Receptors

Question 1

What are features of the pacinian corpuscle

Answer 1

• It responds to one type of stimuli which is mechanical pressure
• it produces a generator potential by acting as a transducer = this means it converts energy of a stimulus to another form, mainly a nerve impulse

Question 2

What is the structure of the pacinian corpuscle?

Answer 2

• Pacinian corpuscles respond to mechanical stimuli like pressure
• They occur deep in the skin and are most abundant on our fingers
• The single sensory neurone of a pacinian corpuscle is at the centre of layers of tissue, each seperated by gel
• The sensory neurone ending at the centre of the pacinian corpuscle has a special type of sodium channel in its plasma membrane called a stretch - mediated sodium channel

Question 3

What is the function of the pacinian corpuscle?

Answer 3

• In its normal resting state, the stretch mediated sodium channels of the membrane around the neurone of the pacinian corpuscle are too narrow to allow sodium ions to pass along them, this means that the neurone of the pacinian corpuscle is at its resting potential
• when pressure is applied to the pacinian corpuscle, it is deformed and the membrane around the neurone becomes stretched
• The stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone
• The influx of sodium ions chnages the potential of the membrane and it becomes depolarised, therefore producing a generator potential
• If the generator potential meets the threshold, it generates an action potential that passes along the neurone and to the CNS

Question 4

What are the light receptors in the eye?

Answer 4

• There are two light receptors = cones and rods
• Both act as transducers and convert light energy to electrical impulses
• Cone cells can distinguish different wave lengths of light whereas rod cells can not, only seeing images in black and white
• In the eye, rod cells are more numerous than cone cells

Question 5

Why do rod cells have high sensitivity?

Answer 5

• Many rod cells are connected to a single sensory neurone in the optic nerve
• A certain threshold has to be exceeded before a generator potential is created in the bipolar cell to which they are connected to
• As a number of rod cells are connected to a single bipolar cell,they have retinal convergence
• This means that each rod cell can sum the light intensity that they detect, allowing us to see in low light intensity as there is a greater chance that the threshold value will be exceeded.
• As they sum their light intensity, there is enough energy to break down rhodopsin in rod cells, allowing us to see

Question 6

Why do rod cells have low visual acuity?

Answer 6

• Many rod cells are linked to a singular bipolar cell, this means that light recieved by rod cells sharing the same neurone will generate a single impulse due to retinal convergence
• This means that the brain can not distinguish between separate sources of light
• therefore, two dots can not be resolved and seen individually and there is low visual acuity

Question 7

Why do cone cells have low sensitivity?

Answer 7

• each cone cell is attached to its own bipolar cell
• This means that the stimulation of each cone cell can not be combined
• As a result, they require higher light energy levels in each individual cone cell to exceed the threshold value and create a generator potential and therefore an action potential
• therefore, cone cells only respond to high light intensities to break down iodopsin
• each cone cell respond to a different wavelength of light

Question 8

Why do cone cells have a high visual acuity?

Answer 8

• Each cone cell has its own connection to a single bipolar cells so therefore the brain can distinguish between two seperate impulses
• This means that two dots that are close together can be resolved and cones have a high visual acuity

Question 9

What is the distribution of cone and rod cells in the eye?

Answer 9

• The distribution of cone and rod cells in the retina are uneven
• Light is focused on the part of the retina that is opposite the pupil, called the fovea
• Only cone cells are found in the fovea to allow light to reach cone cells and therefore maximise our visual acuity
• The concentration of cone cells diminishes further from the fovea as light intensity reduces and therefore rod cells which have high sensitivity are found