An Overview of the Different Parts of a Neuron

Brain Basics: The Life and Death of a Neuron | National Institute of Neurological Disorders and Stroke

An Overview of the Different Parts of a Neuron

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Introduction
The Architecture of the Neuron
Birth
Migration
Differentiation
Death
Hope Through Research

Introduction

Until recently, most neuroscientists thought we were born with all the neurons we were ever going to have.

As children we might produce some new neurons to help build the pathways — called neural circuits — that act as information highways between different areas of the brain.

But scientists believed that once a neural circuit was in place, adding any new neurons would disrupt the flow of information and disable the brain’s communication system.

In 1962, scientist Joseph Altman challenged this belief when he saw evidence of neurogenesis (the birth of neurons) in a region of the adult rat brain called the hippocampus.

He later reported that newborn neurons migrated from their birthplace in the hippocampus to other parts of the brain.

In 1979, another scientist, Michael Kaplan, confirmed Altman’s findings in the rat brain, and in 1983 he found neural precursor cells in the forebrain of an adult monkey.

These discoveries about neurogenesis in the adult brain were surprising to other researchers who didn’t think they could be true in humans.

But in the early 1980s, a scientist trying to understand how birds learn to sing suggested that neuroscientists look again at neurogenesis in the adult brain and begin to see how it might make sense.

In a series of experiments, Fernando Nottebohm and his research team showed that the numbers of neurons in the forebrains of male canaries dramatically increased during the mating season. This was the same time in which the birds had to learn new songs to attract females.

Why did these bird brains add neurons at such a critical time in learning? Nottebohm believed it was because fresh neurons helped store new song patterns within the neural circuits of the forebrain, the area of the brain that controls complex behaviors. These new neurons made learning possible. If birds made new neurons to help them remember and learn, Nottebohm thought the brains of mammals might too.

Other scientists believed these findings could not apply to mammals, but Elizabeth Gould later found evidence of newborn neurons in a distinct area of the brain in monkeys, and Fred Gage and Peter Eriksson showed that the adult human brain produced new neurons in a similar area.

For some neuroscientists, neurogenesis in the adult brain is still an unproven theory. But others think the evidence offers intriguing possibilities about the role of adult-generated neurons in learning and memory.

Neuron

The Architecture of the Neuron

The central nervous system (which includes the brain and spinal cord) is made up of two basic types of cells: neurons (1) and glia (4) & (6). Glia outnumber neurons in some parts of the brain, but neurons are the key players in the brain.

Neurons are information messengers. They use electrical impulses and chemical signals to transmit information between different areas of the brain, and between the brain and the rest of the nervous system. Everything we think and feel and do would be impossible without the work of neurons and their support cells, the glial cells called astrocytes (4) and oligodendrocytes (6).

Neurons have three basic parts: a cell body and two extensions called an axon (5) and a dendrite (3). Within the cell body is a nucleus (2), which controls the cell’s activities and contains the cell’s genetic material.

The axon looks a long tail and transmits messages from the cell. Dendrites look the branches of a tree and receive messages for the cell.

Neurons communicate with each other by sending chemicals, called neurotransmitters, across a tiny space, called a synapse, between the axons and dendrites of adjacent neurons.

The architecture of the neuron.

There are three classes of neurons:

  1. Sensory neurons carry information from the sense organs (such as the eyes and ears) to the brain.
  2. Motor neurons control voluntary muscle activity such as speaking and carry messages from nerve cells in the brain to the muscles.
  3. All the other neurons are called interneurons.

Scientists think that neurons are the most diverse kind of cell in the body. Within these three classes of neurons are hundreds of different types, each with specific message-carrying abilities.

How these neurons communicate with each other by making connections is what makes each of us unique in how we think, and feel, and act.

Birth

The extent to which new neurons are generated in the brain is a controversial subject among neuroscientists. Although the majority of neurons are already present in our brains by the time we are born, there is evidence to support that neurogenesis (the scientific word for the birth of neurons) is a lifelong process.

