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Neuron Structure and Function

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Neuron Structure and Function

In biopsychology, the idea is that if we better understand biological structures and functions, we may be able to unravel the mystery of how the mind and soul (in Greek, 'psyche') work. Although scientists used to think that the mind resided in the heart or liver, we now know that the brain controls the body. Let us take a closer look at the cells that make up the brain. There are two main types:

  • Neurons.
  • Glial cells.

Glial cells are important because they hold the brain's structure together like glue, which is what the word 'glia' means in Greek. But even more critical to human behaviour are the neurons that conduct electrical signals through the body.

Neuron structure and function [+] Toyo Ohashi Bridge [+] StudySmarter

Photograph of the Toyo Ohashi Bridge. Similar to a car bridge like this one, in our nervous system, the neurones are the road that allows the transmission of information, and the glial cells are the posts that provide the infrastructure for the neurones, mazda.com

Think of glial cells as bridge piers and neurons as a concrete road for cars to drive on. The cars would be the information passed from one end to the other via electrical impulses. The difference is that the glial cells and neurons are in a three-dimensional space and the roads can go in any direction.


Neuron structure and function

Neurons are specialised cells found in the nervous systems of all living things. Their job is to transmit nerve impulses. An incredible 86,000,000,000 (yes, that's 86 billion!) of them form a dense network in the brain, which is why we call them 'brain cells' in everyday language.

They relay information not only in the brain but throughout the body. The neurons take in information from the outside world through the senses and relay information from the brain to the muscles, which makes all movement and communication possible - without your brain controlling the movement of your eye muscles, for example, you would not be able to read this text.

Neuron structure and function 3D connections of neurons in human brain StudySmarter

3D rendering of the connections of neurons in the human brain, Pixabay

What's the structure and function of a neuron?

All cells begin as embryonic stem cells. Later they begin to differentiate, i.e., they develop different forms according to their function in the body. The neuron has a membrane, nucleus, and cytoplasm like other animal cells. However, the cell structure of a neuron differs in that its shape is specialised for the transmission of information it generally has an input (the dendrites) and an output (the axon).

Neuron structure and function Neuron parts illustration StudySmarter

Illustration of neuron parts. The nerve impulse travels from left to right via the axon, Katarina Gadže, StudySmarter Originals

What makes neurons different from other cells?

Dendrites

Dendrites are branched structures that grow from the cell body. The word comes from the Greek 'dendritos', meaning tree-like. And like trees, the boot usually develops first in the middle, and the newest growth occurs at the tips. This is where the neighbouring cells take in the information. Think of these cells as the leaves of trees that capture light for photosynthesis.

Axon

The axon is the long part of a neuron along which impulses travel from the cell body to other cells. An axon can be between a few micrometres and a metre long in humans (in the leg) and as long as 25 metres in whales.

The nerve impulse always travels away from the cell body across the axon to the thick parts at the end of the axon. They are called terminal buttons or axon terminals. It can never travel from the axon terminal to the cell body nerve impulses are unidirectional. This is because of the way nerve impulses travel, called the action potential.

Axons can also branch, but not as much as dendrites. These branches are called collaterals. Where the axon terminals or buttons meet another cell is called a synapse. Through the synapse, nerve impulses are transmitted from one neuron to the next.

Myelin sheaths

Axons are often coated with a protein/fatty compound called myelin. Myelin sheaths insulate the electrical activity of the axon to prevent electrical interference with other nerve impulses in the densely packed neuron network of the central nervous system. It is similar to the rubber insulation that wraps around the wires of your phone charging cord.Myelin also speeds up the transmission of nerve impulses. The more myelin wrapped around an axon, the faster the electrical impulse is sent to the next cell. Myelin is made up of glial cells that wrap around the axon. The parts of the axon where there are no myelin sheaths are called nodes of Ranvier.

What is the structural classification of neurons?

Different types of neurons exist in the body, which can be classified either by their appearance (i.e. their structure) or by their operation (i.e. their function). We will first look at the structural classification of neurons and then the functional classification.

The structural classification sorts neurons into types based on how many axons and dendrites a neuron has. Some of these neurons are only found in certain organisms or in certain parts of the body.

