Answer
The message of a nerve impulse is carried from neuron to neuron across fluid filled synaptic clefts. The transfer of the message is mediated by neurotrnsmitters like acetylcholine, norepinephrine, and dopamine.
The speed of nerve impulses is about 300 mph, and the crossing of the synapse slows the transmission (synaptic delay). Still, the period of action of the neurotramsmitter on the post synaptic cell is relatively brief-- about 0.5 seconds. This period is so brief because after the neurotransmitter is released, it has but a short period to bind before it is inactivated or removed from the synaptic cleft. In the case of acetylcholine, the neuotransmitter is degraded and deactivated by the enzyme acetylcholinesterase. That puts an end to its activity.
Work Step by Step
Several kinds of neurotransmitters mediate neural stimuli transnission across synaptic clefts.. Some examples of neurotransmitters are acetylcholine, biogenic amines, amino acids epinephrine, norepinephrine, serotonin, dopamine.
After a neurotransmitter is poured out into a synaptic cleft it binds t receptors on the post synaptic neuron. This action modifies the permeability of the postsynaptic neuron and facilitates transmission of the impulse. But while the neurotransmitter is in the synaptic cleft it blocks transmission of other impulses. Therefore it must be removed after it has done its job to permit the transmission of other messages.
Neurotransmitters are removed or inactivated in three ways; Some are degraded and deactivated by enzymes. This is the case with acetylcholine. In other cases, the neurotransmitter is taken up by astrocyteor by the presynaptic terminal. In still other cases, the neurotransmitter just diffuses out of the synaptic cleft.
