1.
Basic Physiology Of Nerve

2.
Nervous system controls all the activities of the body.
Primarily, nervous system is divided into two parts:
1. Central nervous system
2. Peripheral nervous system.
Central nervous system (CNS) includes brain and spinal cord.
• It is formed by neurons and supporting cells called neuroglia.
• Structures of brain and spinal cord are arranged in two layers, gray matter and
white matter.
• Gray matter is formed by nerve cell bodies and the proximal parts of nerve
fibers, arising from nerve cell body. White matter is formed by remaining parts
of nerve fibers.

3.
Peripheral nervous system (PNS) is formed by neurons and their processes present
in all regions of the body.
• It consists of cranial nerves, arising from brain and spinal nerves, arising from
the spinal cord.
It is again divided into two subdivisions:
a) Somatic nervous system
Somatic nervous system is concerned with somatic functions. It includes the nerves
supplying the skeletal muscles. Somatic nervous system is responsible for muscular
activities and movements of the body
b) Autonomic nervous system.
Autonomic nervous system is concerned with regulation of visceral or vegetative
functions. Also called as involuntary nervous system.
Autonomic nervous system consists of two divisions, sympathetic division and
parasympathetic division.

4.
Neuron
Neuron or nerve cell is defined as the structural and functional unit of nervous system.
STRUCTURE OF NEURON
Neuron is made up of three parts:
1. Nerve cell body
2. Dendrite
3. Axon.
Dendrite and axon form the processes of neuron. Dendrites are short processes and the
axons are long processes. Dendrites and axons are usually called nerve fibers.
CLASSIFICATION OF NEURON
❖ Depending upon the number of poles neurons are divided into three types:
1. Unipolar neurons
2. Bipolar neurons
3. Multipolar neurons.

5.
❖ Depending upon the function nerve cells are classified into two types:
1. Motor or efferent neurons
2. Sensory or afferent neurons.
❖ Depending upon the length of axon, neurons are divided into two types:
1. Golgi type I neurons
2. Golgi type II neurons
The properties of the nerve
a. Excitability
b. Conductivity
c. Refractory period
d. Summation
e. Adaptation
f. Infatigability
g. All or none law.

6.
Excitability
Excitability is defined as the physiochemical change that occurs in a tissue when
stimulus is applied
Excitability in the nerve gets manifested in the form of electrical change. The
electrical change leads to generation of an action potential (impulse) from the
resting state(resting membrane potential) of the nerve.
Rheobase—is the minimum strength of stimulus required to stimulate (excite) a
tissue without considering the time duration for which the stimulus has to be
applied.
Chronaxie—is the minimum time required to excite a tissue with double the
rheobasic current.

7.
Response Due to Stimulation of Nerve Fiber:
When a nerve fiber is stimulated, based on the strength of stimulus, two types of
response develop:
1. Action potential or nerve impulse
Action potential develops in a nerve fiber when it is stimulated by a stimulus with
adequate strength. Adequate strength of stimulus, necessary for producing the
action potential in a nerve fiber is known as threshold or minimal stimulus.
2. Electrotonic potential or local potential
When the stimulus with subliminal strength is applied, only electrotonic potential
develops and the action potential does not develop. Electrotonic potential is non-
propagated.

8.
Conductivity
Conductivity is the ability of nerve fibers to transmit the impulse from the area of
stimulation to the other areas.
Action potential is transmitted through the nerve fiber as nerve impulse.
The important factors which affect the velocity of impulse conduction in nerve
fibers is whether the nerve fiber is myelinated.
In a myelinated nerve fiber the impulse jumps from one node of Ranvier to the
next node. This type of conduction is called as saltatory or leaping conduction

9.
Myelin sheath is not permeable to ions. So, the entry of sodium from extracellular fluid
into nerve fiber occurs only in the node of Ranvier, where the myelin sheath is absent.
It causes depolarization in the node and not in the internode. Thus, depolarization
occurs at successive nodes. So, the action potential jumps from one node to another.
Hence, it is called saltatory conduction (saltare = jumping).
In an unmyelinated nerve the impulse conducted by, the Depolarization occurs first at
the site of stimulation in the nerve fiber. It causes depolarization of the neighboring
depolarization travels throughout the nerve fiber. Depolarization is followed by
repolarization.

