The Nervous System

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  • The Nervous System
    • Central nervous system (CNS) is made up of the brain and spine
      • Enables humans to react to their surroundings and coordinate their behaviour
    • Receptors detect stimuli.
      • Eye receptors detect light
        • Light receptor cells have a nucleus, cytoplasm and cell membrane.
      • Ear receptors detect sound and change in position (balance)
      • Nose and tongue receptors detect chemicals
      • Skin receptors detect pressure, touch, temperature and pain
    • Simple reflex action: Stimulus> Receptors> Sensory neurone> Relay neurone> Motor neurone> Effector (muscle or gland)
      • At junction/ synapse electrical impluse changed to chemical so if can diffuse across synapse, then change back to electrical
      • Eg sprinter detects starting gun> sound receptor in ears> sensory neurone> CNS> motor neurone> effector> response
    • In the human body some conditions are controlled; water content, ion content, blood sugar levels and temperature
      • Water in: drinking + food.  Water out: sweating + water lost as urine via the kidneys
      • Ion minerals in; food.  Ions out by sweat and as urine via kidneys
      • Temperature need to stay constant to allow enzymes to work (37degrees)
      • Blood sugar levels need to stay constant  to provide the cells with a constant supply of energy 


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