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Neurotransmitters and Brain Chemistry
Neurotransmitters and Brain Chemistry
This week we'll look at how our brain cells communicate with one another. We will learn about neurons, synapses, neurotransmitters, and neuromodulators. The interrelationship between the cells of our body and brain determines how we act, think, and respond. Understanding this relationship allows us to recognize how a healthy brain works, and more importantly, what are the factors that can interfere with the communication that occurs between brain cells.
Want to make your own brain cells?
Want to make your own brain cells?
Before the pandemic, Professor Debbie Flores had her students 'in class' create neurons out of play dough!
Before the pandemic, Professor Debbie Flores had her students 'in class' create neurons out of play dough!
Check out some of your classmates' artistic work
Check out some of your classmates' artistic work
If you would like to have some fun and create your own set of neurons, check out this Easy Play Dough Recipe. Please send us pictures of your work, if you do.
The Nervous System
The Nervous System
Let’s start with the bigger picture. If you think of the brain as the computer that controls your body’s functions, the human nervous system is like the complex network of cells and nerves that relays messages between the brain, the spinal cord, and various parts of the body. The nervous system can be thought of as the body’s “electrical wiring system.” It coordinates actions throughout the body, controlling everything from your heartbeat to your emotions. The graphic below depicts the many parts of our complex nervous system.
Neurons
Neurons
Neurons (also called nerve cells or brain cells) are cells that are the fundamental working units of the brain and nervous system. A neuron consists of:
A cell body (soma) containing the nucleus (center) and cytoplasm (fluid within the cell).
Dendrites, tiny branch-like extensions that branch away from the body of the neuron and receive impulses from other cells. The group of dendrites on a neuron is called a dendritic tree, as it resembles a tree.
An axon, the long, slender, tube-like projection of a nerve cell that delivers signals between neurons.
Axon terminals, the end of the axon that branches out and terminates in knobs that contain cellular organs and vesicles, which store neurotransmitters.
To reinforce your understanding of how neurons communicate. Watch this short video (1:27 min)
Synapses
Synapses
A synapse consists of:
A “pre-synaptic ending” that contains neurotransmitters as well as other cell organs.
A “post-synaptic ending” that contains receptor sites for the neurotransmitters to bind to.
A “synaptic cleft”, the space between the pre-synaptic and post-synaptic endings.
Not all synapses are located between an axon terminal and a neighboring dendrite (axo-dendritic). Some connections are made between the axon terminal and receptors on another axon (axo-axonic), or between receptors on the body of the neuron (axo-somatic). In certain specialized neurons, dendrites can form synapses with one another (dendro-dentritic) (Cardoso, n.d.).
In the brain, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron—it can be thought of as a junction between two nerve cells. A synapse contains a very small gap between the axon terminal of one neuron (pre-synaptic ending) and the dendrite of a neighboring neuron (post-synaptic ending). It is where neurons communicate with each other. You can think of the synapse as the meeting point between neurons. There are roughly between 1,000 and 10,000 synapses terminating on each neuron. Estimates of the numbers of these synapses in the mature human brain range between about 60 trillion to about 240 trillion.
Peptides:
Somatostatin: Regulates the endocrine system and affects neurotransmission and cell proliferation by inhibiting the release of various hormones.
Opioids: These naturally occurring opiate-like substances function as neurotransmitters and include endorphins, enkephalins, and dynorphins. They reduce the amount of GABA released.
Purines:
Adenosine triphosphate (ATP): It induces fast, excitatory post-synaptic currents. It also plays a role in neuronal-glial cell and glial-glial cell signaling.
Cholines:
Acetylcholine: The chief neurotransmitter of the nervous system that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows heart rate. It plays an important role in the enhancement of alertness, sustaining attention, and in learning and memory.
This video introduces some of the key neurotransmitters and what their functions are (3:30 min).
Neurotransmitters
Neurotransmitters
A neuron communicates with other neurons to transmit and receive signals (messages). It does so using neurotransmitters, brain chemicals that are responsible for the transmission of electrical signals from one neuron to another. Until relatively recently, it was believed that a neuron could produce only a single type of neurotransmitter to transmit a specific signal. However, evidence has indicated that many types of neurons produce and release two or more different neurotransmitters (El Mestikawy, Wallen-Mackenzie, Fortin, Desarries, & Trudeau, 2011; Trudeau, 2004). It is important to note that stress, diet, toxins, drugs, alcohol, and caffeine can affect the amount of neurotransmitters released.
Chemically, neurotransmitters are simple molecules. Scientists have managed to identify over 100 neurotransmitters in the human brain, but evidence suggests we have significantly more than this number (wiseGEEK, n.d.). Scientists also believe that only about 10 of these brain chemicals do 99% of the work of the brain (King, 2013). Neurotransmitters are categorized into major classes, based on their chemical and molecular properties (Cardoso, n.d.). Included in the following list are some of the more common neurotransmitters we discuss and the categories under which they fall:
Amino Acids:
Glutamate: The most abundant neurotransmitter in our brain and central nervous system. It is involved in virtually every major excitatory brain function.
