Visual Part 1 Flashcards
What part of the brain processes “What” an object is?
The ventral/ Temporal lobe
What part of the brain processes “Where” an object is?
The dorsal/Parietal lobe
How does the CNS maintain a tolerable level os sensory stimulation?
Feedback control
What are the three layers of the eyeball and what dural layers are they analogous to?
fibrous coat (dura); vascular coat (arachnoid and pia); nervous coat (CNS)
What makes up the fibrous coat?
the sclera and the cornea
What part of the fibrous coat is avascular?
the cornea
What is the sclera made of?
dense white CT
What is the uvea/ uveal tract?
the vascular coat
What is in the vascular coat?
the choroid plexus, the ciliary body and the iris
What two structures refract light?
The cornea and the lens
What structure controls a majority of the light refraction?
The cornea
What are the five layers of the cornea?
Epithelium; Bowmans basement membrane; Stroma; Descemets basement membrane; Endothelium
What type of histology is seen in the cornea?
The epithelial layer is stratified squamous; The endothelial layer is simple squamous, all non-keratinizing
What is a function of Bowmans membrane?
reduces the spread of infections. It also cannot regenerate
What two layers in the cornea control the passage of substances from the aqueous humor to the stroma?
The endothelial layer and Descemets basement membrane
Where are corneal epithelial stem cells located?
At the junction of the sclera and the cornea, called corneoscleral limbus
What are corneal stem cells called?
transient amplifying cells (TACs)
How is DNA protected from UV light in the cornea?
By nuclear ferritin
How does the lens receive nutrients?
diffusion from humor
How is the lens held in place?
zonule fibers from the ciliary body called suspensory ligaments
How is the resting convexity of the lens maintained?
outward pull of suspensory ligaments, inward pull by intrinsic elastic fibers
What is the lens capsule made of?
collagen IV and glycoprotein
How and where is the lens regenerated?
The germinal zone- new lens cells migrate to the mediel eye and lose nuclei
What is presbyobia and what is it caused by?
far sightedness- caused by loss of elasticity with age, so loss of resting convexity
What are cataracts caused by?
build-up of Fe or ROS causing damage to the lens and a los of opaqueness
Decreased convexity of the lens causes near or far vision?
far vision
Increased convexity of the lens causes near or far vision?
near vision
What muscle controls lens convexity? What is this process called?
ciliary bodies that control suspensory ligament tension, is called accomodation
When the ciliary muscle is relaxed, what is the shape of the lens? What type of objects are seen? (near/far?)
stretched out, thin; Distant objects are seen
When the ciliary muscle is tensed, what is the shape of the lens? What type of objects are seen? (near/far?)
smaller diameter lens, but is bulged posteriorly; near objects are seen
What is myopia? What is it caused by?
near-sightedness, caused by the eyeball being too long, so light focuses in front of the retina
What is hyperopia? What is it caused by?
far sightedness, caused by the eyeball being too short, so light focuses behind the retina
Do near or distant objects require greater refraction by the lens?
nearby objects (distant objects are close to parallel)
Where is the aqueous humor produced? Where does it drain?
the ciliary body, drains via the canal of Schlemm/scleral venous sinus
What are some causes of glaucoma?
blocked flow of aqueous humor through the canal of schlemm, adherence of the iris to the lens, too much production of aqueous humor.
What is glaucoma? What can result from glaucoma?
increased pressure in the anterior chamber of aqueous humor. Can cause intraocular pressure that can damage the optic nerve
What are three components of the IRIS?
striations of CT, blood vessels and smooth muscle
What are two muscles within the iris?
constrictor and dilator pupilae
Where is the melanin in the iris?
distributed throughout the stroma/CT layer, but highly concentrated in the pigmented posterior epithelial layer.
What determines eye color?
The distribution of melanin throughout the CT or lack thereof (melanin concentrated in the pigmented epithelium causes blue eye color)
What is Rayleigh scattering and how does it explain the blue sky?
shorter wavelengths of light are refracted more that longer wavelengths of light. blue light (shorter wavelength) gets refracted more, so we see it more often.
Why is melanin brown?
it absorbs blue and green colors, reflecting red/yellow/brown colors
What does the iris do?
Controls the aperture of the eye, thereby also controlling the range of focus
What two muscles are in the iris? What type of innervation controls them?
Sphincter pupillae (parasympathetic) and dilator pupillae (sympathetic)
A smaller pupil increases or decreases the range of focus?
Increase
A larger pupil size will increase or decrease the range of focus?
Decrease
What is the parasympathetic pathway of iris innervation?
Oculomotor nerve (CN3) –> parasympathetic ciliary ganglion on posterior eye, decreases pupil size
What is the sympathetic pathway of iris innervation?
Spinal cord–> superior cervical ganglion . Postganglionic nerves project along arteries to the iris
What three cranial nerves enter the superior orbital fissure?
CN III, IV and V
What are some things that can become ‘floaters’?
Hyaloid canal vestiges; age-related depolymerization of collagen, due to water loss the collagen can coagulate.
What is the vitreous body made of?
99% water; hyaluronic acid and type II collagen fibers
Where does the lens placode form?
Where the rostral neural tube contacts ectoderm.
What does the rostral part of the neural tube form?
The cerebral hemispheres and the eyes
Is the lens of the eye derived from neural tissue or ectoderm?
Ectoderm
What does the neural layer of the optic vesicle become?
Neurons and photoreceptors
What does the pigmented layer of the optic vesicle form?
The retinal pigment epithelium
What tissue types are the sclera and choroid derived from?
Embryonic meningeal tissues (mesoderm)
What surrounds the optic nerve?
Dura, arachnoid and pia mater
