Neurons, membranes impulses transmitted along

Another type of communicating junction is also found in synapses of the nervous system. At these specialized contacts a nerve impulse transmitted along the membrane of one neuron triggers the release of a neurotransmitter, a chemical substance that passes across the gap between cells of the synapse and initiates a nerve impulse in the second neuron (Chapter 30). 

Information is transmitted along neurones in the form of electrical impulses, i.e. transient changes in potential across the cell membrane which travel from the cell body along the axon to the axon terminus (Figure 14.5). Impulses are of a fixed size but vary in frequency to convey information. 

Current knowledge of taste perception indicates that within the neuron, in each taste cell, the potassium ion concentration is higher within the cell than without, the converse being true with sodium ions so that a resting potential exists across the cell wall. It is thought that when a chemical stimulant arrives on the surface of a receptor it momentarily modifies the cell wall and allows K+ ions to move out and Na+ ions to move in, and the resultant depolarization is transmitted along the nerve. Once the neuron has fired, the membrane potential is re-established within about a millisecond and the process is repeated as long as there is sufficient stimulant. The frequency with which these impulses are sent to the brain, up to a maximum of 100-200/s, determines the intensity... 

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