ANATOMY AND PHYSIOLOGY OF THE INNER EAR

Question 1

What are the two systems of the inner ear, and what do they control?

Answer 1

Auditory system (hearing) and Vestibular system (balance, equilibrium, and head movement).

Question 2

Where is the labyrinth located?

Answer 2

In the petrous part of the temporal bone, medial to the middle ear.

Question 3

What are the two main components of the labyrinth?

Answer 3

Bony labyrinth and membranous labyrinth.

Question 4

What fluid is found in the bony labyrinth?

Answer 4

Perilymph.

Question 5

What fluid is found in the membranous labyrinth?

Answer 5

Endolymph.

Question 6

What are the three parts of the bony labyrinth?

Answer 6

Vestibule, semicircular canals, and cochlea.

Question 7

What is the function of the vestibule in the bony labyrinth?

Answer 7

It contains the utricle and saccule and connects to the fenestra vestibuli and fenestra cochleae.

Question 8

What are the three semicircular canals, and what do they contain?

Answer 8

Superior (anterior), posterior, and lateral canals; they contain semicircular ducts.

Question 9

What is the cochlea responsible for?

Answer 9

Hearing.

Question 10

What divides the bony cochlea into the scala vestibuli and scala tympani?

Answer 10

The cochlear duct.

Question 11

What are the two sacs of the membranous labyrinth?

Answer 11

Utricle and saccule.

Question 12

What ducts are part of the membranous labyrinth?

Answer 12

Three semicircular ducts and the cochlear duct.

Question 13

What separates the perilymph of the scala vestibuli from the middle ear?

Answer 13

The base of the stapes at the fenestra vestibuli (oval window).

Question 14

What separates the perilymph of the scala tympani from the middle ear?

Answer 14

The secondary tympanic membrane at the fenestra cochlea (round window).

Question 15

What is the cochlea’s central core called, and what passes through it?

Answer 15

Modiolus; the cochlear nerve passes through it.

Question 16

What is the helicotrema?

Answer 16

The apex of the cochlea where the scala vestibuli and scala tympani communicate.

Question 17

Where is the organ of Corti located, and what is its function?

Answer 17

In the scala media; it is the neurosensory organ for hearing.

Question 18

What fluid is found in the scala media, and what maintains its composition?

Answer 18

Endolymph; maintained by the stria vascularis.

Question 19

What are the superior, inferior, and lateral borders of the scala media?

Answer 19

Superior: Reissner’s membrane; Inferior: Basilar membrane; Lateral: Spiral ligament/stria vascularis.

Question 20

What are the differences between inner and outer hair cells?

Answer 20

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.

Question 21

What is the first relay station for auditory information in the central auditory pathway?

Answer 21

Cochlear nucleus at the pontomedullary junction.

Question 22

What structure is responsible for binaural innervation and sound localization?

Answer 22

Superior olivary complex.

Question 23

What are the primary functions of the lateral lemniscus?

Answer 23

Sound localization, processing, and the acoustic startle reflex pathway.

Question 24

What part of the auditory pathway is located in the midbrain and receives input from lower and higher centers?

Answer 24

Inferior colliculus.

Question 25

What is the role of the medial geniculate body?

Answer 25

It serves as the portal for all ascending auditory innervation to the auditory cortex.

Question 26

Where is the primary auditory cortex located?

Answer 26

In the superior temporal lobe (Brodmann area 41).

Question 27

What structure is involved in receptive language processing?

Answer 27

Wernicke's area (Brodmann area 22).

Question 28

What type of fluid is found in the scala vestibuli and scala tympani?

Answer 28

Perilymph.

Question 29

What is the difference between endolymph and perilymph?

Answer 29

Endolymph: High K+, Low Na+, intracellular fluid; Perilymph: Low K+, High Na+, extracellular fluid.

Question 30

What is the embryologic origin of the inner ear?

Answer 30

Ectoderm (otic placode > otic pit > otic vesicle).

Question 31

At what age of gestation does the vestibular apparatus achieve its adult structure?

Answer 31

10th week AOG.

Question 32

Which structure provides vascular supply and homeostasis to the scala media?

Answer 32

Stria vascularis.

Question 33

What are the common diseases affecting the auditory system?

Answer 33

Noise-induced hearing loss, ototoxicity, and presbycusis.

Question 34

What connects the perilymphatic fluid to the CSF?

Answer 34

The cochlear aqueduct.

Question 35

What is the function of the reticular lamina in the cochlea?

Answer 35

It protects the organ of Corti from loud noises.

Question 36

What causes Meniere's disease?

Answer 36

Endolymphatic hydrops (excess endolymph).

Question 37

Which structures contain the ampullae?

Answer 37

The semicircular ducts.

Question 38

What is the main function of the vestibular system?

Answer 38

To detect head position and movement, and coordinate balance and equilibrium.

Question 39

What are the primary functions of the inner hair cells?

Answer 39

To convert motion into electrical activity.

Question 40

What is the importance of the basilar membrane's variation in width and thickness?

Answer 40

It is responsive to high frequencies at the base and low frequencies at the apex.

Question 41

What is the transition zone in the cochlear nerve, and why is it clinically important?

Answer 41

It is the site of origin for acoustic neuromas or vestibular schwannomas.

Question 42

What are the main components of the central auditory pathway?

Answer 42

Cochlear nerve, cochlear nucleus, superior olivary complex, lateral lemniscus, inferior colliculus, medial geniculate body, and auditory cortex.

