Function of the Neuron

The function of a nerve cell is to pass on an electrical impulse. A neuron at rest has a membrane potential of -60mV, this is set by a specific balance of ion gradients and ion permeabilities which is largely controlled by voltage gated sodium and potassium channels, in a resting cell these are usually closed. An electrical stimulus causes the sodium channels to open which makes the membrane ten times more permeable to sodium than to potassium, this causes the sodium to rush into the cell making it positive on the inside instead of negative, the membrane potential peaks at 40 mV. This is called depolarization, once triggered it propagates down the axon toward the axon terminal. Once the membrane potential has peaked, it quickly repolarizes, this happens because the sodium channels are inactivated and remain closed preventing any sodium from entering the cell, and also the potassium channels open so potassium can leave the cell. This eventually restores the membrane potential to the resting -60mV. The wave of depolarization propagates down the axon till it reaches the axon terminal where it causes the terminal buds to release a neurotransmitter which diffuses into the synaptic gap, the space between one neurons axons and another neurons dendrites, and then either causes an inhibitory or excitatory response in the postsynaptic neuron that influences whether that neuron will go through depolarization. The glial cells aid in the propagation of the wave of depolarization because when they wrap around axons they leave a space between each myelin sheath known as nodes of nodes of Ranvier. Myelination decreases the ability of the neuronal membrane to retain electrical charge which permits a depolarization event to spread further and faster than it would along a nonmyelinated axon. This is important in times where a very fast response is beneficial (Becker et al, 2002).