Nervous Transmission

Propagation of a Nerve Impulse

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Ben Whitten

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How is a nerve impulse propagated?
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Once a nerve impulse is generated, the permeability of the cell membrane changes with voltage-gated sodium channels opening, allowing sodium ions to flow into the cell. The flow of ions causes a reversal in charges, the positive charge now on the interior of the cell and the negative charge now on the exterior of the cell. When this occurs, the cell is said to be depolarised


The voltage-gated sodium channels then close, and voltage-gated potassium channels open, allowing for potassium to flow out of the cell and restore the cell's interior back to its negative charge. It is now said to be repolarised.


The voltage-gated potassium channels then shut, but the membrane potential drops below -70mV, which causes hyperpolarisation to occur before returning to the resting state. This change from being polarised to depolarised (called an action potential) occurs as a 'wave', the nerve impulse moving along the axon in a single direction. The sodium-potassium pump then continues to pump sodium out of the cell and potassium into the cell to restore ion concentrations.


The refractory period is the period during which the neuron canot be stimulated again; this period begins at the start of the action potential and a short tmime after, until the resting membrane potential of -70mV is restored.

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Topic Menu
Nervous System
Types of Neurons
Conduction of a Nerve Impulse
Propagation of a Nerve Impulse
Transmission of a Nerve Impulse
Transmission Across a Synapse
Types of Receptors
Reflexes
Comparing Hormonal and Nervous Control
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