Head And Neck Session 6 Flashcards
In which part of the temporal bone are the cochlear and vestibular organs located?
Petrous part (Otic canal)
What provides venous drainage of the inner ear?
Labyrinthine vein into the sigmoid or inferior petrosal sinuses
What provides arterial supply to the bony labyrinth of the inner ear?
Anterior tympanic branch of the maxillary artery, petrosal branch of MMA and stylomastoid branch of the posterior auricular artery
What provides arterial supply to the membranous labyrinth of the inner ear?
Labyrinthine artery, a branch of the inferior cerebellar artery that divides into one cochlear branch and 2 vestibular branches
What are the components of the inner ear?
Cochlear and vestibular organs
What is the membranous labyrinth?
Series of communicating sacs and ducts that contain endolymph
What fluid is endolymph similar to?
ICF
Describe the structure of the utricles.
Contains 5 openings of semicircular ducts and communicates with the saccule via the utriculosaccular duct
Where is the macula of the utricle found?
In the floor, parallel to the base of the cranium
What covers the surface of the macula of the utricle and saccule?
Sensory epithelium with hair cells
What innervates the macula of the utricle and saccule?
Vestibular branch of CNVIII
What do hair cells of the macula of utricle and saccule and hair cells of the crest in the semicircular ducts stimulate?
Primary sensory neurons in the vestibular ganglion of the IAM
What makes the saccule continuous with the cochlear duct?
Ductus reuniens
Where is the macula of saccule located?
Vertically on medial wall
What is the function of the ampullary crest in the semicircular ducts?
Sense movement of endolymph
How is the cochlear duct secured in the inner ear?
Spiral ligament and osseous spiral lamina of modiolus
What is the spiral ligament?
Spiral thickening of the periosteal lining of the cochlear canal
What are the two canals formed by the triangular shape of the cochlear duct?
Scala vestibuli and scala tympani
Describe the passage of excess endolymph from the utricle to its storage reservoir.
Capillaries in membranous labyrinth –> utricle –> endolymphatic duct –> vestibular aqueduct –> endolymphatic sac
Where is the endolymphatic sac located?
Under dura mater on posterior petrous part of the temporal bone
What is Ménière’s disease?
Vertigo, low pitched tinnitus and hearing loss due to excess of endolymph causing progressive distension of ducts in inner ear
What forms the lateral wall of the cochlear duct?
Spiral ligament
What forms the roof of the cochlear duct?
Reissener’s membrane (vestibular membrane) between the cochlear duct and scala vestibuli
What forms the floor of the cochlear duct?
Basilar membrane
Where is the spiral organ of Corti (receptor of auditory stimuli) located?
In basilar membrane overlaid by gelatinous tectorial membrane
Describe the passage of a wave of hydraulic pressure through the inner ear.
Scala vestibuli –> helicotrema –> scala tympani –> secondary tympanic membrane –> tympanic cavity –> deformation of cochlear duct –> disrupted hair cells
What is the internal acoustic meatus?
~1 cm long canal in petrous part of temporal bone, opening in the posteromedial part of the bone in line with the EAM
What closes the IAM laterally?
Thin, perforated plate of bone
What enters the IAM via its lateral end?
CNVII, CNVIII and BV
What happens to CNVIII at the lateral end of the IAM?
Divides into cochlear and vestibular branches
Which fluid is found in the bony labyrinth of the middle ear?
Perilymph
Which fluid is similar to perilymph?
ECF
What is the bony labyrinth of the inner ear?
Fluid-filled space surrounded by Otic capsules
How does the bony labyrinth hold the membranous labyrinth?
Delicate filaments (like arachnoid mater) and spiral ligament
Describe the structure of the cochlea.
Starts at vestibule, makes 2.5 turns around the bony mediolus core to form and anterolateral cone shape
What is found at the base of the modiolus?
BV and branches of the cochlear nerve
What type of bone is the modiolus made up of?
Spongy
What does the cochlea have that is closed by the secondary tympanic membrane?
Round window
What is the vestibule of the inner ear?
Small oval chamber containing utricle, saccule and vestibular labyrinth
How is the vestibule of the inner ear continuous with the posterior cranial fossa?
Via vestibular aqueduct
How does the vestibule of the inner ear open posterolateral to the IAM in the posterior petrous part of the temporal bone?
Via vestibular aqueduct
What does the vestibule of the inner ear transmit?
Endolymphatic duct and 2 small BV
Describe the arrangement of the semicircular canals.
Anterior, posterior and lateral lie posterosuperior to the vestibule and at right angles to each other with bony swellings (ampulla) at one end
Why are there only 5 openings into the vestibule of the inner ear when there are three semicircular canals?
Anterior and posterior canals have one common limb
What are lodged within the semicircular canals to facilitate balance?
Semicircular ducts
What are the components of the middle ear?
Ossicles, muscles, eustaschian tube, mastoid air cells and CNVII