Eye and Ear Flashcards
Which embryonic layer forms the structures of the eye (specifically cornea and lens)?
Surface ectoderm
What 3 things make up the whole “eye”?
-Ocular bulb (eyeball)
-Adnexa (stuff around it)
-CNS (vison processing)
What occurs during eye formation/induction?
A brain outgrowth (optic vesicle then becomes optic cup) induces ectoderm to form lens placode/vesicle. The lens placode/vesicle then induces ectoderm to form the cornea
What structures does neural ectoderm form in the eye?
Optic nerve and retina
What is the difference between the visual axis and the optic axis?
Visual Axis: receives the most precise amount of light (a lil slanted)
Optic Axis: The horizontal axis of the eyeball
What structures make up the outer fibrous tunic?
Sclera and cornea
What structures make up the middle vascular tunic (aka uvea)?
-Choroid
-Ciliary body
-Iris
-Lens (AVASCULAR)
Which structure makes up the inner nervous tunic?
Retina
What is the ora serrata?
The junction between where there are photoreceptors and where there aren’t
What is the area called between the sclera and the cornea?
Limbus
What is the cribiform area and what is it continuous with?
The cribiform area is where the axons of the retina pass into the optic nerve (CN2). Its continuous with the dura mater of CN2
How is the cornea transparent?
Lamellar collagen is oriented at 90 degrees
Which layer contains the tapetum lucidem in some animals?
The choroid. It sits behind the retina and sends like back to increase photoreceptor stimulation
What is a ciliary body?
A choroid thickening with smooth muscle and zonular fibers that suspend the lens and allow for accommodation (focus light on retina)
What are the two muscles in the iris and what do they do?
Sphincter (concentric) muscle that contracts and makes pupil smaller.
Dilator (radial) muscle that contracts and makes pupil bigger.
Which cells in the retina send axons to CN2 through the cribiform area in the sclera?
Ganglionic cells
What is the macula/fovea?
The area of highest visual acuity, densest concentration of receptor cells, defines the visual axis
Which structures refract light?
-Cornea
-Lens
-Aqueous humor in anterior chamber
-Vitreous humor in posterior chamber
What is aqueous humor?
Fluid in the anterior chamber that is produced by the ciliary bodies and continuously replaced. Provides pressure, nutrition, and refraction.
What does aqueous humor drain through?
A venous plexus
What is vitreous humor?
Jelly-like stuff in the posterior chamber. It doesn’t get replaced, holds the retina in place, and refracts light
What 3 structures make up the eye socket?
-Bony orbit
-Fascia
-Ocular fat
What kind of structures are included in the fascia of the eye socket?
-Periorbita (fibrous, continuours with orbit bone periosteum)
-Superficial muscular (levator palpebri, lacrimal gland, fat)
-Deep muscular (ocular muscles, fat)
What is the function of having ocular fat?
Padding, allows for easy movement of eyeball
What are the extraocular muscles?
-Dorsal, ventral, medial, and lateral rectus muscles
-Dorsal and ventral oblique muscles
-Retractor bulbi
What are the dorsal and ventral oblique eye muscles deflected around?
Deflected around trochlea in orbit.
What is the function of the extraocular oblique muscles?
Compensate for rotation caused by rectus muscles and axial rotation (visual axis and cone axis aren’t aligned)
What does the retractor bulbi muscle do?
Pulls eyeball caudally into socket
Where do all the extraocular muscles originate? (except for ventral oblique)
At the apex of the bony orbit near orbital fissure
Where does the ventral oblique muscle originate?
From the medial wall of the orbit
What are the 3 layers of the palpebrae (eyelids)?
-Outer skin
-Middle musculofibrous
-Inner mucous membrane (conjunctiva)
What structures are included in the middle musculofibrous layer of the eyelids?
-Orbicularis oculi
-Levator palpebri
-Tarsus and tarsus glands
What is the conjunctiva?
A continuous membrane between lids and bulb that meet at the fornices
What is the nictitating membrane (conjunctival fold)?
A third eyelid in animals, supported by cartilage and closes when the outer eyelids close
Where is the lacrimal gland located and what does it do?
Located dorsolaterally to eye, produces aqueous fluid (tears)
What are the holes called that tears drain into?
Puncta lacrimalia
Which duct to tears drain into?
Nasolacrimal duct and evaporate in nasal cavity
What does tear film contain?
A fatty film from the tarsal glands and mucous from goblet cells in conjunctiva
Which artery supplies blood to the eye and its adnexa?
External opthalmic artery
Which artery does the external opthalmic artery branch from?
Maxillary artery
What do the ciliary arteries supply blood to?
Retina
Choroid
Ciliary body
Iris
What is the path of venous drainage in the eye?
From vorticose veins into the superior and inferior opthalmic veins, then to cavernous sinus/pterygoid plexus
How many cranial nerves innervate the eye?
6 (CN2-7)
What type of nerve is CN2 (optic) and what does it innervate?
SSA.
Sensory input to brain
What type of nerve is CN3 (oculomotor) and what does it innervate?
SE, VE.
D, V, M recti
V oblique
retractor bulbi
levator palpebri
Ciliary body
Iris sphincter and dilator
What type of nerve is CN4 (trochlear) and what does it innervate?
SE.
Dorsal oblique
What type of nerve is CN5 (trigeminal) and what does it innervate?
SA.
Opthalmic branch: Long ciliary, lacrimal, supraorbital nn.
