Neurotransmitter release occurs from the nervous terminal or varicosities in the neuronal axon. When an action potential reaches the nervous terminal, the neurotransmitter is released by exocytose. The molecule binds to its receptor in the postsynaptic neuron, triggering an answer. As long as the signal molecule is in the synaptic space, it keeps linking to its receptor and causing a postsynaptic response. 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: There are specific enzymes in the synaptic space, which are in charge of inactivating the neurotransmitter by breaking or degrading it. The enzyme acetylcholinesterase prevents ACh from continuing to stimulate contraction.
• Reuptake: Receptors located in the presynaptic membrane 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.
Commensalism is a symbiotic relationship in which one species benefits from the interaction and the other species is neither harmed nor helped. So the bird is being helped and the bison is being neither harmed nor helped.
