Video Transcript
What is acetylcholine an example
of? (A) An ion, (B) an electrical
signal, (C) a transport molecule, or (D) a neurotransmitter.
This question asks us about
acetylcholine, which is a very important molecule in the synapses of the
parasympathetic nervous system. Synapses are the junctions between
neurons or between neurons and effectors, which allow the transmission of the
impulse from cell to cell. There are many different components
of the neural transmission, including ion movement, electrical signals, and
neurotransmitters. So let’s review this process in
order to try and answer our question correctly.
Here is a diagram of a sensory
neuron. When it receives an electrical
signal at its dendrites, several changes in its ion concentrations will cause the
signal to move from the dendrites to the soma, or cell body. Then, this signal is passed down
the axon to the axon terminal, which will now need to pass on the signal to the next
neuron via the synapse. So now let’s look at the synapse in
more detail.
When referring to the synapse, the
axon terminals are often called presynaptic knobs. The prefix pre- is referring to the
synaptic knob that comes before the synapse. In the presynaptic knob, there are
vesicles containing special chemicals called neurotransmitters, which pass, or
transmit, the impulse from neuron to neuron. When the electrical signal reaches
the presynaptic knob, it causes calcium ions to enter, and this brings about the
release of neurotransmitters, such as acetylcholine, into the synaptic cleft, or
gap.
The neurotransmitters then diffuse
across the cleft, down their concentration gradient, and bind to receptors on the
postsynaptic neuron. This then causes the electrical
signal to continue along this neuron. Neurotransmitters are therefore
considered to be chemical messengers, since they carry information to adjacent
neurons.
After reviewing how synapses carry
out their role of passing information between neurons, we should now be able to
answer our question correctly. We are asked about acetylcholine,
which we just learned is a chemical messenger released from vesicles in the
presynaptic knob that enables communication between neurons. Since “neurotransmitter” is the
scientific term given to these chemicals, the correct answer to our question is
(D). Acetylcholine is an example of a
neurotransmitter.