Neurons are born in areas of the brain that are rich in concentrations of neural precursor cells (also called neural stem cells). These cells have the potential to generate most, if not all, of the different types of neurons and glia found in the brain.

Neuroscientists have observed how neural precursor cells behave in the laboratory. Although this may not be exactly how these cells behave when they are in the brain, it gives us information about how they could be behaving when they are in the brain’s environment.

The science of stem cells is still very new, and could change with additional discoveries, but researchers have learned enough to be able to describe how neural stem cells generate the other cells of the brain. They call it a stem cell’s lineage and it is similar in principle to a family tree.

Neural stem cells increase by dividing in two and producing either two new stem cells, or two early progenitor cells, or one of each.

When a stem cell divides to produce another stem cell, it is said to self-renew. This new cell has the potential to make more stem cells.

When a stem cell divides to produce an early progenitor cell, it is said to differentiate. Differentiation means that the new cell is more specialized in form and function. An early progenitor cell does not have the potential of a stem cell to make many different types of cells. It can only make cells in its particular lineage.

Early progenitor cells can self-renew or go in either of two ways. One type will give rise to astrocytes. The other type will ultimately produce neurons or oligodendrocytes.

Migration

Once a neuron is born it has to travel to the place in the brain where it will do its work.

How does a neuron know where to go? What helps it get there?

Scientists have seen that neurons use at least two different methods to travel:

  1. Some neurons migrate by following the long fibers of cells called radial glia. These fibers extend from the inner layers to the outer layers of the brain. Neurons glide along the fibers until they reach their destination.
  2. Neurons also travel by using chemical signals. Scientists have found special molecules on the surface of neurons — adhesion molecules — that bind with similar molecules on nearby glial cells or nerve axons. These chemical signals guide the neuron to its final location.

Not all neurons are successful in their journey. Scientists think that only a third reach their destination. Some cells die during the process of neuronal development.

Some neurons survive the trip, but end up where they shouldn’t be. Mutations in the genes that control migration create areas of misplaced or oddly formed neurons that can cause disorders such as childhood epilepsy. Some researchers suspect that schizophrenia and the learning disorder dyslexia are partly the result of misguided neurons.

Some neurons migrate by riding along extensions (radial glia) until they reach their final destinations.

Differentiation

Once a neuron reaches its destination, it has to settle in to work. This final step of differentiation is the least well-understood part of neurogenesis.

Neurons are responsible for the transport and uptake of neurotransmitters — chemicals that relay information between brain cells.

Depending on its location, a neuron can perform the job of a sensory neuron, a motor neuron, or an interneuron, sending and receiving specific neurotransmitters.

In the developing brain, a neuron depends on molecular signals from other cells, such as astrocytes, to determine its shape and location, the kind of transmitter it produces, and to which other neurons it will connect. These freshly born cells establish neural circuits — or information pathways connecting neuron to neuron — that will be in place throughout adulthood.

But in the adult brain, neural circuits are already developed and neurons must find a way to fit in. As a new neuron settles in, it starts to look surrounding cells. It develops an axon and dendrites and begins to communicate with its neighbors.

Stem cells differentiate to produce different types of nerve cells.

Death

Although neurons are the longest living cells in the body, large numbers of them die during migration and differentiation.

The lives of some neurons can take abnormal turns. Some diseases of the brain are the result of the unnatural deaths of neurons.

— In Parkinson’s disease, neurons that produce the neurotransmitter dopamine die off in the basal ganglia, an area of the brain that controls body movements. This causes difficulty initiating movement.

— In Huntington’s disease, a genetic mutation causes over-production of a neurotransmitter called glutamate, which kills neurons in the basal ganglia. As a result, people twist and writhe uncontrollably.

— In Alzheimer’s disease, unusual proteins build up in and around neurons in the neocortex and hippocampus, parts of the brain that control memory. When these neurons die, people lose their capacity to remember and their ability to do everyday tasks. Physical damage to the brain and other parts of the central nervous system can also kill or disable neurons.

— Blows to the brain, or the damage caused by a stroke, can kill neurons outright or slowly starve them of the oxygen and nutrients they need to survive.

