Neurons

• function of the spinal cord


  to relay information between the brain and the rest of the body

  allows the brain to monitor and regulate bodily processes like digestion and breathing (via the autonomic nervous system) and to coordinate voluntary movements (via the somatic nervous system).
• What are spinal nerves?

  The spinal cord is connected to different parts of the body by pairs of spinal nerves and glands.

  
  

  If the spinal cord is damaged, areas supplied by spinal nerves below the damaged site will be cut off from the brain and stop functioning.

  
  

  Eg: an injury to the lumbar spine would result in paralysis from the hip area below.
• What are the three main types of neuron?

  Sensory, Motor, Relay
• Sensory neurons


  Found in receptors such as eyes, ears, tongue and skin - carry nerve impulses to the spinal cord and brain.

  
  

  When these nerve impulses reach the brain. they're translated into 'sensations' - like vision, hearing, taste and touch.
• Relay neurons


  Found between sensory input and motor output/response.

  
  

  Found in the brain and spinal cord.

  
  

  Allow sensory and motor neurons to communicate.
• Motor neurons


  Found in the CNS and control muscle movements

  
  

  When stimulated, they release neurotransmitters that bind to the receptors on muscles to trigger a response - which lead to a movement.
• Intentional Movement


  in response to sensory information (from the sensory neurons), the brain makes a conscious decision to create movement via control of muscles (motor neurones).

  
  

  For example, seeing a glass of water, making the decision to have a drink, coordinating muscles to raise glass to lips.
• Reflex actions


  Some sensory neurones stop at the spinal cord, not reaching the brain, which allows for quick reflex actions.

  
  

  For example, touching a hot plate and dropping it instantly.
• Dendrites


  receive signals from other neurons or from sensory receptor cells (sensory neurons)

  
  

  typically connected to the cell body - 'control centre' of the neuron as it contains the nucleus.
• Axon


  long slender fibre

  
  

  carries nerve impulses in the form of an electrical signal (action potential) away from cell body towards axon terminals where the neuron ends.
• Myelin sheath


  Most axons are surrounded my a myelin sheath, except from relay neurons, which insulates the axon so electrical impulses can travel faster along the axon.
• Axon terminal


  The axon terminal connects the neuron to other neurons, or directly to organs - using a process called synaptic transmission
• Model Answer - Sensory neurons

  Sensory neurons receive information (heat, pain) from the sensory receptors in the skin on...

  The sensory neurons carry these nerve impulses to the CNS.
• Model Answer - Relay neurons


  Relay neurons in the CNS allow sensory neurons to communicate with motor neurons
• Model Answer - Motor neurons

  Motor neurons form synapses with muscles, enabling ... to react appropriately to events in the environment - in this case, by...
• Model Answer - Reflex action

  This seems to be a reflex action, so the sensory neurons involved may terminate in the spinal cord rather than the brain, allowing for a faster reaction

  
  

  Immediate reaction