The nervous system aims to maintain coordination between all body systems and the environment. It works synergistically with the endocrine system to keep the body in homeostasis. The nervous system provides quick point-to-point connections via neurons, while the endocrine system provides slower chemical integration through hormones. The human nervous system consists of the central nervous system (brain and spinal cord) and peripheral nervous system. The peripheral nervous system includes nerves and is divided into the somatic and automatic systems. Neurons are the basic functional units and communicate via electrical and chemical signals at synapses to coordinate bodily functions.

1. Introduction
THE AIM OF NERVOUS SYSTEM IS TO MAINTAINING COORDINATION
AMONG ALL THE SYSTEMS OF BODY AND ALSO WITH ENVIRONMENT
SYNERGISTICALLY WITH ENDOCRINE SYSTEM (SO AS TO KEEP BODY IN
HOMEOSTASIS)
COORDINATION IS THE PROCESS THROUGH WHICH TWO OR MORE
ORGANS INTERACT AND COMPLEMENT THE FUNCTION OF ONE ANOTHER

2.  In our body the neural system and the endocrine system jointly co-
ordinate and integrate all the activities of organs so that they function in a
synchronised fashion.
 the neural system provides an organised network of point-to-point
connections for a quick coordinationn
 The endocrine system provides chemical integration through hormones.

3. Organisation of nervous system in
human beings
 The human neural system is divided into two divisions as
1. central nervous system and
2. peripheral nervous system.
 Central nervous system/CNS includes brain and spinal cord and is the site of
information processing and control
 Peripheral nervous system/PNS comprises of all the nerves of the body
associated with the CNS. The nerve fibres of the pns are of two types
1. afferent fibres/sensory nerves: these transmit impulse from tissue/organs to
the.
2. Efferent fibers/motor nerves:this translate regulatory impulses from the CNS
to the concerned peripheral tissue/organ.

4.  The peripheral nervous system for the divides into two division
1. somatic neural system:the somatic neural system relays impulses from
the CNS to the skeletal muscles.
2. Autonomic neural system:the autonomic neural system transmits
impulses from the CNS to the involuntary organs and smooth muscles of
the body. This system is further classified by:
. A) sympathetic neural system
B) parasympathetic neural system

5. Cells of nervous system
 There are two types of cells present in nervous system as neurone and
neuroglia/glial cels, where neurones are the basic cells, neuroglia are the
supportive, nutritive and protective cells of the nervous system.
1. Neurones: structural and functional unit of neural system.
Longest cell of the body
neurones do not divide as they are most differentiated cells of
the nervous system with no centriole

7. Parts of neuron
 Neurone is microscopic structure composed of three major parts
1. cell body/cyton : the cell body contains cytoplasm with typical cell organelles
and certain granular body is called nissl’s granules (endoplasmic reticulum
and the site of protein synthesis)
2. Dendrite : short fibres which branch repeatedly and project out of the cell
body called dendrites.
these fibres transmit impulses towards the cell body so are also known afferent
process of neurons.
All receptors of the body are modified dendrites[but all dendrites are not
receptors]
3. Axon /axon fibre : Axon is long fibre and the distal end of which is branched
Each branch terminates as a bulb like structure called scienaptic knob.

8.  Synaptic knob possesses synaptic vesicles containing chemicals called neurotransmitters
 The Axons transmit nerve impulses away from the cell body to a synapse or to a
neuromuscular junction
 A synapse is formed by membrane of Presynaptic neurone or postsynaptic neurone
which may or may not be separated by a gap called synaptic cleft.
 There are two types of synapses namely electrical synapse and chemical synapse
in electrical the membranes of pre and post optic neurone are in very close proximity
Electrical synapses are there in our system
in chemical synapse the membrane of pre and post synaptic neurones are separated by a
fluid filled space called synaptic cleft
and chemicals called neurotransmitter are involved in transmission of impulse at the
synapses

9. Types of neurone
 Based on the number of Axon and dendrites the neurones are divided into
5 types
1. Multipolar neurone: with one Exxon and two or more dendrites; found in
cerebral cortex
2. Bipolar : with one exam and one dendrite; found in retina of eye.
3. Unipolar neurone: Cell body with with one Axon only; found usually
embryonic stage
4. Apolar neurone: carries several processes but without distinction between
dendrites and Axon
5. Pseudo unipolar: it also carries a single process emerging out from site on
that divides into two process as dendrite and axon. It is found in dorsal
sensory fibre of spinal nerve.

