Receptors and Eyes Flashcards
what type of receptors detect changes in mechanical pressure
- pacinian corpuscles
describe how the pacinian corpuscles detects and transmits an impulse
- when pressure is applied the receptor changes shape and the membrane becomes stretched
- the stretching deforms the stretch mediated sodium ion channels and sodium ions diffuse in causing depolarisation
- if the generator potential>threshold level , an action potential is produced and nerve impulses are transmitted along the neurone
what are the two types of light sensitive photoreceptor cells in the eye + their uses
rods - high visual sensitivity
cones- high visual acuity and enable colour vision
2 reasons why rods have higher visual sensitivity
1 - rhodopsin, the photopigment in rods is more sensitive to light than iodopsin (photopigment in cones)
2 - several rods synapse to a single bipolar cells providing an additive effect (spatial summation) enabling the threshold level to be reached
why do cones have lower visual sensitivity
- they have a 1:1 relationship with the bipolar neurone so no spatial summation occurs, making it harder to reach the threshold value
why do cones have high visual acuity
- cones have a 1:1 relationship with bipolar neurones therefore several stimulated cones = several impulses
- several impulses means that there is no blurring/combination of information = higher visual acuity
why is acuity greatest at the fovea
- it contains only cones which have a high visual acuity
why do rods have lower visual acuity
- rods share bipolar neurone therefore even if several rods are stimulated, only one neurone will be stimulated and send only one set of impulses
how does colour vision work?
- each cone contains only one pigment type which each has its own absorption peak at a particular wavelength of light
- when a cone absorbs more light - greater frequency of impulses
- the colour perceived is determined by the relative frequency of impulse from each cone type
