Ear Anatomy and Histology Flashcards
Cutaneous innervation of the EAM
Superior part: CN VII
Anterior part: CN V (via auriculotemporal)
Posterior part: Great auricular (C3)
Inferior part: CN X (via Arnold N.)
Blood supply of the external ear:
Posterior auricular, superficial temporal (branches into anterior auricular arteries)
What type of epithelium lines the EAM
Keratinized stratified squamous epithelium (integument)
Draw the cutaneous innervation of the external ear:
Refer to drawings
Arnold Nerve:
Supplies innervation to the floor of the EAM. Branch of the the Vagus nerve which triggers the cough reflex
Which nerves are involved in the cough reflex?
Efferent: Vagus and Phrenic (diaphragm)
Afferent: Vagus N. (via Arnold N.)
Properties of the External acoustic meatus:
Outer 2/3 = soft connective tissue and cartilage
Inner 1/3 = just skin and bone (skin directly over the bone, no connective tissue etc., bleeds easily)
EAM has ceruminous glands, sebaceous glands and hair follicles
What type of epithelium line the outer and inner layers of the tympanic membrane?
Outer is stratified squamous, inner is simple cuboidal
Properties of the tympanic membrane:
Tip of the malleus is the umbo, section 2 has the cone of light
Has both flaccid and tense part, moves with sound and transmits signals to ossicles
Middle ear:
Location
Parts
Located at petrous part of the temporal bone
Tympanic cavity proper (mesotympanum)
Epitympanic recess (attic)
Walls of the tympanic cavity:
Roof: Tegmental wall Floor: Jugular wall Lateral: Membranous wall Medial: Labyrinthine wall Posterior: Mastoid wall
Draw the organization of the middle ear:
Refer to drawings
Pharyngotympanic tube:
Connects tympanic cavity with nasopharynx (back of throat)
Distal 2/3 is bony while the proximal 1/3 is cartilage (opposite of EAM)
Functions to equalize pressures (ear popping sensation)
Muscles that expand the PT:
Levator veli palatini - contracts longitudinally and pushes one wall
Tensor veli palatini - pulls the other wall of the PT
Pharyngotympanic tube is lined with ….
Pseudostratified epithileum
Auditory ossicles:
Malleus, incus and stapes
Connects the tympanic membrane to oval window
Short process of the incus connected to posterior wall. Base of stapes connected to oval window
Bony labyrinth and membranous labyrinth:
Separated by?
Bony: lined with endosteum
Membranous: made of small sacs of tubes, enclosed with epithelium
Perilymph
2 sections of the membranous labyrinth:
Cochlear duct (spiral part) Utricle (connected to the semicircular ducts) and saccule (connected to the cochlea)
Both contain sensory cells
Label the parts the bony and membranous labyrinth
Refer to drawings
Hair cells of the ear:
Sensory cells of the ear
Tallest one is the kinocilia
Hair cells are in the endolymph
Label the parts of the cochlea:
Refer to drawings
Organization of the cochlea
Each bud contains a scala vestibuli, media and tympani. Cochlear nerve innervates them (looks like a stem to each bud)
Parts of the cochlear duct:
Scala Media - endolymph
Scala vestibuli - perilymph, continuous with scala tympani
Scala tympani - perilymph, connects to round window
Draw the organization of the hair cells in the organ of corti
Refer to drawings
How do the hair cells send signals to the spiral ganglion?
Basilar membrane vibrates with sound causing deflection of stereocilia attached to tectorial membrane and opening of the K+ channels > sends info to the spiral ganglion cells
Function of the external ear:
Catches sound waves and directs them to EAM which transmits the sound waves to the tympanic membrane
Also spot to check temperature
Describe the function of middle ear:
Takes sound waves and turns it to physical movement. Sound waves move the TM > moves the ossicles > pushes the oval window.
Pressure in the middle ear (changes based on what happens to middle ear components) is equalized by the pharyngotympanic tube
Function of the inner ear:
Responsible for balance and taking external sound waves and transforming them to usable info for the brain
Describe the process of sound waves traveling in the inner ear:
Stapes moves the oval window > pressure forms in the perilymph of SV > distorts vestibular membrane > pressure wave in endolymph > displace the basilar membrane and distort the sterocilia of hair cells > pressure in perilymph transferred to scala tympani and exits via the round window
How do semicircular canals work?
Respond to rotation of the head
Cupulla (bulges at the base) have hair cells that bend with rotation > hair cells release neurotransmitters that trigger action potential > tells brain where head is turning
How do utricle/saccule work?
Respond to linear motion Have otoliths (little stone) that sit on top of hair cells and drag them in response to motion > generates neural activity
Utricle senses which way?
Saccule senses which way?
Forward (horizontal plane)
Upward (vertical plane)
What does depolarization and hyperpolarization do to the K+ channels?
Depolarization: opens channels
Hyperpolarization: closes channels
How do hair cells work?
Sterocilia movement to and away from kinocilia is perceived differently
Open K+ channels if directed towards tallest K+ channels
Could be targeted by antibiotics
Perilymph:
High Na, low K
Drains via the perilymphatic duct into the subarachnoid space
Originates from periosteum
Endolymph:
High K, low Na
Drains via the endolymphatic duct into venous sinuses
Cauliflower ear
Cause: perichondrium (supplies nutrients) sheared off the elastic cartilage causing hematoma and necrotic cartilage.
New cartilage tries to heal it and get new cartilage growth in the ear
Common in wrestlers
Tympanic membrane damage:
Usually due to trauma or medial ear pressure
Usually heals. Do not treat with gentamicin (targets the K+ channels)
Mastoiditis:
Infection of mastoid air cells in the inner ear which can spread into the cranial fossa via the petrosquamous cranial suture
Treated with abx
Otitis media:
Middle ear inflammation/infection resulting in pus formation.
Red and bulging TM
Untreated OM can impair hearing and scarring of auditory ossicles
Meniere’s syndrome and viral labyrinthitis:
Increase endolymph volume leading to abnormal signaling
Dizziness, vertigo, high pitched rushing or roaring sound (tinnitus) and fluctuating hearing loss
Conductive hearing loss:
Affects outer or middle ear
Fluid build up, otitis, excessive wax of otoscleosis
Sensorineural hearing loss:
Reduction in sound level due to inner ear or auditory nerve damage
Affects hearing at different frequencies
Age related, noise induced
Central hearing loss
Problems in CNS