— Spinal cord injury can disrupt communication between the brain and muscles when neurons lose their connection to axons located below the site of injury. These neurons may still live, but they lose their ability to communicate.

One method of cell death results from the release of excess glutamate. Macrophages (green) eat dying neurons in order to clear debris.

Hope Through Research

Scientists hope that by understanding more about the life and death of neurons they can develop new treatments, and possibly even cures, for brain diseases and disorders that affect the lives of millions of Americans.

The most current research suggests that neural stem cells can generate many, if not all, of the different types of neurons found in the brain and the nervous system. Learning how to manipulate these stem cells in the laboratory into specific types of neurons could produce a fresh supply of brain cells to replace those that have died or been damaged.

Therapies could also be created to take advantage of growth factors and other signaling mechanisms inside the brain that tell precursor cells to make new neurons. This would make it possible to repair, reshape, and renew the brain from within.

For information on other neurological disorders or research programs funded by the National Institute of Neurological Disorders and Stroke, contact the Institute's Brain Resources and Information Network (BRAIN) at:

BRAINP.O. Box 5801Bethesda, MD 20824(800) 352-9424

www.ninds.nih.gov

Источник: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Life-and-Death-Neuron

4.1 The Neuron Is the Building Block of the Nervous System

An Overview of the Different Parts of a Neuron

  1. Describe the structure and functions of the neuron.
  2. Draw a diagram of the pathways of communication within and between neurons.
  3. List three of the major neurotransmitters and describe their functions.

The nervous system is composed of more than 100 billion cells known as neurons.

A neuron is a cell in the nervous system whose function it is to receive and transmit information. As you can see in Figure 4.

1, “Components of the Neuron,” neurons are made up of three major parts: a cell body, or soma, which contains the nucleus of the cell and keeps the cell alive; a branching tree fibre known as the dendrite, which collects information from other cells and sends the information to the soma; and a long, segmented fibre known as the axon, which transmits information away from the cell body toward other neurons or to the muscles and glands. Figure 4.2 shows a photograph of neurons taken using confocal microscopy.

Figure 4.1 Components of the Neuron. Figure 4.2 The nervous system, including the brain, is made up of billions of interlinked neurons. This vast interconnected web is responsible for all human thinking, feeling, and behaviour.

Some neurons have hundreds or even thousands of dendrites, and these dendrites may themselves be branched to allow the cell to receive information from thousands of other cells.

The axons are also specialized, and some, such as those that send messages from the spinal cord to the muscles in the hands or feet, may be very long — even up to several feet in length.

To improve the speed of their communication, and to keep their electrical charges from shorting out with other neurons, axons are often surrounded by a myelin sheath.

The myelin sheath is a layer of fatty tissue surrounding the axon of a neuron that both acts as an insulator and allows faster transmission of the electrical signal. Axons branch out toward their ends, and at the tip of each branch is a terminal button.

Neurons Communicate Using Electricity and Chemicals

The nervous system operates using an electrochemical process. An electrical charge moves through the neuron itself, and chemicals are used to transmit information between neurons.

Within the neuron, when a signal is received by the dendrites, it is transmitted to the soma in the form of an electrical signal, and, if the signal is strong enough, it may then be passed on to the axon and then to the terminal buttons.

If the signal reaches the terminal buttons, they are signalled to emit chemicals known as neurotransmitters, which communicate with other neurons across the spaces between the cells, known as synapses.

The following video clip shows a model of the electrochemical action of the neuron and neurotransmitters:

The Electrochemical Action of the Neuron []: http://www..com/watch?v=TKG0MtH5crc

The electrical signal moves through the neuron as a result of changes in the electrical charge of the axon. Normally, the axon remains in the resting potential, a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell.

When the segment of the axon that is closest to the cell body is stimulated by an electrical signal from the dendrites, and if this electrical signal is strong enough that it passes a certain level or threshold, the cell membrane in this first segment opens its gates, allowing positively charged sodium ions that were previously kept out to enter. This change in electrical charge that occurs in a neuron when a nerve impulse is transmitted is known as the action potential. Once the action potential occurs, the number of positive ions exceeds the number of negative ions in this segment, and the segment temporarily becomes positively charged.

