single nucleus;
source of information for gene expression
Dendrites – extensions of the cell body;
receive information from other neurons;
transmit the info toward the neuron cell body
Axon – single long cell process; conduct
action potentials from one part of the brain or
spinal cord to another part
➢ Axon of sensory neurons – conduct
action potentials towards the CNS
➢ Axon of motor neurons – conduct
action potentials away from the CNS
Axon hillock – where the axon leaves the
neuron cell body
The “control center” of the body
NERVOUS SYSTEM
"One of the smallest yet
most complex body
system"

2. Nissl bodies – rough ER found in the cell body
of a neuron
Schwann cells – form a myelin sheath
(increases speed of impulse transmission)
Collateral axons – branches of axons.
Types of Neurons
1. Multipolar neurons – many dendrites
+ a single axon
2. Bipolar neurons – two processes: 1
dendrite + 1 axon
3. Pseudo-unipolar neurons – single
process that divides into 2 processes:
extends to the periphery + extends to
the CNS
Neuroglia
• Non-neuronal cells of the CNS + PNS
• More numerous than neurons
• Can divide to produce more cells
1. Astrocytes – major supporting cells in
the CNS; stimulate/inhibit the
signaling activity of nearby neurons;
help limit damage to neural tissue
• Blood brain barrier – protects
neurons from toxic substances in
the blood; allows exchange of
waster products + nutrients
2. Ependymal cells – produce
cerebrospinal
fluid; help
move the
cerebrospinal
fluid through
the CNS
3. Microglia –
act as immune
cells of the
CNS’ protect
the brain by
removing
bacteria and
cell debris
4. Oligodendrocytes (CNS) and (5)
Schwann cells (PNS) – provide an
insulating material that surrounds
axons
Neural Signaling
Communication among neurons
1. Reception – stimuli received by visual
receptors in the eye
2. Transmission – sensory neurons
transmit info to CNS
3. Integration – info given is interpreted
and an appropriate response is
determined
4. Transmission – the CNS transmits
info to motor neurons
5. Actual response – muscle/glands
receive info and instruction from
motor neurons
Myelin Sheaths
Highly specialized insulating layer of cells
• Unmyelinated axons – action
potentials are conducted slowly bcos
in travels along the entire axon
• Myelinating axons – action potentials
are conducted rapidly (3-15
meters/sec) by salutatory conduction
• Nodes of Ranvier – gaps in the
myelin sheath; where ion movement
can occur

3. Continuous Conduction in an Unmyelinated
Axon
Organization of Nervous Tissue
Gray Matter
groups of neuron cell bodies + their dendrites;
very little myelin
In the CNS;
➢ Cortex – GM on the surface of the
brain
➢ Nuclei – GM located deeper within the
brain
In the PNS;
➢ Ganglion – a cluster of neuron cell
bodies
White Matter
bundles of parallel axons + myelin sheaths
In the CNS
➢ Nerve tracts – conduction pathways;
propagate action potentials from one
area of the CNS to another
In the PNS;
➢ Nerves – bundles of axons +
connective tissue sheaths
ELECTRICAL SIGNALS AND NEURAL
PATHWAYS
Resting Membrane Potential
• Polarized cell membrane – uneven
distribution of charge
• Resting membrane potential –
uneven charge, distribution in an
unstimulated/resting cell; polarized
→ Higher concentration of K+ inside
CM
→ Higher concentration of Na+
outside CM
→ Greater permeability of CM to K+
than to Na+
• Leak channels – always open; K+
channels
• Gated channels – closed until opened
by specific signals; Na+
channels
• Chemically gated channels – opened
by neurotransmitters
• Voltage gated channels – opened by
a change in membrane potential
• Sodium potassium pump – required
to maintain the greater concentration
of Na+ outside the CM and K+ inside
Action Potentials

