Question

How is the neurotransmitter stored in the axon terminal before it is released?

1) bound to the mitochondrion
2) bound to Ca₂⁺ channels
3) contained in synaptic vessicles
4) neurotransmitter moves freely throughout the axon terminal

Answer 1

Neurotransmitters are stored in synaptic vesicles within the axon terminal before being released into the synaptic cleft. The release is triggered when an action potential causes Ca²⁺ channels to open, which then facilitates the fusion of vesicles with the presynaptic membrane to release the neurotransmitters via exocytosis. The correct answer is option 3) contained in synaptic vesicles.

Step-by-step explanation:

Storage of Neurotransmitters in Axon Terminals

Neurotransmitters are chemical messengers utilized by the nervous system to transmit signals from one neuron to another across synapses. Prior to release, these molecules are not freely moving within the axon terminal, nor are they bound to structures such as mitochondria or calcium channels. Instead, neurotransmitters are stored within specialized structures known as synaptic vesicles.

When an action potential reaches the axon terminal, it triggers the opening of voltage-gated Ca²⁺ channels. As calcium ions flood into the terminal, they associate with proteins on the surfaces of these vesicles. This interaction induces the vesicles to merge with the presynaptic membrane, leading to the release of neurotransmitters into the synaptic cleft via a process called exocytosis.

The precise and coordinated release mechanism ensures effective communication between neurons. This process is critical for the proper functioning of neural circuits and the execution of complex behaviors.

The correct option for how neurotransmitters are stored in the axon terminal before release is option 3) contained in synaptic vesicles.