The reflex arc

• What are reflex actions and why are they important?

  Reflex actions are automatic and rapid responses that protect the body
• What is the sequence of events in a reflex action?

  The sequence is: pain stimulus detected by receptors, impulses to CNS, relay neurone, motor neurone to effector
• What typically acts as the effector in a reflex action?

  Usually a muscle that responds to withdraw a limb from pain
• What is the role of the receptor in the skin during a reflex action?

  The receptor detects a stimulus, such as a change in temperature.
• What is the role of the effector in a reflex action?

  The effector, such as the biceps muscle, contracts to move the hand away.
• What is a reflex action?

  • An automatic and rapid response to a stimulus
  • Does not require conscious thought
  • Minimizes damage to the body from harmful conditions
• What is the sequence of a reflex action?

  1. Stimulus
  2. Receptor
  3. Sensory neurone
  4. Relay neurone
  5. Motor neurone
  6. Effector
  7. Response
• What is the nerve pathway followed by a reflex action called?

  The nerve pathway is called a reflex arc.
• What happens during the pain withdrawal reflex?

  We rapidly move our hand away after accidentally touching something hot.
• What is the purpose of reflex actions?

  • To provide a quick response to harmful stimuli
  • To protect the body from potential damage
• What are reflexes?

  Automatic responses hardwired into your body
• Which neurones in the spinal cord coordinate a response without you thinking about it ?

  The relay neurones
• What chemical is released by one neurone when an electrical message reaches the synapse?

  Chemicals called neurotransmitters
• What is a voluntary action?

  Actions that are consciously controlled by the brain
• What is an involuntary action?

  involuntary actions are automatic responses not consciously controlled
• An example of a voluntary action


  Picking up a pen from the floor
• An example of an involuntary action

  Moving your hand away from a hot plate
• What are reflexes?


  Automatic responses to stimuli that do not involve conscious thought
• How do reflex arcs function in the nervous system?


  They allow for quick responses to stimuli without involving the brain
• Explain using the diagram below how a reflex arc happens:

  1. Receptor in the skin detects a stimulus (the change in temperature).
  2. Sensory neurone sends electrical impulses to relay neurone, which are located in the spinal cord. They connect sensory neurones to motor neurones.
  3. Motor neurone sends electrical impulses to an effector.
  4. Effector produces a response (muscle contracts to move hand away).

  
• Explain what is happening using the diagram:

  Where two neurones meet there is a small gap, a synapse.

  1. An electrical impulse travels along the first axon.
  2. This triggers the nerve-ending of a neurone to release chemical messengers called neurotransmitters.
  3. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the second neurone.
  4. The receptor molecules on the second neurone bind only to the specificneurotransmittersreleased from the first neurone. This stimulatesthe second neurone to transmit the electrical impulse