Photoreceptors

What are the ‘rods and cones’ in the retina?

Photoreceptors (light-detecting cells)

What are photoreceptors used for?

The conversion of light energy into neuralsignals

What is the structure of a photoreceptor?

A photopigment, cell body, and a synaptic terminal

What are ‘rods’ in the retina?

Low-light photoreceptors, which are highly sensitive to light, but do not discern colours. Mediate SCOPTIC vision (night/dim lighting, decreased visual acuity, no colour perception, use of peripheral vision, detection of movement)

What are ‘cones’ in the retina?

Colour-vision photoreceptors, which work best in higher illumination providing colour information. Mediates PHOTOPIC vision (day/bright lighting, increased visual acuity, colour perception, use of central vision)

How are rods and cones in the retina organised/distributed?

There are a lot more rods than cones, but in the centre of the fovea, there is a concentration of cones

What is the difference between how rods and cones converge in their circuits?

Many rod photoreceptors signal to a retinal ganglion cell (increases light detection, reduces spatial resolution. Cones have low sympathetic convergence because only one cone photoreceptor signals to a retinal ganglion cell (1-1 relationship vs many-to-1), which maximises acuity.

What are ipRGCs and what do they do?

Intrinsically photosensitive retinol ganglion cells. These cells use melanopsin (a photopigment that is maximally sensitive to blue light), which have connections to the superchiasmatic nucleus and are critical for circadian rhythms

Where is the ‘blind spot’ in the retina?

The optic disc - the point where optic nerves converge to exit the eye

Where do most fibres from the retina/optic nerve terminate (meet) to?

The lateral genivulate nucleus (LGN) of the thalamus

What is a neuron’s ‘receptive field’?

Certain cells respond specifically to light hitting a particular area of the cell (usually the center)

What allows us to move our eyes?

The three pairs of extraocular muscles inserted into the sclera

What is light?

Electromagnetic energy emitted in the form of waves

What electromagnetic wavelengths are visible to the human eye?

400-700nm

What is the gross flow of visual information in the retina?

Photoreceptor cells → bipolar cells → retinal ganglion cells

What are the three different cones?

Blue, red, and green cones = this makes them maximally sensitive to different wavelengths of light, which enable colour vision (unlike rods, which all have the same photopigment = monochromatic/achromatic)