14.4 Receptors Flashcards
What is sensory reception vs sensory perception
Reception is the function of receptors whilst perception is making sense of information from these receptors
What is the pacinian corpuscle
Type of sensory receptor
It responds to changes in mechanical pressure, so no response to other stimuli eg heat.
What do all sensory neurones have in common
- Specific to one type of stimulus
How does pacinian corpuscle produce a generator potential
It acts as a transducer:
All stimuli involve a change in some sort of energy, so transducer can turn this energy into a nerve impulse to be understood by the body
Receptors in nervous system convert energy of stimulus into generator potential
Where are pacinian corpuscles
Respond to mechanical stimuli such as pressure , and occur deep in the skin eg fingers and soles of feet.
Occur in joints, tendons and ligaments also
Describe structure of pacinian corpuscle
Stretch mediated sodium channel
The sensory neurone ending of a pacinian corpuscle is in the centre of layers of tissue which are each separated by gel.
The neurone ending has a plasma membrane that contains sodium channels. This is called stretch-mediated sodium channel. Their permeability to sodium ions is changed as they are deformed
What is function of a stretch mediated sodium channel
- In resting state, the sodium channels around plasma membrane are too narrow to allow sodium ions through.
So it has a resting potential. - When pressure is applied, it is deformed and membrane around its neurone is stretched
- This makes it more permeable as sodium channels widen so more sodium ions enter by diffusion
- This changes membrane potential so it becomes depolarised, thereby producing a generator potential which can then produce an action potential to go to central nervous system
Where are light receptors found in the eye
The retina is the innermost layer of eye and millions of light receptor cells are found there
Two main types of light receptors
Rod cells and cone cells
These act as transducers by conserving light energy into electrical energy of nerve impulse.
Rod cells more numerous than cone cells, there are millions in our eyes.
Why are images only seen in black and white in rod cells
Rod cells can’t distinguish between different wavelengths of light
What are rod cells
Many rod cells are connected to single sensory neurone in optic nerve.
They detect light of very low intensity.
Many rod cells are connected to bipolar cell to produce a generator potential. A generator potential is produced by pigment in rods (rhodopsin) being broken down.
There is enough energy in low light to do this so as a result we can see at night.
What is retinal convergence and why does it occur
Where many rod cells go to one bipolar cell.
It increases chance of threshold to be reached to allow a generator potential to be produced due to summation.
If only one rod cell was connected to one bipolar cell, there is a lower chance of this threshold being reached.
What is low visual acuity and why do rod cells give it
Many rod cells link to a single bipolar cell, and this means a single impulse is generated to travel to the brain.
This means the brain can’t distinguish between the separate sources of light that stimulated them
What are cone cells
Why are they only responsive to high light intensity
There are 3 types and each respond to a different wavelength of light
Usually each cone cell is connected to its own bipolar cell, so this means unlike with rod cells they can’t group together to reach threshold value.
So this means threshold is only reached by high light intensity so they don’t respond to low light
Iodopsin is pigment found in cone cells which requires a higher light intensity for its breakdown than rhodopsin in rod cells. So only high light intensity can produce a generator potential.
Each cone cell is sensitive to a different specific range of wavelengths, why
Three types of cone cell each contain a different type of iodopsin.
So this is only broken down by different wavelengths of light.
