Homeostasis

• Define homoseatisis


  Regulation of the internal conditions in an organism or cell to maintain optimum conditions in resonse to external and internal changes
• What is negauve feedback


  counteracts the change to bring it back to the opitmum level
• The journey of stimuli

  1. Receptors detect a change (a stimulus)
  2. coodrinator centre receives the message and organises a response
  3. effectors produce a response which may counteract the change to restore it to the optimum level
• What is the CNS


  connected to the body by senosry and motor neurons
• Sensory neurons


  neurones that carry information as electrical impulses from the receptors to the CNS
• Motor neurons


  carry electrical impulses from the CNS to effectors
• Effectrs


  muscles and glands that rrespond to nervoius impulses
• What are relay neurones?


  connect sensory and motor neurons
• The Brain is made up of


  interconnected neurones it is part of the CNS
• The brain controls


  and coordinates everything you do
• The cerebral cortex:

  responsible for consciousness, intelligence, 


  memory and langiage
• the medulla


  controls unconscioius activities like breating and heartbeats
• cerebellum


  controls muscle contraction
• What is a synapse?


  A connection between two neurones. when the electrical impulse reaches the end of the neurone, it stimulates the release of chemicals which diffuse across the gap to the 2nd neurone, causing an electical impulse
• What is a reflex arc?


  The passage of information from the sensory neurone to the effectors
• 
  

  Journey of a reflex (arc)

  1.) The receptors detect a stimulus (a change in surroundings/conditions)

  2.) The receptors send an electrical impulse via the sensory neurones to the CNS (the spinal cord) to the relay neurones

  3.) Before the electrical impulse reaches the relay neurone, chemicals are released which diffuse across the synapse or gap

  4.) The electrical impulse is then sent along the relay neurone to the motor neurone
• What is a relay neurone?


  connects a sensory neurone and a motor neurone
• motor neurone


  transmits signals from the CNS to the effector
• Why are reflex arcs important


  they are unconscious, rapid and automatic. they prevent injuries
• Practical; reaction time, what should the person be holding


  a ruler with their thumb on the zero end and then let go
• repeat the

  test to calculate the mean and remove anamolous results
• control variable in the practical


  the same person, same hand, same height of ruler
• Computers are used to test reaction time. Why would it be more accurate>


  more precise as the remove the chances of a human error

  and u cant predict the computer
• hypothamus

  mainatins body temp
• how is the brain studied>

  • electrical stimulation
  • mri scans, PET and ct scans
  • studying peoepl with brain damage
• why is it hard to study the brain

  1. can cause trauma, damage and infections
  2. the brain is verycomplex
  3. not fully understood so cant treat with drugs
  4. fragile and kept within the skulll
• What is the cornea


  Transparent layer. 02 diffuses into the cornea as it has no supply of b;lood. refracts light
• Iris


  controls size of pupil, coloured part of the eye
• Pupil


  gap in the middle of the iris. allows light to pass to the lens.
• The lens


  refracts light and chnges shape so can control how strongly it refracts light so u can focus the light on the retina
• What cells is the retina made out of


  cone and rod cells. Cone cells let us see colour, rod cells are more seneitive and help us see in the night
• What strucure in the retina contains only cone cells


  fovea, we focus light on the fovea to see clearly
• optic nerve


  takes electrical impulses and transmits them to the brain
• What is an iris reflex


  it controls the size of the pupil, when the light intensinity is high, the puoil contristc and vice versa
• What happens when the light intensinity is high>

  The circular muscles contract and radial msucles relax to constrict the pupil so less light is refracted into the retina which can damage it
• What happens when the light intensinity is low

  The pupil is dilated because the circular muscles relax and the radial muscles contract to pull open the pupil so more light passes throughthe pupil to the lens and retina