The Ear

Question 1

Divisions of the Ear

Answer 1

1. the external ear
2. the middle ear
3. the internal ear

Question 2

the external ear

Answer 2

composed of the auricle and the external auditory canal

Question 3

the auricle

Answer 3

has a core of elastic cartilage and is surrounded by a layer of thin skin
- has hair follicles and sebaceous glands within the skin layer
- a layer of perichondrium surrounds the elastic cartilage

Question 4

auricle histology

Answer 4

a darkly stained stratified squamous epithelium is present in histological images
the auricle contains skeletal muscle, but the skeletal muscle fibres have little function in humans

Question 5

the external auditory canal

Answer 5

supported by both the elastic cartilage and the temporal bone. the temporal bone supports the external auditory canal superiorly and inferiorly
- has ceruminous and sebaceous glands. the secretions from these glands create a golden-brown waxy material, called cerumen (earwax)

Question 6

glands in the external auditory canal

Answer 6

sebaceous and ceruminous glands
- they are modified coiled tubular sweat glands that open into the skin surface directly or into the hair follicles
- sebaceous glands vary in size and open into the hair follicles

Question 7

the middle ear

Answer 7

AKA tympanic cavity
separated from the external ear by the tympanic membrane
- lined by simple squamous epithelium. epithelium also lines the temporal bone that is covered by a very thin mucosa
- the bone of the middle ear cavity is lined by a mucosa composed of simple squamous epithelium, overlying a thin, vascular CT

Question 8

tympanic membrane layers

Answer 8

outer layer: stratified squamous epithelium
middle layer: dense CT
inner layer: simple low cuboidal or stratified squamous

Question 9

the middle ear is bound to:

Answer 9

bounded by the tympanic membrane laterally and the bony wall of the inner ear medially

Question 10

muscles of the middle ear

Answer 10

there are two small muscles that protect the tympanic membrane and ossicles from violent movements under noisy conditions
- the tensor tympani muscle

Question 11

tensor tympani muscle

Answer 11

pulls on the malleus, which increases the stiffness of the tympanic membrane and reduces amount of movement possible

Question 12

how sound is transferred from middle to inner ear

Answer 12

1. tympanic membrane to malleus, incus, and stapes: malleus transmits vibrations from the tympanic membrane to the incus, then to the stapes. the stapes is in the oval window between the middle ear and the vestibule of the inner ear
2. stapes to oval window: the stapes transmits the sound waves to the internal ear via the oval window. the inward movement of the stapes creates a pressure on the perilymph filling of the osseous labyrinth, initiating the responses in neural receptors of the cochlear duct
3. round window: medially, the ossicles communicate with the inner ear via the oval and round windows

Question 13

the inner ear

Answer 13

composed of an outer bony labyrinth and an inner membranous labyrinth

Question 14

the bony labyrinth

Answer 14

has 3 parts: the vestibule, the semicircular canals, and the cochlea
- these spaces are continuous with the temporal bone and are lined with periosteum
- the structures are filled with perilymph

Question 15

the membranous labyrinth

Answer 15

suspended within the bony labyrinth. a series of interconnected ducts and chambers filled with endolymph
- composed of epithelium and underlying CT
- contains the receptors for hearing and for vestibular senses

Question 16

bony labyrinth parts of corresponding membranous chambers

Answer 16

vestibule : utricle and saccule

semicircular canal : semicircular duct

cochlea : cochlear duct

Question 17

vestibule

Answer 17

a chamber in the petrous part of the temporal bone. contains 2 components of the membranous labyrinth: the utricle and the saccule, which are lined with low cuboidal epithelium
- located next to the middle ear, connected by the oval window

Question 18

utricle and saccule

Answer 18

the utricle is larger than the saccule
both the utricle and saccule possess a macula, which is a neuroepithelial receptor layer that functions to sense equilibrium
- each macula contains hair receptor cells that possess stereocilia embedded in a gelatinous layer. otoliths are suspended in this gel
- changes in position and linear motion displace the otoliths that sit on top of the gel. this movement distorts hair cells, which inhibits an impulse in CN VIII

Question 19

otoliths

Answer 19

calcium carbonate crystals

Question 20

semicircular canals

Answer 20

the three semicircular canals of the bony labyrinth are tubular spaces in the petrous portion of the temporal bone
- a semicircular duct occupies each canal, and the ducts are lined with low cuboidal epithelium
- canals open up into the utricle of the vestibule

Question 21

ampullae

Answer 21

regions of the semicircular canals that open into the utricle. Here, the semicircular ducts contain cristae ampullares, which are modified hair cells involved in sensing rotational motion
- each semicircular duct corresponds to one of the three possible rotational movements

Question 22

cristae ampullaris

Answer 22

a ridge like structure that functions similarly to the macula
- each ampullares is innervated by CN VIII fibres
- in the crista, the gel layer forms a cupula that extends across the ampulla to the opposite wall
- no otoliths in the crista

Question 23

cochlea

Answer 23

a spiral structure in the petrous part of the temporal bone
- contains the cochlear duct (scala media)

Question 24

cochlea divisions

Answer 24

the cochlear duct divides the cochlea into three divisions:
1. vestibular duct (scala vestibuli) above
2. cochlear duct (scala media) middle
3. tympanic duct (scala tympani) below
the tympanic and vestibular ducts communicate at the helicotrema at the apex of the cochlea

Question 25

modiolus

Answer 25

the bony central framework of the cochlea and resembles the core of a screw
- the ‘threads’ of the screw spiralling around the core are formed by the osseous spiral lamina, which is a thin bony process supporting the floor of the cochlear duct. laminae are wider at the base of the cochlea, narrower at the apex
- peripheral dendrites of CN VIII innervate the receptor cells located in the cochlear duct, then pass medially through the osseous spiral lamina to the spiral ganglion

the modiolus and spiral lamina provide a conduit for CN VIII

Question 26

cochlear duct membranes

Answer 26

the cochlear duct is filled with endolymph and it is separated from the perilymph on two sides by the vestibular (Reissner’s) membrane and the basilar membrane

Question 27

organ of Corti

Answer 27

found within the cochlear duct
responsible for transmitting sound waves and vibrations to the vestibulocochlear nerve (CNVIII) and on to the brain. lies on basilar membrane
- sound waves vibrate the basilar membrane, causing movement of hair cells on tectorial membrane

Question 28

Organ of Corti cell types

Answer 28

1. neuroepithelial (inner and outer hair cells
2. outer and inner phalangeal cells
3. piller cells
4. cells of Hensen/border cells

Question 29

process of hearing

Answer 29

1. sound wave moves from external ear to tympanic membrane
2. tympanic membrane moves, displacing ossicles
3. displacement of stapes causes pressure waves in perilymph of vestibular duct
4. pressure waves distort basilar membrane on their way to the round window
5. basilar membrane vibration causes hair cell vibrations against tectorial membrane
6. stimulation travels to CNS via CNVIII