Lecture 8 Eyes and Ears Flashcards
What are the three layers of the eyeball
Sclera, choroid, retina
What is the sclera
dense, white CT that the extrinsic muscles of the eye attach to
What is the cornea
Continuous with sclera, it is a clear protective layer over the anterior chamber
What part of the eye has the greatest refractive index
The cornea
What is the purpose of having different refractive indices in different parts of the eye
The goal is to bend the image so that it hits the best location for viewing
How does the sclera get nutrients
Because it is avascular, it derives nutrients from the aqueous humor via diffusion
Where is the caruncula lacrimalis
In the medial corner of the eye
What is the conjunctiva
Thin, clear mucus membrane that covers the anterior, external part of the eyes and lines the inner eyelids
What is the function of the conjuntiva
- It produces fluid that bathes the eye to keep it moist and nourished
- It contains MALT and secretes IgA!
What is the choroid
Layer of numerous anastomosing blood vessels
What are the two jobs of the ciliary body
- control lens 2. produce aqueous humor
What is the function of the iris
Control pupil size with the sphincter pupillae and dilator pupilla
What is the innervation of the sphincter pupillae and dilator pupillae
Sphincter pupillae has parasympathetic innervation from the Edinger-Westphal nucleus, and the dilator pupillae has sympathetic innervation from the superior cervical ganglion
What is the innervation of the cornea
Sensory innervation from the trigeminal nerve (CN V), Opthalmic branch (V1)
What are the layers of the cornea
Epithelium, collagen, and endothelium
What is a good test for corneal abrasions
Drop some fluorescein in their eye and then shine a black light. Abrasions will fluoresce green
What is the lens composed of
prismatic cells AKA lens fibers
What is accommodation
As things get closer to your face, the pupils narrow and the lens thickens to adjust the optical power and keep the object in focus
What are the Zonules of Zinn
Fibrous strands that connect the ciliary body to the lens
What is presbyopia
Changes in the elasticity of the lens that makes it harder to focus on objects close to the eye.
What is in the anterior chamber
Aqueous humor
What is aqueous humor
Ultra-filtrate of the blood similar to CSF
What is the function of the aqueous humor
Provides nutrients to cornea and assists in immune response
What is a common pathology involving the aqueous humor
If drainage slows or production is greatly increased, fluid and pressure can build up. In Glaucoma, blindness results from this process damaging the optic nerve
What is the retina composed of
Pigmented receptors and neurons and ganglion cells
What is seemingly inefficient about the retina
The receptors are pointed posteriorly so that light has to reflect off the pigmented epithelium before hitting the rods and cones
What is the macula lutea
Area with the highest density of cones
What is the fovea centralis
Pit in the center of the macula lutea
What is the function of cones
To detect color (red, blue, and green) and provide acute vision
What is the function of rods
The are more sensitive to light, provide peripheral vision, and do not respond to red light. This means you can use a red hued light to look at your secret battle plans at night without blinding yourself. Awesome.
What is an essential vitamin for both rods and cones
The vitamin A derivative: retinal
Are rods or cones more plentiful
Rod are more numerous. They have relatively fewer neurons tho, which accounts for why cones are responsible for acuity.
Why is optic ‘nerve’ a misnomer
Because it is really an extension of the brain, it should be called a tract
What surrounds the optic nerve
meninges
How far does the subarachnoid space extend
To the lamina cribrosa
<p>What kinds of cells surround the axons in the optic nerve</p>
<p>Astrocytes and oligodendrocytes</p>
What is papilledema
Increased CSF limits venous return from retina and causes edema under the optic disc
What types of proteins are in the vitreous body (humor)
hyaluronic acid and type II collagen fibrils
What is the function of the vitreous body
Keeps the shape of the eyeball and keeps the retina in place
What is the hyaloid canal
vestige of hyaloid artery used to nourish embryonic lens
What causes ‘floaters’
blood and cell debris that is too large to be cleared by phagocytes
What are the four steps of the visual pathway
- light hitting the retina is transformed into nerve impulses by rods and cones
- impulses travel through optic nerve to optic chiasm
- signals travel to lateral geniculate body of the thalamus
- signals travel through the optic radiations to the primary visual cortex of the occipital lobes
What does the Abducens Nerve (CN VI) innervate
Lateralis rectis
What does the troclear nerve (CN IV) innervate
superior oblique
What is the action of the suerior oblique
internally rotates, depresses and abducts the eye (down and out)
What are the structures of the outer ear
pinna and auditory meatus (so designed to funnel sound to the tympanic membrane)
What is earwax (cerumen)
Secretion from modified sebaceous glands that protects the ear from irritation and infection
What are the ossicles
Malleus, incus, and stapes
What types of articulations are between the ossicles
Synovial!
What are the muscles of the middle ear
tensor tympani attaches to the malleus and stapedius attaches to the stapes. Both contract to reduce movement of the ossicles
What innervates the inner ear
vestibulocochlear nerve
How does sound transfer from the middle to the inner ear
movement of the stapes at the oval window moves the perilymph in the scala vestibuli
What is perilymph and where is it found
filtrate with a high sodium content in the scala vestibuli
What is endolymph and where is it found
filtrate with high potassium content in the scala media (cochlear duct)
Where is the organ of Corti located
In the cochlear duct along its entire length
How are waves in the perilymph converted to electric signals
Movements in the perilymph vibrate the endolymph, basilar membrane and organ of corti. Hair cells in the organ of Corti are moved which starts an AP
How does the ear perceive different pitches
The basilar membrane is thick and stiff near the oval window and becomes more flexible further down the cochlea and is thus affected by lower pitches further away
What nerve transmits impulses from the ear
The cochlear division of the vestibulocochlear nerve
What is the order of structures auditory nerve impulses go through
- cochlear nucleus 2. superior olivary nucleus 3. inferior colliculus 4. thalamus 5. primary auditory cortex (in the temporal lobe)
What coordinates nerve impulses from both ears
The inferior colliculus processes information from both ears to determine location of sound
What are some components of balance
Visual system (see the ground), pressure and proprioception (feel the ground under your feet), and vestibular
What are the 3 parts of the vestibule
saccule, utricle, and 3 semicircular canals all filled with endolymph
how does the vestibular system work
Hair cells generate nerve impulses when moved by gravity or motions of the head
What are otoliths
Crystalline structures composed of gelatinous matrix and calcium carbonate on the tips of hair cells that amplifies the effects of gravity or motion (makes them top heavy). For detecting linear acceleration and found only in the utricle or saccule.
What are the semicircular canals composed of
They are bone lined with periosteum and containing endolymph
How are the semicircular canals arranged
In such away that they correspond to the 3 dimensions of space (x, y, and z)
What are the ampullae
enlargement at the base of each semicircular canal
What is the function of the ampullae
Sense rotational movement with the semicircular canals
What is BPPV
Benign paroxysmal positional vertigo is a condition in which the patient is overcome by a sudden sensation of spinning
What causes BPPV
Thought to be from an otolith from a utricle or saccule that entered the semicircular canals and activates the hair cells
How is BPPV diagnosed
Patient history and Dix-Hallpike maneuver
How is BPPV treated
Epley maneuver or Semont maneuver