What is the functional classification of neurons?

The functional classification of neurons categorises them according to how they work in the body. The main function of all neurons is to transmit information, either into, within, or out of the body. The function of a particular neuron depends on its type and location.

What are the three major functional types of neurons?

There are three classifications of neurons:

  • Sensory neurons gather information and send it to the brain and spinal cord.
  • Relay neurons (interneurons) connect one neuron with another neuron in the brain and spinal cord.
  • Motor neurons send the information back from the brain and spinal cord to the muscles.

Reflex arc: 1. A sensory neuron registers the heat of a flame (blue), 2. The relay neuron passes the information to the motor neuron. 3. The motor neuron sends an impulse to the muscle (red), causing the muscle to contract and pull the hand away from the flame, MartaAguayo, Wikipedia Commons.

Ideally, the three types of neurons work together smoothly. If any one of them is disturbed, it would lead to serious diseases in the organism. The transmission of nerve impulses through these three types of neurons is the process involved in all actions, including reflexes.

Let us consider a scenario:

  1. You feel something wet on your cheek.
  2. Sensory neurons send a nerve impulse into your body, also called an afferent nerve impulse.
  3. Your brain decides how to respond.
  4. Relay neurons pass nerve impulses in the central nervous system from one neuron to another. This is where conscious and automatic decisions are made about what action to take. A command is sent to your muscles. They contract to pull your head away from your bad/friendly dog.
  5. Motor neurons send nerve impulses to the muscles to move away from the surprising stimulus, which is also called an efferent nerve impulse.

Study tip: Afferent neurons receive nerve impulses, efferent neurons exit the control centre.

What is the function of sensory neurons?

Sensory neurons in the body take physical information such as light, pressure in the form of sound, touch, temperature, or chemical information and convert it into information that the brain can process. This conversion of physical or chemical information into electrochemical information of the brain is called transmutation in biology. You can think of it as a kind of energy conversion.

For example, human skin has different receptors for heat, cold, pain, hard pressure, and gentle pressure. When the skin is exposed to a sudden hot temperature (e.g. fire on a stove), the information from a thermoreceptor ('hot') is converted into an electrical signal that travels along the sensory neuron to the brain.

Damage to sensory neurons can be fatal to the body, as in the case of CIPA, a disease in which sufferers cannot feel pain. This means that they cannot avoid dangerous stimuli in the environment. Most of the time, these people have to lead a conscientious life. Loss of sensory receptors is also the cause of many types of disabilities blindness, deafness, and anosmia (in which people cannot smell). People with these disabilities have to navigate their environment differently than most.


'Receptors' is a confusing term in biopsychology because it's both used to describe sensory neuron cells and smaller structures on the cell membrane that react to certain types of neurotransmitter molecules.


What is the function of relay neurons?

Relay neurons are located in the brain stem and brain. Their function is to connect sensory neurons to motor neurons. Their dendrites and axons are usually relatively short because they do not have to span long distances, and they are not myelinated. In the brain, information from nerve impulses is relayed to and from different areas via relay neurons to enable vision and smell, and to use information from existing memory to create what we call 'thought'.

Decisions made consciously and unconsciously are relayed to the motor neurons for execution. Think of it as a command to the muscles that is transmitted through the relay neurons. In the central nervous system, different ways of relaying nerve impulses can be present simultaneously. When you are frightened, there may be one relay that makes you pull back quickly and unconsciously (that's a reflex), but another that consciously tells you that you are not in immediate danger when your dog licks your face.

Most diseases that affect relay neurons, such as Alzheimer's, Parkinson's, and Huntington's disease, are not well researched and are incurable at the moment. Relay neurons are so vital that damage to them can irreversibly alter a person's personality (as in a stroke or brain haemorrhage) or even lead to death.

What's the function of motor neurons?

Motor neurons set the body in motion, just as a motor moves a machine. They transmit nerve impulses from the brain or spinal cord to a muscle or gland. They send impulses to the muscles, causing them to contract or relax. All of life is movement heartbeat, the diaphragm moving up and down to create breathing in the lungs, the conscious muscle movement muscles in your legs when you walk to the kitchen in the morning.

