3.6.1.2 Receptors(A-level only)

Question 1

Examples of sensory receptors and their specific stimuli

Answer 1

Mechanoreceptor: pressure and movement
└ e.g Pacinian corpuscle, skin
Chemoreceptor: chemicals
└ e.g. olfactory receptor, nose
Thermoreceptor: heat
└ e.g. end-bulbs of Krause, tongue
Photoreceptors: light
└ e.g. cone cell, eye

Question 2

Function of sensory receptors

Answer 2

└act as transducers converting the stimulus into electrical energy and producing a generator potential. When the generator potential gets big enough, and the threshold is reached it is converts into an action potential.

Question 3

Transducer role definition

Answer 3

└detects stimulus and converts into a nerve impulse called a generator potential

Question 4

Generator potential definition

Answer 4

└change in potential difference

Question 5

Action potential definition

Answer 5

└a change in the membrane potential that produces a nerve impulse

Question 6

Threshold definition

Answer 6

└ the minimum amount of stimulus a neuron needs to respond

Question 7

Location of Pacinian corpuscle

Answer 7

Skin
└mainly fingers, genitals, hands, feet
└also ligaments, tendons, joints

Question 8

Structure of pacinian corpuscle

Answer 8

└an end of a sensory neurone/sensory nerve ending

└wrapped in/surrounded by connective tissue (lamellae) which is separated by a gel

Question 9

How a generator potential is created by a pacinian corpuscle

Answer 9

No pressure/resting state
└stretch mediated sodium channels are closed/ too narrow for sodium ions (Na+) to pass through
└found in membrane of sensory nerve endings in the pacinian corpuscle
└maintains resting potential difference in Na+ across membrane
└more Na+ outside than inside
Pressure
└deforms/ changes pacinian corpuscles shape
└stretches the surrounding membrane
└widens stretch mediated Na+ channels
└causes Na+ influx as they diffuse into neurone/cell down the concentration gradient
└the positive charge on the Na+ changes the membrane potential
└causes depolarisation to occur
└more Na+ inside than outside
└depolarisation creates a generator potential
└if the generator potential gets large enough, the threshold is reached and an action potential occurs (wave of depolarisation) along the sensory neuron
└aka electrical impulse
└transmitted along neurone to CNS

Question 10

Stretch mediated sodium channels

Answer 10

…

Question 11

Resting potential definition

Answer 11

└potential difference between the inside of the non-stimulated neuron and the surrounding interstitial fluid (humans: -70 mV)

Question 12

Depolarisation definition

Answer 12

└sodium ions rushing into the cell down their concentration gradient, changing the electric charge of the interior

Question 13

Generator potential definition

Answer 13

└change in potential difference

Question 14

Threshold definition

Answer 14

└ the minimum amount of stimulus a neuron needs to respond

Question 15

Action potential definition

Answer 15

└a change in the membrane potential that produces a nerve impulse

Question 16

Lots of pressure

Pacinian corpuscle

Answer 16

└increase pressure
└more sodium ion channels open
└more Na+ diffuse into cell/neurone
└bigger generator potential
└threshold is more likely to be reached so action potential is met more often
└increases the frequency of impulses sent along sensory neurone

Question 17

Slight pressure

Pacinian corpuscle

Answer 17

└slight pressure- may go unnoticed
└fewer sodium ion channels open
└less Na+ diffuse into cell/neurone
└lower generator potential
└threshold is less likely to be reached so no action potentials
└decreases the frequency of impulses sent along sensory neurone/ no impulses

Question 18

Adaptation

Pacinian corpuscle

Answer 18

└continuous stimulation of a sensory neurone
└ decreased frequency of impulses/ stop them-
└useful as it prevents overloading the nervous system with insignificant information
└e.g. the pressure from clothing

Question 19

Light receptor cell/ photoreceptor definition

Answer 19

A specialized structure or cell that is sensitive to light

e.g. rod and cone cells in the eyes retina

Question 20

Light receptor cell location

Answer 20

The retina

Question 21

Light receptor cell/ photoreceptor types

Answer 21

rod cells

cone cells

Question 22

Light receptor cell- transducers

Answer 22

They convert light energy into an electrical impulse.

Question 23

Rod cell location

Answer 23

On the retina.

