going before another in time or order I'd like to follow up on an antecedent question from another reporter Synonyms previous, anterior, foregoing, former, precedent, preceding, priorRelated Words advance, early, premature; earliest, first, inaugural, initial, maiden, original, pioneer; preexisting; introductory, preliminary; erstwhile, whilomNear ...
Neurotransmitters are formed in a presynaptic neuron and stored in small membrane-bound sacks, called vesicles, inside this neuron. When this neuron is activated, these intracellular vesicles fuse with the cell membrane and release their contents into the synapse, a process called exocytosis.
An action potential cannot cross the synaptic cleft between neurones. Instead the nerve impulse is carried by chemicals called neurotransmitters. These chemicals are made by the cell that is sending the impulse (the pre-synaptic neurone) and stored in synaptic vesicles at the end of the axon.. This causes a depolarisation of the post-synaptic cell membrane, which may initiate an action potential, if the threshold is reached. 6. The neurotransmitter is broken down by a specific enzyme in the synaptic cleft; for example the enzyme acetylcholinesterase breaks down the neurotransmitter acetylcholine.