What function does the lateral geniculate nucleus (LGN) serve in the circuit of visual processing?

It takes input from the retina and optic chiasm (fields cross here) and then projects the information to the primary visual cortex in the very rear of the brain

What is the wavelength range of visible light for the human eye?

400-700nm

These change the shape of the lens in the eyes to focus light from different distances onto the retina

Ciliary muscles

Myopia is to (blank) as hyperopia is to (blank)

Nearsightedness, farsightedness

What important action happens to visual stimuli in the body of the eye just past the lense?

The image is vertically inverted

What are the three primary nerve cells that comprise the basic structure of the retina?

Ganglion, bipolar and cone/rod cells

Once input is received onto the retina and information is being sent back out to the optic nerve, what is the most direct pathway for this information?

Photoreceptor cells -> bipolar cells -> ganglion cells

What function do photoreceptor cells serve and how do cones and rods differ?

They transduce light into bioelectrical signals; rods are 100x more sensitive to light intensity than cones although cones detect color

What are photopigments and how do they work?

They are made of protein (opsin) and chromophore (retinal) and are made from short, medium and long wavelength pigments

How are different cones arrainged across the human retina?

There are many long, some medium and few short wavelength cones. The lack of short wavelength cones may be due to the fact that they are less sensitive to light

Why are a disproportionate amount of males colorblind?

Genes that encode for long and medium wavelength cone opsins are X-linked; faulty copies of these genes in men provides no back-up X chromosome so they can not see either red or green colors

What is retinal and what critical function does it serve in photoreception?

It is a vitamin A derivative bound within the helices of opsin; it absorbs light

The binding of a photon activates the GPCR rhodopsin which then cascades to the g-protein transducin which targets phosphodiesterase. This then down-regulated cGMP and causes what two key happenings?

Inward current to the neuron goes down and there is hyperpolarization

How do cGMP Na channels differ in dark and light conditions?

They are open in dark conditions but closed in light conditions

What is one of the key impacts of closed Na channels in photoreceptor cells under dark conditions?

Hyperpolarization of the cells

What is the photopic regime of light?

It is the very slight threshold of light sensity and is even more faint than starlight. In this range, there is no color vision and there is poor acuity

What is the mesopic regime of light intensity?

It begins at the cone threshold and ranges from just under starlight to dim indoor lighting. Both rods and cones are active here but there are few photos per cone

What is the scotopic regime of light sensity?

It is the range of light in which there is good color vision and there is the best acuity. It begins just after dim indoor lighting and continues through intense sunlight (vision damage is possible at the highest intensities in this range)

How are the various locations in the retina specialized?

The fovea (exact center) is specialized for high resolution while the peripheral retina is specialized for high sensitivity

How do the ganglial cell connections differ between peripheral and fovea photoreceptors?

In the periphery, there are many photoreceptors per ganglion cell (called M-cells) while at the fovea, there is typically a 1:1 ratio (called P-cells)

What is eccentricity in relation to the visual field?

It is the degrees of visual angle that an object or location is off of the fovea

Patterns of action potential firing in retinal ganglion cells serves what function?

This is the output of the retina

Off-center bipolar cells in receptive fields are referred to as h bipolars, "h" being shorthand for what?

Hyperpol

On-center bipolar cells in receptive fields are referred to as d bipolars, "d" being shorthand for what?

Depol

Photoreceptors are (blank) when they are activated and on-center and off-center cells have (blank) receptors for glutamate

Hyperpolarized, different

What are horizontal cells in the area of visual perception and how do they function?

They lie between photoreceptor cells and are responsible for the antagonistic response of the "surround" center effect; they act to inhibit the PR cells around the center

What are ribbon synapses?

They are the locations where photoreceptors, bipolar cells and horizontal cells interact