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Question Video: Recalling the Effect of an Action Potential Arriving in the Presynaptic Neuron Biology

Complete the following sentence: An action potential arrives at the synaptic knob of the presynaptic neuron, which stimulates calcium ion channels to _.

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Video Transcript

Complete the following sentence. An action potential arrives at the synaptic knob of the presynaptic neuron, which stimulates calcium ion channels to blank.

To work out what the missing word is in the question, we need to take a quick look at how two neurons communicate with each other. The dendrites of one neuron receive signals from other neurons. The signal is turned into an electrical impulse called an action potential, which travels down the axon of the neuron. But what happens to this action potential when it reaches the axon terminals at the end of the neuron? Let’s find out.

The junction between two neurons is called a synapse. The neuron that the action potential travels down first is called the presynaptic neuron, as it comes before the synapse, while the neuron that needs to be stimulated is called the postsynaptic neuron, as it comes after the synapse.

In the diagram on the right, we can see an action potential arriving at the synaptic knob at the end of the presynaptic neuron. This describes the first part of the sentence that we need to complete in the question. The arrival of the action potential depolarizes the presynaptic neuron’s membrane at the synaptic knob. This means that the space inside the synaptic knob becomes more positively charged than the extracellular space outside the synaptic knob due to the movement of sodium ions.

The depolarization of the presynaptic membrane at the synaptic knob causes calcium ion channels, which have been shown here in blue, to open. This allows calcium ions to diffuse into the synaptic knob. The influx of calcium into the synaptic knob of the presynaptic neuron triggers a series of events that eventually generates a new action potential in the postsynaptic neuron.

Our question is asking us what calcium ion channels do when an action potential arrives at the synaptic knob of a presynaptic neuron. Now we have enough information to answer this question. It stimulates calcium ion channels to open.

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