Question

How is nerve impulse transmitted along a nerve fibre?

Answer 1

The inside of the nerve cell is negative relative to the outside; there is a large concentration of sodium outside the cell and potassium inside the cell. When a sufficient stimulus is reached, voltage-gated sodium channels open and extracellular sodium rushes into the cell. The influx of sodium causes the voltage inside of the cell to increase until it reaches a threshold whereby sodium channels close and potassium channels open, allowing potassium to leave the cells - thus resulting in the return to baseline negative charge. The potassium channels are not as efficient in their closure, so at this point the voltage dips slightly below the baseline voltage, ultimately equilibrating through sodium/potassium pumps.

This reaction is a cascade, which means the action potential will travel down the axon (the extension of the nerve responsible for transmission) in a repeated pattern until it reaches the neuromuscular junction (e.g muscle cell). At that point, the action potential will cause an efflux of calcium to bind to vesicles carrying neurotransmitters, resulting in their release across the synaptic cleft (the space between the initiator and receiver of the signal). The neurotransmitter will bind to the recipient cell and have its desired effect.

Answer 2

Answer:

through axon.

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