ANATOMY AND PHYSIOLOGY OF THE INNER EAR Flashcards
What are the two systems of the inner ear, and what do they control?
Auditory system (hearing) and Vestibular system (balance, equilibrium, and head movement).
Where is the labyrinth located?
In the petrous part of the temporal bone, medial to the middle ear.
What are the two main components of the labyrinth?
Bony labyrinth and membranous labyrinth.
What fluid is found in the bony labyrinth?
Perilymph.
What fluid is found in the membranous labyrinth?
Endolymph.
What are the three parts of the bony labyrinth?
Vestibule, semicircular canals, and cochlea.
What is the function of the vestibule in the bony labyrinth?
It contains the utricle and saccule and connects to the fenestra vestibuli and fenestra cochleae.
What are the three semicircular canals, and what do they contain?
Superior (anterior), posterior, and lateral canals; they contain semicircular ducts.
What is the cochlea responsible for?
Hearing.
What divides the bony cochlea into the scala vestibuli and scala tympani?
The cochlear duct.
What are the two sacs of the membranous labyrinth?
Utricle and saccule.
What ducts are part of the membranous labyrinth?
Three semicircular ducts and the cochlear duct.
What separates the perilymph of the scala vestibuli from the middle ear?
The base of the stapes at the fenestra vestibuli (oval window).
What separates the perilymph of the scala tympani from the middle ear?
The secondary tympanic membrane at the fenestra cochlea (round window).
What is the cochlea’s central core called, and what passes through it?
Modiolus; the cochlear nerve passes through it.
What is the helicotrema?
The apex of the cochlea where the scala vestibuli and scala tympani communicate.
Where is the organ of Corti located, and what is its function?
In the scala media; it is the neurosensory organ for hearing.
What fluid is found in the scala media, and what maintains its composition?
Endolymph; maintained by the stria vascularis.
What are the superior, inferior, and lateral borders of the scala media?
Superior: Reissner’s membrane; Inferior: Basilar membrane; Lateral: Spiral ligament/stria vascularis.
What are the differences between inner and outer hair cells?
Inner hair cells: 3,500 in one row, U-shaped stereocilia, passive transducers; Outer hair cells: 12,000 in three rows, V- or W-shaped stereocilia, active transducers.
What is the first relay station for auditory information in the central auditory pathway?
Cochlear nucleus at the pontomedullary junction.
What structure is responsible for binaural innervation and sound localization?
Superior olivary complex.
What are the primary functions of the lateral lemniscus?
Sound localization, processing, and the acoustic startle reflex pathway.
What part of the auditory pathway is located in the midbrain and receives input from lower and higher centers?
Inferior colliculus.
What is the role of the medial geniculate body?
It serves as the portal for all ascending auditory innervation to the auditory cortex.
Where is the primary auditory cortex located?
In the superior temporal lobe (Brodmann area 41).
What structure is involved in receptive language processing?
Wernicke’s area (Brodmann area 22).
What type of fluid is found in the scala vestibuli and scala tympani?
Perilymph.
What is the difference between endolymph and perilymph?
Endolymph: High K+, Low Na+, intracellular fluid; Perilymph: Low K+, High Na+, extracellular fluid.
What is the embryologic origin of the inner ear?
Ectoderm (otic placode > otic pit > otic vesicle).
At what age of gestation does the vestibular apparatus achieve its adult structure?
10th week AOG.
Which structure provides vascular supply and homeostasis to the scala media?
Stria vascularis.
What are the common diseases affecting the auditory system?
Noise-induced hearing loss, ototoxicity, and presbycusis.
What connects the perilymphatic fluid to the CSF?
The cochlear aqueduct.
What is the function of the reticular lamina in the cochlea?
It protects the organ of Corti from loud noises.
What causes Meniere’s disease?
Endolymphatic hydrops (excess endolymph).
Which structures contain the ampullae?
The semicircular ducts.
What is the main function of the vestibular system?
To detect head position and movement, and coordinate balance and equilibrium.
What are the primary functions of the inner hair cells?
To convert motion into electrical activity.
What is the importance of the basilar membrane’s variation in width and thickness?
It is responsive to high frequencies at the base and low frequencies at the apex.
What is the transition zone in the cochlear nerve, and why is it clinically important?
It is the site of origin for acoustic neuromas or vestibular schwannomas.
What are the main components of the central auditory pathway?
