Ear Flashcards
What are the two functions of the ear?
Hearing and balance
“receptors turn sound, movements of the head and the body’s response to gravity into an electrical energy”
What is the function of the auricle?
Sound localization and amplification
Describe the skin of the auricle.
Think skin with hair follicles, sweat, and sebaceous glands
Does the external acoustic meatus have sweat glands?
NO
It is lined with thin skin and ceruminous glands
What does cerumen contain?
Cerumen contains desquamated skin cells, secretions from sebaceous and ceruminous glands
The lateral 1/3 of the external acoustic meatus is ________ and the medial 2/3 is ___________.
lateral 1/3 = cartilage
medial 2/3 = temporal bone
What is the significance of fibroblasts in the intermediate layer of the tympanic membrane?
you can regrow the tympanic membrane
Describe the external surface of the tympanic membrane.
thin epidermis
Describe the intermediate layer of the tympanic membrane.
- collagen and elastic fibers arranged radially and circularly with fibroblasts
Describe the internal surface of the tympanic membrane.
- Simple squamous to simple cuboidal epithelium
- Mucous membrane of the middle ear cavity
What are the two functions of the middle ear?
1) Convert sound waves into mechanical vibrations
2) Transmit vibrations to the internal ear
What is the lining of the middle ear?
simple squamous epithelium
-also on the surface of the ossicles
Loss of function of the middle ear results in what?
Conductive hearing loss
What are the three ossicles?
1) Malleus (hammer)
2) Incus (anvil)
3) Stapes (stirrup)
Within what bone are all the ossicles located?
Petrous portion of the temporal bone
The tensor tympani is connected to which ossicle? What is its function?
Malleus
Functions to increase the tension of the tympanic membrane (CN V)
The stapedius is connected to which ossicle? What is its function?
Stapes
Dampens movement of the stapes on the oval window (CN VII)
What is the attenuation reflex? What muscles are involved?
Reflex that protects the internal ear form damaging loud sounds
Tensor tympani and stapedius
What is otosclerosis?
Bone remodeling causes the stapes to be fixed onto the oval window
What structure is associated with otitis media?
Auditory (eustachian) tube
What structures does the auditory/eustachian tube connect?
Connects the middle ear cavity to the nasopharynx
What type of cells line the eustachian tube?
Transitions from simple squamous epithelium to pseudostratified columnar epithelium with goblet cells
What is the function of the eustachian tube?
Equalize pressure in the middle ear with atmospheric pressure
Where are mastoid air cells located?
Within the mastoid process of temporal bone
What type of cell lines the mastoid air cells?
simple squamous epithelium
Which structure am I describing: “a membranous labyrinth, series of sacs and tubules, suspended within a bony labyrinth”
The internal ear
What is the fluid filled space within the membranous labyrinth called?
Endolymphatic space
What is the ion composition of endolymph?
High K, Low Na
What is the fluid filled space between the membranous labyrinth and bony labyrinth called?
Perilymphatic space
What is the ion composition of perilymph?
High Na, Low K
What is the fluid filled space within the tunnels of the organ of Corti of the cochlea called?
Cortilymphatic space
What is the ion composition of the cortilymph?
High Na, Low K
Where are the semicircular canals located?
Within the perilymphatic space
What is the ampulla?
Localized dilation at one end of the semicircular ducts
Where do the semicircular canals open into?
The vestibule
What structure sits in the vestibule?
The oval window sits on the vestibule
To what structure does the cochlea attach?
The round window, faces the tympanic cavity
How may turns does the cochlea make? around what structure?
2.75 turns around a central core of bone called the modiolus
What does the cochlear duct attach to?
Connected to the saccule by ductus reuniens
What connects the utricle and saccule?
the utriculosaccular duct
Where is the endolymphatic sac located?
On the floor of the posterior cranial fossa, under the periosteal dura mater
Which cells within the ear function as mechanoelectric transducers?
Hair cells
Describe Type I hair cells.
Cup-shaped ending surrounding almost the entire cell
Describe Type II hair cells.
Connects with just the base of the cell.
Many afferent endings.
What is the cristae ampullaris and where is it located?
