part of the sensory system-the eye

Question 1

What is transduction?

Answer 1

It’s the process in which a change of stimuli by a special cell to a chemical that our brain can read.

Question 2

Explain what ganglion cells are, and then explain the difference between midget and parasol ganglion cells.

Answer 2

Ganglion cells are neurons that give rise to the axons forming the optic nerve. Midget cells have strong lateral inhibition and are particular sensitive to spatial change(edges); produce a ‘red-green’ line drawing. Parasol cells have weaker lateral inhibition but strong delayed inhibition; produce a ‘black and white’ line drawing.

Question 3

What is albedo?

Answer 3

The proportion of incident light that a surface reflects.

Question 4

What is surface reflectance?

Answer 4

The proportion of light falling upon a surface that reflects.

Question 5

How much can we detect from the available range?

Answer 5

Between about 40nm and 700nm.

Question 6

What are our photoreceptors and how do they work?

Answer 6

These are our rods and cones. Cones = color. Rods = black and white. The rod and cone receptor potential is a hyperpolarization, causing a graded reduction in the steady release of the transmitter glutamate. Each receptor thus produces a graded receptor potential, a tiny voltage that depends upon the intensity and wavelength of the light striking it. Since the receptors are very small and densely packed, the overall result, across all receptors, is a very fine-grained ‘neural image’. Then, each retinal ganglion cell responds to light in a small region of the retina, called the cell’s receptive field. Basically, photoreceptor response is transmitted and processed by horizontal, bipolar, and amacrine interneurons.

Question 7

What is rhodopsin?

Answer 7

The visual pigment found in photoreceptors that can be bleached by light to produce a neural response.

Question 8

What is the retinal ganglion cell?

Answer 8

It’s the output stage of the retina; the axons of retinal ganglion cells form the optic nerve.

Question 9

What is a receptive field?

Answer 9

The region of a receptive surface, such as the skin or the retina which, when stimulated, changes a cell’s response.

Question 10

What are S cells?

Answer 10

They produce a ‘blue and yellow’ line drawing.

Question 11

What is opponency?

Answer 11

A theory of color vision in which colors are arranged in antagonistic pairs, with yellow the opponent of blue and green the opponent of red.

Question 12

What is color blindness?

Answer 12

An inability to discriminate between certain wavelengths rather than blindness; occurs when one of the cone types is missing.

Question 13

what is color anomaly?

Answer 13

This is more common, it occurs when all three types of cones are present but the pigment in one of them is altered.

Question 14

What is change blindness?

Answer 14

The inability, under some circumstances, to be able to detect major changes in the visual scene.

Question 15

What is the blind spot?

Answer 15

The spot in which the fibers leave, so that there is no response to light and there are no photoreceptors at that point.

Question 16

Where does the optic nerve project to?

Answer 16

It projects to the optic chiasma, where half of the fibers from each retina cross over in an arrangement that ensures the two images of an object, one in each eye, are processed in the same place.

Question 17

What is the LGN?

Answer 17

The LGN stands for the lateral geniculate nucleus, which is where most fibers synapse for the first time. It has six layers, each receiving input from only one eye. It’s located in the thalamus and projects from there to the visual cortex via the optic radiation. The two innermost layers are the magnocellular layers (receive input from parasol cells and concerned with signaling movement) and the parvocellular layers (receive input from midget cells and concerned with signaling colors and fine detail; blue-yellow opponent cells).