4. • Excitable cells – RMP changes in
response to stimuli that activate gated
ion channels
• Local current – Na+ diffuses quickly
into cell
• Depolarization – a change that causes
the inside of the CM to become
positive
• Local potential – result of
depolarization
• Threshold value – attainable local
potential (critical pt.)
• Action potential – constitution of
depolarization and repolarization
• Hyperpolarization – the charge on
the CM briefly becomes more
negative than the RMP
• All-or-none fashion – threshold is
reached = action potential occurs; if
the threshold is not reached = action
potential doesn’t occur
• Continuous conduction – the action
potential is conducted along the entire
axon CM
• Saltatory conduction – action
potentials jump from one node of
Ranvier to the next
SYNAPSE
a junction where the axon of one neuron
interacts with another
• Presynaptic terminal – end of the
axon
• Postsynaptic membrane – membrane
of the dendrite or effector cell
• Synaptic cleft – space separating the
presynaptic & postsynaptic membrane
• Neurotransmitters – chemical
messengers’
• Synaptic vesicles – where
neurotransmitters are stored
• Hyperpolarized – the inside of the
postsynaptic cell tends to become
more negative

5. REFLEX
• an involuntary reaction in response to
a stimulus applied to the periphery and
transmitted to the CNS
2 types of reflex
Somatic reflexes
→ Reflexes that stimulate the skeletal
muscles
→ Involuntary, although skeletal muscle
is normally under voluntary control
→ Example: pulling your hand away
from a hot object
Autonomic reflexes
→ Regulate the activity of smooth
muscles, the heart, and glands
→ Example: regulation of smooth
muscles, heart and blood pressure,
glands, digestive system
Reflex arc
neuronal pathway by which a reflex occurs
5 elements of Reflex Arc
1. Sensory receptors – reacts to a
stimulus
2. Sensory (afferent) neurons – carries
message to the integration center
3. Interneurons (Association) neuron-
processes information and directs
motor output
4. Efferent (motor) neurons - send
response to effector
5. Effector - muscle, gland, or organ
Types of Reflex Arc
Two – neuron arcs : simplest type
Three – neuron arcs: Consists of five
elements: receptor, sensory neuron,
interneuron, motor neuron, and effector.
Neuronal Pathways
• Converging pathway – two or more
neurons synapse with the same neuron
• Diverging pathway – the axon from
one neuron divides and synapses with
more than one other neuron
• Summation – allows integration of
multiple sub threshold local
potentials; brings the membrane
potential to threshold and trigger an
action potential
• Spatial summation – local potentials
originate from diff. locations on the
postsynaptic neuron
• Temporal summation – local
potentials overlap in time
Converging and Diverging Pathways in the
Nervous System

6. BRAIN
• Soft, wrinkled mass of tissue that is
highly
• complex and adaptive; 3 pounds
• 25 billion neurons
• Requires a continuous supply of
oxygen and glucose
I. Brainstem
• Connects the spinal cord to the
remainder of the brain
• Controls the heart rate, blood pressure,
and breathing
• Damage can cause death
1. Medulla Oblongata
• Most inferior portion of the brainstem
• Important reflex actions like vomiting,
sneezing, coughing, swallowing
• Gray matter consists of various nuclei
that serve as vital centers
→ Cardiac centers – control HR
→ Vasomotor centers – regulates BP but
controlling blood vessel diameter
→ Respiratory centers – initiates and
regulates breathing
• Pyramids – two prominent
enlargements
2. Pons (bridge)
• Relay information bet. the cerebrum
and the cerebellum
• Resembles an arched footbridge
• Regulates respiration, swallowing,
sleep
3. Midbrain
Location: above pons
Function: coordinated eye movement, pupil
diameter, tuning head toward noise.
Smallest region of the brainstem
• 4 mounds called the colliculi
→ 2 inferiors; major relay centers for the
auditory nerve pathways in the CNS
→ 2 superiors; visual reflexes and receive
touch and auditory input
4. Reticular Formation
• A group of nuclei scattered throughout
the brainstem
• Regulating cyclical motor functions;
respiration, walking, chewing
• Damage can result in coma
• Reticular activating system – plays
an important role in arousing and
maintaining consciousness
II. Diencephalon
Part bet. the brainstem and the cerebrum
1. Thalamus
• Largest part of the diencephalon
• Major relay center for all sensory info
(except smell) to the cerebrum; plays a
gating role
• Influences mood and registers an
uncomfortable perception of pain
• Interthalamic adhesion – connects
the two large, lateral parts of the
thalamus
2. Epithalamus
• Smallest area superior + posterior to
the thalamus
• Consists of few small nuclei
(emotional and visceral response to
odors) + pineal gland
Pineal gland – an endocrine gland that may
influence the onset of puberty; role in
controlling some long-term cycles

