Lecture 7

Question 1

What neurotransmitter is used between rods/cones and bipolar cells?

Answer 1

Glutamate

Question 2

What neurotransmitters do amacrine cells use?

Answer 2

8+ including GABA, glycine, dopamine, acetylcholine, indolamine; all inhibitory

Question 3

Photoreceptors

Answer 3

Includes rods and cones; transmit signals to outer plexiform layer (layer of synaptic connections); synapse with bipolar cells and horizontal cells

Question 4

Horizontal Cells

Answer 4

Transmit signals from rods and cones to bipolar cells, transmits signals to outer plexiform layer; output is always inhibitory (lateral inhibition)

Question 5

Bipolar Cells

Answer 5

Transmit signals from rods, cones, and horizontal cells, transmit signals to inner plexiform layer; synapse with amacrine and ganglion cells

Question 6

Amacrine Cells

Answer 6

Transmit signals directly from bipolar to ganglion cells, and within inner plexiform layer from axons of bipolar cells to dendrites of ganglion cells or to other amacrine cells; about 30 kinds (most are interneurons that help analyze visual signals before they leave the retina)

Question 7

Ganglion Cells

Answer 7

Transmit signals from retina to brain; axons make up optic nerves; these are the only retinal cells that transmit action potentials (others use electronic conduction which allows graded conduction of signal strength)

Question 8

Interplexiform Cells

Answer 8

Transmit from inner plexiform layer to outer plexiform layer (retrograde); inhibitory signals (lateral inhibition)

Question 9

Foveal Region

Answer 9

Represents a new type of vision based on cone vision; three neurons in direct pathway (cones, bipolar cells, ganglion cells); note that pure rod vision consists of four neurons (rods, bipolar cells, amacrine cells, ganglion cells)

Question 10

W Ganglion Cells

Answer 10

Make up about 40% of all ganglion cells; small and transmit signals 8m/s; receive most of their excitation from rods transmitted by way of small bipolar cells and amacrine cells; have broad fields in the peripheral retina because their dendrites spread widely in the inner plexiform layer

Question 11

X Ganglion Cells

Answer 11

Make up about 55% of all ganglion cells; medium diameter and transmit signals 14m/s; have small fields (signals represent discrete retinal locations); every x ganglion cell receives input from at least one cone cell; therefore, probably responsible for all color vision

Question 12

Y Ganglion Cells

Answer 12

Make up about 5% of all ganglion cells; large diameter and transmit signals 50m/s or faster; respond to rapid changes in visual a image; presumably apprise the CNS almost instantaneously when a new visual event occurs anywhere in the field without great accuracy with respect to location of field

Question 13

Dorsal Lateral Geniculate Nucleus

Answer 13

Receives input from optic nerve; relays information from optic tract to visual cortex by way of optic radiation (geniculocalcarine tract); 50% decussation in optic chiasm; six nuclear layers in lateral geniculate nucleus:

II, III, V - receive signals from lateral half of ipsilateral retina
I, IV, VI - receive signals from medial half of opposite retina

Question 14

Layers I and II of Dorsal Lateral Geniculate Nucleus

Answer 14

Magnocellular layers; contain large neurons; receive input almost entirely from large Y ganglion cells; provides rapidly conducting pathway to visual cortex; transmits only black and white; point to point transmission is poor

Question 15

Layers III - VI of Dorsal Lateral Geniculate Nucleus

Answer 15

Parvocellular layers; contain small to medium size neurons; receive input almost entirely from large X ganglion cells; provides moderate conducting pathway to visual cortex; transmits color; accurate point to point transmission

Question 16

Transmission Gating

Answer 16

Lateal geniculate nucleus controls how much of the signal is allowed to pass to the cortex; source of gating control is corticofugal fibers from primary visual cortex and reticular areas of the mesencephalon (both are inhibitory and help highlight visual information that is allowed to pass

Question 17

Primary Visual Cortex

Answer 17

Also called striate cortex; located in occipital lobes; signals from macular area terminate near the occipital lobe; signals from the more peripheral retina terminate at or in concentric half circles anterior to the pole but still along the calcarine fissure; six distinct layers; geniculocalcarine fibers terminate mainly in layer IV

Question 18

Color Blobs

Answer 18

Located among the columns of the secondary visual areas; receive lateral signals from adjacent visual columns and are activated specifically by color signals

Question 19

Accommodation in Children

Answer 19

Refractive power of the lens can be voluntarily increased from 20 to 34 diopters (accommodation of 14 diopters)

Question 20

Accommodation in Young Person

Answer 20

When the lens is in a relaxed state with no tension on its capsule, it assumes an almost spherical shape; suspensory ligaments attached radially around the lens create a tension that causes the lens to remain relatively flat under normal eye conditions; CN III controls both sets of ciliary muscles

Question 21

Accommodation in Older Person

Answer 21

Lens becomes larger, thicker, and less elastic with age; power of accommodation decreases to less than 2 diopters by the age of 45-50; decreases to 0 by the age of 70; this is called presbyopia