11. Types of neurons on the basis of
presence or absence of myelin sheath
 MYELINATED :- myelinated nerve fibres are envelope with schwann Cells a type
of neuroglia which forms a myelin sheath around the Axons
Gap between two adjacent myelin sheath is called node of ranvier
Melinated nerve fibres found in spinal and cranial nerves
[the group of cytons there dendrites and Axon terminals of presynaptic neurones
together form ganglion outside the CNS and nucleus within white matter of CNS]
 NON MYELINATED :- nerve fibre is enclosed by schwann cells that does not
form a mile in feet around the Axon
it is commonly found in autonomic and somatic neural system

12. 2) Neuroglial cells: these are nutritive supportive and protective cells of nervous
system
These are of following types;
 Microglia:- smallest and they are type of microfuge cells of nervous system
provides non specific immunity and increase in their number indicates neural
infection
 Astroglia or astrocytes cells:- star shaped cells and are the largest and the most
abundant neuroglial cells.
these cells form blood brain barrier/BBB with the capillaries of brain,it protect the
brain by preventing the crossing of certain substances of blood which could be
harmful to brain.
 Oligodendroglia cells:- help to form the myelin sheath in neurones of CNS.the
plasma membrane of the cells is interrupted at the level of runways so they do
not form continuous sheath around myelin sheath of neurone with in CNS,
therefore neurones of tract are not regenerated.

13.  Schwann cells:- they help to form myelin sheath outside of CNS. The PM of
the cells is continued even at the level of node of ranvier show the
continuous sheath of swan cells is found around myelin sheath.
therefore these neurones can be regenerated due to the continuous
neurilemma.
 Ependymal cells:- these are cuboidal ciliated cells which help to form the
lining of CNS.

14. Physiology of conduction of nerve
impulse
 The conduction of impulse is studied with the help of an instrument known
as cathod ray oscilloscope.
 conduction of impulse across the action of both non myelinated and
unmyelinated neurones takes place the same manner as given below:-
1. Polarized state/resting phase
2. Depolarised state/impulse/action potential
3. Repolarised state

15. Polarised state
 Resting state of neurone when no stimulus is given.
 It shows positive charge towards extracellular Fluid and negative charge
towards axoplasm.
 Polarized state is due to an imbalance on either side causing the potential
difference of -70 mV as resting potential/membrane potential.
 The reason is that the membrane is comparatibly more permeable to
potassium ion and nearly impermeable to sodium ions and is impermeable
to –vely charged protien present in axoplasm.
 In contrast outside the axoplasm contains low amount of conc. Of k+ ions
and high conc. Of Na+ and thus forms conc. Gradient.
 It is due to this fact that k+ channels/voltage gated channel remained
open during polarised state, so k+ returns from ECF to axoplasm just to
bring the hyperpolarised state to polarises state [from -90/-80mV to -
70mV].

16. Depolarised state/impulse/action potential
 This is the state which is observed when some stimulus is applied at site
[site A] on a polarised membrane of Axon that causes the opening of Na+
gates/channels in the axolemma , so Na+ will in flow from ECF along with
concentration gradient through diffusion.
 It is due to the rapid influx of Na+ at site A , that the number of sodium
+potassium in the axoplasm will gradually increase and then it becomes
more than the number of Cl- and negatively charged protien resulting in
reversal of polarity.
 This the resting potential of -70mV will be changed to action potential of
plus 30mV.
 Resultantly the outer surface of the membrane/ axolemma becomes –vely
charged and the inner becomes +vely charged.

18.  At site, immediately ahead, the axon (site B) membrane has a positive
charge on the outer surface and a negative charge on its inner surface.
 As a result, a current flows on the inner surface from site a to b.
 On the outer surface, current flows from side b to a to complete the circuit
of current flow.
 Hence, the polarity at site B is reversed, and and action potential is
generated at site B.
 Thus, the impulse/action potential,generated at site A arrives at B.
 The sequence is repeated along the length of axon and consequently the
impulse is conducted.
 In this manner, the process of depolarization/action potential/impulse
progresses in the form of a wave.
[spike potential/hyper depolarised state:- it is the action potential of +60mV,
which is observed during initial stage of depolarization but its own returns to
the action potential of +30mV by the opening of potassium channel].

19. • Though the number of sodium + potassium has become more than the
chloride negative and negatively charged protein in axoplasm but the
number of sodium ion is still higher in ECF as compared axoplasm.
Repolarised state
 It is the process of returning of axolemma from the polarized
state to polarized state.
 It also progress is in the form of a wave and begains from the
same point Where from the wave of depolarization was started
earlier.
 During this process of repolarization the sodium moves out of
the axoplasm to ECF AGAINST THE CONCENTRATION GRADIENT
THROUGH Na+and K+ PUMP, which is operated byTHE
BREAKDOWN OF ATP IN PRESENCE OF ENZYME ATPase.

