Topic 6—A: Stimuli and responses- 4. Receptors Flashcards

1
Q

How are receptors specific?

A
  • They only detect one particular stimulus
    Example- light
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2
Q

What do receptors in the nervous system convert the energy of the stimulus into?

A
  • They convert the energy of the stimulus into the electrical energy used by neurones
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3
Q

The resting potential

A
  • When a nervous system receptor is in its resting state there’s a difference in charge between the inside and the outside of the cell
  • The inside is negatively charged relative to the outside
  • This means there’s a voltage across the membrane
  • Voltage is also known as potential difference
  • The potential difference when a cell is at rest is called its resting potential
  • The resting potential is generated by ion pumps and ion channels
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4
Q

Generator potential

A
  • When a stimulus is detected, the cell membrane is excited and becomes more permeable allowing more ions to move in and out of the cell- altering the potential difference
  • The change in potential difference due to a stimulus is called the generator potential
  • a bigger stimulus 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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5
Q

Action potential

A
  • If the generator potential is big enough, it will trigger an action potential- an electrical impulse along a neurone
  • An action potential is only triggered if the generator potential reaches a certain level called the thresh hold level
  • action potentials are all one size so the strength of the stimulus is measured by the frequency of action potentials
  • If the stimulus is too weak, the generator potential won’t reach the threshold so there’s no action potential
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6
Q

Pacinian corpuscles

A
  • They are mechano receptors
  • They detect mechanical stimuli e.g. pressure and vibrations
  • found in your skin
  • Pacinian corpuscles contain the end of a sensory neurone called a sensory nerve ending
  • The sensory nerve ending is wrapped in loads of layers of connective tissue called Lamellae
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7
Q

What happens when a pacinian corpuscle is stimulated?

A
  • pressure distorts the pacinian corpmuscles
  • deforming stretch mediated na+ channels
  • channels open and sodium ions diffuse into the cell creating a generator potential
  • If the generator potential reaches the threshold, it triggers an action potential
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8
Q

Photoreceptors

A
  • Receptors in your eye that detects light
  • Light enters the eye through the pupil and the amount of light that enters is controlled by the muscles of the iris
  • Light rays are focused by the lens onto the retina which lines the inside of the eye
  • The retina contains the photoreceptor cells
  • Fovea is an area of the retina where there are lots of photoreceptors
  • Nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve which is a bundle of neurones
  • Where the optic nerve leaves the eye it is called the blindspot- there aren’t any photoreceptor cells so it’s not sensitive to light
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9
Q

How photoreceptors work?

A
  • 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
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10
Q

In the human eye, what are the two types of photo receptor?

A
  1. Rods
  2. Cones
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11
Q

Where are rods mainly found?

A
  • In the peripheral parts of the retina
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12
Q

Where are cones mainly found?

A
  • Packed together in the fovea
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13
Q

Why are rod and cones sensitive to different wavelengths of light?

A
  • They contain different optical pigments
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14
Q

What do rods only give information in?

A
  • Black and white (monochromatic vision)
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15
Q

What do cones give information in?

A
  • In colour (trichromatic vision)
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16
Q

What are the three types of cones containing a different optical pigment?

A
  1. Red sensitive.
  2. Green sensitive.
  3. Blue sensitive.
    - When they’re stimulated in different proportions, you see different colours
17
Q

Sensitivity (rods)

A
  • Rods cells are very sensitive to light (they work well in dim light)
  • This is because many rods join one bipolar neurone so many week generator potentials combine to reach the threshold and trigger and action potential
18
Q

Sensitivity (cones)

A
  • Cones are less sensitive than rods (they work best in bright lights)
  • This is because one cone joins one bipolar neurone so it takes more light to reach the threshold and trigger an action potential
19
Q

Definition of visual acuity

A
  • It is the ability to tell apart points that are close together
20
Q

Visual acuity (rods)

A
  • 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
21
Q

Visual acuity (cones)

A
  • cones give high visual acuity because cones are close together and one cone joins one bipolar neurone
  • When light from two points hits two cones, two action potentials one from each cone goes to the brain- so you can distinguish two points that are close together as two separate points
22
Q

Rods

A
  • Mainly located in the peripheral parts of the retina
  • Give information in black and white
  • Many rods join one bipolar neurone
  • High sensitivity to light
  • Give low visual acuity
  • contains pigment Rhodopsin
23
Q

Cones

A
  • Mainly located in the fovea
  • Give information in colour
  • One cone joins one bipolar neurone
  • Low sensitivity to light
  • give high visual acuity
  • Contains pigment Iodopsin
24
Q

How do rods allow us to see in lowlight intensities?

A
  • Lower threshold potential (less Rhodopsin) needs to be broken down to initiate an action potential
  • several rods share a sensory neurone
25
Q

What is always open during resting potential?

A
  • k+ channels are open so potassium can leave
  • Pump is going the whole time
  • Na+ channels are closed
25
Q

What is open when there is a stimulus?

A
  • Na+ channels
26
Q

What is open when there is an action potential?

A
  • More na+ channels
27
Q

Resting potential (channels)

A
  • Outside the neurone= positive due to presence of Na+ and k+
  • Inside of neurone= negative due to presence of anions
  • Gated na+ channels are closed so little diffusion of na+ into neurone
  • k+ channels are open, so k+ can diffuse out of neurone
  • Na+ and k+ pump, pumping 3 na+ out of neurone and 2k+ into neurone
28
Q

Generator potential (channels)

A
  • Outside of neurone- gets more negative due to loss of na+ and k+ ions
  • Inside the neurone is more positive due to the presence of na+ and K+ ions
  • Stimulus causes gated na+ channels to open, increasing the permeability of the membrane to na+
  • 2k+ na+ diffuses down its concentration gradient into the neurone making potential difference more positive if there is enough na+ diffusing across membrane then threshold potential is reached and membrane is depolarised