The nervous system and homeostasis

• Nervous system


  Enables humans to react to their surroundings and to coordinate their behaviour - this includes both voluntary and involuntary actions
• Nervous system responses


  1. Stimulus detected by receptors

  2. Information from receptors passes along cells (neurones) to the CNS as electrical impulses

  3. CNS coordinates the body's response to the stimulus

  4. Effectors bring about a response, such as glands secreting hormones or muscles contracting

  5. Body responds to the stimulus
• Structure of the nervous system

  • Made up of the central nervous system (CNS) and a network of nerves
  • CNS comprises the brain and spinal cord
• Homeostasis


  Regulation of internal conditions (of a cell or whole organism) in response to internal and external changes, to maintain optimum conditions for functioning
• What homeostasis controls in the human body

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Automatic control systems of homeostasis

  May involve nervous responses or chemical responses
• Components of control systems

  • Receptor cells, which detect stimuli (changes in the environment)
  • Coordination centres (such as the brain, spinal cord, or pancreas), which receive and process information from receptors
  • Effectors (muscles or glands), which produce responses to restore optimum conditions
• Factors affecting reaction time

  • Tiredness
  • Distractions
  • Caffeine
  • Alcohol
• Reflex actions


  Automatic and rapid - they do not involve the conscious part of the brain
• Reflex arcs


  • Sensory receptor in skin of finger
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • Effector (muscle)
• Neurones


  Carry electrical impulses around the body - relay neurones connect sensory neurones to motor neurones
• Synapses


  Gaps between neurones, which allow electrical impulses in the nervous system to cross between neurones
• Myelin sheath increases speed of electrical impulses along the axon
• Chemicals are released into the gap between neurones, which attach to the surface of the next neurone and set up a new electrical impulse
• Reaction time experiments involve dropping a ruler and having a participant catch it to measure their reaction time
• Reaction time experiments should be repeated multiple times before and after consumption of a caffeinated drink to test the effect of caffeine on reaction time
• The same person should not drop and catch the ruler in a reaction time experiment, as this would not be a fair test
• Variables that must be controlled in a reaction time experiment include...