Conduction of nerve impulse Across synapse
In a synapse, there is a narrow fluid-filled
gap of 10-20 nm, called synaptic cleft. The
nerve terminal has a bulbous expansion called
synaptic knob or synaptic button.
In the cytoplasm of the synaptic knob,
numerous tiny membrane-bound synaptic
vesicles are present. These synaptic vesicles
contain as many as 10,000 molecules of the
neurotransmitter. When a nerve impulse
reaches the presynaptic membrane, the
voltage-gated calcium channels concentrated
in the synapse, open.
Calcium ions from the fluid in the synapse
diffuse into the synaptic button and stimulate
the vesicles to move to the terminal membrane,
fuse with it and then rupture to release the
neurotransmitter.
The neurotransmitters quickly diffuse to the
other side of the gap, combine with specific
receptor molecules of the other nerve cell and
cause sparking a second electrical current,
passing its signal.