3.4.2 Receptors Flashcards

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1
Q

Receptors only detect …

A

one particular stimulus

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2
Q

Describe a receptor in its resting state (not being stimulated)

A

There’s a difference in charge between inside and outside of cell

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3
Q

What is the difference in charge between inside and outside of receptor cell generated by and what does this mean?

A
  • Difference is generated by ion pumps and ion channels
  • Means there’s a potential difference (voltage) across the membrane
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4
Q

What is meant by resting potential?

A

Potential difference when cell is at rest

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5
Q

Describe how a generator potential is created

A
  1. When stimulus is detected, cell membrane is excited and becomes more permeable
  2. Allows more ions to move in & out = alerting potential difference
  3. Change in p.d. due stimulus = generator potential
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6
Q

Explain how a bigger stimulus results in a bigger generator potential being produced

A

Bigger stimulus excites membrane more = bigger movement of ions and bigger change in p.d.

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7
Q

State when an action potential is generated

A

If generator potential is big enough i.e. reaches threshold level, it’ll trigger an action potential

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8
Q

Describe the size of action potentials

A

Action potentials are all same size

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9
Q

How is the strength of a stimulus measured?

A

By frequency of action potentials

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10
Q

State what SOPI stands for

A

Sodium Out Potassium In

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11
Q

What type of receptors are Pacinian corpuscles?

A

Mechanoreceptors

(Detect mechanical stimuli e.g. pressure, vibrations)

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12
Q

Pacinian corpuscles the contain end of a _____ ____

A

Pacinian corpuscles contain the end of a sensory neurone

(Called sensory nerve ending)

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13
Q

What is the sensory nerve ending wrapped in?

A

Lamellae

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14
Q

Describe what happens when a Pacinian corpuscle is stimulated

A
  1. When the Pacinian corpuscle is stimulated the lamellae are deformed and press on the sensory nerve ending
    • = the sensory neurone’s cell membrane to stretch
  2. This deforms (stretch-mediated) sodium ion channels
  3. This opens the channels = greater pressure & allows for Na+ to diffuse into the cell creating a generator potential
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15
Q

Where are photoreceptors found?

A

Retina

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16
Q

What is the fovea?

A

An area of retina where there’s loads of photoreceptors

17
Q

Nerve impulses from photoreceptor cells are carried from retina to brain by ___ ___ (bundle of neurones)

A

Optic nerve

18
Q

Where is the blind spot located?

A

Where optic nerve leaves eye

(aren’t any photoreceptor cells)

19
Q

What do photoreceptors do?

A

Convert light into electrical impulse

20
Q

What happens when light enters the eye?

A

It hits photoreceptors and is absorbed by light-sensitive pigments

21
Q

Light _____ pigments

A

bleaches

22
Q

What happens when light bleaches pigments?

A
  1. Causes chemical change and alters membrane permeability to sodium ions
  2. Generator potential is created & if it reaches threshold = nerve impulse is sent along bipolar neurone
23
Q

What do bipolar neurones do?

A

Connect photoreceptors to optic nerve, which takes impulses to brain

24
Q

Name the 2 types of photoreceptor the human eye has

A
  • Rods
  • Cones
25
Q

Where are rods found?

A

Found in peripheral parts of retina

26
Q

Where are cones found?

A

Cones packed together in fovea

27
Q

Why do rods and cones give information in different colours?

A

Rods and cones contain different optical pigments making them sensitive to different wavelengths of light

28
Q

Rods give information in ____

A

B&W (monochromatic vision)

29
Q

Cones give information in ____

A

Colour (trichromatic vision)

30
Q

Name the 3 types of cones (each containing a different pigment)

A
  1. Red-sensitive
  2. Green-sensitive
  3. Blue-sensitive

When stimulated in different proportions = see different colours

31
Q

State which one is more sensitive to light: rods or cones?

A

Rods

32
Q

Explain why rods are very sensitive to light (work well in dim light)

A
  • ∵ many rods join one neurone = so many weak generator potentials combine to reach threshold and trigger action potential
  • & rhodopsin can be broken down easily (pigment needs to be broken down in order to create an action potential)
33
Q

Explain why cones are less sensitive than rods (work best in bright light)

A
  • ∵ one cone joins one neurone
  • Takes more light to reach threshold and trigger action potential
  • & requires lots of light intensity to breakdown iodopsin
34
Q

Which one gives a higher visual acuity (ability to tell apart points
that are close together): rods or cones?

A

Cones

35
Q

Explain why cones give a high visual acuity

A
  • ∵ cones are close together and one cone joins one neurone
  • When light from 2 points hits 2 cones, 2 action potentials (one from each cone) go to the brain
  • Can distinguish 2 points that are close together as 2 separate points
36
Q

Explain why rods give a low visual acuity

A
  • Give low visual acuity ∵ many rods join same neurone
  • Which means light from 2 points close together can’t be told apart
37
Q

The membrane potential at Q was the same whether medium or heavy pressure was applied to the finger tip. Explain why.

A
  • Threshold has been reached
  • (Threshold or above) causes all or nothing principle
38
Q

Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness. (2)

A
  • rhodopsin bleached / broken down by light
  • time for resynthesis