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Neurons - Anatomy & Physiology (view source)
Revision as of 09:27, 25 August 2011
, 09:27, 25 August 2011→Unmyelinated Axons
Nerves are able to create, amplify and propogate electrical impulses that run along their axon. These nerve impulses are a form of action potential that is carried by ions. The nerve impulse is in effect an electrical difference between the inside and outside of the axon and is caused by ion movements across the membrane. Nerve impulses can occur from a number of sources including sensiry cells, action potentials from other connected nerves or spontaneous depolarisation of the nerve cell membrane.
Nerves are able to create, amplify and propogate electrical impulses that run along their axon. These nerve impulses are a form of action potential that is carried by ions. The nerve impulse is in effect an electrical difference between the inside and outside of the axon and is caused by ion movements across the membrane. Nerve impulses can occur from a number of sources including sensiry cells, action potentials from other connected nerves or spontaneous depolarisation of the nerve cell membrane.
====Unmyelinated Axons====
====Unmyelinated Axons====
Conduction of an action potential along an unmyelinated axon, i.e. an axon not covered by some form of glial cell, is a much slower form of nerve impulse propagation than that of a myelinated axon.
Conduction of an action potential along an unmyelinated axon, i.e. an axon not covered by some form of glial cell, is a much slower form of nerve impulse propagation than that of a myelinated axon.
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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'''.
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'''.
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The internal electrical resistance within the axon is the determining factor regarding how fast the local positive current impulse can pass through. The less the internal resistance, the higher the conduction velocity of the nerve impulses due to the locally positive current being able to depolarise the membrane to threshold level over a greater distance. This internal resistance decreases as a function of axon diameter an therefore thicker axons are able to conduct nerve impulses more rapidly.
====Myelinated Axons====
====Myelinated Axons====