The Structure & Function of Neurons (AQA A Level Psychology)

Sensory, relay & motor neurones

• Neurones are cells which exist within the nervous system

• Neurones are the building blocks of communication within the body and are essential to everyday survival

• Neurones send electrical and chemical messages around the body to sense organs, glands and other organs

  • This information is then directed to the central nervous system (CNS)

• A neurone is composed of:

  • The cell body contains a nucleus (where the DNA of the neurone is stored)

  • Dendrites (like tree branches) which carry the electrical charges from one neurone to the next

  • The axon which carries the electrical charge down the length of the neurone and is covered in a protective fatty myelin sheath

  • The myelin sheath has gaps in it called Nodes of Ranvier which speed up the message’s transmission

  • Terminal knobs are found at the end of the neurone; they communicate across the synaptic cleft to the next neurone

• There are three main types of neurones, each with a distinct function:

  • Sensory neurones

  • Motor neurones

  • Relay neurones

Sensory Neurones

• The role of sensory neurones is to send information from the peripheral nervous system (PNS) towards the central nervous system (CNS)

• Sensory neurones keep the brain informed about the external and internal environment information coming from the sense organs

• Sensory neurones can only transmit messages one way and cannot receive messages i.e. like a one-way street

• Sensory neurones have long dendrites and short axons

• The cell body is usually to the side of the cell

Motor Neurones

• The role of motor neurones 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 neurones control physical movements such as contraction/relaxation of muscles

• They have short dendrites and long axons

Relay Neurones

• Relay neurones connect sensory neurones to motor neurones

• Relay neurones 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