14.4 receptors

Question 1

example of a receptor

Answer 1

• pacinian corpuscle

Question 2

features of sensory reception as illustrated by the pacinian corpuscle

Answer 2

1. is specific to a dingel type of stimulus
   - response only to mechanical pressure
2. produces a generator potential by acting as a transducer
   - role of a transducer to convert the change in the form of energy by the stimulus into another that the body can understand (nerve impulse)
   receptors in the nervous system convert the energy of the stimulus into a generator potential

Question 3

where is the pacinian corpuscle most abundant

Answer 3

• deep in the skin on fingers, soles of the feet and external genitalia
• joints ligaments and tendons which enable organisms to know when joints are changing direction

Question 4

structure of the pacinian corpuscle

Answer 4

• sensory neuron is at the centre of layers of tissue each separated by gel

Question 5

what type of sodium channel does the pacinian corpuscle have

Answer 5

stretch mediated sodium channel

Question 6

how do stretch mediated sodium channels work

Answer 6

• permeability to sodium changes when they are deformed
  1. in resting state the stretch mediated sodium channels are too narrow to allow sodium to pass
  2.when pressure is applied to the pacinian corpuscle it is deformed and the membrane around its neuron becomes stretched
  3. stretching widens the sodien changes in the remembrance and sodium ions diffuse in
  4. influx of sodium ions changes the potential of the membrane, producing generator potential
  5. generator potential creates an action potential that passes along the neuron

Question 7

what are the types of cells found in the eye

Answer 7

• cone cells
• rod cells
• act as transducers by conserving light energy into the electrical energy of a nerve impulse

Question 8

how much rod cells are there in the eye

Answer 8

• 120 million in each eye
• more numerous than cone cells

Question 9

how do rod cells work

Answer 9

• detect light of low intensity
• many rod cells are connected to a single sensory neuron in the optic nerve
• a certain threshold value has to be exceeded before a generator potential is created in the bipolar cell ro which they are connected
• as a lot of rod cells are connected to a singular bipolar cell there is a greater chance that the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell
• in order to create a generator potential the pigment in the rod cell must be broken down , there is enough energy in low intensity light to break it down

Question 10

why do rod cells give low visual acuity

Answer 10

because many rod cells are linked to a singular bipolar cell, light received by rod cells sharing the same neuron will only generate a single impulse travelling to the brain meaning the brain cannot distinguish between the sources of light that stimulated them

Question 11

ho many different types of cone cells are there

Answer 11

• 3
• all have different types of iodopsin which means they are sensitive to different specific ranges of wavelength

Question 12

how many cone cells are there

Answer 12

6 million in each eye

Question 13

how do cone cells work

Answer 13

• each cone cell is connected to their own bipolar cell which is connected to a sensory neuron in the optic nerve
• stimulation of a number of cone cells cannot be combined to help exceed the threshold value and create a generator potential
• cone cells only respond to a high light intensity
• pigment in rod cells requires light of high intensity to provide enough energy to create a generator potential

Question 14

what pigment is found in cone cells

Answer 14

iodopsin

Question 15

what pigment is found in rod cells

Answer 15

rhodopsin

Question 16

why do cone cells give good visual acuity

Answer 16

• as each cone cell is connected to its own bipolar cell, if adjacent cells stimulate the brain receives two separate sources of light
• two dots close together can be resolved as toe separate dots

Question 17

what cells are found in the fovea

Answer 17

• cone cells
• receives the highest intensity of light

Question 18

what cells are found in the retina

Answer 18

• rod cells
• light intensity is lowest