The Open Door Web Site
Animal Physiology Index
There are many useful sites with some good animations.
The synapse is where the nerve impulse passes from one cell to the next. In most cases the electrical signal (the action potential) stops and a chemical signal takes over to cross the gap between the cells.
The chemical messenger is called a neurotransmitter. It crosses the gap by diffusion, which creates a small delay, up to a millisecond, in the nerve signal transmission.
The advantage of using neurotransmitter is that the nerve impulse can be given some more specificity (all action potentials are the same, they only vary in their frequency and in the neurone they are travelling along). Neurotransmitters can also control the operation of the nervous system by inhibition or excitation. Many drugs that try to cure problems in the nervous system operate at synapses.
In many ways neurotransmitters are hormones working over a very short distance (about 20nm). Indeed some of them (e.g. noradrenaline) work both at synapses and in the circulatory system.
The neuromuscular junction is a synapse
The motor end plate is the terminal button of a motor neurone which makes contact with a muscle cell. The motor end plate releases the neurotransmitter acetylcholine that ultimately causes the muscle cell to contract.
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