As you can see in Figure 4.3, “The Myelin Sheath and the Nodes of Ranvier,” the axon is segmented by a series of breaks between the sausage- segments of the myelin sheath. Each of these gaps is a node of Ranvier.

The electrical charge moves down the axon from segment to segment, in a set of small jumps, moving from node to node.

When the action potential occurs in the first segment of the axon, it quickly creates a similar change in the next segment, which then stimulates the next segment, and so forth as the positive electrical impulse continues all the way down to the end of the axon.

As each new segment becomes positive, the membrane in the prior segment closes up again, and the segment returns to its negative resting potential. In this way the action potential is transmitted along the axon, toward the terminal buttons. The entire response along the length of the axon is very fast — it can happen up to 1,000 times each second.

Figure 4.3 The Myelin Sheath and the Nodes of Ranvier. The myelin sheath wraps around the axon but also leaves small gaps called the nodes of Ranvier. The action potential jumps from node to node as it travels down the axon.

An important aspect of the action potential is that it operates in an all or nothing manner. What this means is that the neuron either fires completely, such that the action potential moves all the way down the axon, or it does not fire at all.

Thus neurons can provide more energy to the neurons down the line by firing faster but not by firing more strongly.

Furthermore, the neuron is prevented from repeated firing by the presence of a refractory period — a brief time after the firing of the axon in which the axon cannot fire again because the neuron has not yet returned to its resting potential.

Neurotransmitters: The Body’s Chemical Messengers

Not only do the neural signals travel via electrical charges within the neuron, but they also travel via chemical transmission between the neurons.

Neurons are separated by junction areas known as synapses, areas where the terminal buttons at the end of the axon of one neuron nearly, but don’t quite, touch the dendrites of another. The synapses provide a remarkable function because they allow each axon to communicate with many dendrites in neighbouring cells.

Because a neuron may have synaptic connections with thousands of other neurons, the communication links among the neurons in the nervous system allow for a highly sophisticated communication system.

When the electrical impulse from the action potential reaches the end of the axon, it signals the terminal buttons to release neurotransmitters into the synapse. A neurotransmitter is a chemical that relays signals across the synapses between neurons.

Neurotransmitters travel across the synaptic space between the terminal button of one neuron and the dendrites of other neurons, where they bind to the dendrites in the neighbouring neurons.

Furthermore, different terminal buttons release different neurotransmitters, and different dendrites are particularly sensitive to different neurotransmitters. The dendrites will admit the neurotransmitters only if they are the right shape to fit in the receptor sites on the receiving neuron.

For this reason, the receptor sites and neurotransmitters are often compared to a lock and key (Figure 4.4, “The Synapse”).

Figure 4.4 The Synapse. When the nerve impulse reaches the terminal button, it triggers the release of neurotransmitters into the synapse. The neurotransmitters fit into receptors on the receiving dendrites in the manner of a lock and key.

When neurotransmitters are accepted by the receptors on the receiving neurons, their effect may be either excitatory (i.e., they make the cell more ly to fire) or inhibitory (i.e., they make the cell less ly to fire).

Furthermore, if the receiving neuron is able to accept more than one neurotransmitter, it will be influenced by the excitatory and inhibitory processes of each.

If the excitatory effects of the neurotransmitters are greater than the inhibitory influences of the neurotransmitters, the neuron moves closer to its firing threshold; if it reaches the threshold, the action potential and the process of transferring information through the neuron begins.

Neurotransmitters that are not accepted by the receptor sites must be removed from the synapse in order for the next potential stimulation of the neuron to happen.

This process occurs in part through the breaking down of the neurotransmitters by enzymes, and in part through reuptake, a process in which neurotransmitters that are in the synapse are reabsorbed into the transmitting terminal buttons, ready to again be released after the neuron fires.

More than 100 chemical substances produced in the body have been identified as neurotransmitters, and these substances have a wide and profound effect on emotion, cognition, and behaviour.

Neurotransmitters regulate our appetite, our memory, our emotions, as well as our muscle action and movement. And as you can see in Table 4.

