Properties of Nerve fibers

The properties of the nerve fibers can be explained under the following headings:

1. Excitability
2. Conductivity
3. Refractory period
4. Summation
5. Adaptation
6. Infatigability
7. All-or-none law

1) Excitability

It is the response of the tissue when stimulated.

Nerve fibers have very less threshold for stimulus as compared to other cells.

When a nerve fiber is stimulated, based on the strength of the stimulus the response can be of 2 types

a)Development of Electrotonic potential or local potential
b)Development of Action potential or nerve impulse

a) Development of Electrotonic potential or local potential

When a stimulus of subminimal strength is applied, there is development of miniature or local potential. Here action potential or the nerve impulse is not generated. Local potential is non propagative.

b) Development of Action potential or nerve impulse

When a stimulus of adequate strength is applied, there is development of action potential. Action potential is propagative.

The minimum strength of stimulus required to develop an action potential is known as threshold strength or minimal stimulus.

2) Conductivity

It 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.

• Non-myelinated nerve fiber: continuous conduction.
• Myelinated nerve fiber: saltatory conduction (impulse jumps from node to node).

3) Refractory Period

It is the period at which the nerve does not give any response to a stimulus.

There are two types of Refractory Period:

• Absolute Refractory Period
• Relative Refractory Period

Absolute Refractory Period

It is the period during which the nerve does not show any response at all, whatever may be the strength of stimulus.

Relative Refractory Period

It is the period, during which the nerve fiber shows response, if the strength of stimulus is increased to maximum.

4) Summation

When one subminimal stimulus is applied, it does not produce any response in the nerve fiber because, the subminimal stimulus is very weak.

However, if two or more subminimal stimuli are applied within a short interval of time the response is produced.

It is because the summation of subminimal stimuli.

5) Adaptation

When a nerve fiber is stimulated continuously, the excitability is greater in the beginning. But later on the response decreases slowly and finally the nerve fiber does not show any response at all. This is called adaptation or accommodation.

Cause for adaptation

• Continuous depolarization inactivates the sodium pump and increases the efflux of potassium ions.

6) 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.

At that time, it is completely refractory and does not conduct another action potential.

7) All or None law

It states that when a nerve is stimulated by a stimulus it gives maximum response or does not give response at all.