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.

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

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.

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).

What makes neurons different from other cells?

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:

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.

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.

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.