1, “The Major Neurotransmitters and Their Functions,” some neurotransmitters are also associated with psychological and physical diseases.

Drugs that we might ingest — either for medical reasons or recreationally — can act neurotransmitters to influence our thoughts, feelings, and behaviour. An agonist is a drug that has chemical properties similar to a particular neurotransmitter and thus mimics the effects of the neurotransmitter.

When an agonist is ingested, it binds to the receptor sites in the dendrites to excite the neuron, acting as if more of the neurotransmitter had been present. As an example, cocaine is an agonist for the neurotransmitter dopamine.

Because dopamine produces feelings of pleasure when it is released by neurons, cocaine creates similar feelings when it is ingested. An antagonist is a drug that reduces or stops the normal effects of a neurotransmitter.

When an antagonist is ingested, it binds to the receptor sites in the dendrite, thereby blocking the neurotransmitter. As an example, the poison curare is an antagonist for the neurotransmitter acetylcholine.

When the poison enters the brain, it binds to the dendrites, stops communication among the neurons, and usually causes death. Still other drugs work by blocking the reuptake of the neurotransmitter itself — when reuptake is reduced by the drug, more neurotransmitter remains in the synapse, increasing its action.

Table 4.1 The Major Neurotransmitters and Their FunctionsNeurotransmitterDescription and functionNotes
[Skip Table]
Acetylcholine (ACh)A common neurotransmitter used in the spinal cord and motor neurons to stimulate muscle contractions. It’s also used in the brain to regulate memory, sleeping, and dreaming.Alzheimer’s disease is associated with an undersupply of acetylcholine. Nicotine is an agonist that acts acetylcholine.
DopamineInvolved in movement, motivation, and emotion, Dopamine produces feelings of pleasure when released by the brain’s reward system, and it’s also involved in learning.Schizophrenia is linked to increases in dopamine, whereas Parkinson’s disease is linked to reductions in dopamine (and dopamine agonists may be used to treat it).
EndorphinsReleased in response to behaviours such as vigorous exercise, orgasm, and eating spicy foods.Endorphins are natural pain relievers. They are related to the compounds found in drugs such as opium, morphine, and heroin. The release of endorphins creates the runner’s high that is experienced after intense physical exertion.
GABA (gamma-aminobutyric acid)The major inhibitory neurotransmitter in the brain.A lack of GABA can lead to involuntary motor actions, including tremors and seizures. Alcohol stimulates the release of GABA, which inhibits the nervous system and makes us feel drunk. Low levels of GABA can produce anxiety, and GABA agonists (tranquilizers) are used to reduce anxiety.
GlutamateThe most common neurotransmitter, it’s released in more than 90% of the brain’s synapses. Glutamate is found in the food additive MSG (monosodium glutamate).Excess glutamate can cause overstimulation, migraines, and seizures.
SerotoninInvolved in many functions, including mood, appetite, sleep, and aggression.Low levels of serotonin are associated with depression, and some drugs designed to treat depression (known as selective serotonin reuptake inhibitors, or SSRIs) serve to prevent their reuptake.

Key Takeaways

  • The central nervous system (CNS) is the collection of neurons that make up the brain and the spinal cord.
  • The peripheral nervous system (PNS) is the collection of neurons that link the CNS to our skin, muscles, and glands.
  • Neurons are specialized cells, found in the nervous system, which transmit information. Neurons contain a dendrite, a soma, and an axon.
  • Some axons are covered with a fatty substance known as the myelin sheath, which surrounds the axon, acting as an insulator and allowing faster transmission of the electrical signal.
  • The dendrite is a tree extension that receives information from other neurons and transmits electrical stimulation to the soma.
  • The axon is an elongated fibre that transfers information from the soma to the terminal buttons.
  • Neurotransmitters relay information chemically from the terminal buttons and across the synapses to the receiving dendrites using a lock and key type of system.
  • The many different neurotransmitters work together to influence cognition, memory, and behaviour.
  • Agonists are drugs that mimic the actions of neurotransmitters, whereas antagonists are drugs that block the actions of neurotransmitters.

