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Eyebrows and eyelids
Eyebrows- protect from sun and sweating
- eyelids- also known as palpebrae, meet each other at lateral canthi. The medial canthus has the reddish lateral caruncle which gathers grit.
- They are supported internally by tarsal plates and is lifted by the levator palpebrae superioris.
- Tarsal glands are modified sebaceous glands located on tarsal plate which lubricate the eye (chalazion=infection)
- Ciliary glands for eyelashes (infection=sty)
- a protective mucus membrane that lines the inside of the palpebrae and white outer surface of the eye (never the cornea)
- conjunctivitis causes eyes to be red
Lacrimal Apparatus (Tears)
- superolateral of the orbit, the lacrimal gland creates tears which flow through excretory lacrimal ductules to the conjunctival sac. The tears drain from the lacrimal punctum, near the caruncle, to the lacrimal canals to the lacrimal sac. The nasolacrimal duct drains fluid into the nasal cavity
Extrinsic eye muscles (6)
Four rectus muscles orginate from the common tendinous ring: lateral
(moves eye superior and medially) and inferior
(moves inferior and medially) rectus muscles
- two oblique muscles:
- superior oblique muscle- sent through trochlea and depresses and turns eye laterally (down and out)
- inferior oblique- elevates and turns eye laterally (up and out)
The fibrous layer (Most external layer of eye)
- Two regions: Sclera and cornea
- Sclera: outermost tough white layer of the eye, 5/6 of the eye
- cornea:anterior 1/6 outer layer. a layer of dense connective tissue between corneal epithelium. bends and transmits light to lens
The vascular layer (middle layer of outer eye)
- choroid, ciliary body and iris
- Choroid: high vascular, darkened by melanocytes, continuous with --
- ciliary body: encircles and controls shape of the lens through suspended ligaments, ciliary zonules (suspensory ligament).
- iris "rainbow": colored, smooth muscle extension of the choroid that regulates amount of light let into the eye. This round opening is the pupil
The inner layer (inner most outer layer of the eye)
- retina and optic nerve
- retina: 2 layers. outer pigmented layer lies against choroid preventing scattered light and supports the neural layer
- Neural layer is thicker with photoreceptors. Photoreceptors receive light send message to bipolar cells, then to ganglion cells. Axons of ganglion cells form the optic nerve
Retina (regional specifications)
- in anterior eye, neural layer ends at ciliary body at a junction called ora serrata
- the macula lutea is at the posterior pole of the eye, and in the middle is the fovea centralis which has a concentration of cones whose concentration declines as you move away.
- The optic disc lies a few mm medial to the fovea, where the optic nerve exits the eye
internal chambers of the eye
Anterior chamber- located between the iris and the cornea filled with aqueous humor
posterior chamber- portion of the anterior segment between the iris and the lens (aqueous humor)
- vitreous chamber- posterior segment of the eye between the posterior lens and the retina (vitreous humor)
Fluids of the eye
- aqueous humor- similar to plasma, renewed continuously, provides intraocular pressure
- (glaucoma- aqueous humor builds up and increases intraocular pressure)
vitreous humor- viscous fluid that fills the vitreous chamber and provides intraocular pressure
The lens of the eye
biconvex disc that changes shape to alter the light entering the eye. focuses light onto the fovea centralis and other parts of the eye.
Cataract- is clouding of the lens
is what looks like the ear. It's shape is good at capturing sound waves
external acoustic meatus
- about 2.5 cm long, lined with hairs and ceruminous glands, directs sounds into the ear toward tympanic membrane
, the eardrum.
- inside the petrous part of the temporal bone. starts at the tympanic membrane which vibrates from sound.
- Passes sound to Auditory ossicles and then through to the vestibular (oval) window to the inner ear. Another hole inferior to oval window is the cochlear (round) window
- Bones of the middle ear that connect the tympanic membrane to the inner ear via the oval window
- Malleus: "hammer" lateral most bone that touches the tympanic membrane, has rounded head
- Incus: "anvil" middle ossicle, looks toothlike
- Stapes: "stirrup" looks like stirrup, most medial and attaches to oval window
Tubes and windows in middle ear
- Vestibular (oval) window: attaches stapes transferring sound to vestibular tract
- cochlear (round) window: inferior window membraneous partition between middle and inner ear
- Auditory tube (eustachian tube): joins tympanic cavity of middle ear to nasopharanx. can be opened to equalize pressure, but also can allow bacteria and viruses through.
tensor tympani muscle
- skeletal msucles that runs along auditory tube and inserts on malleus, protects hearing receptors from possible movements
The internal ear
- bony labyrinth- semicircular canals, vestibule and cochlea (filled with perilymph)
- membraneous labyrinth- semicircular ducts, urticle and saccule, cochlear duct (filled with endolymph)
- an enclosure in the inner ear between the cochlea and semicircular canals. oval window is in its walls.
- innervated by the vestibular nerve of the vestibucocohclear nerve, transmits impulse to balance the brain
- Spiral tube that attaches to the vestibule. 2.5 turns around a bone called modiolus which the cochlear nerve runs through.
- functional unit of hearing, spiral unit whose inner ear chamber is divided into three compartments (scala and duct)
- Located in the basalar part of the cochlear duct.
- branches from the vestibulocochlear cranial nerve from the organ of Corti which transmits impulses of hearing to the brain
- Scala vestibuli superior chamber of the cochlea that receives sound from the oval window. it is filled with perilymph fluid.
- Transmits sound up to the apex of the cochlea and down the scala tympani.
- located in between the scala vestibuli (separated by vestibular membrane) and tympani (separated by basilar membrane) in the cochlea. Filled with endolymph.
- Contains the spiral organ of Corti, which is the functional unit of hearing, works through cochlear hair cells (sound receptors) on the basilar membrane (anchored to tectorial membrane) which connect with the cochlear nerve.
- The most lateral part of the inner ear that connects to the oval window. Between the cochlea and the semicircular canals.
- Inside are utricle (continuous with the semicircular canals) and saccule (continuous with cochlea) both of which contain macula which are involved in equilibrium and linear acceleration
The semicircular canals
- receptors for the rotational acceleration of the head
- Three canals: anterior, posterior and lateral
Auditory and equilibrium pathways
Auditory: Cochlear nerve > cochlear nuclei > brain stem (superior olivary nuclei>lateral lemniscus>inferior collicus) > primary auditory cortex (temporal lobe)
- Equilibrium: vestibular nerve>brain stem (primarily reflex centers), minor pathway then sends to thalamus and inferior insula
Disorders of equilibrium and hearing
- Motion sickness: mismatch of sensory inputs
- Meniere's syndrome: excess endolymph, causes disturbed equilibrium
- Deafness: either conduction deafness or sensorneural deafness (loss of receptor hairs)