❤️ 3.6 - 3.6.1 - 3.6.1.2 Receptors (A-level only) Flashcards
Receptors are specific. What does this mean?
They only detect one particular stimulus, e.g. light, pressure or glucose concentration.
What are the two things receptors can be?
They can be cells (e.g. photoreceptors are receptor cells that connect to the nervous system).
They can be proteins on cell surface membranes (e.g. glucose receptors are proteins found in the cell membranes of some pancreatic cells).
When a nervous system receptor is in its resting state (not being stimulated), what is there a difference in?
The charge between the inside and the outside of the cell. The difference is generated by ion pumps and ion channels.
What does it mean if there is a difference in change between the inside and outside of the cell?
That there is a voltage across the membrane.
What is voltage also known as?
Potential difference.
What is the potential difference when a cell is at rest called?
Its resting potential.
When a stimulus is detected, the cells membrane is excited, which causes the membrane to become more …
… permeable.
If the cell membrane becomes more permeable, what does this mean? What does this cause?
More ions can move in and out of the cell. This alters the potential difference.
What is the change in potential difference due to?
A stimulus and is called the generator potential.
A bigger stimulus excites the membrane more, what does this cause?
A bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is products.
If the generator potential is big enough, what will it trigger?
An action potential.
What is 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 what?
Threshold level.
What is the strength of the stimulus measured by, as action potentials are all one size?
The frequency of action potentials (the number of action potentials triggered during a certain time period).
What happens if the stimulus is too weak?
The generator potential won’t reach the threshold, so there is no action potential.
What type of receptors are pacinian corpuscles in your skin?
Pressure receptors.
What type of receptors are pacinian corpuscles?
Mechanoreceptors - they detect mechanical stimuli, e.g. pressure and vibrations. They are young in your skin.
Where are the pressure receptors, pacinian corpuscles found?
In your skin.
What type of neurone do pacinian corpuscles contain the end of? What is it wrapped in?
Sensory called the sensory nerve ending. It is wrapped in loads of layers of connective tissue called lamellae.
What happens when a pacinian corpuscles is stimulated?
The lamellae become deformed and press on the sensory nerve ending.
What happens when the lamellae on the sensory nerve ending become deformed?
The sensory neurone’s cell membrane stretched, deforming the stretch-mediated sodium ion channels. The channels open and sodium ions diffuse into the cell, creating a generator potential.
What do pacinian corpuscles only respond to?
Mechanical stimuli.
What are photoreceptors?
Light receptors in your eye.
What does light enter the eye through?
The pupil.
How is the amount of light that enters the eye through the pupil controlled?
By the muscles of the iris.
Light rays are focused by the lens onto the …
… retina - which lines the inside of the eye.
What does the retina contain?
Photoreceptor cells - these detect light.
What is the fovea?
An area of the retina where there are lots of photoreceptors.
Where are nerve impulses from the photoreceptor cells carried from and to and by what?
From the retina to the brain by the optic nerve - which is a bundle of neurones.
What is the blind spot?
Where the optic nerve leaves the eye.
Why is the blind spot (where the optic nerve leaves the eye) not sensitive to light?
Because there are not any photoreceptor cells.
What do photoreceptor cells convert light into?
An electrical impulse.
What happens as light enters the eye?
- It hits the photoreceptors and is absorbed by light-sensitive optical pigments.
- The light then bleaches the pigments which causes a chemical change and alters the membrane permeability to sodium ions.
- A generator potential is therefore created and if it reaches the threshold,, a nerve impulse is sent along a bipolar neurone.
What are bipolar neurones?
Neurones which connect photoreceptors to the optic nerve, which takes impulses to the brain.
What two things does light pass straight through to get to the photoreceptor?
The optic nerve and the bipolar neurone.
Name the two types of photoreceptors.
Rods and cones.
Where are rods mainly found and where are cones found?
Rods are mainly found in the peripheral parts of the retina, and cones are found packed together in the fovea.
What makes rods and cones sensitive to different wavelengths of light?
The different optical pigments they each have.
What colour do both rods and cones each give information in?
Rods - black and white (monochromatic vision)
Cones - colour (trichromatic vision)
What are the 3 types of cones?
What makes the 3 types of cones different from each other?
Red-sensitive, green-sensitive and blue-sensitive.
They all contain different optimal pigments.
When they are stimulated in different proportions you see different colours.
Rods are more …, but cones let you see more … .
sensitive
detail.
Are rods or cones very sensitive to light?
Rods.
Do rods or cones work well in dim light?
Why?
Rods (very sensitive to light).
Because many rods join one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential
Do rods or cones work best in bright light?
Why?
Cones (less sensitive to light).
Because one cone joins one neurone, so it takes more light to reach the threshold and trigger an action potential.
Give a definition of visual acuity?
The ability to tell apart points that are close together.
Do rods or cones give low visual acuity?
Why?
Rods.
Because many rods join the same neurone, which means light from two points close together can’t be told apart.
Do rods or cones give high visual acuity?
Why?
Cones.
Because cones are close together and one cone joins one 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.
In rods does the brain get separate information about two close points?
Regarding visual acuity.
No.
In cones does the brain get separate information about two close points?
Regarding visual acuity.
Yes.
