The Ear Flashcards
Divisions of the Ear
- the external ear
- the middle ear
- the internal ear
the external ear
composed of the auricle and the external auditory canal
the auricle
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
auricle histology
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
the external auditory canal
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)
glands in the external auditory canal
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
the middle ear
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
tympanic membrane layers
outer layer: stratified squamous epithelium
middle layer: dense CT
inner layer: simple low cuboidal or stratified squamous
the middle ear is bound to:
bounded by the tympanic membrane laterally and the bony wall of the inner ear medially
muscles of the middle ear
there are two small muscles that protect the tympanic membrane and ossicles from violent movements under noisy conditions
- the tensor tympani muscle
tensor tympani muscle
pulls on the malleus, which increases the stiffness of the tympanic membrane and reduces amount of movement possible
how sound is transferred from middle to inner ear
- 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
- 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
- round window: medially, the ossicles communicate with the inner ear via the oval and round windows
the inner ear
composed of an outer bony labyrinth and an inner membranous labyrinth
the bony labyrinth
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
the membranous labyrinth
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
bony labyrinth parts of corresponding membranous chambers
vestibule : utricle and saccule
semicircular canal : semicircular duct
cochlea : cochlear duct
vestibule
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
utricle and saccule
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
otoliths
calcium carbonate crystals
semicircular canals
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
ampullae
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
cristae ampullaris
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
cochlea
a spiral structure in the petrous part of the temporal bone
- contains the cochlear duct (scala media)
cochlea divisions
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
modiolus
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
cochlear duct membranes
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
organ of Corti
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
Organ of Corti cell types
- neuroepithelial (inner and outer hair cells
- outer and inner phalangeal cells
- piller cells
- cells of Hensen/border cells
process of hearing
- sound wave moves from external ear to tympanic membrane
- tympanic membrane moves, displacing ossicles
- displacement of stapes causes pressure waves in perilymph of vestibular duct
- pressure waves distort basilar membrane on their way to the round window
- basilar membrane vibration causes hair cell vibrations against tectorial membrane
- stimulation travels to CNS via CNVIII
