<unk> s, or<unk> s, are cells in the retina of the eye which only function in relatively bright light. The<unk> s gradually become more sparse towards the periphery of the retina.
A commonly cited figure of six million in the human eye was found by Osterberg in 1935. Oyster's textbook (1999) cites work by Curcio et al. (1990) indicating an average closer to 4.5 million<unk> s and 90 million rod cells in the human retina.<unk> s are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods.  Because humans usually have three kinds of<unk> s, with different photopsins, which have different response curves, and thus respond to variation in color in different ways, they have trichromatic vision. Being color blind can change this, and there have been reports of people with four or more types of<unk> s, giving them tetrachromatic vision.
Cone cell
Granule cell
Ganglion cell
Interneuron
Spindle neuron
Neuron
Alpha cell
Sensory receptor