L9, L10, L11 - PHYSIOLOGY OF VISUAL SYSTEM Flashcards
(68 cards)
The projection of visual fields (area of environment that is perceived by each eye) onto the retina is ___ and ___
Reversed and inverted
- medial visual fields project onto lateral retina
- lateral visual fields project onto medial retina
- upper visual fields project onto lower retina
- lower visual fields project onto upper retina
The projection of visual fields onto the retina is reversed and inverted
What causes this?
Refraction of light through the cornea and lens
What are the 2 smooth muscle groups in the iris?
What occurs when they contract?
What kind of neural control are they under?
- Sphincter muscle - miosis - parasympathetic control
2. Radial muscle - mydriasis - sympathetic control
The shape of the lens and its strength is regulated by the ___ muscle
Ciliary muscle
part of the ciliary body
The ciliary muscle is a circular ring of ___ muscle attached to the lens by ____
Smooth muscle
Suspensory ligaments
A. ___ stimulation relaxes the ciliary muscle via ___ receptor activation; this causes the lens to be ___ for far vision
B. ___ stimulation contracts the ciliary muscle via ___ receptor activation; this causes the lens to be ___ for near vision
A. Sympathetic, B2 adrenergic, flat (far)
B. Parasympathetic, M3 cholinergic, convex (near)
The “near response” is a three-part response that consists of
- accommodation
- convergence of visual axis
- pupillary constriction
Unlike the pupillary light reflex, the near (or accommodation) reflex requires the participation of the ___
cerebral cortex
Age-related reduction in accommodative ability of the lens is known as
Presbyopia
middle aged ~50 = reading glasses
A. Myopia (i.e. ___ ) occurs when distant parallel rays are focused ___ the retina; it is corrected with a ___ lens
B. Hyperopia (i.e. ___ ) occurs when distant parallel rays are focused ___ the retina; it is corrected with a ___ lens
A. nearsightedness, in front of, concave lens
B. farsightedness, behind, convex lens
What are the 5 major neuronal cell classes in the retina
What is the main pathway?
- Photoreceptors
- Bipolar cells
- Horizontal cells
- Amacrine cells
- Ganglion cells
Mnemonic:
Peanut Butter HAG
Photoreceptor to bipolar cell to ganglion cell
Mnemonic:
Peanut Butter & Gelly
A. Axons of ___ cells form the optic nerve that conducts APs
B. ___ cells modulate signals from photoreceptors to bipolar cells
C. ___ cells modulate output of bipolar cells to ganglion cells
A. ganglion cells
B. horizontal cells
C. amacrine cells
P => (H) => B => (A) => G
The exact center of the retina is the ___
It is the area of HIGHEST visual acuity as it ONLY contains only ___ cells
Fovea
Cone cells
The area immediately surrounding the fovea is known as the ___
It contains a high concentration ___ cells
Macula lutea
Cone cells
thus fairly high acuity
In the fovea, the ___ cells and ___ cells are pulled aside so that light strikes photoreceptors directly
Bipolar cells + ganglion cells
Why does central vision have a high resolution?
Because each ganglion cell is devoted to a very small portion of the visual field
(most foveal receptors synapse on only 1 bipolar cell which synapses on only 1 ganglion cell)
A. ___ (or S) cones absorb light of short wavelength
B. ___ (or M) cones absorb light of medium wavelength
C. ___ (or L) cones absorb light of long wavelength
A. Blue (S)
B. Green (M)
C. Red (L)
A. Packing density of ___ cells decreases sharply outside of the fovea
B. Packing density of ___ cells increases at the periphery of the retina
(emphasized)
A. Cones
B. Rods
A. What are the light-sensitive pigments in the rods?
B. What are the light-sensitive pigments in the cones?
A. Rhodopsin
B. Cone pigments
or color pigments
The 2 key components of rhodopsin are:
A. the aldehyde of Vit A ___
B. the protein ___
A. Retinal (or retinol)
B. Opsin
A. ___ is the cascade of chemical and electrical events through which light energy is converted into a receptor potential
B. Rods and cones are unusual in that their receptor potential is a ____
hyperpolarization
A. ___ is the conformation of retinal in the dark
B. The only action of light is to change the conformation of retinal into the ___ isomer
A. 11-cis retinal
B. trans isomer
A. Inactive rhodopsin is composed of ___ and ____
B. When light enters and retinal is activated, what occurs?
A. opsin and retinal
B. opsin dissociates from retinal and is released (bleached)
A. After opsin dissociates from retinal its conformation changes leading to activation of a heterotrimeric G-protein known as ___
B. What events occur following the activation of this heterotrimeric G-protein?
A. Transducin
B. activation of phosphodiesterase => decreased intracellular cGMP => closure of Na+ channels => HYPERpolarization of photoreceptor cells
