Neurones

• Nervous system is responsible for detecting changes in the internal and external environment (stimulus)

  This information needs to be processed and an appropriate response is triggered
• Neurones 


  = transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment
• Cell body


  = contains the nucleus surrounded by cytoplasm

  • within the cytoplasm there are also large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters= chemicals which are used pass signals from one neurone to the next.
• dendrons 


  = short extensions which come from the cell body. These extensions divide into smaller and smaller branches known as dendrites.

  They are responsible for transmitting electrical impulses towards the cell body.
• Axons 


  = Singular, elongated nerve fibres that transmit impulses away from the cell body. The fibre is cylindrical in shape consisting of a very narrow region of cytoplasm surrounded by a plasma membrane.
• Sensory neurone 


  = transmit impulses from a receptor cell to a relay neurone, motor neurone or the brain

  • they have 1 dendron which carries the impulse to the cell body, and 1 axon which carries the impulse away from the cell body.
  • towards the central nervous system
• Relay neurone 


  = transmit impulses between neurones.

  • have many short axons and dendrons
  • within the central nervous system
• Motor neurone 


  = transmit impulses from the relay neurone to an effector such as a muscle or a gland

  • have 1 long axon and many short dendrites
• Myelinated neurones 


  Axons are covered in a myelin sheath, made of many layers of plasma membrane

  • Schwann cells produce these layers of membrane by growing around the axon many times. Each time they grow around the axon, a double layer of phospholipid bilayer is laid down
  • myelin sheath acts as an insulating layer and allows these myelinated neurones to conducts the electrical impulse at a faster speed.
• • between each adjacent Schwann cell there is a small gap known as a node of Ranvier= creates gaps in the myelin sheath.
  • the electrical impulse ‘jumps’ from one node to the next as it travels along the neurone which allows the impulse to be transmitted faster.
• Neurones

  • sensory
  • relay
  • motor