Types Of Neurons

Neurons make up the core components of the brain, and specialise in transmitting messages via electrochemical impulses.

Structurally, neurons can be simplified by breaking them down into dendrites, the axon and the axon terminal.

Dendrites

Dendrites are the roots of a neuron, and project from the cell body just like roots do from a plant. Their purpose is to pick up information from the surrounding environment and carry it towards the cell body.

Axon

The axon transmits impulses away from the cell body towards the axon terminal. To help speed up this process, the axon is insulated with a myelin sheath that is made up of Schwann cells.

Axon Terminal

At the very end of the axon is the axon terminal, and this is what transmits information to a neighbouring neuron via the release of neurotransmitters.

Once these neurotransmitters have been released, they will then travel across the synaptic cleft and dock with the receptor sites on the dendrites of an adjacent neuron.

And so the whole process begins again, with the dendrites sending information to the cell body, and the cell body sending information down the axon and onto the next neuron.

Neurotransmitters & Mental Disorders

It is believed that neurotransmitters may be responsible for many mental disorders.

For example, low levels of the neurotransmitter serotonin are thought to cause depression, whilst excessive amounts of the neurotransmitter dopamine are thought to cause schizophrenia.

Certain drugs such as ecstasy also work by influencing the activity neurotransmitters. In the case of ecstasy, the massive release of serotonin it causes results in feelings of euphoria.

“Firing” Of Neurons

When a neuron releases its neurotransmitters, it does so through a process known as depolarisation.

This involves the neuron alternating from a resting negative electrical potential to a positive electrical potential, and then back again to a negative electrical potential.

Types Of Neurons

The brain has roughly 3 billion neurons, and the nervous system has around the same amount. This is almost the same number as the entire population of Earth, which as of March 2009, is said to be at around 6.76 billion people.

Below you will find a brief description of the three main types of neurons; sensory neuron, interneuron and motor neuron.

Sensory Neurons

Sensory neurons allow you to receive information from the outside world via your senses. For example, there are sensory neurons that allow you to see light, hear sound, feel things, taste food and smell odours.

Interneurons

Interneurons communicate with other neurons, and represent the majority of neurons in your brain. They allow you to think, remember and perceive your surrounding environment.

Motor Neurons

Motor neurons are neurons which communicate with muscle fibres, the result of which makes them contract or relax thereby allowing you to move your body.

Nerves

A nerve is a bundle of axons which are twisted together just like the individual fibres of a rope. Nerves can be classified as being afferent or efferent.

Afferent Nerve

Afferent nerves carry information inwards to the brain. For example, the optic nerve is an afferent nerve because it carries visual information towards the brain.

Afferent = (A)nything that comes into the brain.

Efferent Nerve

Efferent nerves carry information outwards from the brain. For example, motor nerves carry information to muscle fibres which allows them to contract.

Efferent = (E)verything that exits the brain.

Note : It is possible for nerves to carry two way information (i.e. be both afferent and efferent).

Summary

• Dendrites receive information from other neurons, and pass it on to the cell body.

• Axons send information away from the cell body.

• Neurotransmitters are chemicals messengers which dock at the receptor sites of an adjacent neuron.

• Neurotransmitters are thought to be associated with certain mental disorders.

• Low levels of serotonin are associated with depression.

• Excessive amounts of dopamine are associated with schizophrenia.

• There are three main types of neurons:

• Sensory neurons allow us to experience the outside world via our senses.

• Interneurons communicate with other neurons, and are what makes consciousness possible.

• Motor neurons communicate with muscle fibres and allow you to move your body.

• Neurotransmitters are released through a process known as depolarisation.

• A nerve is a bundle of axons.

• Afferent nerves send information towards something.

• Efferent nerves move information away from something.