AQA A Level Biology

Revision Notes

6.2.1 Neurones

Myelinated Motor Neurones

  • Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
  • A bundle of neurones is known as a nerve
  • Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
  • Neurones have a long fibre known as an axon
  • The axon of some neurones is insulated by a fatty sheath with small uninsulated sections along its length (called nodes of Ranvier)
    • The sheath is made of myelin, a substance made by specialised cells known as Schwann cells
    • Myelin is made when Schwann cells wrap themselves around the axon along its length
  • The presence of Schwann cells means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
    • The ‘jumping’ of the electrical impulse between nodes of Ranvier is called saltatory conduction
    • This speeds up the conduction of the impulse and its transfer from one cell to another
  • Neurone cell bodies contain many extensions called dendrites
    • This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication

A neurone, IGCSE & GCSE Biology revision notes

An example of a neurone

  • There are three main types of neurone: sensory, relay and motor
    • Sensory neurones carry impulses from receptors to the CNS (brain or spinal cord)
    • Relay (intermediate) neurones are found entirely within the CNS and connect sensory and motor neurones
    • Motor neurones carry impulses from the CNS to effectors (muscles or glands)
  • Each type of neurone has a slightly different structure
  • Motor neurones have:
    • A large cell body at one end, that lies within the spinal cord or brain
    • A nucleus that is always in its cell body
    • Many highly-branched dendrites extending from the cell body, providing a large surface area for the axon terminals of other neurones

Exam Tip

You are not expected to know the structure of sensory and relay neurones. However it can be helpful to memorise the key identfiying features of motor neurones – such as the location and size of the cell body.

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Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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