10.
Refractory period
Refractory period is the period at which the nerve does not give any response to
a stimulus.
Refractory period is of two types:
1. Absolute Refractory Period
Absolute refractory period is the period during which the nerve does not
show any response at all, whatever may be the strength of stimulus.
2. Relative Refractory Period
It is the period, during which the nerve fiber shows response, if the strength
of stimulus is increased to maximum.

11.
Summation
When one subliminal stimulus is applied, it does not produce any response in the
nerve fiber because, the subliminal stimulus is very weak. However, if two or
more subliminal stimuli are applied within a short interval of about 0.5
millisecond, the response is produced. It is because the subliminal stimuli are
summed up together to become strong enough to produce the response. This
phenomenon is known as summation
Adaptation
While stimulating a nerve fiber continuously, the excitability of the nerve fiber is
greater in the beginning. Later the response decreases slowly and finally the nerve
fiber does not show any response at all. This phenomenon is known as
adaptation or accommodation.

12.
Infatigability
Nerve fiber cannot be fatigued, even if it is stimulated continuously for a long
time. The reason is that nerve fiber can conduct only one action potential at a
time.
All-or-none law
All-or-none law states that when a nerve is stimulated by a stimulus it gives
maximum response or does not give response at all.

13.
Resting membrane potential (RMP)
Resting membrane potential (RMP) is the potential difference that exists between
the extracellular fluid (ECF) and intracellular fluid regions (ICF) (that is across the
cell membrane)
For a cell’s membrane potential, the reference point is
the outside of the cell. In most resting neurons,
neurons have a resting membrane potential of about -
30mV to -90 mV
Because there is a potential difference across the cell
membrane, the membrane is said to be polarized.

14.
If the membrane potential becomes more positive than it is at the resting potential,
the membrane is said to be depolarized.
If the membrane potential becomes more negative than it is at the resting
potential, the membrane is said to be hyperpolarized.

15.
when the tissue is at rest, Normally when compared to extracellular fluid, the intra-
cellular fluid part is negative. Hence the resting membrane potential value is always
is prefixed with a -ve symbol. In a nerve fiber it is mostly around -79mV.
Resting membrane potential is always due to the
unequal distribution of the charged Substances
in extracellular and intracellular fluid regions.
Types of ions found in neurons In neurons
are:
Positively charged (cations): Sodium Na+
and potassium k+
Negatively charged (anions): Chloride Cl-
and organic anions

16.
Sodium tries to move (diffuse) into intra-cellular fluid along the electrochemical
gradient, potassium tries to move out into extracellular fluid along concentration
gradient and chloride tries to move in along concentration gradient alone.
The cell membrane is more permeable for potassium ion diffusion than sodium.
Unlike for the inorganic ions, the cell membrane is impermeable for the organic
anions. Hence the retention of the organic anions inside the cell is responsible for
the negative membrane potential at rest.
Even at rest there will be some amount of diffusion of the inorganic ions along
either the concentration or electrical gradient or both.
But the restoration of the ions at respective regions is brought about by the activity
of the pump, Na+ - K+ ATPase pump which removes sodium from intra cellular to
extra cellular fluid and vice versa for potassium.

17.
Action potential
An action potential is a rapid rise and fall in voltage or membrane potential across a
cellular membrane.
An action potential occurs when a neuron sends information down an axon, away
from the cell body.
• During the action potential development the membrane of the tissue becomes
permeable for sodium.
• So the sodium ions move from the extracellular fluid into the intracellular fluid
region. Because of the influx of the sodium ions, the interior becomes positive as
against the negative state observed during the resting condition.
• The reversal of polarity due to sudden influx of sodium ions is responsible for the
process of depolarization.
• The sodium ion influx is so much that the membrane potential exceeds the zero
potential and over shoots. The potential reaches as much as + 35 mV.

18.
• During the later part of depolarization the sodium channels begin to close and
potassium channels start opening up.
• Because Of this there will be efflux of potassium ions. The outward movement
of potassium ions will bring about the re-establishment of Polarized state
(repolarisation) of the membrane.

19.
THANK YOU
PRESENTED BY: DINU DIXON
MPT(NEUROLOGY)