The functional junction between the dendritic region of one neuron or nerve and the axon ending of another neuron is commonly called as the synaptic region or synapse.
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Sir Charles Sherrington (1861-1954) was first who applied the term “synapsis” to the point of contact between two nerve cells or neurons.
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Its physiological importance for the transmission of nerve impulses was established by McLennan (1963).
According to recent findings of electron microscope there are many different forms and arrangements of synapses, but they nearly all have the same basic structure.
The most important feature of synapse is that the membranes of the two nerve cells or neurons or nerves are separated by a space called synaptic cleft about 10-50mm wide.
It sometimes shows traces of some contained material and in some synapses from the brain it is covered by filaments.
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The presynaptic cell membrane on the side of the cleft at which the nerve impulse arrives, and the post-synaptic or subsynaptic membrane on the side where the new impulse starts, has the usual triple structure.
Clusters of synaptic vesicles are found near the pre-synaptic membrane which probably contains the transmitter substance.
It is believed that the transmitter substance is produced by the synaptic vesicles at the junction of pre- and post-synaptic membranes of two neurons which induces as change in permeability to certain ions in the postsynaptic membrane.
It is thought that an increase in permeability to the inflow of sodium ions promotes the spread of electrical activity in the post-synaptic cell or neuron.
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An increase in permeability to the inflow of potassium ions or outflow of chloride ions leads to inhibition of the spread of electrical activity.