When an action potential reaches the end of an axon, the – release neurotransmitters. these bind to receptors on the – neuron. eventually, the neurotransmitters are removed from the synapse. some are reabsorbed by the – neuron, a process called –, and some are broken down, in a process called

When an action potential reaches the end of an axon, the nervous terminal or the varicosities release neurotransmitters. These bind to receptors on the postsynaptic neuron. Eventually, the neurotransmitters are removed from the synapse. Some are reabsorbed by the presynaptic neuron or sending neuron, a process called reuptake, and some are broken down, in a process called enzymatic degradation.

Explanation:

Neurotransmitter liberation occurs from the nervous terminal or varicosities, in the neuronal axon. There are vesicles in the sending neuron that have neurotransmitters in their interior. When an action potential reaches the nervous terminal or the varicosities, it occurs a notable increase in the neurotransmitter liberation by exocytose. This is possible because calcium channels open letting the ion in the cell through the membrane, and letting the neurotransmitter out to the synaptic space. The molecule binds to its receptor in the postsynaptic neuron. This receptor is a protein structure that triggers an answer. As long as the signal molecule is in the synaptic space, it keeps linking to its receptor and causing a postsynaptic answer.  To stop this process, the neurotransmitter must be taken out from the synaptic space. There are two mechanisms by which the neurotransmitter can be eliminated:

Enzymatic degradation/deactivation: In the synaptic space, there are specific enzymes that can inactivate the neurotransmitter by breaking it down or degrading it. In this case, the new molecule won’t be able to bind to the neurotransmitter receptor.

Reuptake: There are receptors located in the presynaptic membrane that can capture de molecule to store it back in new vesicles, for posterior use. These transporters are active transport proteins that easily recognize the neurotransmitter.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.