7. 3. Hypothalamus
• Most inferior part
• Consists of several small nuclei;
maintaining homeostasis
• Control of body temp., hunger, and
thirst
• Sensations such as sexual pleasure,
rage, fear, and relaxation
Important Homeostatic Mechanisms
1. Control center of the ANS.
2. The link bet. the nervous and endocrine
systems.
3. Helps maintain fluid balance.
❖ Anti-diuretic hormone (ADH) –
regulates water excretion by the
kidneys
4. Regulates body temperature.
5. Regulates food intake (appetite and satiety
centers).
6. Regulates sleep-wake cycles.
7. Influences sexual behavior and emotional
aspects of sensory input.
Infundibulum – controlling the secretion of
hormones from the pituitary gland
Mammillary bodies – involved in emotional
responses to odors and in memory
III. Cerebellum
• Second largest part of the brain;
2hemispheres
• Responsible for coordination of
movements
• Comparator – a sensing device that
compares data from two sources
• Proprioceptive neurons – innervate
joints, tendons, muscles; provide info
about the position of body parts
1. Helps in smooth and coordinated body
movements (comparator function).
2. Maintains muscle tone posture.
3. Maintain balance and equilibrium
4. Important in learning motor skills.
IV. Cerebrum
Largest and most prominent part of the brain
1. Sensory Function – receives info
from sensory receptors and interprets
it
2. Motor Function – responsible for all
voluntary movement and some
involuntary ones
3. Association Function – responsible
for all of the intellectual activities of
brain
4 LOBES
1. Frontal Lobe
• Control of voluntary motor functions,
• motivation, aggression, mood,
olfactory reception
• Primary motor area: consciously move
our skeletal muscles
• Broca’s area – speech center
• Prefrontal area – responsible for
executive functions
2. Parietal Lobe
• General Sensory Area – receives info
from the sensory receptors in the skin
and joints
• Wernicke’s area – sensory speech
area
3. Occipital Lobe
• Receiving and perceiving visual input
• Primary visual area – receives visual
info
• Visual association area – portion
where visual info is integrated
4. Temporal Lobe
Primary auditory area – center for reception
of auditory messages
Auditory association area – where auditory
messages are integrated
Psychic cortex – abstract thoughts and
judgments
Gyri – folds and convolutions; increase the
surface area of the cortex and intervening
grooves (sulci)
Sulci – shallow grooves
Fissures – deep groves
Longitudinal fissure – divides the cerebrum
into left and right hemispheres
Cerebral cortex – outermost layer of the
cerebrum; consists of gray matter
Corpus callosum – connects the right and left
hemispheres
Central sulcus – separates the frontal and
parietal lobes
Lateral fissure – separates the temporal love
from the rest
Insula – fifth lobe; deep within the fissure
Basal Nuclei
• Group of functionally related nuclei

8. • Corpus striatum – located deep
within the cerebrum
• Substantia nigra – darkly pigmented
cells in the midbrain
Right and Left Hemispheres
• Right hemisphere – three
dimensional or spatial perception,
musical ability
• Left Hemisphere – analytical
hemisphere; mathematics and speech
Memory
• Working memory – stores info
required for the immediate
performance of a task; 7-digit phone
no.
• Short-term memory – last longer;
can be retained for a few mins. to a few
days
• Long-term memory – stored for only
a few minutes or become permanent
by consolidation
• Consolidation – a gradual process
involving the formation of new and
stronger synaptic connections
• Declarative memory – explicit
memory; retains facts and related
emotional undertones
• Procedural memory – reflexive
memory; development of motor skills
• Memory engrams – memory traces;
long-term retention of a thought/idea
Limbic System
A group of interconnected nuclei involved in
memory and regulation of emotion
Hippocampus – formation and retrieval of
memories
Amygdala – filter sensory info and evaluates
it in terms of emotional needs
MENINGES, VENTRICLES, AND
CEREBROSPINAL FLUID
Meninges
Surround and protect the brain and spinal cord
1. Dura mater
Most superficial and thickest meninges
❖ Epidural space – bet. the dura mater
& the vertebrae
❖ Epidural anesthesia – clinically
important as the injection site of spinal
nerves; given to women during
childbirth
2. Arachnoid mater
Thin, wispy, 2nd meningeal membrane
❖ Subdural space – space bet. the dura
mater and the arachnoid mater;
contains small amt. of serous fluid
❖ Spinal block – to inject anesthetic into
the area
❖ Spinal tap – to take a sample of CSF
3.Pia mater
3rd meningeal membrane; very tightly bound
to the surface of the brain and spinal cord;
filled with CSF and contains blood vessels
❖ Subarachnoid space – bet. the
arachnoid and pia matter
Ventricles
• Fluid filled cavities
Lateral ventricle – relatively large cavity in
each cerebral hemisphere
Third ventricle – a smaller, midline cavity
Fourth ventricle – located at the base of the
cerebellum