Question 43

Where is the vestibular apparatus located?

Answer 43

Enclosed in the bony labyrinth of the petrous temporal bone.

Question 44

What are the five sensory organs in the vestibular apparatus?

Answer 44

Three semicircular canals (anterior, lateral, posterior) and two otolith organs (utricle and saccule).

Question 45

What type of movements do the semicircular canals detect?

Answer 45

Angular accelerations or rotations, such as head turns or looking up.

Question 46

What type of movements do the otolith organs detect?

Answer 46

Linear accelerations, such as riding an elevator or a car.

Question 47

What is the function of the utricle?

Answer 47

Detects linear accelerations in the horizontal plane.

Question 48

What is the function of the saccule?

Answer 48

Detects linear accelerations in the vertical plane.

Question 49

What connects the vestibule and cochlea?

Answer 49

The ductus reuniens.

Question 50

What is the functional pairing of semicircular canals?

Answer 50

LARP (Left Anterior-Right Posterior) and RALP (Right Anterior-Left Posterior).

Question 51

What is the crista ampullaris, and where is it located?

Answer 51

The organ for balance, found at the dilated ends (ampullae) of the semicircular canals.

Question 52

What deflects the hair cells in the crista ampullaris?

Answer 52

Movement of the cupula and stereocilia during head rotations.

Question 53

What is the primary difference between the maculae and crista ampullaris?

Answer 53

Maculae have otoconia on the utricle and saccule, while crista ampullaris does not.

Question 54

What is the role of otoconia?

Answer 54

Calcium carbonate crystals in the maculae that detect gravity and linear acceleration.

Question 55

What is the function of the cupula in the crista ampullaris?

Answer 55

It acts as a fluid-tight gelatinous structure that deflects hair cells during head movements.

Question 56

What is benign paroxysmal positional vertigo (BPPV) caused by?

Answer 56

Displaced otoconia moving into the semicircular canals.

Question 57

What are the two divisions of the vestibulocochlear nerve (CN VIII)?

Answer 57

Cochlear division and vestibular division.

Question 58

What is the role of the Scarpa (vestibular) ganglion?

Answer 58

It provides afferent innervation to the cristae and maculae of the vestibular system.

Question 59

What structures are supplied by the superior vestibular ganglion?

Answer 59

Utricle, superior semicircular canal, and horizontal semicircular canal.

Question 60

What structures are supplied by the inferior vestibular ganglion?

Answer 60

Saccule and posterior semicircular canal.

Question 61

What is the blood supply to the vestibular apparatus?

Answer 61

Labyrinthine artery, which branches into the anterior vestibular artery and common cochlear artery.

Question 62

What does the anterior vestibular artery supply?

Answer 62

Utricle, superior semicircular canal, and horizontal semicircular canal.

Question 63

What does the posterior vestibular artery supply?

Answer 63

Saccule and posterior semicircular canal.

Question 64

What is the innervation of the horizontal crista?

Answer 64

Kinocilia are oriented closest to the utriculus.

Question 65

What is the innervation of the vertical cristae?

Answer 65

Kinocilia are oriented farthest from the utriculus.

Question 66

What are otoliths made of?

Answer 66

Calcium carbonate crystals ranging from 0.5 to 30 µm.

Question 67

What happens if the specific gravity of the cupula differs from the endolymph?

Answer 67

It causes imbalance, potentially leading to nystagmus.

Question 68

What structures extend beneath the dura of the posterior cranial fossa?

Answer 68

Endolymphatic duct and sac.

Question 69

What is the orientation of the semicircular canals?

Answer 69

Orthogonal (at right angles to each other) to detect head rotation in any plane.

Question 70

What is the function of the ductus reuniens?

Answer 70

It connects the vestibule and cochlea, allowing communication of endolymph.

Question 71

What is the role of the otolithic membrane?

Answer 71

It holds otoconia and interacts with hair cells in the maculae during linear accelerations.

Question 72

Which nerve exits through the stylomastoid foramen?

Answer 72

Facial nerve (CN VII).

Question 73

Which nerve splits to supply the cochlea and vestibule?

Answer 73

Vestibulocochlear nerve (CN VIII).

Question 74

What is the primary role of the maculae in the utricle and saccule?

Answer 74

To detect gravity and linear accelerations.

Question 75

Why do children experience motion sickness more often than adults?

Answer 75

Their otoliths are more sensitive to linear accelerations due to incomplete development of vestibular compensation mechanisms.

Question 76

What is the primary function of the vestibular system?

Answer 76

To detect head position and movement, and coordinate balance and equilibrium.

Question 77

What is the significance of the labyrinthine artery?

Answer 77

It provides the primary blood supply to the vestibular and auditory systems.

Question 78

What is the mnemonic '7up, Coke down' used for?

Answer 78

To remember the relative positions of nerves in the internal auditory canal: 7 (facial nerve) is superior, and cochlear nerve is inferior.

Question 79

What are the functional zones of the crista ampullaris?

Answer 79

Central (near apex) and peripheral (on slopes) zones, based on vestibular afferent innervation.

Question 80

How is balance maintained during head movements?

Answer 80

The endolymph deflects the cupula, activating hair cells in the semicircular canals.

Question 81

What is the role of the striola in the macula?

Answer 81

It divides the macula into regions and helps orient the hair cells.

Question 82

What type of sensory cells are found in the mammalian labyrinth?

Answer 82

Type I and Type II sensory cells.