Question

Explain the following process:

Transmission of a nerve impulse across a chemical synapse

Answer 1

• A nerve impulse is sent across a chemical synapse, which is a fluid-filled gap between the membranes of pre- and post-synaptic neurons known as the synaptic cleft. These synapses use chemicals known as neurotransmitters to convey impulses. These neurotransmitters are stored in vesicles at the axon terminals.
• When an impulse (action potential) arrives at the axon terminal, it stimulates synaptic vesicles to migrate towards the membrane, where they fuse with the plasma membrane and burst, releasing neurotransmitters into the synaptic cleft.
• The released neurotransmitters bind to certain receptors found on the post-synaptic membrane. This interaction opens ion channels, allowing ions to enter and generate a new potential in the postsynaptic neuron. The new potential created can be either excitatory or inhibitory.

Answer 2

• There is a synapse between the end button located at the end of the axon and the dendrite of another nerve cell.
• Therefore, transmission of impulses at this place takes place through a special chemical substance called a neurohormone called acetylcholine.
• On receiving the impulse, the secretory vesicles present in the end button secrete acetylcholine. This substance establishes the functional potential in the dendrite of the second nerve cell.
• Now this potential, in the form of an impulse, continues to move forward along the entire length of the next nerve fibre.
• Thus, acetylcholine acts like a chemical messenger. Later, acetylcholine is degraded by the coenzyme acetylcholinesterase.