Neurons are the most fundamental unit of the nervous system, and yet, researchers are just beginning to understand how they perform the complex computations that underlie our behavior. We asked Boaz Barak, previously a postdoc in Guoping Feng’s lab at the McGovern Institute and now Senior Lecturer at the School of Psychological Sciences and Sagol School of Neuroscience at Tel Aviv University, to unpack the basics of neuron communication for us. Show
“Neurons communicate with each other through electrical and chemical signals,” explains Barak. “The electrical signal, or action potential, runs from the cell body area to the axon terminals, through a thin fiber called axon. Some of these axons can be very long and most of them are very short. The electrical signal that runs along the axon is based on ion movement. The speed of the signal transmission is influenced by an insulating layer called myelin,” he explains. Myelin is a fatty layer formed, in the vertebrate central nervous system, by concentric wrapping of oligodendrocyte cell processes around axons. The term “myelin” was coined in 1854 by Virchow (whose penchant for Greek and for naming new structures also led to the terms amyloid, leukemia, and chromatin). In more modern images, the myelin sheath is beautifully visible as concentric spirals surrounding the “tube” of the axon itself. Neurons in the peripheral nervous system are also myelinated, but the cells responsible for myelination are Schwann cells, rather than oligodendrocytes.
“Myelin’s main purpose is to insulate the neuron’s axon,” Barak says. “It speeds up conductivity and the transmission of electrical impulses. Myelin promotes fast transmission of electrical signals mainly by affecting two factors: 1) increasing electrical resistance, or reducing leakage of the electrical signal and ions along the axon, “trapping” them inside the axon and 2) decreasing membrane capacitance by increasing the distance between conducting materials inside the axon (intracellular fluids) and outside of it (extracellular fluids).” Adjacent sections of axon in a given neuron are each surrounded by a distinct myelin sheath. Unmyelinated gaps between adjacent ensheathed regions of the axon are called Nodes of Ranvier, and are critical to fast transmission of action potentials, in what is termed “saltatory conduction.” A useful analogy is that if the axon itself is like an electrical wire, myelin is like insulation that surrounds it, speeding up impulse propagation, and overcoming the decrease in action potential size that would occur during transmission along a naked axon due to electrical signal leakage, how the myelin sheath promotes fast transmission that allows neurons to transmit information long distances in a timely fashion in the vertebrate nervous system. Myelin seems to be critical to healthy functioning of the nervous system; in fact, disruptions in the myelin sheath have been linked to a variety of disorders. Former McGovern postdoc, Boaz Barak. Photo: Justin Knight“Abnormal myelination can arise from abnormal development caused by genetic alterations,” Barak explains further. “Demyelination can even occur, due to an autoimmune response, trauma, and other causes. In neurological conditions in which myelin properties are abnormal, as in the case of lesions or plaques, signal transmission can be affected. For example, defects in myelin can lead to lack of neuronal communication, as there may be a delay or reduction in transmission of electrical and chemical signals. Also, in cases of abnormal myelination, it is possible that the synchronicity of brain region activity might be affected, for example, leading to improper actions and behaviors.” Researchers are still working to fully understand the role of myelin in disorders. Myelin has a long history of being evasive though, with its origins in the central nervous system being unclear for many years. For a period of time, the origin of myelin was thought to be the axon itself, and it was only after initial discovery (by Robertson, 1899), re-discovery (Del Rio-Hortega, 1919), and skepticism followed by eventual confirmation, that the role of oligodendrocytes in forming myelin became clear. With modern imaging and genetic tools, we should be able to increasingly understand its role in the healthy, as well as a compromised, nervous system. Do you have a question for The Brain? Ask it here.
Neurotransmitters are your body’s chemical messengers. They carry messages from one nerve cell across a space to the next nerve, muscle or gland cell. These messages help you move your limbs, feel sensations, keep your heart beating, and take in and respond to all information your body receives from other internal parts of your body and your environment.
