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Neurons - Anatomy & Physiology (view source)
Revision as of 09:21, 25 August 2011
, 09:21, 25 August 2011→Unmyelinated Axons
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At a given moment voltage-gated sodium channels within the membrane of the axon will open resulting in an influx of ions following their electro-chemical gradient. This Na<sup>+</sup> influx causes the axon to accumulate a positive charge and results in cellular depolarisation. The extracellular
At a given moment voltage-gated sodium channels within the membrane of the axon will open resulting in an influx of ions following their electro-chemical gradient. This Na<sup>+</sup> influx causes the axon to accumulate a positive charge and results in cellular depolarisation. The extracellular area of the axon therefore looses its positive charge, becoming more negative resulting in a current of positive charge that flows through the tissue towards the axon. The membrane of the axon is not a perfect insulator and at some regions on the axon, particularly within the area of the axon infront of the action potential, the voltage-dependant ion channels have not activated yet. This means that some of the positive charge is able to flow out of the axon membrane in these regions and this positive charge outflow is mainly via potassium. This outward leakage of potassium results in the current within the axon only being able to travel a short distance before the nerve impulse decays. However the effect of the current locally on the voltage-gated channels means that the nerve impulse is able to open voltage-gated channels within it's immediate vicinity and this is enough for the signal to propagate along the nerve.
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The axon membrane at rest has a slightly negative charge and the local current of positive charge during an action potential reduces this negative charge. This process is called '''depolarisation''' and when this has progressed sufficiently, it results in the membrane potential reaching threshold level allowing the voltage-gated sodium channels to open. These channels only stay open for approximately 0.5ms and when they close the membrane is depolarised for a further 0.1-0.5ms. These voltage-gated channels are unable to open again for a short period post depolarisation. This is called the '''refractory period'''.
====Myelinated Axons====
====Myelinated Axons====