B10 - The human nervous system

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes
• Homeostasis is important for maintaining optimal conditions for enzyme action and all cell functions
• Internal conditions controlled in the human body

  • Body temperature
  • Water content
  • Blood glucose concentration
• Control systems


  • Involve automatic nervous and chemical responses
  • Include receptors, coordination centres, and effectors
• Receptors detect changes in the internal or external environment
• Coordination centres receive and process information from receptors, and send out signals to coordinate the response
• Effectors are muscles or glands that bring about responses to restore optimum conditions
• External environment varies


  Affects the body
• The nervous system uses electrical signals (impulses) to enable quick reactions and coordination
• Neurone


  A nerve cell that carries electrical impulses
• Nerve


  A bundle of neurones
• Types of neurones


  • Sensory neurones
  • Motor neurones
• Receptors detect stimuli (changes in the environment)
• How the nervous system works

  1. Stimulus

  2. Receptor

  3. Coordinator (CNS)

  4. Effector
• Sensory nerves carry impulses to the CNS, which processes the information and sends out impulses along motor nerves to produce a response
• Reflexes are automatic and rapid responses that do not involve the conscious part of the brain
• Reflex actions


  • Involve sensory neurones, relay neurones in the CNS, and motor neurones
  • Help avoid danger and maintain basic body functions
• Reflexes


  Automatic and rapid responses that do not involve the conscious part of the brain
• Reflexes


  • Help avoid danger or harm
  • Take care of basic body functions like breathing and digesting food
• Reflex arc


  1. Stimulus

  2. Receptor

  3. Sensory neurone

  4. Relay neurone

  5. Motor neurone

  6. Effector
• Synapse


  Junction between neurones where electrical impulses cross a physical gap via chemical diffusion
• Reflexes bypass the conscious areas of the brain
• The time between stimulus and reflex action is as short as possible in a reflex arc
• Reflexes are important for controlling everyday bodily functions and helping avoid danger
• What happens when you step on a pin

  1. Stimulus (pin)

  2. Receptor (in skin)

  3. Sensory neurone (electrical impulse)

  4. Relay neurone (chemical impulse)

  5. Motor neurone (electrical impulse)

  6. Effector (muscle contraction to withdraw foot)
• The brain is made up of billions of interconnected neurones that form different regions
• Cerebral cortex


  • Concerned with consciousness, intelligence, memory, and language
• Cerebellum


  • Concerned with coordinating muscular activity and balance
• Medulla


  • Concerned with unconscious activities like controlling heartbeat, gut movements, and breathing
• The brain has many other specialised areas like the hypothalamus and pituitary gland
• Ways scientists find out about the brain

  1. Studying people with brain damage

  2. Electrically stimulating different brain areas

  3. Using MRI scans
• Sclera


  The white outer layer of the eye, relatively tough and strong
• Cornea


  Transparent area at the front of the eyeball that lets light into the eye
• Cornea


  • Its curved surface is very important for changing the direction of the light rays coming into the eye, making sure they are focused on the retina
• Iris


  Muscular structure that controls the size of the pupil, the hole through which light enters the eye
• Pupil


  The hole through which light enters the eye, its size is controlled by the iris
• In dim light


  The pupil is enlarged so as much light as possible enters the eye
• In bright light


  The iris makes the pupil very small to reduce the amount of light going into the eye and prevent damage to the light-sensitive cells
• Lens


  Clear disc that 'fine tunes' the focusing of the light rays, changing their direction to produce a clear image on the retina
• Lens


  • Held in place by suspensory ligaments and the ciliary muscles