BIOLOGY TOPIC 5 - HOMEOSTASIS & RESPONSE

• homeostasis


  all the processes that happen in a cell or organism to maintain optimal conditions
• conditions regulated by homeostasis

  - water levels

  - carbon dioxide levels

  - blood sugar levels

  - body temperature

  - urea concentration
• receptor cells


  detect changes in the environment
• coordination centre


  receives and processes information from receptors
• effectors


  carry out responses to stimuli to help restore optimum levels
• negative feedback


  returns internal conditions to optimum
• central nervous system (CNS)

  - brain

  - spinal cord

  - nerve cells (neurones)
• synapses


  gaps between neurones
• how nerve impulses travel across synapses

  - neurotransmitters diffuse across synapse

  - neurotransmitters bind to receptors on next neurone
• neurotransmitters


  chemicals that diffuse across synapses and bind to receptors on the next neurone
• reflex action


  unconscious response that allows a person to respond to a dangerous situation automatically and rapidly via a reflex arc
• components of reflex arc

  stimulus

  receptor

  neurones

  effector

  response
• sensory neurone


  Carries the signal in the form of an electrical impulse to the CNS
• relay neurone


  relays the electrical impulse from the sensory neurone to the appropriate motor neurone
• motor neurone


  Carries the electrical impulse from CNS to the effector
• reflex arc


  stimulus is detected by a receptor.

  sensory neurone carries the signal, in the form of an electrical impulse, to CNS

  motor neurone carries the electrical impulse from the CNS to an effector

  effector brings about an action in response to the change in the internal or external environment.
• cerebal cortex


  conscious thought eg. memory, language, intelligence
• medulla


  unconscious activities eg. breathing and heartbeat
• cerebellum


  muscle coordination and balance
• researching the brain


  study brain damage - linking regions of the brain w/ functions

  electrical stimulation - treat disorders of the brain

  MRI scanning - learn which parts of the brain are active during different activities
• sclera


  white of the eye, protective outer layer
• cornea


  refracts light
• optic nerve


  transmits visual information from retina to brain
• retina


  full of receptor cells that are sensitive to the brightness and colour of light
• pupil


  where light passes through the centre of the iris
• iris


  controls pupil diameter
• ciliary muscles


  changes shape of lens to focus light
• suspensory ligaments


  ring of fibres connecting ciliary muscles to lens
• accomodation


  lens changes shape to focus on an object as its distance changes
• focus on a distant object

  ciliary muscles relax, suspensory ligaments tighten, lens becomes flatter and thinner, minor refraction
• focus on a close object

  ciliary muscles tighten, suspensory ligaments loosen, lens becomes thicker and rounder, significant refraction
• pupil's reaction to too much light

  contracts
• pupil's reaction to not enough light

  dilates
• myopia


  short-sightedness, light focuses in front of the retina
• hyperopia


  long sightedness, light focuses behind the retina
• where are receptors that detect temperature change ?

  skin and brain (hypothalamus)
• what happens when the body is too hot?

  - sweat released from glands under skin

  - hairs lie flat

  - vasodilation
• what happens when the body is too cold?

  - muscle contractions increase, shivering

  - hairs stand on end

  - vasoconstriction in capillaries
• how does sweating reduce body temperature?

  warm water evaporates, taking heat energy with it
• how does shivering increase body temperature?

  muscles contract automatically, and needs energy generated through respiration, respiration produces heat, warming us up