Lecture 22: Ear Histology Flashcards
Describe the auricle of the outer ear
- This is the pinna of the ear and the auditory canal.
- Integument overlying elastic cartilage
- Integument is thin, keratinized stratified squamous epithelium.
- Hair follicles can be observed in the dermis.
Describe the external auditory means of the outer ear
- Outer third of the ear canal is composed of elastic cartilage.
- Inner two thirds is composed of bone.
- Lining of ear canal is stratified squamous epithelium with sebaceous glands and ceruminous glands (modified sebaceous glands)
Describe the tympanic membrane of the outer ear
- The tympanic membrane (eardrum) separates the external auditory canal from the middle ear.
- The core is formed from vascularized, innervated connective tissue.
- External surface is covered by thin skin.
- Internal surface is covered by simple cuboidal epithelium.
Describe the 3 auditory ossicles of the middle ear (tympanic cavity)
- Malleus (hammer):
- The malleus attaches to the tympanic membrane.
- This bone is so-named because it articulates with the “anvil”.
- Incus (anvil):
- This is an intermediate bone between the stapes and the malleus.
- The name “incus” refers to an anvil, on which the hammer strikes.
- Stapes:
- This is the third bone in the series.
- The stapes is so-named because it is shaped like a stirrup due to the opening for the stapedial artery.
- The stapes inserts onto the oval window.
Describe the openings of the middle ear (tympanic cavity)
- Oval window:
- The stapes attaches to the membrane covering the oval window.
- The oval window opens into the scala vestibuli.
- Round window:
- This membrane-covered region is at the end of the scala tympani.
Describe the muscles of the middle ear (Tympanic Cavity)
- Tensor tympani:
- Inserts on the malleus
- Stapedius:
- Inserts on the stapes
- These muscles contract reflexively in response to loud sounds in order to dampen the vibrations of the auditory ossicles.
Review slide 10
Notice small bone shapes
Notice anything emphasized in the last few slides
Eustachian tube is that sink tube thing towards the bottom.
The three semicircular canals on the top of the cochlea are called 3 semicircular canals.
List the 4 regions of the inner ear
- Bony labyrinth
- Membranous labyrinth
- Vestibular organ
- Auditory organ
Describe the bony labyrinth of the inner ear
- Complex system of canals and chambers embedded in the petrous portion of the temporal bone.
- Filled with high-sodium content perilymph.
- Consists of:
- Semicircular canals
- Cochlea
- Scala vestibuli
- Scalia Tympani
Describe the membranous labyrinth of the inner ear
- Complex system of membranous structures embedded within the chambers of the bony labyrinth.
- Filled with high-potassium content endolymph.
Describe the vestibular organs of the inner ear
- Patches of sensory structures that respond to changes in position.
- Consist of:
- Maculae of the saccule and utricle
- Cristae ampullaris of the semicircular canals
- See Slide 12-13, Figure 9-26, and 9-27
Describe the maculae of the saccule and utricle
- Epithelium:
- Columnar supporting cells
- Vestibular hair cells: Numerous stereocilia and Single kinocilium
- Hair cells are in contact with afferent nerve endings
- Otolithic membrane:
- This is actually a gelatinous layer containing calcium carbonate crystals called otoliths that overlies the epithelium.
- Stereocilia of the vestibular hair cells are embedded in this gelatinous layer.
- Movements of the head displaces the otolithic membrane and causes a sensory impulse.
See Slides 15-16
Describe the Cristae Ampullares of Semicircular Ducts
- Epithelium:
- Columnar supporting cells
- Hair cells: Similar to those of maculae
- Cupula:
- This is a gelatinous layer similar to the otolithic membrane but without the ostoliths.
- Movement of the head creates shear forces between the semicircular canals and the contained fluid.
- Movement of the fluid displaces the cupula and causes the stereocilia to bend.
- See Slide 18
Describe the auditory organ of the inner ear
- Consists of:
- Cochlear duct (scala media)
- Scala vestibuli
- Scala tympani
- Vestibular membrane
- Basilar membrane
- Stria vascularis
- Organ of Corti
- See Slide 20
Describe how the components of the inner ear are structured
- Cochlear duct (scala media) divides the bony cochlea into:
- Scala vestibuli
- Scala tympani
- Vestibular membrane:
- Forms the roof of the duct
- Basilar membrane:
- Forms the floor of the duct.
- Stria vascularis:
- Forms the lateral aspect of the duct
- Participates in the formation of the endolymph.
- Organ of Corti:
- Lies on the basilar membrane
- See Slides 21-31
