Sensory, relay and motor neurons

• Reflex arc


  1. Sensory neuron

  2. Relay neuron

  3. Motor neuron
• Neuron


  • Cell body containing nucleus
  • Axon
  • Dendrites
• Axon terminals


  Almost but not quite touch the dendrite of the next neuron
• Synapse


  Structure where axon terminals and dendrites meet
• Myelin sheath


  Made of Schwann cells, protects the cell and increases speed of electrical transmission
• Effector


  Muscle activated by the motor neuron
• Reflex arc function


  1. Sensation detected in sensory receptors

  2. Electrical signal rushes along neuron

  3. Converted to chemical signal at synapse

  4. Detected by relay neuron

  5. Reflex response passed to motor neuron

  6. Effector (muscle) activated
• Reflex responses are passed immediately to the motor neuron, information also sent to central nervous system for processing
• The fastest neural in the body is the alpha motor neuron in the spinal cord, transmitting information at 119 m/s or 266 mph
• Some of the slowest neurons are pain type C neurons, travelling as slow as 1 mph, due to being smaller and unmyelinated
• Proprioception is the sense of where our body is in space at any moment