Exercises and Critical Thinking

  1. Draw a picture of a neuron and label its main parts.
  2. Imagine an action that you engage in every day and explain how neurons and neurotransmitters might work together to help you engage in that action.

Figure 4.2: “Confocal microscopy of mouse brain, cortex” by ZEISS Microscopy (http://www.flickr.com/photos/zeissmicro/10799674936/in/photostream/) used under CC BY-NC-ND 2.0  (http://creativecommons.

org/licenses/by-nc-nd/2.0/deed.en_CA) license.

Источник: https://opentextbc.ca/introductiontopsychology/chapter/3-1-the-neuron-is-the-building-block-of-the-nervous-system/

Neuron Function, Parts, Structure, and Types

An Overview of the Different Parts of a Neuron

By Olivia Guy-Evans, published Feb 15, 2021

Neurons are the information processing units of the brain which have a responsibility for sending, receiving, and transmitting electrochemical signals throughout the body.

Neurons, also known as nerve cells, are essentially the cells that make up the brain and the nervous system. Neurons do not touch each other, but where one neuron comes close to another neuron, a synapse is formed between the two.

Behance Discovery — Alexey Kashpersky

The function of a neuron is to transmit nerve impulses along the length of an individual neuron and across the synapse into the next neuron.

The central nervous system, which comprises the brain and spinal cord, and the peripheral nervous system, which consists of sensory and motor nerve cells all contain these information processing neurons.

According to new research, the human brain contains around 86 billons neurons (Herculano-Houzel, 2009). These cells develop around fully around the time of birth but un other cells, cannot reproduce or regenerate once they die.

Anatomy of a Neuron

The neuron contains the soma (cell body) from which extend the axon (a nerve fiber conducting electrical impulses away from the soma) and dendrites (tree- structures that receive signals from other neurons). The myelin sheath is an insulating layer that forms around the axon and allows nerve impulses to transmit more rapidly along theaxon.

Neurons do not touch each other, and there is a gap, called the synapse, between the axon of one neuron the dendrite of the next.

The unique structure of neurons permits it to receive and carry messages to other neurons and throughout the body.

Dendrites

Dendrites are the tree-root-shaped part of the neuron which are usually shorter and more numerous than axons. Their purpose is to receive information from other neurons and to transmit electrical signals towards the cell body.

Dendrites are covered in synapses, which allows them to receive signals from other neurons.Some neurons have short dendrites, whilst others have longer ones.

In the central nervous system, neurons are long and have complex branches that can allow them to receive signals from many other neurons.

For instance, cells called Purkinje cells which are found in the cerebellum have highly developed dendrites to receive signals from thousands of other cells.

Soma (Cell Body)

The soma, or cell body, is essentially the core of the neuron. The soma’s function is to maintain the cell and to keep the neuron functioning efficiently (Luengo-Sanchez et al., 2015).

The soma is enclosed by a membrane which protects it, but also allows it to interact with its immediate surroundings.

The soma contains a cell nucleus which produces genetic information and directs the synthesis of proteins. These proteins are vital for other parts of the neuron to function.

Axon

The axon, also called a nerve fiber, is a tail- structure of the neuron which joins the cell body at a junction called the axon hillock.

The function of the axon is to carry signals away from the cell body to the terminal buttons, in order to transmit electrical signals to other neurons.

Most neurons just have one axon which can range in size from 0.1 millimeters to over 3 feet (Miller & Zachary, 2017). Some axons are covered in a fatty substance called myelin which insulates the axon and aids in transmitting signals quicker.

Axons are long nerve processes that may branch off to transfer signals to many areas, before ending at junctions called synapses.

Myelin Sheath

The myelin sheath is a layer of fatty material that covers the axons of neurons. Its purpose is to insulate one nerve cell from another and so to prevent the impulse from one neuron from interfering with the impulse from another. The second function of the myelin sheath is to speed up the conduction of nerve impulses along the axon.

The axons which are wrapped in cells known as glial cells (also known as oligodendrocytes and Schwann cells) form the myelin sheath.

