Summary
Chemical transmission of the neural signal through the synapse at different levels of stimulation.Select a stimulation level then click on
.Learning goals
- To understand the transmission of nerve messages at the level of the neuron, and their chemical transmission between neurons at synapses.
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The Action Potential, or nerve impulse, propagates gradually along the length of the neuron’s axon. Transmission of impulses between neurons occurs at their point of junction, called the synapse. It is estimated that about 40% of the total surface of a neuron is composed of synapses. These have three main zones: the presynaptic and postsynaptic zones, and, between these, the intersynaptic gap (or intersynaptic cleft). The message is transmitted between neurons by chemical messengers known as neurotransmitters.When it reaches the end of an axon, the nerve impulse causes the release of neurotransmitters via exocytosis at the intersynaptic gap. These attach to the postsynaptic neuron, and trigger an opening of ion channels, which permits ions to enter the cell. The stronger the impulse, the more neurotransmitters are released. To stop the stimulation of the postsynaptic neuron, neurotransmitters are removed from the intersynaptic gap in two ways :
- By degradation: specific enzymes metabolize the neurotransmitters, nullifying their effects on the postsynaptic neuron.
- By recapture: the neurotransmitters and their derivatives are reabsorbed by the presynaptic neuron, to be reused, or destroyed.
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