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A-level Biology > 6A - Receptors > Flashcards

6A - Receptors Flashcards

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1
Q

What are receptors specific to?

A

One kind of stimulus

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2
Q

Examples of receptors

A
  • Cells (e.g. photoreceptors)

- Proteins on cell surface membranes (e.g. glucose receptors)

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3
Q

What do transducers do?

A

Convert one form of energy into another (energy of stimulus –> energy of electrical impulse).

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4
Q

What occurs when a receptor is stimulated?

A

A generator potential.

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5
Q

What happens if a generator potential reaches a threshold?

A

An action potential occurs.

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6
Q

What is there when a nervous system receptor is in its resting state (not being stimulated)?

A

Difference in charge between the inside and the outside of the cell.

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7
Q

What is the difference in charge between the inside and the outside of the cell generated by?

A

Ion pumps and ion channels.

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8
Q

What is there across a membrane if there is a difference in charge between the inside and the outside of a cell?

A

A voltage.

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9
Q

What is the potential difference when a cell is at rest called?

A

Resting potential.

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10
Q

Resting potential

A

Potential difference when a cell is at rest.

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11
Q

What happens when a stimulus is detected?

A

The cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference.

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12
Q

What is the change in potential difference due to a stimulus called?

A

The generator potential.

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13
Q

Generator potential

A

The change in potential difference due to a stimulus.

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14
Q

What does a bigger stimulus do?

A

Excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is produced.

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15
Q

What happens if the generator potential is big enough?

A

An action potential is triggered.

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16
Q

When is an action potential triggered?

A

if the generator potential reaches a certain level called the threshold.

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17
Q

Action potential

A

An impulse along a neurone.

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18
Q

Size of different action potentials:

A

All the same size.

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19
Q

What is the strength of the stimulus measured by?

A

By the frequency of action potentials (the number of action potentials triggered during a certain time period).

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20
Q

What happens if the stimulus is too weak?

A

The generator potential won’t reach the threshold, so there’s no action potential.

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21
Q

What type of receptor are pacinian corpuscles?

A

Mechanoreceptors.

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22
Q

What receptors do we need to know?

A

Pacinian corpuscles.

Rods and cones.

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23
Q

Stimulus of pacinian corpuscles

A

Mechanical e.g. pressure and vibrations.

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24
Q

Location of pacinian corpuscles

A

Skin and joints, ligaments and tendons.

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25
What do pacinian corpuscles contain?
The end of a sensory neurons called a sensory nerve ending.
26
What is the sensory nerve ending of a pacinian corpuscle wrapped in?
Loads of layers of connective tissue called lamellae.
27
What happens when a pacinian corpuscle is stimulated?
- The lamellae are deformed and press on the sensory nerve endings. - This pressure causes the sensory neurone's cell membrane to stretch, deforming the stretch-mediated sodium ion channels (widening them). The channels open and sodium ions diffuse into the cell (depolarisation), creating a generator potential. - If the generator potential reaches the threshold, it triggers an action potential.
28
What are photoreceptors?
Light receptors in your eye - found in the retina.
29
Where does light enter the eye?
Through the pupil.
30
What controls the amount of light that enters the eye?
The muscles of the iris.
31
What are light rays focused by?
The lens.
32
What are light rays focussed onto?
The retina.
33
Where is the retina?
Lines the inside of the eye.
34
What does the retina contain?
Photoreceptor cells.
35
What do photoreceptors do?
Detect light.
36
What is the fovea?
An area of the retina where there are lots of photoreceptors.
37
How are nerve impulses from the photoreceptor cells carried from the retina to the brain?
By the optic nerve.
38
What is the optic nerve?
A bundle of neurones connecting the retina to the brain.
39
Where the optic nerve leaves the eye is called what?
The blind spot.
40
What is the blind spot in the eye?
Doesn't contain any photoreceptor cells, so it's not sensitive to light.
41
How is light absorbed in the eye - briefly?
Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments.
42
How do photoreceptors convert light into an electrical impulse?
- Light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments. - Light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions. - A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone. - Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain.
43
What does the absorption of light cause to happen?
- Light bleaches the light-sensitive optical pigments, causing a chemical change and altering the membrane permeability to sodium ions.
44
What do bipolar neurones do?
Bipolar neurones connect photoreceptors to the optic nerve.
45
What are the two types of photoreceptor in the human eye?
Rods and cones.
46
Where are rods found?
In the peripheral parts of the retina.
47
Where are cones found?
Packed together in the fovea (retina).
48
What do rods and cones contain and what does this mean?
Different optical pigments making them sensitive to different wavelengths of light.
49
What happens when light hits a rod cell?
- Light strikes rod cell. - Rhodopsin breaks down to form retinal and opsin. - Causes rod cells to depolarise (less negative). - Generator potential occurs. - Leads to an action potential in the bipolar neurone.
50
What pigment do rod cells contain and what is this formed from?
Rhodopsin - formed from opsin and retinal.
51
What stimulates the rod cells?
Low light intensity.
52
What stimulates the cone cells?
Bright light.
53
What pigment do cone cells contain?
Iodopsin.
54
How many types of rod cells are there?
1
55
How many types of cone cells are there?
3
56
What are the 3 types of cone cells?
Red-sensitive, green-sensitive and blue-sensitive.
57
What happens when light hits a cone cell?
- Light strikes cone cell. - Iodopsin breaks down. - Causes cone cell to depolarise (less negative). - Generator potential occurs. - Leads to an action potential in bipolar neurone.
58
What colour do rod cells produce?
Black and white (monochromatic vision).
59
What colour do cone cells produce?
Colour - different proportions of blue, green and red (trichromatic vision). Different cones for different wavelengths of light = colour vision.
60
Which type of photoreceptor are more sensitive?
Rods.
61
Which type of photoreceptor produce more detail?
Cones.
62
Why are rod cells sensitive to low light intensities?
Because many rods join to one bipolar neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential.
63
Why do cone cells respond to high light intensities only?
Because one cone joins to one bipolar neurones, so it takes more light to reach the threshold and trigger an action potential.
64
Which type of photoreceptor responds to low light intensities?
Rods.
65
Which type of photoreceptor responds to high light intensities?
Cones.
66
Which type of photoreceptor give high visual acuity?
Cones.
67
Which type of photoreceptor give low visual acuity?
Rods.
68
Why do rods give low visual acuity?
Because many rods join the same bipolar neurone, which means light from two points close together can't be told apart. (Because of the summation.)
69
Why do cones give high visual acuity?
Because cones are close together and one cone joins to one bipolar neurone. When light from two points hits two cones, two action potentials (one from each cone) go to the brain - so you can distinguish two points that are close together as two separate points.
70
Describe an inhibitory synapse
- Some synaptic vesicles release a NT that binds to chloride ion channels on the postsynaptic neurone. - Binding causes the chloride ion channels to open and chloride ions to diffuse into the cell. - Also causes the potassium ion channels to open to the potassium ions leave the cell. - The postsynaptic neurone becomes more negative. - Therefore it is harder to reach the threshold. - And so an action potential is less likely.
71
Spatial summation
Simultaneous summation of many presynaptic terminals (lots of neurones).
72
Temporal summation
Repeated summation of one presynaptic terminal (one neurone).
73
In which type of photoreceptor is there summation?
In rods.
74
Why is there summation in rods but not in cones?
Because more than one rod cell synapses with the one bipolar neurone.

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