The Reflex Arc: Sensory, Relay and Motor Neurons

• What cells are responsible for quick reactions to pain?

  Neurons
• What structure do neurons form to facilitate quick reactions?

  A reflex arc
• What are the three types of neurons in a reflex arc?

  • Sensory neuron
  • Relay neuron
  • Motor neuron
• Where is the relay neuron located?

  In the spine
• What does the cell body of a neuron contain?

  The nucleus of the cell
• What are the two main structures on a neuron that carry information?

  Axon and dendrites
• What are axon terminals responsible for?

  Converting electrical signals to chemical signals
• What is the function of the myelin sheath?

  Protects the cell and increases transmission speed
• What type of cells make up the myelin sheath?

  Schwann cells
• What is the effector in a reflex arc?

  The muscle activated by the motor neuron
• What are the steps in the reflex arc process?

  1. Sensation detected by sensory receptors
  2. Electrical signal travels along dendrite to axon
  3. Signal converts to chemical at axon terminal
  4. Chemical crosses synapse to relay neuron
  5. Relay neuron sends signal to motor neuron
  6. Motor neuron activates effector (muscle)
• What happens when the signal reaches the axon terminal?

  It converts into a chemical signal
• What does the relay neuron do in the reflex arc?

  Passes signals to the motor neuron
• How does the brain respond during a reflex action?

  It processes information after the body moves
• What is proprioception?

  A sense of body position in space
• What is the speed of the fastest neuron in the body?

  119 meters per second
• What is the speed of type C neurons that transmit pain?


  One mile per hour
• Why are type C neurons slow?

  They are smaller and unmyelinated
• What are the differences between fast and slow neurons?

  Fast neurons:

  • Example: Alpha motor neuron
  • Speed: 119 m/s (266 mph)
  • Function: Quick reflex actions

  
  

  Slow neurons:

  • Example: Type C neurons
  • Speed: 1 mph
  • Function: Transmit pain signals