9. Cerebral aqueduct – a narrow canal that
connects the 3rdand 4th ventricle
Cerebrospinal fluid
• Provides a protective cushion around
the CNS
• Fluid that bathes the brain and spinal
cord
Choroid plexus – produces CSF; specialized
structures made of ependymal cells
Arachnoid villi – structures that project from
the arachnoid layer; where blood is reabsorbed
Hydrocephalus – accumulation of CSF in the
ventricles
Motor Functions
Involuntary movements – occur without a
conscious thought
Voluntary movements – consciously
activated to achieve a specific goal; walking,
typing
Upper motor neurons – have cell bodies in
the cerebral cortex
Lower motor neurons – have cell bodies in
the anterior horn
Motor Areas of the Cerebral Cortex
Primary motor cortex – control voluntary
movements of skeletal muscles
Premotor area – where motor functions are
organized before they are actually initiated in
the primary motor cortex
Pre-frontal area – where planning and
initiating movements occur
Other Brain Functions
Communication bet. the Right & Left
Hemispheres
Commissures – connection bet. the two
hemispheres
Corpus callosum – largest commissure
Speech
Sensory speech area – Wernicke area; a
portion of the parietal lobe; where words are
heard and comprehended
Motor speech area – Broca area; inferior
portion of the frontal lobe; where words are
formulated
Aphasia – absent/defective speech/language
comprehension
Brain Waves and Consciousness
Electroencephalogram (EEG) - electrodes
plated on scalp to record brain’s electrical
activity
Brain waves – wave like patterns
Alpha waves – awake but in a quiet, resting
state with eyes close
Beta waves – occur during intense mental
activity
Delta waves – occur during deep sleep in
infants and in patients
Theta waves – observed in children; also, in
adults who are frustrated or have brain
disorders
INNERVATION OF ORGANS BY THE
ANS

10. SPINAL CORD
• Extends from
the foramen
magnum to
the 2nd
lumbar
vertebra
• Provides a
two-way
conduction
pathway to
and from the
brain
Cauda equina – inferior end of the SC; spinal
nerves exiting there resemble a horse’s tail
2 Main Functions
1. Transmits info to and from the brain.
2. Controls many reflex activities of the
body.
White Matter of the SC
Outside of spinal cord
Contains myelinated fibers
1. Dorsal (posterior)
2. Ventral (anterior)
3. Lateral Columns
a. Ascending tracts – conduct
action potentials toward the brain
b. Descending tracts – conduct
action potentials away from the
brain
Gray Matter of the SC
1. Posterior horns
2. Anterior horns
3. Small lateral horns
→ Central canal – fluid filled space in
the center of the cord
→ Ventral root – formed by ventral
rootlets;
→ Dorsal root – formed by dorsal
rootlets
→ Dorsal root ganglion – ganglion in a
dorsal root
Reflex Action
• Predictable, automatic response to a
specific stimulus
1. Reception of the stimulus.
2. Transmission of info to the CNS.
3. Integration (interpretation and
determination of an appropriate
response).
4. Transmission of info from the CNS to
a muscle.
5. Actual response.
SPINAL CORD REFLEXES
Knee-Jerk Reflex
• Stretch flex – simplest reflex; muscles
contract in response to a stretching
force applied to them
• Knee-jerk reflex – patellar reflex;
used to determine if the higher CNS
centers that normally influence this
reflex are functional
Withdrawal Reflex
Withdrawal Reflex – flexor reflex; to remove
a limb from a painful stimulus
ASCENDING TRACTS
• Pathways that carry impulses form the
periphery to various parts of the brain
Spinothalamic tract – transmits pain, light
touch, and deep pressure
Dorsal column – transmission of
proprioception, touch, deep pressure, vibration
Spinocerebellar tracts – proprioception to
cerebellum
DESCENDING TRACTS
• Pathways that carry impulses from the
brain to the periphery
Lateral corticospinal – muscle tone and
skilled movements (hand)
Anterior corticospinal – muscle tone and
movement of trunk muscles
Rubrospinal – movement coordination

