12 Visual System Flashcards
The wall of the eye consists of three concentric layers?
fibrous tunic
vascular tunic
neuroepithelial (or inner) tunic
These maintain pressure within the eyeball, thus preventing the eyeball from collapsing
vitreous body
aqueous humor
fibrous tunic consists of
sclera
cornea
It provides mechanical support and protection of the eye
Fibrous tunic
-covers the entire outside surface of the eye except for the cornea
-consists of dense connective tissue and provides rigidity, helping to maintain the shape of the eyeball.
Sclera
-is a transparent layer covering the iris, the colored portion of the front of the eye.
-is curved and therefore helps bend light toward the retina.
Cornea
The vascular tunic consists of
iris
ciliary body
choroid
-contains dilator and sphincter muscles.
Iris
Contraction of the sphincter muscle results in a ____ in pupillary size (miosis) while Contraction of the dilator muscle results in pupillary dilation (mydriasis).
decrease
____ reflects the general state of sympathetic tone, and certain emotions such as pain, fear, and anger
Pupillary dilation
consists of the ciliary processes and ciliary muscles
Ciliary body
-are folds of tissue containing capillaries that secrete aqueous humor.
-Extending from this to the lens are zonular fibers (suspensory
ligaments).
ciliary processes
-are a bundle of smooth muscles that alter the shape of the lens to allow for near or far vision.
-plays a key role in accommodation. This process involves the change in the curvature of the lens when focusing on near or far objects. When focusing on near objects, it contracts resulting in a more convex lens.
ciliary muscles
-this consists of loose connective tissue with numerous vasculature and melanocytes.
-It serves a nutritive function for ocular tissue.
choroid
-is an additional layer in the choroid found in many species of domestic animals, including cats, dogs, horses, and ruminants
-This causes the animal’s eyes to appear to glow when shined with light.
-this reflects light toward the retina so that the animal can see in low light.
tapetum lucidum
What is the innermost tunic of the eye
retina
What are the two layers of the retina
outer pigmented layer
inner neural layer
layer of the retina that is one cell- a thick layer of melanin-containing epithelial cells, similar to the choroid. These cells also act as phagocytes and store vitamin A
pigmented layer
The neural layer has three major layers?
photoreceptor layer
bipolar cell layer
ganglion cell layer
What do you call the layers that separate the three major layers of the neural layer from each other
outer and inner synaptic layers
Before reaching the photoreceptor layer, light must first pass through the ____
ganglion and bipolar cell layers
two types of photoreceptor cells
rod cells (95%)
cone cells
photoreceptor cells consist of two portions?
outer segment
inner segment
portion of the photoreceptor cells wherein the photosensitive region contains photopigments that convert light stimulus to receptor potential
outer segment
portion of the photoreceptor cells that is the metabolic region
inner segment
-the photochemical in rod cells
-responsible for the perception of shades of gray.
-has a low threshold of excitability and is easily stimulated by low intensity light.
Rhodopsin
-have a higher threshold of excitability than rod cells
-photochemical iodopsin requires relatively high-intensity light to be stimulated.
-less sensitive to light than rod cells.
-provide color.
Cone cells
In primates, each cone cell has one of three opsins:
a pigment primarily sensitive to blue, green, or red colors
In the dog, each cone has one of two opsins:
a pigment sensitive to light with a wavelength of either violet or yellow-green
cells that convert the physical energy of light signals into electrical impulses
Photoreceptor cells (rods and cones)
in the retina, this give rise to axons of the optic nerve
Ganglion cells
Optic nerve fibers terminate in three nuclei:
lateral geniculate nucleus of the thalamus (that projects fibers to the visual cortex
rostral colliculus (which mediates such visual reflexes as turning the head in response to a sudden visual stimulus or pupillary dilation; and
the pretectal nucleus (which is responsible for pupillary constriction)
Opsins serve as G-protein coupled receptors and they contain chromophore ____ that undergo photoisomerization when struck by photons.
11-cis-retinal
Cones contain a photosensitive pigment called _____ whereas rods contain ____
opsins
rhodopsin