Rod cells most abundant at the peripheries of the retina

Question 24

Rod cell distribution

Answer 24

Periphery of retina = mostly rod cells

Question 25

Rod cell light intensity

Answer 25

Can see in the dark (low light intensity)
└ Responds to low intensity light because the threshold value can be exceeded as a number of rod cells are attached to a single bipolar cell (retinal convergence)

Question 26

Rod cell creating a generator potential

Answer 26

Rhodopsin must be broken down into retinal and opsin. Low light intensity is sufficient

Question 27

Rod cell sensitivity to colour

Answer 27

black and white

└as they cannot distinguish between different wavelengths of light

Question 28

Rod cell exhibit summation

Answer 28

Number of them connected to single bipolar cell (retinal convergence) - neurotransmitters released by each combine to exceed threshold and trigger an action potential which is called spatial summation

Question 29

Rod cell visual acuity

Answer 29

Low
└ Multiple rod cells share the same bipolar neurone so light received by many rod cells sharing the same neurone only generates a single impulse
└ many rods join the same neurone which means light from 2 objects close together cannot be told apart

Question 30

Rod cell sensitivity

Answer 30

High sensitivity

└ many rods join one neurone so many week generator potentials combine to reach the threshold

Question 31

Rod cell optical pigments

Answer 31

Black and white

Question 32

Different types of cone cell

Answer 32

3 └ respond to different wavelengths of light

└ red, green, and blue

Question 33

Cone cell location

Answer 33

On the retina.
Cone cells most abundant on the fovea.
└because Fovea receives the highest intensity of light and cone cells can only respond to high intensity light

Question 34

Cone cell distribution

Answer 34

High concentration of cone cells around fovea as high light intensity.

Question 35

Cone cell light intensity

Answer 35

High (not low)
└Each connected to different bipolar neuron so stimulation of a number of cone cells cannot be combined to exceed threshold
└Also contains pigment (iodopsin) which can only be broken down by high light intensities

Question 36

Cone cell sensitivity to colour

Answer 36

Can see in colour

└have three different cone cells (red, green and blue) that can respond to different wavelengths of light

Question 37

Cone cell visual acuity

Answer 37

High
└ Each cone cell has its own single bipolar neurone so the brain receives separate impulses allowing it to distinguish between the separate sources of light.
└ cones are close together and 1 cone joins 1 neurone

Question 38

Cone cell sensitivity

Answer 38

Low sensitivity

└1 cone joins 1 neurone so it takes more light to reach the threshold and trigger an action potential

Question 39

Cone cell optical pigments

Answer 39

red, blue, green

Question 40

Sensitivity to light definition

Answer 40

..

Question 41

Sensitivity to colour definition

Answer 41

Color vision is the ability of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit.

Question 42

Visual acuity definition

Answer 42

The ability to distinguish between two separate points

Question 43

Summation definition

Answer 43

Retinal summation describes the relationship between different types of cells in the retina
High retinal summation is an adaptation to low light levels, and low retinal summation to high light levels (thus sharpening the images).

Question 44

Optic nerve definition

Answer 44

a bundle of neurones

carries nerve impulses from the retina to the brain

Question 45

Photoreceptor definition

Answer 45

Receptors that detect light

Question 46

Generator potential definition

Answer 46

generates action potentials in a sensory neuron

Question 47

How rods and cones (light receptor cells) react to light as a stimulus

Answer 47

1) Light is absorbed by light-sensitive optical pigments
2) Pigments are bleached causing a chemical change
3) Permeability of membrane to Na⁺ is increased
4) Generator potential is created
5) If threshold is reached, action potential is sent along a bipolar neurone to the optic nerve and then the brain

Question 48

Fovea definition

Answer 48

an area of the retina where there are lots of photoreceptor

Question 49

How light enters the eye

What happens when light enters the eye

Answer 49

through the pupil

it hits the photoreceptors and is absorbed by the light sensitive pigments

Question 50

Role of iris muscles

Answer 50

control the amount of light that enters the eye

Question 51

What light rays are focused by

Answer 51

the lens onto the retina which lines the inside of the eye

Question 52

What is the blind spot?

Why isn’t it sensitive to light?

Answer 52

where the optic nerve leaves the eye

there aren’t any photoreceptor cells

Question 53

What does light bleach? What does this cause?

Answer 53

the pigments

a chemical change and alters the membrane’s permeability to sodium

Question 54

What happens when a generator potential is created and it reaches the threshold?

Answer 54

a nerve impulse is sent along a bipolar neurone

Question 55

What happens when light from 2 points hits 2 cones?

Answer 55

2 action potentials go to the brain so you can distinguish 2 points that are close together as separate points