Stimuli and Responses- Receptors Flashcards
What does it mean that receptors are specific?
They only detect one particular stimulus
What is a receptor like in resting state?
There’s a difference in charge between the inside and the outside of the cell
What is potential difference?
Voltage- generated by ion pumps and ion channels
What is resting potential?
Potential difference when a cell is at rest
What happens when a stimulus is detected?
Cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell (altering potential difference)
What is a generator potential?
Change in potential difference due to a stimulus
Why is a bigger generator potential produced when there is a bigger stimulus?
A bigger stimulus excites the membrane more so causes a bigger movement of ions and a bigger change in potential difference
When will an action potential be generated?
Only if the generator potential reaches the threshold level
What are Pacinian corpuscles?
Mechanoreceptors (detect mechanical stimuli)
Where are Pacinian corpuscles found?
In your skin
What do Pacinian corpuscles contain?
The end of a sensory neurone (sensory nerve ending) wrapped in lots of layers of connective tissue called lamellae
What happens when a Pacinian corpuscle is stimulated?
Lamellae are deformed and press on the sensory nerve ending causing the sensory neurone’s cell membrane to stretch, deforming the stretch-mediated sodium ion channels. The channels open and sodium ions diffuse into the cell, creating a generator potential
When is an action potential triggered?
If the generator potential reaches the threshold
How does light enter the eye?
Through the pupil
What controls the amount of light entering the eye?
Muscles of the iris
How are light rays focused?
By the lens onto the retina which lines the inside of the eye
What does the retina contain?
Photoreceptor cells that detect light
What is the fovea?
An area of the retina where there are lots of photoreceptors
How are nerve impulses from photoreceptor cells carried from the retina to the brain?
By the optic nerve which is a bundle of neurones
Why is the area where the optic nerve leaves the eye called the blind spot?
There aren’t any photoreceptor cells so it isn’t sensitive to light
What happens when light enters the eye?
It hits the photoreceptors and is absorbed by light-sensitive optical pigments
What does light bleaching the pigments cause?
A chemical change and alters membrane permeability to sodium ions
What happens if a generator potential and it reaches the threshold is created in the eye?
A nerve impulse is sent along a bipolar neurone
What do bipolar neurones do?
Connect photoreceptors in the optic nerve which takes impulses to the brain
What are the two types of photoreceptors in the human eye?
Rods and cones
Where are rods found?
In the peripheral parts of the retina
Where are cones found?
Packed together in the fovea
What makes rods and cones sensitive to different wavelengths of light?
They contain different optical pigments
Which photoreceptors give monochromatic vision (black and white)?
Rods
Which photoreceptors give trichromatic vision (colour)?
Cones
What are the three different types of cones with different optical pigments?
Red-sensitive, green-sensitive, blue-sensitive
What happens when different types of cones are stimulated in different proportions?
You see different colours
Why are 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
Why are 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
What does visual acuity mean?
The ability to tell apart points that are close together
Why do rods give lower visual acuity?
Because many rods join the same neurone which means light from two points close together can’t be told apart
Why do cones give higher visual acuity?
Because cones are close together and one cone joins one neurone- when light from two points hits two cones, two action potentials go to the brain so you can distinguish two points that are close together as two separate points
