coordination (bio)

• nervous system and endocrine system (hormones) help mammals respond to changes in their environment:

  • they must coordinate automatic response to both internal and external environments.
  • this response requires a stimulus, receptor, coordination centre and effector
• CNS is linked to sense organs (that contain many receptors) by nerves.
• synapse = junction between two neurones where electrical signals pass from one neurone to another.
• at a synapse, neurotransmitters diffuse across the gap and makes the next neurone transmit an electrical signal across
• the CNS consists of the brain and spinal cord
• reflex = quick automatic response to a stimulus that can reduce the chances of being injured
• reflex arc:

  • stimulus
  • receptor
  • sensory neurone
  • coordinator and relay neurone
  • motor neurone
  • effector
  • response
• Dim light:

  • radial muscles contract
  • circular muscles relax
  • pupil dilates
• Bright light:

  • radial muscles relax
  • circular muscles contract
  • pupil constricts
• Distant objects:

  • ciliary muscles relax
  • suspensory ligaments tighten
  • shape of lens is thin and flat
  • refract less light
• Near objects:

  • ciliary muscles contract
  • suspensory ligaments loosen
  • shape of the lens is thick
  • refracts more light
• conjunctiva lubricates and protects the surface of the eye
• sclera is the tough outer layer that protects the eye
• cornea refracts light into eye, it is transparent and has no blood vessels to supply it with oxygen therefore oxygen diffuses in from the outer surface
• the iris controls the diameter of the pupil and therefore how much light enters the eye
• the lens focuses light onto the retina - the rods are more sensitive to dim light but can't sense colour however cones are sensitive to colour but aren't good in dim light and many in the fovea
• the optic nerve carries impulses from the receptors to the brain
• when you are too hot:

  • lot's of sweat is produced - when it evaporates it transfers energy from your skin to the environment cooling you down
  • vasodilation - allows more blood to flow near the surface so it can transfer more energy into the surroundings which cools you down.
  • hairs lie flat
• when your cold:

  • very little sweat is produced
  • vasoconstriction - means less blood flows near the surface so less energy is transferred to the surroundings
  • you shiver - increases rate of respiration which transfers more energy to warm the body (exercise does the same)
  • hairs stand up to trap an insulating layer of air which helps keep you warm