Generation and Conduction of Nerve Impulse: Meaning, Process

Generation and Conduction of Nerve Impulse: A living creature is made up of several cell types that help it govern and coordinate with its environment. Coordination is the result of two systems in an animal’s body: the neurological and endocrine systems. Have you ever observed how quickly we react to stimuli such as removing our hands from hot objects? The nervous system is one such system that controls and coordinates with the working of the entire body. This coordination is achieved by the Generation and Conduction of Nerve Impulses.

This Nerve Impulse system receives information from the environment and responds accordingly. The neuron is the unit of this system. Let us have an overview of how the Generation and Conduction of Nerve Impulses occur. This article will teach you about neurons and the creation and transmission of nerve impulses. Let us understand more about nerve impulse generation and conduction with various examples. 

Generation and Conduction of Nerve Impulse Definition

Nerve impulse refers to the temporary changes in the neuron due to the disturbance created by the stimulus of adequate strength. This nerve impulse propagates through the Axon, synapse and, neuromuscular junction is called Nerve Impulse conduction.

Diagram

Fig: Generation and Conduction of Nerve Impulse

The Process for Generation and Conduction of Nerve Impulse

The neuron is the unit of the nervous system. It has the following parts, namely:
1. Cell body
2. Axon
3. Dendrites

Axon may or may not be covered with a myelin sheath. Depending on the myelin sheath, there are two Axon-
a. Myelinated nerve fibres- Axon is myelinated at intervals in some neurons. The gap is called the nodes of Ranvier. These types of nerve fibres are found in cranial and spinal nerves and white matter of the brain.
b. Non-Myelinated nerve fibres- Here, the myelin sheath is absent in the neurons. This type of neuron is present in autonomic and somatic neural systems.

Steps to Conduction of Impulse

Polarisation (Resting Potential)

Resting nerve fibre means nerve fibre is not conducting an impulse. This is called the polarised state of the nerve fibre.

During this state, axoplasm contains a high concentration of potassium ions, \({K + }\) with negatively charged proteins and a low concentration of sodium ions, \( {Na + }.\) While outside the axoplasm, the concentration of sodium ions, \( {Na + }\) are high and low \({K + }\) ions. This forms a concentration gradient between the inside and outside of the membrane.
There is a sodium-potassium pump \(\left({Na + /K + \,{\text{pump}}} \right)\) present in the membrane of the axon, which allows influx and efflux of ions across the membrane. With every \(3Na + \) ions transported outside the membrane, \(2K + \) ions are transported inside the membrane. This creates a difference of charges between membranes, and there is the production of positive charge \(\left({ + ve} \right)\) in the outer axonal membrane, while inside the membrane, there is a generation of negative charge \(\left( { – ve} \right)\) with negatively charged proteins. This is resting potential.

Depolarisation (Action Potential)

Depolarisation is acquired when a nerve fibre starts conducting a nerve impulse. During this stage, a stimulus of adequate strength or stimulus above a threshold value to the polarised membrane arrives. (If the stimulation strength is above this threshold value, then it may not result in a much stronger impulse. This is called all or none-law.) This results in a rapid influx of (Na + ) ions to the membrane. As a result, there is the reversibility of the polarised state to the depolarised state. There is a generation of \( + ve\) charge inside the membrane and \( – ve\) charge outside the membrane. This potential difference across the membrane is called an action potential, which is called nerve impulse and is conducted through the length of the nerve fibre. This depolarised state of the nerve is short-lived.

Repolarisation

The rise in permeability of \(Na + \) (occurred in a depolarised state)  is quickly followed by the rise in permeability of K+ inside the membrane. Again, generation of ( – ve) charge inside the membrane and ( + ve) charge outside the membrane within a fraction of second results in restoration of the polarised state or resting potential.
The time taken by the fibre to gain the potential resting state again is a refractory period. This period is very short of about one millisecond, which means that \(1000\) impulses can be sent in a second. Unidirectional flow of impulse: Impulse conduction along the nerve fibre is unidirectional and not bidirectional. This occurs due to the generation of refractory periods.

