Voluntary and Reflex actions

• Receptor


  Stimulated by a stimulus, each type of receptor responds to a type of stimulus (e.g. sight, sound, touch)
• Central nervous system (CNS)


  Includes the brain and spinal cord, links receptors and effectors, has a coordinating (control centre) role
• Figure 6.1 The nervous system
• Voluntary and reflex actions


  When stimulated, an effector (muscle) produces a response (e.g. muscle contracting and moving arm)
• Types of nervous action


  • Voluntary
  • Reflex
• Voluntary actions


  • Conscious control (brain and thinking time) involved
  • Speed of action is variable, usually much slower
• Reflex actions


  • No conscious control involved
  • Speed of action is fast
• Table 6.1 Voluntary and reflex actions
• The two parts of the central nervous system are the brain and spinal cord
• Reflex actions often protect the body, such as the withdrawal of a hand from a hot object
• Reflex arc


  The pathway of neurones in a reflex action
• Figure 6.2 A reflex arc
• Reflex arc


  • Sensory neurone carries nerve impulses from receptors to spinal cord
  • Motor neurone carries nerve impulses from spinal cord to effector (muscle)
  • Association neurone joins sensory and motor neurones in grey matter of spinal cord
  • Small gaps between neurones are called synapses
• Figure 6.3 Drawing a reflex arc
• Direction of hand


  free neurones link in the grey matter immediately
• Voluntary and Reflex Actions
• Voluntary actions


  • We deliberately choose to do them
  • They include conscious thought
• Reflex actions


  • They are rapid
  • They do not involve conscious control
• Reflex actions are useful in protecting the body
• Reflex pathway


  • It is kept as short as possible
  • It uses a minimum number of neurones to transfer the electrical impulses
  • There are very few gaps between the neurones as these are areas where the electrical impulse will slow down
• Reflex arc


  1. Sensory neurone carries information from the receptor to the CNS

  2. Motor neurone carries information from the CNS to the effector

  3. Association neurone carries information between the sensory neurone and the motor neurone
• The three neurones link in the grey matter (butterfly-shaped part) of the spinal cord; the outer part is the white matter
• The association neurone and motor neurone begin the cell body
• There are only two synapses
• Synapses are short gaps between neurones where communication occurs
• The reflex pathway is short to allow for faster responses
• Stimulus receptor CNS Effector Response is the word equation that summarises a nervous response
• Stimulus


  Something that causes a response
• Reflex arc