Ear Flashcards
Ear
receptor organ for both hearing and equilibrium
Ear regions
external ear – functions in hearing: transference of sound to internal ear
- middle ear – functions in hearing
- internal ear – participates in both hearing and equilibrium
(External) Auricle
elastic cartilage, functions to gather and direct sound waves into external acoustic meatus
External acoustic meatus
a short canal running M from auricle to tympanic membrane (eardrum) and conducting sound (2~3 cm in adults)
Tympanic membrane
forms the boundary between external and middle ears (1 cm d.), thin skin externally and mucous membrane of middle ear internally, translucent and pearly grey when examined using otoscope
TM and innervation
responds to air vibrations that pass to it through external acoustic meatus.
- Membrane movements transmitted by auditory ossicles (malleus, incus, stapes) through middle ear to internal ear.
- Innervation: external – auriculotemporal nerve (CN V3); small area supplied by CN X; internal surface – CN IX
Middle ear
a narrow, air-filled space lined by mucous membrane, located within petrous portion of TB
- 2 parts: tympanic cavity proper directly internal to tympanic membrane, epitympanic recess S to membrane
- Connected AM w/ nasopharynx by pharyngotympanic tube, PS w/mastoid antrum (a cavity in mastoid process)
Pharyngotympanic Tube
Connects tympanic cavity to nasopharynx opens P to I nasal meatus
- Structure: PL 1/3 is bony; remainder of tube is cartilaginous, lined w/mucous membrane continuous w/lining of
nasopharynx.
- Function: equalize pressure in middle ear w/atmospheric pressure to allow
free movement of tympanic membrane
Internal ear
Contains vestibulocochlear organ: sound reception and balance maintenance
Vestibulocochlear Nerve
CN VIII passes through internal acoustic meatus and divides near L end of meatus into 2 parts:
- cochlear nerve for hearing
- vestibular nerve for equilibrium
Sound transmission
Sound waves enter external ear, strike tympanic membrane, & it vibrates
- Vibrations transmitted through ossicles of middle ear and their articulations.
- Base of stapes vibrates in oval window, small membrane at base of cochlea, which transmits amplified vibrational energy to fluids of cochlea
Sound transmission part 2
- Vibrations from stapes at oval window transmitted through perilymph chamber to cochlear duct where hair cells of cochlear nerve (CN VIII) are stimulated.
- Vibrations dissipated back into middle ear cavity at round window, releases remaining energy into air of tympanic cavity
Motor
V3 – Tensor tympani muscle
VII – Stapedius muscle
General sensory
V3 – Some of skin of external ear
VII – Some of skin of external ear
IX – Mucosa of tympanic cavity, pharyngotympanic tube & internal surface of tympanic membrane
X – skin P to ear & external acoustic meatus
Special sense
VIII – Hearing (cochlear nerve); balance/equilibrium (vestibular nerve)
