Properties of nerve fibres 1)Excitability 2)Conductibility 3) Unfatigability 4) Summation 5) Accomodation

1. PHYSIOLOGY SEMINAR
BY,
KARTHIK G R
1st YEAR MBBS
RIMS RAICHUR
TOPIC:-
PROPERTIES
OF NERVE
FIBRES.

2. 01
02
03
04
05
PROPERTIES
OF NERVE
FIBERS.
EXCITABILITY
CONDUCTIVI
TY
UNFATIGABILI
TY
ACCOMMODATI
ON
SUMMATION

3. NERVE FIBRE
WHAT IS AN
A thread like extensions (as axons or
dendrites ) of a nerve cell that carry nerve
impulses

4. 1.)EXCITABILITY.
✓ ABILITY to produce action potential towards
various types stimulus.
4
Factors Affecting Excitability
1. Effect of extracellular Ca++
i. in ECF Ca++ excitability of
neuron
ii. Increase in ECF Ca++ stabilizes the
membrane by decreasing excitability
2. Strength and duration of the
stimulus

5. STRENGTH DURATION CURVE
The relationship between the strength
and duration of stimuli depicted in
graph form is known as strength-
duration curve. These two parameters
are inversely related to each other.
Rheobase.
To excite a tissue, the lowest
amplitude of current required.
Utilization time.
The minimumtime for which the rheobase
must be applied to elicit an action
potential
Chronaxie.
The time required for a stimulus of
double the rheobase strength to
produce an action potential.
01
02
03
5
The lesser the chronaxie, the
greater is the excitability

6. circular pattern of cur
rent flow occurs across the
membrane;
i.e. inside the , positive
charges flow away from the
site of action potential,
whereas outside the
membrane, positive charges
flow towards the site of action
potential
In Unmyelinated Axon.
In Myelinated Axon (Saltatory
Conduction).
✓Myelin acts as an insulator
✓concentration of positive charges
does not decrease fast because of
less ‘leakage’. This helps the
charges to spread farther along the
axo
✓action potential is generated at
Conductiv
ity
On stimulation, action potential is
generated in the nerve fiber, which
is propagated along its entire
length to the axon terminal
large influx of positive charges into the membrane ,At
the site of genesis of an action potential.
current sink

8. 01
02
03
ACCOMMODATIO
N
Application of continuous stimuli may decrease the
excitability of the nerve fiber, a phenomenon called
accommodation.
If a nerve is submitted to the passage of constant strength
of current, the site of stimulation shows decrease in
excitability.
A similar feature observed at at nerve
endings is called adaptation.
WHAT IS IT?
Causes.
The accommodation consists of a rise in
threshold of the membrane during stimulation.

9. Unfatigability
✓Nerve fibers cannot be fatigued, even when they
are stimulated continuously.
✓because the nerve fibers primarily conduct
impulses (propagation of action potential) that do
not involve expenditure of energy (ATP).

10. Summation.
Application of a subthreshold stimulus does not evoke an
action potential. However, if subthreshold stimuli are applied
in rapid succession, they are summated and they produce an action
potential.

11. APPLIED PHYSIOLOGY.
L E T U S U N D E R S T A N D T H E M A T H.
LOCAL
ANESTHESIA.
✓ It is used to block the
conduction of action potentials
in sensory and motor nerve
fibers.
✓occurs as a result of blockade
of voltage-gated Na+ channels
on the nerve cell membrane.
✓causes a gradual increase in
the thresholdand a slowing of
axonal conduction velocity

12. Thank You
For Your Attention!