14.4 Receptors

%%Specific to a particular type of stimulus%% - in this case mechanical pressure
%%Produces generator potential by acting as transducer%% - all stimulus involve change of type of energy, %%transducer have to change energy to a form recognised by the body%%, Pacinian corpuscle turns mechanical energy to a generator potential

Occur in %%joints, ligaments and tendons%%
%%Single sensory neurone%%, covered in %%layers of tissue each separated by a gel%%
Has a %%stretch mediated sodium channel%% - %%permeable to sodium changes when deformed i.e. stretched%%
Functions as follows…
- Normal state: stretch mediated sodium channel on membrane of Pacinian corpuscle too narrow to allow sodium ions through, has resting potential
- When %%pressure applied, becomes deformed and membrane is stretched%%
- %%Stretching widens sodium channels and allows ions to diffuse into neurone%%
- %%Influx of ions cases membrane to become depolarised%%
- %%Generator potential becomes action potential, passing along neurone%%

Rod cells: %%rod shaped, in greater numbers than cone cells, placed in periphery of fovea, poor visual acuity, sensitive to low intensity light, 1 type only%%
Cone cell: %%cone shaped, in fewer numbers, conc. in fovea, better visual acuity, not sensitive to low intensity light, 3 types%%
%%Many rod cells%% are attached to %%1 bipolar cel%%l
%%Retinal convergence%%, lots of cells to meet threshold
As lots of cells provide for 1 bipolar cell, %%unable to distinguish individual points of light so low visual acuity%%
To create generator potential, %%rhodopsin needs to broken down, only requires low level of energy in rod cells so only needs low light intensity for generator potential%%
%%Cone cells only detect high light intensity%%. This is because each %%cone cell connects to only one neurone, so it takes higher intensities of light to trigger a generator potential%%
%%They have high visual acuity%%. Visual acuity is the ability to tell apart two points that are close together. Cone cells only connect to one other neurone, so each individual stimuli can be distinguished.