20.  It is due to the outflow of sodium Ion that the number of sodium and
potassium ion will again become less than the number Chloride negative
and negatively charged protein in the axoplasm so axolemma regains
positive charge towards ECF and –ve charge towards axoplasm.
 And thus action potential of +30 return to the action potential of -70 mV.
 Since, the process of repolarization ,the Na+ gated remainopend for long
time, so resting potential of -80 to -90mV [hyper polarised state] is
achieved , but soon it returns to the resting potential of -70mV by the
opening of K+ hatred channels.
 THE RATIO OF Na+ AND K+EXCHANGES ACROSS THE AXOLEMMA IS
FOUND TO BE 3:2
 No new stimulus can be generate the impulse in a neuron , the wave o
repolarization/refractory period is completed.
 Speed of conduction of impulse in the non – myelinated neuron is
50cm/sec.

22.  Conduction of nerve impulse in the axon of myelinated neuron
The exchange of ions takes place only at the level of node of ranvier, where
actually mama is exposed to ecf, show impulse conduction in jumping
manner from node to node and is also known as saltatorial conduction of
impulse.
 The speed of conduction of impulse in myelinated neurone is therefore
found to be relative li higher and it is 132 -150 metre per second.

23. Conduction of impulse across the
synapse
 Conduction of impulse across the Axon is electrical conduction, which is
caused by exchange of electrical ions, but the conduction of impulse
across the synapse is chemical conduction, which is caused by the release
of neurotransmitters,show overall conduction of impulse is electrochemical
conduction
 The impulse is conducted across the synapse in following manner
1. in response to wave of depolarization or impulse, the calcium Ion
channels open in the plasma membrane of synaptic knobs, So diffusion of
calcium ion will take place from the synapse (calcium ions are found to be
almost 10000 times more in synapse as compared to synaptic knobs) into
synapse knob, along with the concentration gradient.

24. 2. These calcium ions the synaptic vesicles to attach themselves to the plasma
membrane of synaptic knob, which is followed by the release of
neurotransmitters [acetylcholine] into the synaptic cleft through exocytosis.
3.The released acetylcholine binds with the receptor proteins on plasma
membrane of postsynaptic cell, and acetylcholine receptor complex is formed
that generates excitatory postsynaptic potential/EPSP,which causes the
opening of sodium gated channels in the postsynaptic membrane and the
impulse is conducted.
4. In response to wave of repolarization, calcium ions came out of synaptic
Knob against the gradient by breakdown of ATP and stimulate the enzyme
acetylcholinesterase, which brings about the breakdown of acetylcholine
receptor complex.
5. acetylcholine is also broken down into acetic acid and choline, which are
taken back into the synaptic knobs through endocytosis
and finally acetylcholine is Resynthesized in synapse techno under the
influence of another enzyme acetylcholine transferase.

26. Neurotransmitter/Neurohumour
 These are chemical substances which help in conduction of impulse across
the synapse
 Basically there are two types of neurotransmitters as per their action, as
excitatory type and inhibitory type
 There have been almost 90 types of neurotransmitters identified so far and
some of them are
1. Acetylcholine:-it is most abundant neurotransmitter of body. It is
excitatory neurotransmitter in whole body except at the level of heart,
where it is inhibitory in nature
2. Noradrenaline/norepinephrine
3. Adrenaline/epinephrine

27. 4.Nitric oxide:-It is secreted by parasympathetic nerve at the level of class
venison clitoris
5. Histamine
6. Serotonin
7. Melatonin
8. Dopamine:- it is secreted by basal nucleus, and is found to be antagonistic
to acetylcholine and prolactin hormone
9.GABA/GAMMA AMINOBUTYRIC ACID:- it is any battery at the level of brain
10.Glycine:- it is inhibitory at the level of spinal chord
11.Glutamic acid:- it is excitatory at the level of whole CNS.

28. Receptors and their classification
 The receptors are modified dendrites of sensory neurone and all of them
are enclosed into an elastic capsule except pain receptor which are the
receptor devoid of elastic capsule.
 Due to presence of receptors CNS can exert influence on
1. perception of stimulus
2. Regulation of many of the activities.
These specialised structure convert any form of energy into electrical impulse
in afferent neurone, this action known as transduction and receptors are
called biological transducers.

29. Classification of receptors
 Based on the type of stimulus for which they respond, They can be
classified Into :-
1. Mechanoreceptor :-Response for mechanical energy like touch pressure
and Vibration. They are present all over the body parts.
In SKIN
a)Markel‘s disc
b)Meissner corpuscles (touch receptor)
c)Pacinian corpuscles etc.

30. In VECERAL ORGANS
1. Baroreceptors
2. Volume receptors
3. Auditory receptors etc.
Some of the example of CHEMORECEPTORS
1. Taste receptor
2. Olfactory receptor
3. Osmoreceptors
Thermoreceptors present in skin
Nociceptive respond for Painful stimulus
Electromagnetic receptor present in eye