Final answer:
In response to a nerve impulse, the axon terminal of a presynaptic neuron releases neurotransmitters
Step-by-step explanation:
In response to a nerve impulse, the axon terminal of a presynaptic neuron releases neurotransmitters, which are chemical messengers that transmit signals to other cells. One well-known neurotransmitter is acetylcholine (ACh), which is pivotal in transmitting impulses across the synapse to post-synaptic cells such as muscle cells or other neurons. The release of acetylcholine occurs when an action potential reaches the axon terminal, causing voltage-gated Ca²⁺ channels to open. The influx of calcium ions triggers the fusion of synaptic vesicles with the presynaptic membrane, facilitating the release of ACh into the synaptic cleft through a process known as exocytosis.
Once in the synaptic cleft, ACh binds to its receptors on the postsynaptic cell. This binding alters the electrochemical potential of the target cell, initiating a new electrical impulse. Acetylcholine is then rapidly degraded by the enzyme acetylcholinesterase, or reabsorbed by the presynaptic cell, allowing the synaptic junction to be quickly cleared and ready for the next signal.