The Reflex Arc

• What is the structure called that neurons form to enable quick reactions to pain?


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

  Sensory neuron, relay neuron, motor neuron
• What is the function of the sensory neuron in a reflex arc?

  To detect sensations
• Where is the relay neuron located in the reflex arc?

  In the spine
• What is the role of the motor neuron in a reflex arc?

  To activate the effector
• What does the cell body of a neuron contain?

  The nucleus of the cell
• What are the two main structures on the length of a neuron?

  Axon and dendrites
• What is the function of the axon terminals?

  To transmit signals to the next neuron
• What is the synapse?

  The junction where one neuron communicates with another
• What is the myelin sheath made of?

  Schwann cells
• How does the myelin sheath affect the transmission of electrical information?

  It increases the speed of transmission
• What is the effector in a reflex arc?

  The muscle activated by the motor neuron
• What happens when a sensation is detected by sensory receptors?

  An electrical signal rushes along the dendrite to the axon
• What occurs at the axon terminal when an electrical signal reaches it?

  It converts into a chemical signal
• What is the role of the relay neuron in the reflex arc?

  To pass reflex responses to the motor neuron
• What does the central nervous system do with information from the relay neuron?

  Processes it after the body's already moved
• What is proprioception?

  A sense that informs the body of its position in space
• What is the fastest type of neuron in the body?

  Alpha motor neuron
• How fast can the alpha motor neuron transmit information?

  119 meters per second
• Why is the speed of the alpha motor neuron important?

  It enables lightning-fast reactions
• What is the speed of type C neurons that transmit pain?

  One mile per hour
• Why do type C neurons transmit signals slowly?

  They are often smaller and unmyelinated
• What are the steps involved in the reflex arc process?


  1. Sensation detected by sensory receptors
  2. Electrical signal travels along dendrite to axon
  3. Signal reaches axon terminal and converts to chemical signal
  4. Chemical signal crosses synapse to relay neuron
  5. Relay neuron passes response to motor neuron
  6. Motor neuron activates effector (muscle)
  7. Information sent to central nervous system for processing
• What are the differences between fast and slow neurons in the body?

  • Fast neurons (e.g., alpha motor neurons):
  • Speed: 119 m/s
  • Function: Quick reactions
  • Slow neurons (e.g., type C neurons):
  • Speed: 1 mph
  • Function: Transmit pain signals