Biology topic 2-paper 1

• The Nervous System

  Coordinates a response to what you eat and what goes on around you
• Central Nervous System (CNS)

  • Made up of the brain and spinal cord
  • Coordinates the response
• Response to a stimulus

  1. Receptors detect the stimulus

  2. Information is sent to the CNS

  3. CNS coordinates the response

  4. CNS sends information to an effector

  5. Effector responds accordingly
• Reaction time

  The time it takes to respond to a stimulus
• Neurones

  • Have a cell body with nucleus, cytoplasm and other structures
  • Have extensions (dendrites and axons) that connect to other neurones
  • Surrounded by a myelin sheath which acts as an electrical insulator
• Transmission of nerve impulses

  1. Electrical impulses travel along neurones

  2. Synapses allow transmission of impulses between neurones
• Synapses

  • Allow transmission of nerve impulses between neurones
  • Neurotransmitters are released across the synaptic gap
  • Neurones can be very long to speed up impulse transmission
• Sensory, motor and relay neurones

  • Sensory neurones carry impulses from receptors to CNS
  • Motor neurones carry impulses from CNS to effectors
  • Relay neurones carry impulses between sensory and motor neurones
• Reflex arc

  1. Receptor detects stimulus

  2. Sensory neurone carries impulse to CNS

  3. Relay neurone carries impulse to motor neurone

  4. Motor neurone carries impulse to effector
• Reflexes bypass conscious parts of the brain to provide a quick response
• The brain and spinal cord

  • Make up the Central Nervous System
  • The brain has different regions with different functions
• Damage to the CNS can be difficult to treat as neurones don't readily repair themselves
• Medulla oblongata

  Controls unconscious functions like breathing and heart rate
• Cerebellum

  Responsible for coordinated movement
• The eye

  • Allows light to enter and be focused onto the retina
  • Contains light receptors (rods and cones) that convert light into electrical impulses
• Focusing on near and distant objects

  1. Lens changes shape to focus light onto retina

  2. Muscles contract/relax to change lens shape
• Long-sightedness

  Light focused behind the retina, can't see near objects clearly
• Short-sightedness

  Light focused in front of the retina, can't see distant objects clearly
• Colour blindness

  Caused by faulty colour receptors (cones) in the retina
• Cataracts

  Clouding of the lens, causing blurred vision