5.2 Nervous System

• Brain

  Allows reaction to surroundings and the coordination of actions
• Nervous system

  • Transmission via neurones
  • Receptors detect stimulus
  • Central Nervous System: brain, spinal cord
  • Coordinator: effectors (muscles, glands) carry out a response
• Reflex arc

  1. Importance: protection, fast, automatic, subconscious

  2. Sensory neurone detects stimulus

  3. Relay neurone transmits signal from sensory to motor neurone

  4. Motor neurone transmits impulse to effector
• Cerebral cortex


  Conscious thought, personality, language
• Cerebellum


  Balance, coordination, muscle movement
• Medulla


  Non-voluntary movement, heart rate, breathing rate
• Investigation and treatment of the nervous system

  1. MRI

  2. Electrical stimulation

  3. Studying patients with brain damage
• Difficulties in investigating the nervous system: membranes prevent some drugs from reaching the brain, complex, delicate
• Eye


  • Retina - light sensitive layer at the back
  • Optic nerve - carries impulses from eye to brain
  • Sclera - tough outer layer, protects internal structures
  • Cornea - allows light into eye to focus on retina
  • Iris - controls amount of light entering eye
  • Suspensory ligaments and ciliary muscles - control shape of lens for accommodation
• Accommodation - focusing

  1. Close object: ciliary muscles contract, suspensory ligaments loosen, lens thickens, stronger refraction

  2. Distant object: ciliary muscles relax, suspensory ligaments contract, lens thins, weaker refraction
• Myopia


  Lens too curved, light focused in front of retina
• Hyperopia

  Lens too flat, light focused behind retina
• Nervous system response


  1. Stimulus

  2. Receptor

  3. Coordinator

  4. Effector

  5. Response
• Brain


  • Controls complex behaviour
  • Made of billions of interconnected neurones
  • Different regions carry out different functions
• Cerebral cortex


  Outer layer of the brain, important for consciousness, intelligence, memory, and language
• Hypothalamus


  Part of the brain
• Cerebellum


  Part at the back of the brain, coordinates muscle activity
• Medulla oblongata


  Part above the spinal cord, controls unconscious activities such as breathing and heart beating
• Pituitary gland


  Part of the brain
• Eye


  • Sense organ containing receptors sensitive to light intensity and colour
• Accommodation


  1. Ciliary muscles contract, suspensory ligaments are slack, lens is thicker and more curved

  2. Ciliary muscles relax, suspensory ligaments are pulled tight, lens is thinner and flatter
• Reflex arc


  Automatic and rapid response, does not involve the conscious part of the brain
• Reflex actions


  Important for survival, help prevent damage to the body
• Synapse


  Gap between neurones, allows electrical impulses to cross between neurones
• Neurones


  Carry electrical impulses around the body, relay neurones connect sensory neurones to motor neurones
• Myopia


  Short-sightedness, distant objects look blurred
• Hyperopia


  Long-sightedness, near objects look blurred
• Neuroscientists have mapped the regions of the brain to particular functions by studying patients with brain damage, using MRI scanning techniques, and electrically stimulating parts of the brain
• The brain is very complex and delicate, making investigating and treating brain disorders difficult
• Brain damage and diseases can involve many different neurones, chemicals, and areas of the brain. Treatment is difficult because it is not fully understood what each area of the brain does, drugs do not always reach the brain through its membranes, and surgery can easily cause unintended damage