B2.5 response & regulation

• Central nervous system (CNS)

  The brain and spinal cord
• Neurons


  Nerve cells that send messages in the form of electrical impulses
• Reflex actions

  • Minimise damage
  • Protect
• Reflex arc

  1. Stimulus

  2. Receptor

  3. Sensory neurone

  4. Relay neurone

  5. Motor neurone

  6. Effector
• Nerves


  Bundles of individual neurons
• Central Nervous System

  Brain and spinal cord
• Eye

  • Cornea
  • Pupil
  • Iris
  • Lens
  • Retina
  • Optic nerve
  • Sclera
  • Choroid
  • Ciliary muscles
• Conditions controlled by hormones

  • Temperature
  • Sugar
  • Water
• When body is too hot


  Blood vessels dilate, hairs lie flat, sweat produced
• When body is too cold


  Blood vessels constrict, hairs , no sweat, shivering
• Glucose


  Needed by cells for respiration
• Blood glucose regulation

  1. Blood glucose rises

  2. Pancreas releases insulin

  3. Insulin lowers blood glucose
• Type 1 diabetes

  Pancreas fails to produce insulin
• Type 2 diabetes

  Body produces insulin but fails to respond to it properly (often associated with poor diet/obesity)
• Negative feedback

  If level of something rises, control systems reduce it again; if level falls, control systems raise it again
• Auxin

  Plant hormone responsible for growth
• Phototropism

  Growth in response to direction of light
• Hydrotropism


  Growth in response to direction of water
• Positive tropism


  Growth towards stimulus
• Lens

  changes shape to focus light onto retina
• Cornea

  Clear part of sclera, allows light to enter
• Pupil

  Hole that allows light to enter
• Blind spot

  Where optic nerve leaves the eye
• Optic nerve


  Carries impulses from retina to brain