Neurons and synapses

It is not necessary to have an in-depth knowledge of the biology of the brain. However, there are some basic brain structures that you will need to know about, as these may form part of your exam. You are most likely to be asked to identify specific aspects of how the brain sends signals and this is what we will look at now, within the section.

Neurons

A neuron is a cell in the body’s nervous system, which processes and sends information within the body using both chemical and electrical signals. Neurons can be sensory, which receive messages from the senses, such as touch, smell, light and sound, or they can be motor neurons, which receive messages regarding the movement of muscles.

Neurons are extremely sensitive and they respond to information from an individual’s environment or from within their own body and they communicate with the nervous system to ensure that relevant parts of the body act upon the information. For example, if it is cold outside, neurons react to the temperature and the central nervous system receives this message and sends responses for the relevant parts of the body to react – in this instance it makes the hair on the body stand up and the individual begins to shiver in response and to try and get warm.

The function of neurotransmitters and synaptic functioning

Neurotransmitters are chemicals which are located at the end of a neuron (the axon) and which send messages to nerve cells across a synapse. The chemical message is then passed to the next neuron by synaptic functioning.

The brain uses neurotransmitters to tell the heart to beat, lungs to breathe, and stomach to digest.

They can also affect mood, sleep, concentration and can cause problems when they are out of balance. For example, too much of the neurotransmitter dopamine is thought to be a potential cause of schizophrenia and not enough of the neurotransmitter serotonin is thought to be a potential cause of depression.

The interaction between neurons and synapses

The way in which interaction between neurons and synapses happens can be summarised in several steps:

Step 1: an electrical impulse is triggered from the cell of one neuron, which then travels down the axon – this is known as action potential.

Step 2: when the impulse reaches the end of the axon, it releases a neurotransmitter, which is found there.

Step 3: the neurotransmitter then has to cross what is referred to as a synaptic gap, to get to the next neuron and enable the chemical message to continue to its destination.

Step 4: the neurotransmitter enters the gap, where it is either taken up by dendrites or lost. Dendrites are short branch extensions of nerve cells, which enable signals to be transmitted from one neuron to the next.

Step 5: if the dendrites take up the neurotransmitter, which is in the gap, the chemical gets picked up.

Step 6: the neurotransmitter then sets off an electrical signal and drops back into the synaptic gap, where it can be taken back up by the dendrites and used again when needed.

Step 7: the change in chemical balance from the receptors triggers an electrical impulse from the cell body, which then travels back down to the axon and the whole process is repeated from step 1.