Biology 12: The Importance of Neurotransmitters
The term “synapse” designates the point where the axon of one neuron connects to a dendrite of
another. This word comes from the Greek syn(together) and haptein (join). In the animal kingdom,
neurons can be connected to each other in two very different ways:

by an electrical synapse, in which the two cells touch and are connected by tiny holes, which
lets the nerve impulse pass directly from one neuron to the other; or

by a chemical synapse, where the two cells do not touch and the nerve impulse needs
particular molecules to bridge the
gap between them.
Chemical synapses are slower than
electrical ones but are also far more
flexible. This valuable flexibility is
the foundation of all learning.
Neurotransmitters are chemical
molecules that “ferry” nerve
impulses across the synapse from
one neuron to the next.
Each type of neurotransmitter has a molecular form that lets it bind to the
right site on the second neuron to produce its particular effect.
The neurotransmitter thus acts somewhat like a key. If it is the right shape
for the next neuron (shown here as a lock), it will produce an effect on that
neuron.
Neurotransmitters are divided into two categories according to the effect that they have on the second
neuron once they are released into the synaptic gap.
Neurotransmitters that help this neuron to propagate the nerve impulse are classified as excitatory
neurotransmitters.
Neurotransmitters that reduce the likelihood of this neuron’s propagating the impulse are called
inhibitory neurotransmitters.
Dopamine is a chemical messenger (neurotransmitter) that is not very common in the brain. Scarcely
more than 0.3% of the neurons in the brain produce dopamine. Nevertheless, these neurons play an
essential role in many of our behaviours.
Biology 12: The Importance of Neurotransmitters
For example, they are involved in controlling the body’s movements. When some of these neurons
are destroyed, the person displays the trembling characteristic of Parkinson’s disease.
The opposite problem–too much dopamine in certain regions of the brain–produces the terrible
symptoms associated with schizophrenia. In fact, the most effective medications for treating
schizophrenia are those that prevent dopamine from binding to dopamine receptors.
Lastly, certain dopamine-producing neurons, such as those discussed here, come into play when the
person or animal in question experiences desire or pleasure.
Questions:
1. Explain the “Lock and Key” analogy. Include a description of WHAT and WHERE each structure is, as well as its
function.
2. Describe the difference between an excitatory and inhibitory neurotransmitter.
3. Sketch a pre-synaptic neuron, a post-synaptic neuron, and the important structures involved in synapse transmission.
4. Why do you think prescription drugs are sometimes used to treat mental illnesses such as depression and anxiety?
5. Use a Venn diagram to compare and contrast serotonin and norepinepherine.
6. Identify 5-10 new words for your vocabulary scribbler. Highlight them so you can include them later.