Gamma-aminobutyric acid (GABA): The chief inhibitory neurotransmitter in the central nervous system. Its principal role is to reduce neuronal excitability.
Glycine: An inhibitory neurotransmitter in the central nervous system, involved in the processing of movement, vision, and hearing.
Biogenic Amines:
Dopamine: Associated with reward-motivated behavior as well as motor control.
Norepinephrine: Also called noradrenaline, it mobilizes the body and brain for action.
Serotonin: Plays a role in emotions (especially maintaining mood balance), appetite, motor, cognitive, and autonomic functions. It helps regulate the body’s sleep-wake cycles and internal clock, and has been used to treat pain and nausea.
Melatonin: Plays a role in the regulation of body functions, including the body’s circadian rhythm.
Histamine: Plays a role in the regulation of the sleep-wake cycle and promotes arousal when activated.
Peptides:
Somatostatin: Regulates the endocrine system and affects neurotransmission and cell proliferation by inhibiting the release of various hormones.
Opioids: These naturally occurring opiate-like substances function as neurotransmitters and include endorphins, enkephalins, and dynorphins. They reduce the amount of GABA released.
Purines:
Adenosine triphosphate (ATP): It induces fast, excitatory post-synaptic currents. It also plays a role in neuronal-glial cell and glial-glial cell signaling.
Cholines:
Acetylcholine: The chief neurotransmitter of the nervous system that contracts smooth muscles, dilates blood vessels, increases bodily secretions, and slows heart rate. It plays an important role in the enhancement of alertness, sustaining attention, and in learning and memory.
Neuromodulators
Neuromodulators
Neuromodulators are brain chemicals that are released from a neuron that affect not just a single neighboring neuron (like a neurotransmitter does), but a diverse population of neurons that have the appropriate receptors. Neuromodulators have a long-lasting influence on neurons both near and far away from the release site because, unlike neurotransmitters, they are not reabsorbed or broken down. In a sense, they act like a radio signal with a very long range of action. They control how “loudly” neurons communicate with each other by strengthening the transmission signal. Neuromodulators are released when something happens that signals the brain that the event should be stored and remembered.
This graphic shows the visual difference between the function of a neurotransmitter and a neuromodulator. A neurotransmitter goes from a neuron to another single neuron. A neuromodulator will transmit from one neuron to many, thus creating an overall effect.
The target areas of a neuromodulator include areas of the brain such as the cerebellar nuclei, the basal ganglia, the hippocampus, and the basal forebrain. These areas are associated with learning, short-term memory, arousal, and reward.
Some examples of neuromodulators are enkephalins, endorphins, and dynorphins. There are also certain neurotransmitters that have been categorized as neuromodulators because they almost always work in the way a neuromodulator does. Those include dopamine, serotonin, acetylcholine, noradrenaline, and histamine.
To summarize, the things that distinguish neuromodulators from neurotransmitters are:
1. Neuromodulators are released diffusely into the synaptic gap and function as a chemical broadcast signal to a brain region, rather than to a specifically targeted receptor.
2. Neuromodulators generally use a different type of receptor that is slow acting and that modulates the functioning of the neuron over longer periods of time.
3. Neuromodulators are not reabsorbed or broken down, so they can produce long-lasting effects.
Communication Within the Brain: How it Works
Communication Within the Brain: How it Works
Communication within our vast network of brain cells is accomplished by one of two means, both of which relay information, but use different means (Neuroscience, 2008):
Chemical: Chemical transmission, the most common type of transmission in the nervous system, occurs when neurotransmitters and neuromodulators are released to physically bind with a neighboring neuron.
Electrical: Electrical transmissions (electrotonic) occur when ions flow through gap junctions of pre- and post-synaptic cell membranes that are in very close proximity to each other. They follow a low-resistance pathway without leakage into the extracellular space. Gap junctions are formed from hexameric pores, called connexons, which connect cells with each other for robust electrical coupling. These connections enable very fast communications, and are usually found where normal functions require that the activity of neighboring neurons be highly synchronized, as in non-neural cells including smooth cardiac muscle cells, epithelial cells, and glandular cells (Cardoso, n.d.).
Chemical Transmission
Chemical Transmission
Because chemical transmissions are the most common type of signal transmission in the nervous system, we will focus on understanding this process more. The chemical process of communication in the brain involves electrical impulses, which create chemical signals that travel from one neuron to another. Following is a brief description of this process:
When a neuron receives a chemical transmission from a neighboring neuron, and if the signal is strong enough, it triggers an action potential, or electrical impulse, which moves from the dendrite toward the cell body.
After the action potential reaches the cell body, it is joined with other signals and passed on to the axon, which conducts nerve impulses away from the cell body.
At the end of the axon, there are branch-like extensions called axon terminals. At the end of each axon terminal is a swelling called a synaptic knob or terminal button. Each synaptic knob communicates with the dendrites of another neuron through a synapse. The synaptic knobs contain “vesicles” that store and release neurotransmitters into the synapse.
