stimuli, both internal and external, are detected and lead to a response: Receptors

Question 1

describe what happens in a Pacinian corpule

Answer 1

1. extreme pressure deforms and stretches the stretch-mediated sodium ion channels
2. this opens the sodium ion channel
3. causes a greater influx of sodium ions
4. this causes depolarisation
5. reaching the threshold of -55 leads to a generated potential causing an action potential

Question 2

what do rod cells and cone cells do?

Answer 2

Act as transducers by converting light energy into the electrical energy of the nerve impulse

Question 3

what are the differences between cone cells and rod cells?

Answer 3

cone cells detect colour- blue, green and red
rod cells detect black, white, and grey
cone cells have the iodopsin pigment, rod cells have rhodopsin
cone cells have low light sensetivity caused by temporal summation
rod cells have high light sensetivity caused by spatial summation
cone cells have high visual acuity- each cone cell is attached to an individual bipolar neuron, producing individual impulses
rod cells have low visual acuity-many rod cells connected to one bipolar neuron, producing one electrical impulse
highest concentration of cone cells found at the fovea
highest concentration of rod cells found futher away from the fovea and optic blind spot

Question 4

what are the wavelengths of light each photoreceptor absorbs?

Answer 4

cone cells: rod cells:
blue - 420nm green- 500nm
green- 531nm
red- 558nm

Question 5

what causes high visual acuity?

Answer 5

each cone cell is connected to 1 bipolar neuron

Question 6

what causes low visual acuity?

Answer 6

groups of rod cells connected to a single bipolar neuron, cannot distinguish between separate light sources

Question 7

explain why rod cells have a high light sensitivity

Answer 7

due to spatial summation
stimuli are applied to many rod cells at the same time
easier to reach the threshold to stimulate an action potential and so an electrical impulse

Question 8

what is meant by retinal convergence?

Answer 8

multiple rod cells connected to a single bipolar neurone

Question 9

define transducer

Answer 9

converts light energy into the electrical energy of a nerve impulse

Question 10

describe the distribution of rod and cone cells

Answer 10

highest concentration of cone cells found at fovea

highest concentration of rod cells found at the peripheries of the retina