Edexcel A (SNAB) A Level Biology:复习笔记8.1.2 Neurones: Structure & Function

Neurones: Structure & Function

  • Neurones are specialised cells of the nervous system which carry electrical impulses around the body
  • A bundle of neurones is known as a nerve
  • There are different types of neurones, but the following features are found in all types
    • A long fibre known as an axon
    • A cell body that contains the nucleus and other cellular structures
    • The end of the axon, known as the axon terminal, has many nerve endings
      • The nerve endings at the axon terminals allow neurones to connect to and receive impulses from other neurones, forming a network for easy communication
  • Some neurones are myelinated, meaning that their axon is insulated by a fatty layer known as the myelin sheath
    • The myelin sheath is made up of specialised cells known as Schwann cells which wrap themselves around the axon
    • There are uninsulated gaps between the Schwann cells known as the nodes of Ranvier
    • Electrical impulses in myelinated cells do not travel down the whole axon, but jump from one node to the next, speeding up impulse transmission
  • In non-myelinated neurones the axon is not insulated by Schwann cells
    • The impulse travels more slowly as it moves through the entire length of the axon

Neurones have a long axon, a cell body, and an axon terminal, and some neurones are myelinated

  • There are three main types of neurones
    • Sensory neurones carry impulses from receptors to the brain and spinal cord in the CNS
    • Relay neurones are found entirely within the CNS and connect sensory and motor neurones
    • Motor neurones carry impulses from the CNS to effector muscles or glands
  • Each type of neurone has a slightly different structure
    • Motor neurones
      • A large cell body at one end that lies within the spinal cord or brain
      • Many highly-branched dendrites extending from the cell body, providing many connections with the axon terminals of other neurones
    • Relay neurones
      • Short neurones with axons and highly branched dendrites
    • Sensory neurones
      • A cell body that branches off in the middle of the axon and has no dendrites
      • The axon terminal is attached to a receptor cell
      • The section of neurone that links the axon terminal with the cell body is known as a dendron
      • The section of neurone that connects the cell body with the CNS is the axon

Different types of neurone differ in both structure and function