stimuli and responses Flashcards
what is a stimulus
any change in external environment
what are receptors
can be cells or proteins that detect a stimulus
what are effectors
cells that bring about a response to stimulus to produce an effect
what do sensory neurones do
transmit electrical impulses from receptors to the cns
what do motor neurones do
transmit electrical impulses from the cns to the effectors
what do relay neurones do
transmit electrical impulses between sensory and motor neurones
describe nervous system
1- stimulus detected by receptor cell and electrical impulse sent along a sensory neurone
2-when electrical impulse reaches end of the neruones chemical neurotransmitters take info to next neurone which then sends electrical impulse
3-the cns processes the info and sends electrical impulse along motor neurone to effector
what is a reflex
rapid automatic response to a stimuli
explain hand withdrawal from heat reflex
- thermodetectors in the skin detect heat
- sensory carries impulse to relay neurone
- relay neurone connects to motor neurone
- motor neruone send impulse to effector
- muscle contracts to withdraw hand
how is nervous system response localised
when electrical impulse reaches end of neurone neurotransmittors are secreted directly onto target cells
how is nervous system communication short lived
neurotransmitters quickly removed
what is a tropism
a plants growth response to directional stimulus
what is a tropism
a plants growth response to external stimulus
whats positive tropism
growth towards stimulus
what is phototropism
plant growth in response to light
positively phototrophic means towards light growht
what is gravitropism
growth of plant in response to grvaity
negatively gravitrophic if grows up
what are growth factors
hormone like chemicals whihc speed up or slow down growth
whats auxins and how does it work
a growth factor
stimulate growth of shoot by cell elongation
what does high concentrations of auxin do
inhibit growth of root
whats IAA
an auxin in tips of shoot in flowering plants
how does pacinian corpuscle work
when under pressure the stretch mediated sodium channels become deformed
meaning they open and allow rapid influx of sodium ions
the positive charge on sodium ions causes membrane to become depolarised
results in generator potential being made leading to action potential. in the axon
describe pacinian corpuscle
have single sensory neurone in middle of connective tissue called lamellae forming layers seperated by gel
what are photoreceptors
light receptors in eye
how is light recieved in the eye
light enters eye in pupil
amount of light controlled by iris
lens focuses light rays onto retina
Nerve impulses from the photo receptor cells are carried from the retina to the brain by the optic nerve
what is the fovea
area in retina with lots of photoreceptors
how do photoreceptors convert light into electrical impulses
when light hits photoreceptors they are absorbed by light sensitive optical pigments
light bleaches the pigments causing chemical change altering membrane permeability to na+
generator potential is created if reaches threshold nerve impulse sent along bipolar neurone
bipolar neurone connect photoreceptors to optic nerve taking impulse to brain
what are the two photoreceptors found in eye
rod and cone cells
details on rod cells
found in peripheral part of retina
only give information on black and white
details on cone cells
packed together in the fovea
give info in colour
three types red green and blue sensitiove
sensitivity and visual acuity of rod cells
sense- very sensitive to light as many rods join one neurone so many weak generator potentials combine to reach th threshold and trigger ap
va- low visual acuity as many rods join one neurone
sensitivity and visual acuity of cone cells
sensitivity - low sensitivity as one cone joins one neurone so lots of light required to reach threshold and trigger ap
va- high visual acuity as only one cone joins neurone
why can the heart be described as myogenic
can contract and relax without signals from nerves
where and what is the SAN
in right atrium
like a pacemaker sets rythm of heart beat by sending out regular waves of electrical activity to atrial walls
describe process of regualr beating of the heart
1-SAN sends out wave of electrical activity to atrial walls
2- causes both atria to contract at same time
3- band on non conducting collagen tissue prevents electrical activity to be passed on to ventricles
4- electrical activity transfered from san to avn
5-slight delay before avn reacts to make sure atria empty before ventricles contract
6-avn passes waves of electrical activity to bundle of his into purkyne tissue
7-purkyne tissue carries waves to both ventricle wallas making them contract
