(d) Transmission of a nerve impulse across a chemical synapse
Answers (1)
A synapse is formed by the membranes of the pre-synaptic neuron and the post-synaptic neuron.
A synapse may or may not be separated by a gap which is called the synaptic cleft.
At a chemical synapse, the pre-synaptic and post-synaptic neurons are separated by the synaptic cleft.
When an impulse arrives at the axon terminal, the calcium ions present in the synaptic cleft enter the synaptic knobs present at the axon terminals of the pre-synaptic neuron.
The synaptic vesicles in the synaptic knobs of the pre-synaptic neuron move towards the plasma membrane and fuse with it.
The vesicles release the neurotransmitter acetylcholine in the synaptic cleft. (Empty synaptic vesicles return to the cytoplasm of the pre-synaptic neuron where they are refilled.)
The molecules of the acetylcholine bind to the protein receptors present on the plasma membrane of the post-synaptic neurons.
This binding opens the channels and sodium ions enter the post-synaptic neuron, while potassium ions leave the post-synaptic membrane.
This generates an action potential in the membrane of the post-synaptic neuron, and hence, the impulse is transmitted to the post-synaptic neuron.