Q.Distinguish between:
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Start your 14-day free trial to unlock the full solution →Afferent fibres bring signals in and efferent fibres take commands out; a myelinated fibre conducts fast by saltatory conduction (jumping node to node) while an unmyelinated fibre conducts slowly as a continuous wave; and cranial nerves connect to the brain while spinal nerves connect to the spinal cord.
(a) Afferent neurons and efferent neurons
The nerve fibres of the peripheral neural system are distinguished by the direction in which they carry impulses.
- Afferent, or sensory, fibres carry impulses from the tissues and organs towards the central neural system. They are the pathway by which information about the body and its surroundings reaches the brain and spinal cord.
- Efferent, or motor, fibres carry regulatory impulses from the central neural system out to the concerned peripheral tissues and organs. They are the pathway by which the central system sends its commands to the body.
(b) Impulse conduction in a myelinated and an unmyelinated nerve fibre
The difference lies in the covering of the axon and, because of that covering, in HOW the impulse actually travels along it.
- A myelinated fibre is enveloped by Schwann cells that form a myelin sheath around the axon, broken by gaps called nodes of Ranvier. Because the sheath insulates the membrane in between, ion movement (and so the action potential) can only occur at these exposed nodes — the impulse effectively jumps from one node of Ranvier to the next. This node-to-node jumping is called saltatory conduction, and because the impulse skips the insulated stretches instead of exciting every point in between, conduction is considerably faster in a myelinated fibre. …
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