25. Unidirectional propagation of electrical signal in nervous system is
(1) proportional to the length of axon.
(2) due to chemical synapse.
(3) due to electrical synapse.
(4) proportional to myelination
Introduction
Nerve impulses or action potentials in neurons typically travel in a unidirectional manner—from the cell body toward the axon terminals. Understanding the mechanism behind this one-way flow is fundamental in neurophysiology. Various factors influence directional conduction, but a principal cause is the specialized structure and function of synapses between neurons.
Mechanism of Unidirectional Propagation
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Nerve impulses propagate along the axon as electrical signals, but at synapses, the signal must cross a tiny gap known as the synaptic cleft through chemical means.doubtnut+1
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Chemical synapses, the most common type of synapse, transmit signals via the release of neurotransmitters from the presynaptic axon terminal (telodendrons) to the postsynaptic dendrites or soma of another neuron.vedantu
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Receptors for neurotransmitters exist only on the postsynaptic membrane, ensuring that signaling occurs exclusively in one direction, preventing backward flow of signals.askfilo+1
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This anatomical and biochemical arrangement ensures the unidirectional flow of information from axon to dendrite across synapses.
Analysis of the Provided Options
| Option | Explanation | Correctness |
|---|---|---|
| (1) | Propagation proportional to axon length (affects speed, not direction) | Incorrect |
| (2) | Unidirectional flow due to chemical synapse | Correct |
| (3) | Due to electrical synapse (these allow bidirectional flow) | Incorrect |
| (4) | Proportional to myelination (affects speed, not direction) | Incorrect |
Additional Points
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Though the electrical signal travels along the axon membrane in both directions in experimental conditions when stimulated in the middle, under physiological conditions, unidirectional propagation is enforced by the synaptic structure and neurotransmitter release mechanism.wikipedia
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The absolute refractory period also helps prevent backward propagation along axonal membrane but the ultimate unidirectionality in neural circuits is dictated by synaptic function.wikipedia
Summary Table
| Factor | Role in Nerve Impulse Direction |
|---|---|
| Chemical synapse structure | Ensures signal moves presynaptic to postsynaptic |
| Absolute refractory period | Prevents backward propagation on axon |
| Electrical synapse | Allows bidirectional conduction, rare in CNS |
| Axon length or myelination | Affects conduction velocity, not direction |
Conclusion
The unidirectional propagation of electrical signals in the nervous system is primarily:
(2) due to chemical synapse
1 Comment
Bhawna Choudhary
September 25, 2025Unidirectional flow due to chemical synapse