The brain constantly sends nerve impulses to the body via motor neurons. These neurons have some of the longest axons in the human body, extending from the spine to the foot.

When motor neurons are damaged, people have trouble moving or controlling vital functions such as breathing, chewing, and swallowing. Muscle movement and coordination may be impaired, and sufferers may have twitching limbs or be paralysed. This is the case with ALS and other motor neuron diseases such as multiple sclerosis.


Neuron structure and function - Key takeaways

  • There are about 86 billion neurons in the human brain.
  • Like other cells, neurons have a cell membrane, a cell body, and a nucleus.
  • Unlike other cells, neurons have dendrites and an axon.
  • Dendrites are branched structures that act as the input of the neuron.
  • The axon is the long, thin output of the neuron.
  • There are three types of neurons: sensory neurons, relay neurons, and motor neurons.
  • Sensory neurons relay information to the central nervous system.
  • Relay neurons connect sensory and motor neuron cells in the central nervous system.
  • Motor neurons relay information from the central nervous system to the periphery.
  • The function of neurons is to transmit information in the form of nerve impulses.

Frequently Asked Questions about Neuron Structure and Function

Motor neurones have dendrites, a cell body and an axon and transmit electrochemical signals from the brain to the body.

Neurons are specialised cells in the nervous system, and they transmit nerve impulses to send information through both the brain and the body. 

Neurons can be classified by their structure/appearance or function. The different structural types of neurons are unipolar neurons (one cell body, an axon, and no dendrites), bipolar and pseudounipolar neurons (have a dendrite and an axon), and multipolar neurons (multiple dendrites, a cell body, and an axon). Functional types of neurons are sensory neurons (gather information to send to the brain and spinal cord), relay neurons/interneurons (connect one neuron to another in the brain and spinal cord), and motor neurons (send information from the brain and spinal cord to the muscles). 

Final Neuron Structure and Function Quiz

Question

 What are the two main cells in our 

central nervous system?



Show answer

Answer

The two main cells in the central nervous system are neurones and glial cells.

Show question

Question

Why do we look at structures of 

neurones in psychology?



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Answer

We look at the structure of neurones in psychology 

to better understand how thinking 

and behaviour work.

Show question

Question

What is the scientific word for 'brain cell'?

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Answer

The scientific word for 'brain cell' is the neuron. There are other brain cells, but they're often forgotten (poor glial cells!).

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Question

Approximately how many brain cells are there in the human brain?

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Answer

According to the latest estimates, there are about 86 billion brain cells in the human brain.

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Question

True or false: In general, animals have different neurons than humans.

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Answer

False. Animals generally have neurons similar to human neurons.

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Question

True or false: Only neurons have a cell body, membrane, and nucleus.


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Answer

False. Other cells also have a cell body, membrane, and nucleus. They don’t have dendrites or axons.

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Question

True or false: The dendrites of the neuron receive the input.

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Answer

True. The dendrites are the part of the neuron that receives input.

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Question

What does the axon do?

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Answer

The axon passes on an electric impulse to another cell.

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Question

True or false: The axons of human cells are up to 25m long.

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Answer

False. Axons of human neuron cells are up to a metre long. Those of whales, however, can have up to 25m in length.


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Question

What's the name of the protein/fat layer around axons which insulates the electrical signal?

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Answer

The protein/fat layer around axons is called myelin.

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Question

What are the three structural categories of neurons?

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Answer

The three structural categories are unipolar, bipolar/pseudounipolar and multipolar.

Show question

Question

What are the three functional types of neurons?

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Answer

The three functional types of neurons are sensory neurons, relay neurons and motor neurons.

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Question

You hear an alarm close to you. You startle. Describe how the three functional neurones work together to create your startle response.

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Answer

Sensory neurons in your ear transmit a nerve impulse to your central nervous system. A relay neuron sends the nerve impulse to your brain. Motor neurons send an impulse to your muscles that make your muscles contract and startle.

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Question

Which type of neurons connects the brain to muscles?


