Receptors Flashcards
What are receptors?
a specific cell or protein on a cell-surface membrane, that detects a stimulus
What do receptors in the nervous system do?
Convert the energy of the stimulus into the electrical energy used by neurones
What are the three potentials of a cell membrane?
Resting
Generator
Action
What is the resting potential of a membrane?
It is not being stimulated.
The inside of the membrane is relatively negative compared to the outside so there is a voltage across the membrane, also known as potential difference
How is the resting potential maintained?
Through ion pumps and ion channels
What is the resting membrane potential in mV?
about -70 mV
What happens to the membrane when a stimulus is initially detected?
The cell membrane becomes excited and more permeable, allowing more ions to more in and out of the cell, altering the potential difference
What is a generator potential?
A change in potential difference due to a stimulus
What happens to the generator potential when the stimulus is bigger?
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
What is an action potential?
An electrical impulse sent along a neurone
How is an action potential triggered?
When the generator potential is enough to reach the threshold level
How is the strength of the stimulus measured? Why?
The frequency of action potentials as all action potentials are the same size
What happens when the stimulus is too weak?
The generator potential will not reach the threshold level and there won’t be an action potential
What are pacinian corpuscles?
mechanoreceptors
What do mechanoreceptors detect?
Mechanical stimulus such as pressure and vibrations
Where are pacinian corpuscles found?
In the skin at the end of a sensory neurone
What is the sensory nerve ending wrapped up in?
Layers of connective tissue called lamellae
What happens when the pacinian corpuscles are stimulated?
The lamellae become deformed and press on the sensory nerve ending, deforming the stretch-mediated sodium ion channels
What happens when the stretch-mediated sodium ion channels become deformed?
They open and sodium ions diffuse into the cell, creating a generator potential. If the generator potential reaches the threshold, it’ll trigger an action potential
What are photoreceptors?
Receptors in the eye which detect light
What does the retina contain?
Photoreceptor cells
Where in the retina are there the most photoreceptors?
Fovea
Where are nerve impulses carried from and to in the eye?
From the photoreceptor cells in the retina to the brain by the optic nerve
What is the blindspot?
Where the optic nerve leaves the eye
Why is the blindspot not sensitive to light?
There aren’t any photoreceptor cells
How do photoreceptors work?
The light that hits the photoreceptors is absorbed by light-sensitive optical pigments. The 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, an action potential is triggered and the nerve impulse is sent along a bipolar neurone
What do bipolar neurones connect?
photoreceptors to the optic nerve which takes it to the brain
What are the two types photoreceptors?
Rods and cones
Where are rods mainly found?
Mainly found in peripheral parts of the retina
Where are cones mainly found?
Packed together in the fovea
What type of vision do rods give you?
monochromatic - black and white
What type of vision do cones give you?
trichromatic - colour vision
What are the three different optical pigments in the 3 different cones?
red-sensitive, green sensitive and blue-sensitive
Are rods sensitive to light? Why?
Yes
Many rods join one bipolar neurone, so many weak generator potentials can combine to reach the threshold and trigger an action potentials
Are cones sensitive to light? Why?
No
One cone joins one bipolar neurone so it takes more light to reach the threshold and trigger and action potential
What is visual acuity?
The ability to tell apart points that are close together
Do rods have a high or low visual acuity? Why?
Low
Many rods jin the same bipolar neurone which means light from two points close together can’t be told apart
Do cones have a high or low visual acuity? Why?
High
Cones are close together and one cone joins one bipolar neurone. When light from two points hit two cones, two action potentials go to the brain so you can distinguish between two points
