Types of Neurones (Cambridge (CIE) IGCSE Biology): Revision Note

Neurone diagrams

• There are three main types of neurone: sensory, relay and motor:

  • sensory neurones carry impulses from sense organs to the CNS (opens in a new tab) (brain or spinal cord)

  • relay neurones (also known as intermediate neurones) are found inside the CNS and connect sensory and motor neurones

  • motor neurones carry impulses from the CNS to effectors (muscles or glands)

• Neurones also contain extensions of the cytoplasm:

  • short, branched extensions called dendrites carry impulses towards the cell body

  • a longer extension called the axon carries impulses away from it

• The axon is insulated by a fatty sheath with small uninsulated sections along it (called nodes)

  • This means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next

• Sensory neurones are long and have a cell body branching off the middle of the axon

• Relay neurones are short and have a small cell body at one end with many dendrites branching off it

• Motor neurones are long and have a large cell body at one end with long dendrites branching off it