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Answer

Motor neurons are the type of neurons that connects the brain and spinal cord to muscles.

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Question

Which type of neuron links sensory input and the nerves that control muscles?

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Answer

Relay neurons connect sensory input neurons and motor neurons that control muscles.

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Question

What is a neurotransmitter?

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Answer

It is a chemical messenger that allows for communication between one neurone and another.

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Why do neurones need neurotransmitters to communicate?

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Answer

The synaptic cleft means that neurones do not connect, so neurotransmitters bridge this gap.

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Question

What is the synaptic cleft?

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Answer

It is the small gap between neurones.

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Question

What are synaptic vesicles?


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Answer

They are the small, bubble-like structures that hold neurotransmitters in the presynaptic neurone, and release them into the synaptic cleft.

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What is the presynaptic neuron?


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Answer

The neuron proceeding the synaptic cleft from which the action potential originates.

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What is the postsynaptic neuron?


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The neuron that receives the neurotransmitter.

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What does the function of a neurotransmitter depend on?


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Answer

The type of neurotransmitter, as well as the receptor it binds to.

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What is an excitatory neurotransmitter?


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Answer

These neurotransmitters increase the likelihood of a resulting action potential occurring in the postsynaptic neurone or receiving cell.

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What is an inhibitory neurotransmitter?


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These neurotransmitters decrease the likelihood of a resulting action potential occurring in the postsynaptic neurone or receiving cell.

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What are some examples of excitatory neurotransmitters?


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Answer

Glutamate, norepinephrine/noradrenalin, epinephrine, dopamine.

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What are some examples of inhibitory neurotransmitters?


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Answer

GABA, serotonin, dopamine.

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How does a neurotransmitter affect behaviours? 

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Answer

They affect behaviours by inducing certain feelings. Serotonin may make a person calmer and more relaxed, whilst epinephrine, an essential factor in the fight-or-flight response, can have the complete opposite effect on behaviour. A person will feel more alert and anxious and experience feelings of fear with epinephrine.

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What can we classify neurotransmitter types into?


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Amino acids, peptides, monoamines, gasotransmitters, purines, and trace amines. Acetylcholine has its own class.

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What neurotransmitters are amino acids?


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Answer

Glutamate, GABA.

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Name a monoamine neurotransmitter.


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Answer

Epinephrine, dopamine, or serotonin.

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The fight-or-flight response is a psychological response that happens when an individual is faced with perceived danger.

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Answer

False

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The fight-or-flight response is an acute stress response.

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Answer

True

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To initiate the fight-or-flight response, there has to be a real danger.


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True


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Which of the following is not an example of the fight-or-flight response?

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Answer

Blushing when someone shouts at you.

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‘Flight’ refers to the act of removing yourself from danger.

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Answer

True

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Freeze is another response the body can have to danger.


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True


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The fight-or-flight response uses the parasympathetic nervous system to signal the adrenal glands to produce adrenaline.

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Answer

True

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Seeing blood can trigger the fight-or-flight response.

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Answer

True

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The fight-or-flight response is a combination of the nervous system and the endocrine system.


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Answer

True


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Question

Which one of the following is not an area of the body known to be affected by the fight-or-flight signal?


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Answer

Testes

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Question

You are very nervous about singing for a crowd for the first time. When you try to sing, your voice wobbles, goes off-key, and is weaker than usual. Explain this reaction using what you learned in this explanation.


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Answer

The fight-or-flight reaction has affected your muscles, particularly the muscles that control your voice box as well as your breathing. Also, the faster breathing triggered by adrenaline can mean that your breathing isn't as deep as usual, which can make your singing seem weaker.

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Question

 How do the physiological changes triggered by adrenaline help survival?


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Answer

They enable the body to quickly react to dangerous stimuli and focus on the danger.

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What is the main hormone that is associated with the fight-or-flight response?


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Answer

Adrenaline

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Question

What evolutionary advantage does the fight-or-flight response give us?


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Answer

It enables our body to respond quickly and appropriately to danger.

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Question

It's possible to not feel pain during life-or-death situations even if seriously injured.


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Answer

True

Show question

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