receptors Flashcards
what is a stimulus and how can it lead to a response?
a detectable change in the environment. its detected by a receptor, which responds to specific stimuli leading to the establishment of a generator potential which can cause a response
what are some types of receptors?
Pacinian corpuscles, rods and cones, chemoreceptors, osmoreceptors, pressure receptors
what types of receptors do the retina contain?
2 photoreceptors : rods and cones
describe rod cells
sensitive to low light levels, show convergence, poor visual acuity, see monochromatic - only have rhodopsin.
how are rod cells sensitive to low light levels?
to be triggered, a stimulus must exceed a threshold value. many rods share a bipolar region and so they show convergence. this means the effects can add up (summation) and there is greater chance the threshold value will be exceeded at low light intensities to produce a generator potential.
why do rod cells have low visual acuity?
many rods link to a bipolar region (convergence) and so only one generator potential is made no matter the number of rods stimulated. the brain cant distinguish between separate sources of light that stimulate them
why do rod cells see in monochromatic vision?
they only have one type of pigment - rhodopsin
describe cone cells
insensitive to low light, good visual acuity, trichromatic vision.
why are cone cells insensitive to low light levels?
to be triggered a stimulus must exceed a threshold value. cones have a single bipolar neurone so don’t show convergence. this means there is no summation and only if each cone is hit by enough light to exceed the threshold value will a generator potential be produced.
why do cones have good visual acuity?
each cone has a single connection to a bipolar neurone (no convergence) so if two adjacent cells are stimulated the brain receives two separate impulses. the brain can distinguish between the two separate sources of light that hit the cone cells, two dots close together will appear as separate.
why do cones have trichromatic vision?
there are three primary colours of light- blue, green and red.
all colours can be produced by mixing the primary colours in various proportions. theres three different types of cones, blue-sensitive, red-sensitive and green-sensitive as theres 3 forms of iodopsin
define colour-blindness
deficiency in one or more types of cone. red/green colour-blindness is a sex-linked characteristic.
give differences between rods and cones
rod =
outer segment is rod outer segment is cone
shaped shaped
visual pigment is visual pigment is iodopsin
rhodopsin
1 type of rod cell - 1 3 types of cone cell - 3
type of rhodopsin types of iodopsin
monochromatic vis trichromatic vision - can
-ion as cant distinguish distinguish
between wavelengths
of light
sensitive to low light not sensitive …
intensities
poor visual acuity good visual acuity
more common less common
distributed mainly in distributed mainly in
periphery and fewer in central region and fewer
central region. none in in the periphery. fovea
fovea or blind spot contain greatest conc.
no cones in blind spot.
what are Pacinian corpuscles?
found deep in skin, many in the fingers and soles of feet. also in joints, ligaments and tendons, allowing brain to receive info and co-ordinate it.
respond to changes in mechanical pressure only.
transduce mechanical energy from stimulus into a generator potential, which is transmitted to brain to process info.
list structures in the Pacinian corpuscle
capsule of connective tissue, lamellae separated by gel, single neurone ending, myelin sheath/ Schwann cells., axon of sensory neurone.
describe the stimulation of a stretch-mediated sodium ion channel
at rest the channels in the membrane around the Pacinian corpuscle are too narrow to allow sodium ions through so they’re closed. when pressure is applied to the Pacinian corpuscle it changes its shape due to the gel between the connective tissue layers which is compressed and the membrane around the neurone becomes stretched. this widens the stretch-mediated sodium channels in the receptor cell (neurone) membrane and they open so sodium ions can flood into it. the sodium ions move through the channels and change the potential difference across the membrane as the ion distribution changes. the membrane is depolarised and the generator potential is produced. the generator potential in the neurone creates an action potential that passes along the neurone and then via synapses and other neurones to the CNS
