What are neurotransmitters and what do they do?

Imagine sitting down in the doctor’s office for your yearly check-up and the doctor says

she is going to check your reflexes. She taps a reflex hammer to the bottom of your knee, causing

your leg to jerk upwards in reflex. “All good,” she says. But what exactly was she looking for

when she examined your reflexes? Was it to make sure your bottom half isn’t paralyzed? Or

perhaps to test how fast you can move in case of emergencies? Neither. In checking your

reflexes, the doctor is checking for a working peripheral and central nervous system. Essentially,

how well the signals travel through your peripheral nervous system (PNS) into your central

nervous system (CNS) from the point your leg is hit with the hammer to when you react.

The nervous system is upheld by chemical and electrical signals that transport messages

from one part of the body to another. Neurons are nerve cells that take on the job of transporting

the electric signals between each other. A neuron is composed of a cell body will small

projections called dendrites and a long projection called an axon. Dendrites, being close to the

cell body, are used for receiving signals from other nerve cells. The axon is used to sending

messages to other cells. At the end of the axon, where it approaches another cell, is the synaptic

terminal. It is called a terminal because it is the end of the electrical charge that passes through

the neuron to produce the signal. Electrical signals are sent within the neuron and chemical

signals are used between neurons and cells.

At the synaptic terminal, little chemical messengers called neurotransmitters enable

neurotransmission. An axon is often connected to a dendrite from another neuron in order to pass

the signal forward. That dendrite will then be called the postsynaptic area containing the synaptic

cleft. Here, receptors are found on the cell’s surface to receive the chemical signals coming out

of the axon terminal. Neurotransmitters are released when an action potential comes to the end of

the cell. These neurotransmitters are transported within a synaptic vesicle to the end of the cell

and out the cell membrane.

Once outside the cell, it is close enough to quickly bind to the receptors in the

postsynaptic cell membrane. The release of neurotransmitters into the next cell is completely

random, leading to multiple failures the smaller the synapse, such as those in the central nervous

system. Large synapses like the ones found between neurons and muscles (called neuromuscular

junction) are able to take more of the neurotransmitters. If the postsynaptic cell is a neuron, the

receptor opens ion channels within the membrane of the cell that changes the transmembrane

potential for a change in voltage. The receptor can inhibit (calm) or excite (stimulate) a response

in the next cell. The neurotransmitter does not stay in the postsynaptic cell, and only touches the

receptors for a bit, enough to pass on the signal. It is then released back into the synaptic

terminal, where it can do three things. 1) It can be taken by enzymes and metabolized back into

the presynaptic cell or 2) taken back up by the presynaptic cell through active transport in the

cell membrane or 3) diffuse to other parts outside the cells.

Neurotransmitters are the reason why our bodily processes occur so efficiently, and why

we never have to worry about not feeling a bug on our hand and process it quickly enough to

move our hands away (unless you don’t mind). They are the way signals are transmitted through

our bodies between neurons and work resourcefully to not miss its function. Neurons mostly give

off thousands of synapses, with some exceptions. Each of these synapses are sending

neurotransmitters back and forth. Now if you can imagine how many neurons and

neurotransmitters are at work while you are simply moving your eyes back and forth on this

page. Oh, what a world we live in!

References:

  1. “Neurogistics.” What are Neurotransmitters? - Neurogistics,

www.neurogistics.com/the-science/what-are-neurotransmitters.

2. “Integrative Psychiatry.” The Four Major Neurotransmitters and the Neurotransmitter

Imbalances, www.integrativepsychiatry.net/neurotransmitter.html.

Naile Ruiz