Saltatory Conduction of Nerve Impulse

In myelinated nerve fibres, fast transmission of the nerve impulse occurs as depolarisation occurs only at the nodes of Ranvier, which are present at intervals of the myelin sheath.
Nerve impulse jumps from one node to another. This is called saltatory conduction of nerve impulses.

Importance of Saltatory Conduction;
a. Fast conduction of nerve impulse in myelinated nerve fibres than unmyelinated fibres.
b. Expense of energy is less in saltatory conduction in myelinated nerve fibres than nerve impulse in unmyelinated nerve fibres.

Now, after the arrival of impulse till the axonal terminal, neurotransmitters are secreted in the gap between the presynaptic membrane and postsynaptic membrane. This junction between the neurons is called a synapse. Moreover, the transmission of impulse through this junction by chemicals is called a chemical synapse.

Here action potential triggers the calcium ions from the synaptic cleft to enter the presynaptic knob, which stimulates the movement of synaptic vesicles containing neurotransmitters to the surface of the knob. Then neurotransmitters bind with specific protein on the postsynaptic knob, resulting in the opening of channels in the membrane of the next neuron, thereby allowing sodium ions to enter the next neuron. This causes depolarisation in the next neuron.

Fig: Chemical Synapse

If no chemicals are involved in transmitting the nerve impulse from one neuron to the other, then that type of impulse is called an electrical synapse. The post and presynaptic membranes of neurons are in close proximity. Transmission of impulse through an electrical synapse is faster than a chemical synapse. Postsynaptic and presynaptic membranes are separated by a fluid-filled space called the synaptic cleft.

Fig: Saltatory Conduction

Summary

Generation and conduction of nerve impulses are done by three steps, i.e. polarisation, depolarisation and repolarisation. The polarised state is the resting stage of the nerve fibre. There is a positive charge outside the axonal membrane during a polarised state while inside, it is negatively charged and vice-versa during the depolarised state. Depolarisation is acquired when a nerve fibre starts conducting a nerve impulse. The nerve impulse propagates through the axon, synapse and neuromuscular junction. The time between depolarisation and repolarisation is called the refractory period. From the axon end of the neuron, nerve impulse can be transferred to the other neuron either by chemical synapse or electrical synapse.

FAQs related to Conduction of Impulse

Below here we have provided some of the most asked questions related to nerve transmission:

Q.1. How does nerve impulse generate and conducted through a nerve Fibre?
Ans: Nerve impulse is generated and conducted through a nerve Fibre through the following three steps:-
a. Polarisation
b. Depolarisation
c. Repolarisation

Q.2. What are the factors affecting the generation and conduction of nerve impulses?
Ans: Factors affecting the generation and conduction of nerve impulses are-
a. Myelinated nerve fibres- Generation and conduction of nerve impulses get faster in the myelinated nerve fibres than in unmyelinated nerve fibres.
b. Axon diameter- More diameter of axon accounts for more generation and conduction of nerve impulses.
c. Temperature- More the temperature of the body, the more the permeability of ions across the axonal membrane and as a result more the conduction of nerve impulses.

Q.3. What is the major function of a Generation and Conduction of Nerve Impulse?
Ans: Control and coordination is the major function of a Generation and Conduction of Nerve Impulse. Other functions are memory and homeostasis.

Q.4. What is the conduction of nerve impulses?
Ans: Nerve impulse that is generated passes along the neuron. Propagation of nerve impulses through the axon and synapses is called conduction of nerve impulses.

Q.5. What is the generation of nerve impulses?
Ans: Nerve impulse is generated by a strong stimulus that causes temporary reversal of resting potential in the neuron to the depolarised state.

We hope this detailed article on Generation and Conduction of Nerve Impulse helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.