Homeostasis: Biology AQA GCSE

regulation of internal conditions (of a cell or organism) to maintain optimum conditions for function in response to internal/ external changes (eg best conditions for enzymes)

-blood glucose concentration
-body temp
-water levels

-receptors, which detect stimuli/ changes in environment
-coordination centres (eg brain, spinal cord and pancreas) which receive and process info from receptors
-effectors (muscles or glands) which respond and restore optimum levels

-nervous responses (muscle contracting)
-chemical responses (glands secrete hormones)

central nervous system including brain and spinal cord

1. stimulus
2. receptor
3. coordinator
4. effector
5. response

neurones

-info from receptors passes along neurones as electrical impulses to CNS
-CNS coordinates response of effectors (muscles or glands)

1) stimulus detected by receptor
2) electrical impulses pass from receptor along sensory neurone to CNS
3) at synapse, chemical released which diffuses across to relay neurone in CNS
4) triggers electrical impulse which passes across relay neurone reaching another synapse
5) at synapse, chemical released which diffuses across to motor neurone
6) triggers electrical impulse which passes down motor neurone to effector which causes response (through muscles or glands)

receptors

a junction at the end of neurone between neurone and CNS

sense organ (containing receptors)

light intensity and colour

to start focussing the light rays

Suspensory ligament

Cornea

Iris

Pupil

ciliary muscle

lens

sclera

retina

optic nerve