Maxillary branch: Zygomatic (to lower eyelid)
What type of nerve is CN6 (abducens) and what does it innervate?
SE.
Lateral rectus
Retractor bulbi
What type of nerve is CN7 (facial) and what does it innervate?
SE.
Auriculopalpebral nn. to orbicularis oculi
What does having eyes on the front of the head improve?
Stereoscopic vision (depth perception).
Better for predators
What does having eyes on the side of the head improve?
Field of vision. Seen in prey species
Which cranial nerve supplies the ear structures?
CN8 (vestibulocochlear)
What does the vestibule part of the vestibulocochlear organ do?
Perception of position and movement of head and body in space
What does the cochlear part of the vestibulocochlear organ do?
Perception of sound (hearing)
What are the 3 parts that make up the ear?
External ear
Middle ear
Internal ear
What structures make up the external ear?
-Auricle (pinna)
-External auditory meatus
-Tympanic membrane
What structures make up the middle ear?
-Tympanic cavity
-Auditory ossicles
-Auditory (eustachian tube)
What structures make up the internal ear?
-Vestibular apparatus
-Cochlea
What is the internal ear contained within?
Petrous temporal
Which parts of the ear are involved in hearing and which parts are involved in balance?
Hearing: external, middle and internal
Balance: Internal only
What are the functions of the auricle?
-Receives and directs soundwaves through meatus towards tympanic membrane
-Protects ear canal and tympanic membrane
How can auricles be independently mobile?
If cartilage and auricular muscles are sufficient (from auriculopalpebral branch of CN7)
What are features of the external acoustic meatus?
-Long and curved
-Distal cartilaginous part (long)
-Proximal osseous part (short)
What epithelium is the external acoustic meatus lined with and what do the glands in it produce?
Lined with stratified squamous epithelium. Sebaceous glands produce cerumen (earwax)
What are the 3 histologic layers of the tympanic membrane?
1) Outer epithelial lining
2) Connective tissue with collagen and elastic fibres (tympanic ring)
3) Inner mucous membrane towards tympanic cavity
Which ossicle inserts on the tympanic membrane?
Malleus
What is the function of the tympanic membrane?
Transmission of sound waves from air to auditory ossicles (mechanical vibration)
What structures are in the dorsal part of the tympanic cavity?
Auditory ossicles
Tensor tympani m.
Stapedius m.
What structures are in the middle part of the tympanic cavity?
Tympanic membrane
Eustachian tube
What structures are in the ventral part of the tympanic cavity?
Tympanic bulla
What are the 4 fenestrae in the tympanic cavity?
-Tympanic membrane
-Oval window
-Round window
-Eustachian tube opening
Which muscle inserts on the malleus?
Tensor tympani
Which muscle inserts on the stapes?
Stapedius
What is the function of the tensor tympani m. and stapedius m.?
Adjust tension, modulate vibration, dampen internal sounds (like chewing)
Which part of the malleus is embedded in the tympanic membrane?
Manubrium (handle)
Which part of the stapes is attached to the vestibular (oval) window?
The footplate
Why are the middle ear ossicles important?
They magnify soundwave energy by >20x and initiate the wave in endolymph of inner ear
What is the function of the eustachian tube?
Connect nasopharynx and tympanic cavity for pressure equalization (when u open mouth to pop ears)
What type of fluid is the bony labyrinth filled with?
Perilymphatic fluid
What type of fluid is the membranous labyrinth filled with?
Endolymphatic fluid
Which of the two inner ear fluids is responsible for stimulating receptor cells?
Endolymphatic fluid
How many semicircular canals does the vestibular organ have and how are they oriented?
3 semicircular ducts WITHIN semicircular canals.
There’s anterior, posterior, and lateral oriented at 90 degrees from each other
Which structures in the semicircular canals contain sensory receptors (hair things) for movement of endolymphatic fluid?
Ampullae (near the utriculus)
What are maculae?
Structures in the utriculus/sacculus that contain statoconia (otoliths) and stimulate sensory cells when head is moved
Which structures make up the cochlea?
-Spiral canal
-Modiolus
-Spiral lamina
-Cochlear duct
*Pls look at diagrams of cochlea i do not know how to describe this thing srry
Which part of the cochlea contains receptors?
Cochlear duct
What are the two chambers of the cochlea?
Scala vestibuli (SV)
Scala tympani (ST)
What separates the SV and the ST?
Cochlear duct, spiral lamina, and spiral membrane
What kind of fluid are the SV and ST filled with?
Perilymphatic fluid
What is the helicotrema?
The apex of the spiral canal where the SV and ST connect
What type of fluid is in the cochlear duct?
Endolymphatic fluid
Which cochlear chamber communicates with the oval (vestibular) window?
Scala vestibuli
Which cochlear chamber communicates with the round window?
Scala tympani
Which direction does fluid movement in the cochlea always move in?
From SV to ST
What is the membrane called that the waves in the SV move?
The spiral (Reissner) membrane
How do waves in the SV get transmitted to receptor cells?
The waves in the SV move the spiral (Reissner) membrane, which displaces the endolymph in the cochlear duct and the basilar membrane, which contains the receptor cells
What is the organ of Corti?
The receptor cells of the cochlea that get stimulated
What is the receptor cell impulse communicated to?
Spiral ganglion in spiral canal of modiolus and onto CN8
Which area of the cochlea responds to lower frequencies?
Farther up sections (if that makes sense)
Which area of the cochlea responds to higher frequencies?
The closer sections
What is another name for the round window?
Cochlear fenestra