When an action potential nears the synaptic knob, an impulse is generated, resulting in the release of chemical neurotransmitters from the vesicles into the synaptic gap.
The neurotransmitters then bind with receptors located on the receiving neuron. These receptors are specially designed to fit with the neurotransmitter like a lock and key.
Once the neurotransmitter binds with a receptor, the signal is converted back into an electrical signal that travels through the receiving neuron. The signal can promote either excitatory or inhibitory changes in the membrane of the receiving neuron, and the signal continues through that neuron to the next.
The chemical neurotransmitter that delivered the message is no longer needed and is then recycled by a transporter back to the originating neuron to be taken back up (reuptake), restored, and reused, or is lost in the extracellular fluid, or degraded by enzymes.
For visual explanations of how electrochemical communication happens in the brain, watch the following short videos.
Neurotransmitters, Mental Disorders, and Medications
Neurotransmitters, Mental Disorders, and Medications
We have seen that neurotransmitters and neuromodulators affect cognition, memory, mood, and many other things in the body and brain. They can contribute to the plasticity of the brain, but problems with brain chemicals may also manifest as mental disorders. Following are some of these disorders and how brain chemicals are thought to play a part:
Schizophrenia is a psychiatric condition resulting from a relative overproduction of dopamine in certain parts of the brain. It is characterized by disturbances in thinking and emotions. Medications that block the dopamine receptors in the brain help alleviate symptoms by blocking the actions of dopamine.
Depression appears to be caused by abnormal signals that control mood, thoughts, pain, and other sensations. With depression, the flow of serotonin is defective and the serotonin molecules flow back to the originating site (the pre-synaptic membrane) instead of to the receptor site (the post-synaptic membrane). A drug such as Prozac blocks the reabsorption of serotonin into the pre-synaptic membrane and makes it more available to bind with post-synaptic receptors.
Alzheimer’s disease seems to be caused by a loss of cells that secrete acetylcholine in the basal forebrain (the part of the brain responsible for sensory and associative information processes and motor activities).
Generalized anxiety disorder is characterized by excessive and persistent worry about things. Evidence suggests that this disorder involves several neuromodulators including norepinephrine and serotonin.
Attention-deficit/hyperactivity disorder is characterized by difficulties in attention, over-activity, impulse control, and distractibility. Research shows that dopamine and norepinephrine imbalances are implicated in causing ADHD.
Parkinson’s disease is related, in part, to the failure of dopamine-producing cells in the brain.
The BrainHQ Connection
The BrainHQ Connection
Did you know that neurons don't touch when they communicate? Read "The Brain 101” to learn more. By now you've learned and hopefully are seeing the positive effects that are generated from doing the BrainHQ exercises consistently. They were designed to speed up and sharpen the brain by inducing the production of brain chemicals to keep our brains fit. We will learn more about brain plasticity in our next lesson!
Conclusion
Conclusion
We have learned that a neuron is a cell within the nervous system, and that neurons communicate with each other via electrical and chemical messages. We learned that the chemical messengers are called neurotransmitters and neuromodulators, and that they cross a synaptic gap between neurons to deliver their messages. We reviewed several of the more important neurotransmitters, the roles they play, and how problems with these brain chemicals can lead to mental disorders. Hopefully we have learned to appreciate even more the beauty and complexity of our brain’s communication processes and the delicate balance required for the brain to function optimally. This may serve to motivate us to take better care of ourselves and make wiser lifestyle choices so we can ensure a better, more brain-healthy life.
Works Cited
Works Cited
Cardoso, S. H. (n.d.). Communication between nerve cells. Brain & Mind Fundamentals. [Website]. Retrieved from: http://www.cerebromente.org.br/n12/fundamentos/neurotransmissores/neurotransmitters2.html
El Mestikawy, S., Wallen-Mackenzie, A., Fortin, G. M., Descarries, L., Trudeau, L. E. (2011). From glutamate co-release to vesicular synergy: Vesicular glutamate transporters. Nature Reviews Neuroscience 12(7): 425. Retrieved from: https://www.ncbi.nlm.nih.gov/pubmed/21415847
King, P. (Apr. 2, 2013). How many types of neurotransmitters are there in a human brain? Quora [Website blog]. Retrieved from: https://www.quora.com/How-many-types-of-neurotransmitters-are-there-in-a-human-brain
Neuroscience. (2008). Chemical and electrical synapses. Neuroscience, Fourth Edition.
Retrieved from: http://cbm.msoe.edu/teacherWorkshops/ddtyResources/documents/synapseTypes.pdf
Trudeau, L. E. (2004). Glutamate co-transmission as an emerging concept in monoamine neuron function. Journal of Psychiatry & Neuroscience 29(4): 296-310. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC446224/
wiseGEEK. (n.d.). How many neurotransmitters are there? [Website]. Retrieved from: https://www.wisegeek.com/how-many-neurotransmitters-are-there.htm
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