Cochlear nerve, cochlear nucleus, superior olivary complex, lateral lemniscus, inferior colliculus, medial geniculate body, and auditory cortex.
Where is the vestibular apparatus located?
Enclosed in the bony labyrinth of the petrous temporal bone.
What are the five sensory organs in the vestibular apparatus?
Three semicircular canals (anterior, lateral, posterior) and two otolith organs (utricle and saccule).
What type of movements do the semicircular canals detect?
Angular accelerations or rotations, such as head turns or looking up.
What type of movements do the otolith organs detect?
Linear accelerations, such as riding an elevator or a car.
What is the function of the utricle?
Detects linear accelerations in the horizontal plane.
What is the function of the saccule?
Detects linear accelerations in the vertical plane.
What connects the vestibule and cochlea?
The ductus reuniens.
What is the functional pairing of semicircular canals?
LARP (Left Anterior-Right Posterior) and RALP (Right Anterior-Left Posterior).
What is the crista ampullaris, and where is it located?
The organ for balance, found at the dilated ends (ampullae) of the semicircular canals.
What deflects the hair cells in the crista ampullaris?
Movement of the cupula and stereocilia during head rotations.
What is the primary difference between the maculae and crista ampullaris?
Maculae have otoconia on the utricle and saccule, while crista ampullaris does not.
What is the role of otoconia?
Calcium carbonate crystals in the maculae that detect gravity and linear acceleration.
What is the function of the cupula in the crista ampullaris?
It acts as a fluid-tight gelatinous structure that deflects hair cells during head movements.
What is benign paroxysmal positional vertigo (BPPV) caused by?
Displaced otoconia moving into the semicircular canals.
What are the two divisions of the vestibulocochlear nerve (CN VIII)?
Cochlear division and vestibular division.
What is the role of the Scarpa (vestibular) ganglion?
It provides afferent innervation to the cristae and maculae of the vestibular system.
What structures are supplied by the superior vestibular ganglion?
Utricle, superior semicircular canal, and horizontal semicircular canal.
What structures are supplied by the inferior vestibular ganglion?
Saccule and posterior semicircular canal.
What is the blood supply to the vestibular apparatus?
Labyrinthine artery, which branches into the anterior vestibular artery and common cochlear artery.
What does the anterior vestibular artery supply?
Utricle, superior semicircular canal, and horizontal semicircular canal.
What does the posterior vestibular artery supply?
Saccule and posterior semicircular canal.
What is the innervation of the horizontal crista?
Kinocilia are oriented closest to the utriculus.
What is the innervation of the vertical cristae?
Kinocilia are oriented farthest from the utriculus.
What are otoliths made of?
Calcium carbonate crystals ranging from 0.5 to 30 µm.
What happens if the specific gravity of the cupula differs from the endolymph?
It causes imbalance, potentially leading to nystagmus.
What structures extend beneath the dura of the posterior cranial fossa?
Endolymphatic duct and sac.
What is the orientation of the semicircular canals?
Orthogonal (at right angles to each other) to detect head rotation in any plane.
What is the function of the ductus reuniens?
It connects the vestibule and cochlea, allowing communication of endolymph.
What is the role of the otolithic membrane?
It holds otoconia and interacts with hair cells in the maculae during linear accelerations.
Which nerve exits through the stylomastoid foramen?
Facial nerve (CN VII).
Which nerve splits to supply the cochlea and vestibule?
Vestibulocochlear nerve (CN VIII).
What is the primary role of the maculae in the utricle and saccule?
To detect gravity and linear accelerations.
Why do children experience motion sickness more often than adults?
Their otoliths are more sensitive to linear accelerations due to incomplete development of vestibular compensation mechanisms.
What is the primary function of the vestibular system?
To detect head position and movement, and coordinate balance and equilibrium.
What is the significance of the labyrinthine artery?
It provides the primary blood supply to the vestibular and auditory systems.
What is the mnemonic ‘7up, Coke down’ used for?
To remember the relative positions of nerves in the internal auditory canal: 7 (facial nerve) is superior, and cochlear nerve is inferior.
What are the functional zones of the crista ampullaris?
Central (near apex) and peripheral (on slopes) zones, based on vestibular afferent innervation.
How is balance maintained during head movements?
The endolymph deflects the cupula, activating hair cells in the semicircular canals.
What is the role of the striola in the macula?
It divides the macula into regions and helps orient the hair cells.
What type of sensory cells are found in the mammalian labyrinth?
Type I and Type II sensory cells.