The myelin sheath which surrounds these neurons has a purpose to insulate and protect the axon. Due to this protection, the speed of transmission to other neurons is a lot faster than the neurons that are unmyelinated.

The myelin sheath is made up of broken up gaps called nodes of Ranvier. Electrical signals are able to jump between the nodes of Ranvier which helps in speeding up the transmission of signals.

Axon Terminals

Located at the end of the neuron, the axon terminals (terminal buttons) are responsible for transmitting signals to other neurons.

At the end of the terminal button is a gap, which is known as a synapse. Terminal buttons hold vessels which contain neurotransmitters.

Neurotransmitters are released from the terminal buttons into the synapse and are used to carry signals across the synapse to other neurons. The electrical signals convert to chemical signals during this process.

It is then the responsibility of the terminal buttons to reuptake the excess neurotransmitters which did not get passed onto the next neuron.

Types of Neurons

Although there are billions of neurons and vast variations, neurons can be classified into three basic groups depending on their function: sensory neurons (long dendrites and short axons), motor neurons (short dendrites and long axons) and relay neurons (short dendrites and short or long axons).

Sensory Neurons

Sensory neurons (sometimes referred to as afferent neurons)are nerve cells which carry nerve impulses from sensory receptors towards the central nervous system and brain.When these nerve impulses reach the brain, they are translated into ‘sensations’, such as vision, hearing, taste and touch.

This sensory information can be either physical – through sound, heat, touch, and light, or it can be chemical – through taste or smell. An example of this can be when touching an extremely hot surface. Once this happens, the sensory neurons will be sending signals to the central nervous system about the information they have received.

Most sensory neurons are characterized as being pseudounipolar. This means that they have one axon which is split into two branches.

Motor Neurons

Motor neurons (also referred to as efferent neurons) are the nerve cells responsible for carrying signals away from the central nervous system towards muscles to cause movement. They releaseneurotransmitters to trigger responses leading to muscle movement.

Motor neurons are located in the brainstem or spinal cord (parts of the central nervous system) and connect to muscles, glands and organs throughout the body.

These types of neurons transmit signals from the spinal cord and brainstem to skeletal and smooth muscle to either directly or indirectly control muscle movements.

For instance, after touching a hot surface with your hand, the message has been received from the sensory neurons. The motor neurons then cause the hand to move away from the hot surface.

There are two types of motor neurons:

  • Lower motor neurons – these are neurons which travel from the spinal cord to the muscles of the body.
  • Upper motor neurons – these are neurons which travel between the brain and the spinal cord.

Motor neurons are characterized as being multipolar. This means that they have one axon and several dendrites projecting from the cell body.

Relay Neurons

A relay neuron (also known as an interneuron) allows sensory and motor neurons to communicate with each other. Relay neurons connect various neurons within the brain and spinal cord, and are easy to recognize, due to their short axons.

A to motor neurons, interneurons are multipolar. This means they have one axon and several dendrites.

As well as acting as a connection between neurons, interneurons can also communicate with each other through forming circuits of differing complexities.

The communication between interneurons assists the brain to complete complex functions such as learning and decision-making, as well as playing a vital role in reflexes and neurogenesis – which means the regeneration of new neurons.

Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years.

How to reference this article:

Guy-Evans, O. (2021, Feb 15). What is a neuron? Function, parts, structure, and types. Simply Psychology. www.simplypsychology.org/neuron.html

APA Style References

Herculano-Houzel, S. (2009). The human brain in numbers: a linearly scaled-up primate brain. Frontiers in human neuroscience, 3, 31.

Luengo-Sanchez, S., Bielza, C., Benavides-Piccione, R., Fernaud-Espinosa, I., DeFelipe, J., & Larrañaga, P. (2015). A univocal definition of the neuronal soma morphology using Gaussian mixture models. Frontiers in neuroanatomy, 9, 137.

Miller, M. A., & Zachary, J. F. (2017). Mechanisms and morphology of cellular injury, adaptation, and death. Pathologic basis of veterinary disease, 2.

Источник: https://www.simplypsychology.org/neuron.html

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