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Once the action potential has finished in the neuromuscular junction, the used acetylcholine is cleared out of the synaptic cleft by the enzyme acetylcholinesterase. Several diseases and problems can be caused by the inability of enzymes to clear away the neurotransmitters from the synaptic cleft leading to continued action potential propagation.
The synaptic cleft—also called synaptic gap—is a gap between the pre- and postsynaptic cells that is about 20 nm (0.02 μ) wide. [12] The small volume of the cleft allows neurotransmitter concentration to be raised and lowered rapidly.
In general, action potentials that reach the synaptic knobs cause a neurotransmitter to be released into the synaptic cleft. [z] Neurotransmitters are small molecules that may open ion channels in the postsynaptic cell; most axons have the same neurotransmitter at all of their termini.
Axon terminals (also called terminal boutons, synaptic boutons, end-feet, or presynaptic terminals) are distal terminations of the branches of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body to transmit those ...
Furthermore, psychoactive drugs could potentially target many other synaptic signalling machinery components. In fact, numerous neurotransmitters are released by Na+-driven carriers and are subsequently removed from the synaptic cleft. By inhibiting such carriers, synaptic transmission is strengthened as the action of the transmitter is prolonged.
About once every second in a resting junction randomly one of the synaptic vesicles fuses with the presynaptic neuron's cell membrane in a process mediated by SNARE proteins. Fusion results in the emptying of the vesicle's contents of 7000–10,000 acetylcholine molecules into the synaptic cleft, a process known as exocytosis. [6]
Synaptic connections from an axon Neurotransmitter released from presynaptic axon terminal, and transported across synaptic cleft to receptors on postsynaptic neuron Most axons carry signals in the form of action potentials, which are discrete electrochemical impulses that travel rapidly along an axon, starting at the cell body and terminating ...
A diagram of the proteins found in the active zone. The active zone is present in all chemical synapses examined so far and is present in all animal species. The active zones examined so far have at least two features in common, they all have protein dense material that project from the membrane and tethers synaptic vesicles close to the membrane and they have long filamentous projections ...