Sensory receptor of angular movements of the head
Located within the ampulla of the semicircular ducts
In which planes do the macula of the utricle and saccule function as sensory receptors?
Utricle- horizontal plane
Saccule- vertical plane
Oriented at right angles to each other
Specialized to sense linear movement of the head and gravity
Where are the macula of utricle and saccule located?
Located in the vestibule
How is the cristae ampullaris orientated?
perpendicular to the long axis of the semicircular canal
What is the Cupula? What does it look like?
Gleatinous protein-polysaccharide mass attached to the hair cells of each crista (part of cristae ampullaris)
Cone-shaped, no otoliths
What is the function of the Cupula?
Sense angular (rotational) movements of the head
What are the macula of utricle an saccule?
Innervated sensory thickenings of the epithelium that face the endolymph of the saccule and utricle
** What do hair cells consist of?
stereocilia and one cilium/kinocilium
What is the otolithic membrane?
Gelatinous polysaccharide material that overlies the maculae
What are otoliths?
Crystalline bodies of clacium carbonate and a protein [heavier than endolymph]
What divides the cochlea into three parallel compartments?
Cochlear duct
What is the scala media?
Another name for the Cochlear duct
What is the cochlear duct filled with?
endolymph
Where does the cochlear duct end?
At the helicotrema [apex]
What does the cochlear duct contain?
the spiral organ of corti
Where is the scala vestibuli located?
Above the cochlear duct
Starts at the oval window on the vestibule
What is the scala vestibuli filled with?
perilymph
Where is the scala tympani located?
Below the cochlear duct
Ends at the round window on the medial wall of the middle ear cavity facing the tympanic cavity
What is the scala tympani filled with?
perilymph
What is the apex attache to osseous spiral lamina?
Triangular space
What separates the cohlear duct from scale vestibuli?
Vestibular (Resissner’s) membrane
also functions as the ‘roof’ of scala media
Describe the structure of the vestibular (Reissner’s membrane).
Two layers of squamous epithelium, joined by extensive tight junction preserving high ionic gradients across this membrane
What does the stria vascularis produce?
Endolymph
What structure is described as the ‘floor’ of scala media?
Basilar membrane
Extends from the spiral lamina of the modiolus to the lateral wall
What is a function of the basilar membrane?
Supports the spiral organ of Corti via the spiral ligament
Do the inner and outer hair cells have kinocilium?
NO
This allows symmetry to stereocilia which is important in sound transduction
What is the function of phalangeal cells?
Support cells for the hair cells
Inner phalangeal cells surround the inner hair cells completely
What contains the cortilymph?
the outer and inner tunnels which are formed by the inner and outer phalangeal cells
What forms the inner spiral tunnel?
Pillar cells
What structural elements are found in the tectorial membrane?
- Collagen type II, V and IX
- Otogelin and tectorin (glycoproteins)
Where is the the tectorial membrane located?
Attached medially to the modiolus
Lateral edge projects over and attaches to the organ of Corti by the stereocilia of the hair cells
Describe the steps of sound perception.
1) Sound vibrations enter the ear from the middle ear cavity.
2) Basilar membrane vibrates and tectorial membrane also vibrates.
3) Shearing effect between the basilar and tectorial membrane deflect stereocilia and apical portion of the hair cells.
4) Depolarization generates action potentials carried by cochlear part of CN VIII to the brainstem.
5) Discrimination between sound frequencies depends upon the response of the basilar membrane.
Where along the basilar membrane are high frequencies detected? low frequencies?
high = basal end low = apex of the spiral organ of Corti
What causes Meniere’s disease, dizziness, tinnitus and/or vertigo?
Increased pressure of endolymph
What sensation is the vestibular nerve responsible for?
Equilibrium
What sensation is the cochlear nerve responsible for?
Hearing
Where is the vestibular ganglion located?
Internal Auditory meatus
What are the saccule, utricle, and semicircular canals innervated by?
Vestibular nerve
Where is the spiral gaglion located? what nerve is it associated with?
Located in the modiolus
Associated with the cochlear nerve
What nerve innervates the cochlear duct and spiral organ of Corti?
Cochlear nerve