Neurotransmitters carry chemical signals (“messages”) from one neuron (nerve cell) to the next target cell. Neurotransmitters are chemical messengers that your body can’t function without. Their job is to carry chemical signals (“messages”) from one neuron (nerve cell) to the next target cell. The next target cell can be another nerve cell, a muscle cell or a gland. Your body has a vast network of nerves (your nervous system) that send and receive electrical signals from nerve cells and their target cells all over your body. Your nervous system controls everything from your mind to your muscles, as well as organ functions. In other words, nerves are involved in everything you do, think and feel. Your nerve cells send and receive information from all body sources. This constant feedback is essential to your body’s optimal function. What body functions do nerves and neurotransmitters help control?Your nervous system controls such functions as your:
How do neurotransmitters work?You have billions of nerve cells in your body. Nerve cells are generally made up of three parts:
Neurotransmitters are located in a part of the neuron called the axon terminal. They’re stored within thin-walled sacs called synaptic vesicles. Each vesicle can contain thousands of neurotransmitter molecules. As a message or signal travels along a nerve cell, the electrical charge of the signal causes the vesicles of neurotransmitters to fuse with the nerve cell membrane at the very edge of the cell. The neurotransmitters, which now carry the message, are then released from the axon terminal into a fluid-filled space that’s between one nerve cell and the next target cell (another nerve cell, muscle cell or gland). In this space, called the synaptic junction, the neurotransmitters carry the message across less than 40 nanometers (nm) wide (by comparison, the width of a human hair is about 75,000 nm). Each type of neurotransmitter lands on and binds to a specific receptor on the target cell (like a key that can only fit and work in its partner lock). After binding, the neurotransmitter then triggers a change or action in the target cell, like an electrical signal in another nerve cell, a muscle contraction or the release of hormones from a cell in a gland. What action or change do neurotransmitters transmit to the target cell?Neurotransmitters transmit one of three possible actions in their messages, depending on the specific neurotransmitter.
What happens to neurotransmitters after they deliver their message?After neurotransmitters deliver their message, the molecules must be cleared from the synaptic cleft (the space between the nerve cell and the next target cell). They do this in one of three ways. Neurotransmitters:
How many different types of neurotransmitters are there?Scientists know of at least 100 neurotransmitters and suspect there are many others that have yet to be discovered. They can be grouped into types based on their chemical nature. Some of the better-known categories and neurotransmitter examples and their functions include the following: Amino acids neurotransmittersThese neurotransmitters are involved in most functions of your nervous system.
Monoamines neurotransmittersThese neurotransmitters play a lot of different roles in your nervous system and especially in your brain. Monoamines neurotransmitters regulate consciousness, cognition, attention and emotion. Many disorders of your nervous system involve abnormalities of monoamine neurotransmitters, and many drugs that people commonly take affect these neurotransmitters.
Peptide neurotransmittersPeptides are polymers or chains of amino acids.
AcetylcholineThis excitatory neurotransmitter does a number of functions in your central nervous system (CNS [brain and spinal cord]) and in your peripheral nervous system (nerves that branch from the CNS). Acetylcholine is released by most neurons in your autonomic nervous system regulating heart rate, blood pressure and gut motility. Acetylcholine plays a role in muscle contractions, memory, motivation, sexual desire, sleep and learning. Imbalances in acetylcholine levels are linked with health issues, including Alzheimer’s disease, seizures and muscle spasms. Why would a neurotransmitter not work as it should?Several things can go haywire and lead to neurotransmitters not working as they should. In general, some of these problems include:
Problems with other parts of nerves, existing diseases or medications you may be taking can affect neurotransmitters. Also, when neurotransmitters don’t function as they should, disease can happen. For example:
How do medications affect the action of neurotransmitters?Scientists recognized the value and the role of neurotransmitters in your nervous system and the importance of developing medications that could influence these chemical messengers to treat many health conditions. Many medications, especially those that treat diseases of your brain, work in many ways to affect neurotransmitters. Medications can block the enzyme that breaks down a neurotransmitter so that more of it reaches nerve receptors.
Medications can block the neurotransmitter from being received at its receptor site.
Medications can block the release of a neurotransmitter from a nerve cell.
A note from Cleveland Clinic Neurotransmitters play a role in nearly every function in your body. More specifically, neurotransmitters are the chemical communicators that carry a nerve’s message from one nerve cell to the next cell. Without neurotransmitters, your body can’t function. Too high of a level or too low of a level of specific neurotransmitters results in specific health problems. Medications work by increasing or decreasing the amount of or the action of neurotransmitters.
Last reviewed by a Cleveland Clinic medical professional on 03/14/2022. References
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