Microanatomy of the Ear- Lecture 36

what re the 3 divisions of the ear?

-inner ear

-middle ear

-external ear

describe the inner ear

• Sensory organs for hearing and balance.

• A system of membranes (membranous labyrinth) surrounded by perilymph, all housed in the bony labyrinth.

• The perilymph in the bony labyrinth communicates with the cerebrospinal fluid of the subarachnoid space, via the perilymphatic duct

describe the middle ear

• Transmits and converts sound waves to fluid waves in the inner ear.

• Connected to nasopharynx via auditory tube.

• The facial nerve runs adjacent to it, so it can be affected when ear is inflamed.

describe the external ear

Collects and directs sound waves to tympanic membrane. Lined with skin.

what is the vestibular window?

where stapes contacts the membrane of the inner ear

what does the chorda tympani nerve branch from?

facial n

what part of the ear does chorda tympani nerve pass through?

middle ear

what nerve does the chorda tympani nerve join?

lingual n

the facial n enters the internal acoustic meatus with what nerve?

CN VIII

describe the facial n enters the internal acoustic meatus

courses through facial canal in the temporal bone to exit the stylomastoid foramen caudal to the external acoustic meatus

what is the smallest skeletal muscle in the body?

stapedius m

what is the function of the stapedius m?

pulls on the stapes to dampen the effect of loud noises

what are the modified apocrine sweat glands called?

ceruminous glands

describe ear wax

cerumen; product of sebaceous and ceruminous glands

what type of sweat gland empties into the hair follicle?

apocrine

describe the tympanic membrane

skin on one side, mucous membrane on other side

describe the epithelium of the middle ear

mainly lined with epithelium of simple flattened to cuboidal cells resting on a thin lamina propria, which is tightly connected to the subjacent periosteum

what is the simple epithelium in the ventral part of the tympanic bulla gradually replaced by?

ciliated pseudo stratified columnar epithelium containing goblet cells

what does the auditory tube connect?

middle ear to pharynx

what is the auditory tube supported by?

hyaline cartilage

what is the auditory tube lined by?

ciliated pseudostratified columnar epithelium with goblet cells

what are semicircular canals?

one oriented for each dimension. Each has a sensory organ, to detect rotational movement in any direction

what is the saccule and utricle?

have sensory organs to detect horizontal and vertical

movement

what is the cochlea?

a spiral structure, with sensory cells to detect vibrations at

different frequencies, which the brain interprets as sound

all sensory structure in the membranous labyrinth use what?

hair cells, and some variation of a gelatinous cap to stimulate the hairs.

what is included in the membranous labyrinth?

-semicircular canals

-saccule and utricle

-cochlea

what are the microscopic stones of the saccule and utricle called?

otoliths

the cochlea is a spiraling tube consisting of ______

bony labyrinth

what does the bony labyrinth house?

membranous endolymph-filled cochlear duct surrounded by the membranous perilymph filled scala tympani and scala vestibuli

what is the cochlear duct?

houses the sensory organ for hearing (Organ of Corti, or Spiral organ)

what is the scala tympani and scala vestibuli?

continuous at the top of the spiral

where does the scala vestibuli and scala tympani communicate?

apex of spiral; the communication is the helicotrema

vibration of the basilar membrane causes what?

moves the hair cells, and the stereocilia are stimulated.

the ________ membrane should be attached to the hair cells

tectorial

where is the spiral ganglion located?

center of cochlea

describe the neurons of the spiral ganglion

bipolar neurons of the spiral ganglion have dendrites that

make synaptic contact with the base of hair cells, and their axons form the auditory portion of eighth cranial nerve

in regards to the spiral ganglion where do the axons come from?

-axons coming from hair cells

-axons leaving to form auditory part of CN VIII

what is the modiolus?

the central pillar of bone that supports the spiral organ (organ of Corti) and the spiral ganglion

what does the ampulla of a semicircular canal contain?

sensory organ called a crista ampullaris

what is crista ampullaris?

conical structure that has an epithelium of hair cells, covered by a gelatinous cap called the cupola. ("cupola" means a small dome)

in the crista ampullaris supporting cells are _______

basal

in the crista ampullaris sensory cells are _______

at the surface

in the crista ampullaris, the surrounding endolymph moves (from rotational motion of the head) the gelatinous cap moves, and ___________

the hair cells are stimulated

what are the sensory cells of the crista ampullaris?

-supporting cells

-sensory cells

-gelatinous cap

in the otoliths in the macula the supporting cells are _______

basal

in the otoliths in the macula the sensory cells are ________

at the surface

in the otoliths in the macula, when the surrounding endolymph moves (from linear motion of the head) the gelatinous cap moves, and ___________

the hair cells are stimulated.

what are the otoliths subject to?

gravity