3.4.2 Receptors Flashcards
Receptors only detect …
one particular stimulus
Describe a receptor in its resting state (not being stimulated)
There’s a difference in charge between inside and outside of cell
What is the difference in charge between inside and outside of receptor cell generated by and what does this mean?
- Difference is generated by ion pumps and ion channels
- Means there’s a potential difference (voltage) across the membrane
What is meant by resting potential?
Potential difference when cell is at rest
Describe how a generator potential is created
- When stimulus is detected, cell membrane is excited and becomes more permeable
- Allows more ions to move in & out = alerting potential difference
- Change in p.d. due stimulus = generator potential
Explain how a bigger stimulus results in a bigger generator potential being produced
Bigger stimulus excites membrane more = bigger movement of ions and bigger change in p.d.
State when an action potential is generated
If generator potential is big enough i.e. reaches threshold level, it’ll trigger an action potential
Describe the size of action potentials
Action potentials are all same size
How is the strength of a stimulus measured?
By frequency of action potentials
State what SOPI stands for
Sodium Out Potassium In
What type of receptors are Pacinian corpuscles?
Mechanoreceptors
(Detect mechanical stimuli e.g. pressure, vibrations)
Pacinian corpuscles the contain end of a _____ ____
Pacinian corpuscles contain the end of a sensory neurone
(Called sensory nerve ending)
What is the sensory nerve ending wrapped in?
Lamellae
Describe what happens when a Pacinian corpuscle is stimulated
- 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
- This deforms (stretch-mediated) sodium ion channels
- This opens the channels = greater pressure & allows for Na+ to diffuse into the cell creating a generator potential
Where are photoreceptors found?
Retina
What is the fovea?
An area of retina where there’s loads of photoreceptors
Nerve impulses from photoreceptor cells are carried from retina to brain by ___ ___ (bundle of neurones)
Optic nerve
Where is the blind spot located?
Where optic nerve leaves eye
(aren’t any photoreceptor cells)
What do photoreceptors do?
Convert light into electrical impulse
What happens when light enters the eye?
It hits photoreceptors and is absorbed by light-sensitive pigments
Light _____ pigments
bleaches
What happens when light bleaches pigments?
- Causes chemical change and alters membrane permeability to sodium ions
- Generator potential is created & if it reaches threshold = nerve impulse is sent along bipolar neurone
What do bipolar neurones do?
Connect photoreceptors to optic nerve, which takes impulses to brain
Name the 2 types of photoreceptor the human eye has
- Rods
- Cones
Where are rods found?
Found in peripheral parts of retina
Where are cones found?
Cones packed together in fovea
Why do rods and cones give information in different colours?
Rods and cones contain different optical pigments making them sensitive to different wavelengths of light
Rods give information in ____
B&W (monochromatic vision)
Cones give information in ____
Colour (trichromatic vision)
Name the 3 types of cones (each containing a different pigment)
- Red-sensitive
- Green-sensitive
- Blue-sensitive
When stimulated in different proportions = see different colours
State which one is more sensitive to light: rods or cones?
Rods
Explain why rods are very sensitive to light (work well in dim light)
- ∵ 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)
Explain why cones are less sensitive than rods (work best in bright light)
- ∵ one cone joins one neurone
- Takes more light to reach threshold and trigger action potential
- & requires lots of light intensity to breakdown iodopsin
Which one gives a higher visual acuity (ability to tell apart points
that are close together): rods or cones?
Cones
Explain why cones give a high visual acuity
- ∵ 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
Explain why rods give a low visual acuity
- Give low visual acuity ∵ many rods join same neurone
- Which means light from 2 points close together can’t be told apart
The membrane potential at Q was the same whether medium or heavy pressure was applied to the finger tip. Explain why.
- Threshold has been reached
- (Threshold or above) causes all or nothing principle
Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness. (2)
- rhodopsin bleached / broken down by light
- time for resynthesis