11. Reticulospinal – posture adjustment
Vestibulospinal – posture & balance
Tectospinal – movement in response to visual
reflexes
CROSS SECTION OF THE SPINAL CORD
CRANIAL NERVES
• Transmit info to the brain form the
sensory receptors
SPINAL NERVES
Arise along the spinal cord; contains mixed
nerves
• 31 pairs
• 8 Cervical
• 12 Thoracic
• 5 Lumbar
• 5 Sacral
• 1 Coccygeal
Mixed nerves
contains both sensory and somatic motor
neurons
Plexuses
where nerves come together and then separate
Cervical Plexus
• Originates from spinal nerves C1 to
C4
• Innervates muscles attached to hyoid
bone and neck
• Contains phrenic nerve which
innervates diaphragm
Phrenic nerve - most important branch of the
CP; innervates the diaphragm (responsible for
our ability to breathe)
Brachial Plexus
• Originates from the spinal nerves C5
to T1
• Supply nerves to upper limb, shoulder
and hand
1. Axillary nerve – innervates 2
shoulder muscles the skin over part of
it
2. Median nerve – innervates the
anterior forearm and intrinsic muscles
3. Radial nerve – innervates all the
muscles in the posterior arm and
forearm + skin over the posterior
surface of the arm, forearm, hand
4. Musculocutaneous nerve -innervates
the anterior muscles of the arm + skin
over the radial surface of the forearm
5. Ulnar nerve – innervates most of the
anterior forearm muscles and some of
the intrinsic hand muscles + skin over
the radial side of the hand
Lumbosacral Plexus
• Originates from spinal nerves L1 to S4
• Supply nerves lower limbs
1. Obturator nerve – innervates the
muscles of the medial thigh + skin
over it

12. 2. Femoral nerve – innervates the
anterior thigh muscles + skin over it &
medial side of the leg
3. Tibial nerve – innervates the posterior
thigh muscles, the anterior & posterior
leg muscles, most of the intrinsic foot
muscles + skin over the sole of the foot
4. Common fibular nerve – innervates
the muscles of the lateral thigh & leg,
some intrinsic foot muscles + skin
over the anterior & lateral leg, dorsal
surface of the foot
Sciatic nerve – CT sheath that bounds the
tibial and common fibular nerve
AUTONOMIC NERVOUS SYSTEM
• Preganglionic neuron
• Postganglionic neuron
• Maintain internal homeostasis
Autonomic ganglia
Where preganglionic neurons synapse with
postganglionic neurons
I. Sympathetic ANS
• ’Fight-or-flight’
• Prepares the body for action
• Most active during stressful situations
• Norepinephrine (main
neurotransmitter)
II. Parasympathetic ANS
• Activities result in conserving and
restoring energy
• Helps return the body to resting
conditions
• Active during periods of calm and rest
• PS fibers are in the vagus nerve
Autonomic Neurotransmitters
• Acetylcholine – neurotransmitters of
the parasympathetic division
• Norepinephrine – postganglionic
neurons of the sympathetic division
Functions of the Autonomic Nervous System
Sympathetic Division
 Prepares a person for action by
increasing HR, BP, respiration, release
of glucose
Parasympathetic Division
 Involuntary activities at rest: digestion
of food, defecation, urination
Enteric Nervous System
Consists of plexus within the wall of the
digestive tract
1. Sensory neurons – connect the digestive
tract to the CNS
2. Sympathetic & parasympathetic neurons
–connect the CNS to the digestive tract
3. Enteric neurons – located entirely within
enteric plexus
 Capable of monitoring and controlling
the digestive tract independently of the
CNS