Unit 6: Receptors Flashcards
what are pacinian corpuscles
- receptors that respond to changes in mechanical pressure
-act as transducers they detect pressure and convert it into a generator potential which creates a nerve impulse
what happens to the receptor (pacinian corpuscles) when pressure is applied
changes of shape and the membrane of the receptor become stretched
what effect does stretching have on the receptor
Stretching causes deformation of the stretch mediated Na+ channels and Na+ diffuse in (depolarisation) would produces a generator potential
What happens during the resting potential of the receptor?
stretch mediated Na+ channels in the membrane are closed and don’t allow sodium ions to pass into the receptor
What happens if the generators potential is above threshold?
An action potential is produced and nerve impulses are transmitted along the neuron
What are rods for?
useful for vision at low light intensity
possess high visual sensitivity
what are cones for?
important for good discrimination of detail
posses high visual acuity and enable coloured vision
Why do rods have higher visual sensitivity than cones?
- they contain rhodosin a photo sensitive pigment which is broken down at lower light intensity than iodopsin in cones
- Several rods synapse with one bipolar neuron were as in cones one cone synapses with one bipolar neuron
what happens when many rods synapse to a singular bipolar cell?
several rods next to each other has an additive effect and spatial summation occurs on the bipolar neuron and impulses are transmitted to the brain
What are the differences between cones and rods?
- many rods and few cones
- rods are spread across the retina and a 90% of cones are in the fovea
- Only one type of rod cell and they can’t detect colour and there are three types of cones with different photos sensitive pigment
- Sensitive to low light intensity and cones are active in a highlight intensities’
- rods have low visual acuity and cones have high visual acuity
Why do cones have low visual sensitivity?
cones have a 1:1 relationship with a bipolar neuron so .no spatial summation occurs
this means threshold is less likely to be reached so low light intensity can don’t generate impulses.
Where is vision best in dim light?
in dim light vision is poorest at the fovea of the retina where cones are concentrated and the best at the edges where there are more rods
What is acuity?
The ability to discriminate detail
The position/sharpness of the image
Why do cones have high visual acuity?
They only synapse with one bipolar
the 1:1 relationship provides maximum acuity because each part of the image is being detected by a different cell and there is no blurring of information
Where is acuity the greatest
in the fovea as it only contains cones
Why do rods have low visual acuity?
They share a bipolar neuron
so several rods may be stimulated, but only one bipolar neuron will be stimulated and the brain only receives one impulse
what are the three types of cones
Red, green and blue light sensitive cones
How is colour absorbed?
each pigment has its own absorption peak at a particular wavelength
colours other than those corresponding with the absorption peak will result in different degrees of stimulation of each type of cone
what happens when a cone cell absorbs more light?
It produces a greater frequency of impulses
What is the visual cortex?
in the brain
Receives impulses from the different types of cone and the colour perceived is determined by the relative frequency of impulses
