I/E: Receptors Flashcards
How is the strength of the stimulus measured?
Why is this?
The frequency of action potentials, as all action potentials are one size.
Mechanoreceptors
Receptors that detect mechanical stimuli, eg. pressure and vibrations.
Pacinian corpuscles
Pressure receptors in the skin.
Describe the structure of a pacinian corpuscle:
- Contains a sensory nerve ending.
- SNE is wrapped in layers of lamellate (connective tissue).
What happens when a Pacinian corpuscle is stimulated?
- Lamellae are deformed and press on sensory nerve ending.
- Sensory neurone’s cell membrane stretches.
- Deforms streth-mediated sodium ion channels.
- Channels open and sodium ions diffuse into the cell.
- Creates a generator potential.
- If this reaches threshold, action potential is triggered.
Photoreceptors
Light receptors in the eye.
Describe how light is detected in the eye
- Light enters eye through pupil (amount is controlled by the retina).
- Light rays focused by the lens onto retina containing photoreceptors, mainly the fovea.
- Nerve impulses are carried from retina to brain by the optic nerve.
Fovea
Area of the retina where there are lots of photoreceptors.
Where is the blindspot in the eye?
Where the opctic nerve leaves the eye - there aren’t any photoreceptors there, so it’s not sensitive to light.
Describe how photoreceptors convert light into an electrical impulse:
- Light is absorbed by light-sensitive optical pigments in photoreceptors.
- Bleaches the pigment, causes a chemical change and alters the membrane permeability to sodium ions.
- Generator potential is created and nerve impulse is sent along bipolar neurone if this reaches threshold.
- Connects to optic nerve and impulse is carried to the brain.
What connects photoreceptors to the optic nerve?
Bipolar neurones
What are the two types of photoreceptors in the human eye?
Rods and cones
Where are rods found?
Where are cones found?
Rods are mainly found in the peripheral parts of the retina.
Cones are mainly found in the fovea, tightly packed.
What type of vision do rods give?
Monochromatic vision = only give information in black and white.
What type of vision do cones give?
Trichromatic vision = give information in colour.
What are the three types of cones?
What happens when they’re stimulated in different proportions?
Red-sensitive
Green-sensitive
Blue-sensitive
You see different colours when they are stimulated in different proportions.
Describe the sensitivity of rods and cones:
Why is this?
Rods = very sensitive to light (work well in dim light).
Because many rods join one neurone, so many weak generator potentials combine to reach threshold.
Cones = less sensitive than rods (work best in bright light).
Because only one cone joins one neurone, so it takes more light to reach threshold.
Describe the visual acuity of rods and cones:
Rods = low visual acuity
Because many rods join the same neurone, which means light from two close points can’t be told apart.
Cones = high visual acuity
Because cones are close together and only joins one neurone, so when light hits two cones, two action potentials go to the brain and are distinguishable.
