Sensory, Relay & Motor Neurons (AQA GCSE Psychology)
Revision Note
Written by: Claire Neeson
Reviewed by: Lucy Vinson
Neurons & their functions
Neurons are cells within the nervous system
There are thought to be as many as 100 billion neurons in the brain and over 1 billion in the spinal cord i.e. about as many neurons in the brain as there are stars in the Milky Way
Neurons are the building blocks of communication within the body and are essential to our everyday survival
Neurons send electrical and chemical messages around the body to the sense organs, glands and to each other (neurotransmission) and then relay information back to the central nervous system
There are three main types of neurons, each with its distinct function:
Sensory neurons
Motor neurons
Relay neurons
The three types of neuron cells
A neuron is composed of:
The cell body containing a nucleus (the DNA of the neuron)
Dendrites (like tree branches) which carry the electrical charges from one neuron to the next
The axon which carries the charge down the length of the neuron and is covered in a protective fatty myelin sheath
The myelin sheath has gaps called Nodes of Ranvier which speeds up the message’s transmission
The terminal knobs which communicate across the synaptic cleft to the next neuron
Sensory Neurons:
The role of sensory neurons is to send information to the brain from the peripheral nervous system (PNS) towards the central nervous system (CNS)
They keep the brain informed about the external and internal environment information coming from the sense organs
Sensory neurons can only transmit messages one way and cannot receive messages i.e. like a one-way street
They have long dendrites and short axons
The cell body is usually to the side of the cell
Motor Neurons
Their role is to carry signals from the CNS toward organs, muscles and glands (PNS)
They can both transmit and receive messages i.e like a two-way street
Motor neurons control physical movements such as contraction/relaxation of muscles
They have short dendrites and long axons
Relay Neurons
They connect sensory neurons to motor neurons
Relay neurons are located in the CNS and carry signals/messages across this part of the nervous system
Messages can be both transmitted and received i.e. a two-way street
They have short axons and short dendrites
Examiner Tips and Tricks
You may be asked to label a diagram of a neuron in the exam so make sure that you know each type of neuron well.
Worked Example
Here is an example of a question you might be asked on this topic - for AO1.
AO1: You need to demonstrate knowledge and understanding of key concepts, ideas, theories and research.
After each featured question there is a ‘model’ answer i.e. one which would achieve top marks in the exam.
Question: Briefly explain the function of a motor neuron. [2]
Model answer:
The motor neuron carries an electrical signal to a muscle which will cause that muscle to either contract or relax (move).
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