Generation And Conduction Of Nerve Impulse – NCERT Notes

CBSE Class 11- Neural Control and Coordination: The generation And Conduction Of Nerve Impulses consist of three steps – Polarization, Depolarization, and Repolarization. Due to the presence of active and electronic potentials along the conductors conduction of nerve impulses arises. The nerve impulse is the electric signal which passes along with the dendrites to generate a nerve impulse. Nerve impulse can either be depolarized or be in an action potential. 

Generation and Conduction of Nerve Impulses, also known as Action Potentials. Neurons are the main factor that generates and conduct the impulse when they get any stimulus. Nerve impulses helps neurons to communicate and transmit information throughout the organism body. These electrical signals generat when there is a change in the electrical potential across the cell membrane of a neuron.

Generation And Conduction Of Nerve Impulse

The nerve impulse is defined as the temporary changes in the neuron because of the disturbance which is created by the stimulus of adequate strength. The nerve impulse is propagated through the Axon, synapse, and neuromuscular junction which is known as Nerve Impulse conduction.

Process for Generation and Conduction of Nerve Impulse

The neuron is known as the unit of the nervous system. It has three main parts-

1. Axon
2. Cell Body
3. Dendrites

There are two axons depending upon the myelin sheath. 

• Myelinated nerve: In some neurons, the axon is myelinated at intervals. The gaps which are in between them are known as nodes of Ranvier. They are mainly found in the white matter of the brain and spinal and cranial nerves.
• Non-Myelinated nerve: In these neurons the myelin sheath is absent. They are found in somatic and autonomic neural systems.

Steps for Conduction of Impulse

Polarization (Resting Potential)

When a nerve fiber is not conducting an impulse it is known as a Resting nerve fiber. This is known as the polarized state of the nerve fiber. In this state, the axoplasm contains a low concentration of sodium ions, Na⁺, and a high concentration of potassium ions, K⁺. On the other hand outside the axoplasm, the concentration of potassium ions is low and sodium ions are high. This creates a concentration gradient between the outside and inside of the membrane. 

There is a sodium-potassium pump (Na ⁺ / K⁺ pump) that is present in the membrane of the axon which allows the efflux and influx across the membrane. It creates a difference of charges between membranes when every 3Na ⁺ ions are transported outside the membrane and 2K⁺ ions are transported inside the membrane. There is a production of positive charge and negative charge in the outer axonal membrane and inside the membrane respectively. This is known as the Resting Potential.

Depolarization (Action Potential)

When a nerve fiber starts conducting a nerve impulse depolarization occurs. When the stimulation strength is above the threshold value then it may not result in a much stronger impulse. This is known as the all-or-none law which results in a rapid influx of Na⁺ ions to the membrane. There is the reversibility of the polarized state to the depolarized state. There is a generation of positive and negative charges on the inside and outside of the membrane respectively. This type of potential difference across the membrane is known as action potential which is known as nerve impulse. 

Repolarization

The rise in permeability of Na+ occurs in a depolarized state which is followed by the rise in permeability of K+ inside the membrane. In the next generation positive charge outside the membrane and negative charge inside the membrane within a fraction of seconds further results in the restoration of resting potential. The refractory period is the time taken by the fiber to gain the potential resting state again. This type of period is short of about one millisecond which means a thousand impulses can be sent in a second. Unidirectional and not bidirectional are the impulse conduction along the nerve fiber. This generally occurs due to the generation of refractory periods.

Saltatory Conduction of Nerve Impulse

Fast transmission of nerve impulses occurs as depolarization which occurs only at the nodes of Ranvier which are present at intervals of the myelin sheath. Nerve impulse jumps from one node to another which is known as saltatory conduction of nerve impulses.

Feature of Saltatory Conduction:

• Energy usage is less in saltatory conduction in myelinated nerve fiber than the nerve impulse in the unmyelinated nerve fiber.
• Fast conduction of nerve impulse in myelinated nerve fiber than in unmyelinated fiber.

Conclusion

Therefore, There are three types of processes that are involved in the generation and conduction of nerve impulses – Polarization, Depolarization, and Repolarization. The polarized condition in a nerve fiber is its resting state and the refractory period is the period of time that occurs between the depolarization and repolarization. A chemical or electrical synaptic connection is formed between two neurons from their axon ends.

FAQs on Conduction of Nerve Impulse

Q1: Define the Generation and Conduction of Nerve Impulses.

Answer:

It refers to the temporary changes in the neuron because of the disturbance which is created by the stimulus of adequate strength. The nerve impulse is propagated through the Axon, synapse, and neuromuscular junction which is known as Nerve Impulse conduction.

Q2: Name the parts of the Neuron.

Answer:

 There are three main parts of neuron-

• Axon
• Cell Body
• Dendrites

Q3: Define Polarization.

Answer:

When a nerve fiber is not conducting an impulse it is known as a Resting nerve fiber. This is known as the polarized state of the nerve fiber. In this state, the axoplasm contains a low concentration of sodium ions, Na⁺, and a high concentration of potassium ions, K⁺. 

Q4: What are the steps for the conduction of Impulse

Answer:

There are three steps for conduction of Impulse:

• Polarization (Resting Potential)
• Depolarization (Action Potential)
• Repolarization