nervous system

• homeostasis 


  the maintenance of a constant internal environment

  • water levels
  • temperature
  • oxygen levels
  • carbon dioxide levels
  • salt concentration
• an animals response to a stimulus is co-ordinated by it's central nervous system (CNS)
• the CNS consists of the brain and spinal chord
• The CNS gathers information about the environment and responds to changes
• receptors


  specialised cells found in the sense organs to detect stimuli and send impulses along sensory neurones to the CNS
• stimulus 


  changes in the environment
• sense organs

  • eye
  • ear
  • tongue
  • nose
  • skin
• epidermis


  outside layer of your skin
• dermis


  inside layer of your skin
• stimulus

  receptor

  sensory neurone

  CNS

  relay neurone

  motor neurone

  effector

  response
• reflex actions


  quick unconscious actions to prevent harm
• reflex actions are automatic and rapid
• synapse 


  the small gap where two neurones meet
• at the synapse electrical impulses are translated to chemical messengers (neurotransmitters) to cross the gap
• neurotransmitters diffuse across the synapse
• neurotransmitters bind with receptor molecules on the membrane of the second neurone to stimulate an electrical impulse
• the brain controls complex behaviours
• the brain is made of billions of interconnected neurones
• the brain 


  has different regions to carry out different functions

  • cerebral cortex - intelligence, personality, thoughts
  • cerebellum - balance, co-ordination, muscular activity
  • medulla - unconscious activities (breathing, HR...)
  • hypothalamus - regulates temperature and water balance
• ciliary muscles adjust the thickness of the eye lens
• ciliary muscles are attached to the edge of the lens by suspensory ligaments
• accommodation


  the process of changing the shape of the lens to focus on near or distant objects
• to focus on near objects the lens becomes thicker to allow light rays to refract more
• to focus on distant objects the lens becomes thinner to allow light rays to refract less