Conduction of Nerve Impulse — Core Principles
Core Principles
Nerve impulse conduction is the process by which electrical signals, called action potentials, travel along a neuron. It begins with a neuron at its resting membrane potential, maintained by the sodium-potassium pump and leak channels, making the inside negative.
A sufficient stimulus triggers depolarization, where voltage-gated sodium channels open, allowing Na+ ions to rush in and make the inside positive. This is followed by repolarization, as voltage-gated potassium channels open, allowing K+ ions to exit, restoring negativity.
A brief hyperpolarization may occur before returning to rest. This action potential propagates along the axon, either continuously in unmyelinated fibers or by 'jumping' from node to node (saltatory conduction) in myelinated fibers, which is much faster.
The absolute refractory period ensures unidirectional flow. Axon diameter and myelination are key factors determining conduction speed.
Often confused with
Side-by-side differences the NEET paper likes to test.
| Aspect | Conduction of Nerve Impulse | Continuous Conduction |
|---|---|---|
| Type of Axon | Myelinated axons | Unmyelinated axons |
| Speed of Conduction | Very fast (up to $120\,\text{m/s}$) | Relatively slow (up to $2\,\text{m/s}$) |
| Energy Efficiency | More energy efficient (Na+/K+ pump activity concentrated at nodes) | Less energy efficient (Na+/K+ pump active along entire axon) |
| Mechanism of Propagation | Action potential 'jumps' from Node of Ranvier to Node of Ranvier (saltatory) | Action potential regenerated at every point along the axon membrane (continuous) |
| Ion Channel Distribution | Voltage-gated channels concentrated at Nodes of Ranvier | Voltage-gated channels distributed uniformly along the axon |
| Role of Myelin Sheath | Acts as an insulator, preventing ion leakage and forcing current to jump | Absent |
The primary distinction between saltatory and continuous conduction lies in the presence of a myelin sheath. Saltatory conduction, occurring in myelinated axons, is significantly faster and more energy-efficient because the action potential 'jumps' between Nodes of Ranvier, where ion channels are concentrated.
In contrast, continuous conduction in unmyelinated axons involves the sequential regeneration of the action potential at every point along the membrane, making it a slower and more energy-intensive process.
This difference is crucial for the varied speed requirements of neural communication.
Why it is tested: For NEET, understanding this difference is fundamental. Questions often test the advantages of myelination, the mechanism of saltatory conduction, and the factors influencing nerve impulse speed. It's a high-yield topic for conceptual and application-based questions related to nervous system function and disorders like multiple sclerosis, where demyelination occurs.