Question Video: Describing the Structure of a Synapse Biology

The diagram provided shows a simple outline of a cholinergic synapse. What part of the synapse is indicated by the question mark?


Video Transcript

The diagram provided shows a simple outline of a cholinergic synapse. What part of the synapse is indicated by the question mark?

This question asks us to identify a part of the synapse in a cholinergic neuron. Let’s review the structures involved in a synapse in order to answer this question correctly.

Neurons make up the nervous system, which is one of the most complex biological systems known to man. Neurons link to each other and their effectors, muscles and glands, through junctions called synapses. Information is passed on through the nervous system via nerve impulses. These are first received by the dendrites of the neuron. The impulse then moves past the soma, or cell body, along the axon and to the axon terminals. It is here at the end of the axon that the synapses are found.

Let’s now look at a synapse in more detail. There are three main parts to a synapse, as we can see in this diagram. The neuron coming into the synapse is the presynaptic neuron, pre- meaning before, so it is the neuron before the synapse. At the end of the presynaptic neuron are the axon terminals, which are shaped like a doorknob, so are called presynaptic knobs. These knobs contain vesicles of neurotransmitter. After the presynaptic knob comes the synaptic cleft or gap.

When an electrical signal arrives at the presynaptic knob, it causes a rapid influx of calcium ions. This influx causes the fusion of the vesicles with the membrane of the presynaptic knob and the release of the neurotransmitter into the synaptic cleft. This is the step that is illustrated in the diagram provided with the question.

In this question, we are looking at a cholinergic synapse, so the type of neurotransmitter released is acetylcholine. This then diffuses across the cleft to the third part of the synapse, the postsynaptic neuron. On the membrane of the postsynaptic neuron are receptors for the neurotransmitter. In the case of this cholinergic synapse, the neurotransmitter acetylcholine binds to its receptors, causing sodium ion channels to open and sodium ions to enter, as illustrated on our diagram. This depolarizes the postsynaptic neuron, and so the process of neural transmission begins all over again.

Now that we have reviewed the process of signal transduction and how it involves the synapse between each neuron, we are able to take another look at our question. This question asks us to identify the term for space between two neurons where the neurotransmitter can be released and received, as indicated by the question mark. We now know the correct answer is the synaptic cleft.

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