Structure and function of sensory, relay and motor neurons

• Neurons carry electrical impulses around the body via the nervous system.

  Structure -

  • cell body = house of nucleus, dendrites protrude from it
  • nucleus = genetic material of the cell
  • dendrites = receive signals from neurons/sensory receptors
  • axon = impulses away from the body, down the neuron
  • myelin sheath = protects axon, speeds electrical transmission of impulses
  • nodes of Ranvier = speeds impulse by providing gaps in MS for impulse to jump along
  • axon terminal = communicates with the next neuron in the chain across the synapse
• Sensory neurons are found in receptors they carry nerve impulses to the CNS and convert them into sensations. Some stop at the spinal cord for quick reflex action. Receptor cells detect a change in the environment and stimulate electrical impulses in response.

  Long dendrites, short axons.
• Relay neurons are between sensory input and motor output. They facilitate communication between the sensory and motor neurons.

  short dendrites, short axon
• Motor neurons are in the CNS and release neurotransmitters when stimulated. They bind to receptors in muscles and trigger responses such as movement. They connect the CNS to effectors such as muscles and glands. Control muscle movement.

  short dendrites, long axons.
• Receptors to effectors in NS

  • stimulus - receptor - sensory neuron - relay neuron - motor neuron - effector - response.

  Reflex action allows the body to automatically and quickly respond to a stimulus to minimise further damage to the body. Nerve pathway followed by a reflex action is a reflex arc. Doesn't involve conscious parts of the brain.

  Reflex arc -

  1. receptor in skin detects stimulus
  2. sensory neurons send electrical impulses to relay neurons in spinal cord. connect sensory to motor.
  3. motor neurons send electrical impulses to the effector
  4. effector produces response
• Describe the structure + function of a neuron -

  • Neurons enable communication within the nervous system
  • the cell body contains the genetic material
  • branch-like dendrites extend from the cell body
  • dendrites carry functional information towards the cell body
  • dendrites can receive information from other neurons
  • axons carry messages away from the cell body
  • axons can be myelinated to increase speed of nerve transmission (saltatory conduction between nodes of Ranvier which allows the electrical impulse to jump along and pass the message quicker)
  • axon terminals contain neurotransmitters.
• Which of the following neurons carries electrical impulses towards the brain?

  sensory