B5 - Homeostasis and response

• What is homeostasis?


  the regulation of the conditions inside your body to maintain a stable environment in response to both internal and external conditions
• What is negative feedback?


  mechanism that restores a level back to optimum in a system
• How does the body regulate the body using negative feedback?

  • receptor dectects a stimulus - level is to high/low

  • coordination centre receives and proccesses information, organises a response

  • effector produces response to counteract the change and restores optimum level - level decreased/increased
• What does the cenral nervous system (CNS)?

  • brain and spinal cord

  • CNS connected to body via sensory neurones and motor neurones
• What does the sensory neurone do?


  carry information as electrical impulses from receptors to CNS
• What does the motor neurone do?

  carry electrical impulses from CNS to effectors
• What do the effectors do?

  • muscles and glands

  • respond to nervous impulses from motor neurones
• What route are impulses sent through when a stimulus is detected?

  • receptor

  • sensory neurone

  • CNS

  • motor neurone

  • effector
• What is the connection between two neurones called?

  synapse
• What happens at the synapse?


  • nerve signal is transferred by chemicals which diffuse across gap

  • chemicals then set off a new electrical signal in next neurone
• What are reflexes?

  rapid, automatic response to certain stimuli - doesn't involve conscious part of the brain
• What is the passage of information in a reflex (receptor to effector) called?

  reflex arc
• Where are impulses sent to in a reflex arc?

  spinal cord or unconscious part of brain
• What does the cerebral cortex do?


  responsible for consciousness, intelligence, memory and language
• What does the medulla do?


  control unconscious activities (breathing and heartbeat)
• What does the cerebellum do?


  responsible for muscle coordination
• What mehtods do scientists use to study the brain?

  • study patients with brain damage

  • electrically stimulating the brain

  • MRI scans
• How does studying patients with brain damage help us know how the brain works?

  studying the damaged part of brain and seeing the effects it has shows what that part does (if vision isn't working - controls vision)
• How does electrically stimulating the brain help us know how the brain works?

  • stimulated by electrodes into tissue

  • can observing what the effect is helping identify what that part does
• How do MRI scans help us know how the brain works?

  • produces detailed picture of brains structures
• What does the sclera do?


  tough supporting wall
• What does the cornea do?


  transparent layer at front of eye, refracts (bends) light into eye
• What does the iris do?


  contains muscles that control the diameter of pupil and amount of light let in
• What does the lens do?


  focuses light onto retina
• What does the retina do? 


  contains receptor cells sensitive to light intensity and colour
• What controls the shape of the lens?


  ciliary muscles and suspensory ligaments
• What does the optic nerve do?


  carries impulses from receptors on retina to brain
• How does the iris relfex work in a bright light?


  • light receptors detect bright light

  • reflex triggered - circular muscles contract and radial muscles relax

  • reducing amount of light that can enter - pupil narrower
• How does the iris relfex work in a dim light?


  • light receptors detect dim light

  • reflex triggered - circular muscles relax and radial muscles contract

  • increasing amount of light that can enter - pupli wider
• What happens to eye when looking at close objects?


  • ciliary muscles contract - suspensory ligaments relax

  • lens become fat (more curved)

  • increasing the amount it refracts light
• What happens to eye when looking at distant objects?


  • ciliary muscles relax - suspensory ligaments contract

  • lens become thin (less curved)

  • decreasing the amount it refracts light
• What does it mean if you cannot focus on close objects?

  • long-sighted (hyperopia)

  • lens is wrong shape - doesn't refract light enough or eyeball is to short

  • near object in focus behind retina

  • convex lens (fatty)- refracts light more to focus on retina
• What does it mean if you cannot focus on distant objects?

  • short-sighted (myopia)

  • lens is wrong shape - refracts light to much or eyeball is to long

  • distant object in focus in front retina

  • concave lens (skinny)- refracts light less to focus on retina
• What other ways can be used to correct vision defects?

  • contact lenses

  • laser eye surgery

  • replacement lens surgery
• How does laser eye surgery help with vision defects?

  vaporises tissue changing shape of cornea
• How does replacement lens surgery help with vision defects?

  natural lens is replaced with artificial clear plastic lens
• How is temperature controlled?

  thermoregulatory centre - receptors to temperature of blood flowing to brain and receptors in skin
• What happens during vasoconstriction?


  blood vessels to skin constrict closing off skins blood supply
• What happens during vasodilation?


  blood vessels in skin dilate so more blood flows close to surface
• What are hormones?


  a chemical messenger which travels to the blood to activate target cells