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.
