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Question Video: Recalling the Defining Features of Synapses Biology

Which of the following is a defining feature of synapses? [A] Synapses can only pass information in one direction. [B] Synapses transmit information as electrical signals only. [C] Synapses only form between two neurons. [D] Acetylcholine receptors are only located on the presynaptic neuron.

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Video Transcript

Which of the following is a defining feature of synapses? (A) Synapses can only pass information in one direction. (B) Synapses transmit information as electrical signals only. (C) Synapses only form between two neurons. Or (D) acetylcholine receptors are only located on the presynaptic neuron.

This question is asking us about synapses, so let’s review the key points about their features to help us answer it. The nervous system is one of the body’s internal communication networks that helps us to respond to changes in the environment around us. Neurons are the nerve cells that make up this network. And they are interconnected to carry nerve impulses all around the body. The junctions between neurons or between neurons and effectors, such as muscles, are called synapses. Synapses transmit the impulse from cell to cell.

Let’s now take a closer look at their structure and how this allows them to carry out their role. Here you can see there are three main parts to a synapse. Coming into the synapse is the presynaptic neuron, pre- meaning before, so it is the neuron before the synapse. Then there is the synaptic cleft or gap and, finally, the postsynaptic neuron, post- meaning after. The presynaptic neuron carries the electrical impulse towards the synapse.

At its ends are synaptic bulbs, or synaptic knobs. When the impulse arrives here, it causes a special type of chemical called a neurotransmitter to be released into the synaptic cleft. An example of a neurotransmitter is acetylcholine. The neurotransmitter will then diffuse across the synaptic cleft down its concentration gradient to the other side. The synapse shown here is a cholinergic synapse. So in this example, acetylcholine binds to receptors on the membrane of the postsynaptic neuron, causing an impulse to be triggered. The neurotransmitter can only be released from the presynaptic neuron. And there are only receptors for it on the postsynaptic neuron, so the impulse can only pass in one direction. This is important to prevent confusion with the messages.

Now that we have revised over the structure and function of the synapse, let’s return to the question, which asks, which of the following is a defining feature of synapses? We can rule out option (B) as we now know that chemicals carry the information across the synaptic cleft. We can also rule out option (C) as we know that synapses can form between one or more neurons and also with effectors. Option (D) is also incorrect as the receptors are found on the postsynaptic neuron membrane not the presynaptic. This leaves us with the correct answer (A). A defining feature of a synapse is that they can only pass information in one direction.

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