Types of synapse
It is of two types:
1. Electrical synapse : At electrical syrapse there is continuity between the pre-synaptic and post-synaptic neurons. The continuity is provided by the gap junctions between the two neurons. In electrical synapse there is minimal synaptic delay because of the direct flow of electrical current from one neuron to the other through gap junctions.
Thus, impulse transmissiorn across an electrical synapse is always faster than that across a chemical synapse. Impulse transfer through electrical synapse does not involve any neurotransmitter. Electrical synapses
are rare. They are found in the cardiac
muscle fibres, smooth muscle fibres of
intestine and the epithelial cells of lens.
2. (i) Chemical synapse : At a chemical synapse, when an impulse arrives at a pre-synaptic knob, calcium ions from the synaptic cleft enter the cytoplasm of the pre-synaptic knob. The calcium ions cause the movement of synaptic vesicles to the surface of the knob.
The synaptic vesicles are fused with the pre-synaptic membrane and get ruptured to discharge their content(neurotransmitters) into the synaptic cleft.
The neurotransmitter of the synaptic cleft binds with protein receptor molecules on the post-synaptic membrane. This binding action changes the membrane potential of the post-synaptic membrane, openingchan channelsthe membrane and allowing sodium ions to enter the cell. This causes the depolarisation and
generation of action potential in the post-synaptic membrane. The new potential develop may be either excitatory or inhibitory. Thus, the impulse is transferred
to the next neuron.
