The Ear Flashcards
Divisions of the Ear
- External
- Middle
- Internal
External Ear (2)
- Auricle- cartilage that protects external auditory canal, captures waves and sound and “funnels” into ear
- External Acoustic Meatus- directs sound waves into the ear, lateral 2/3 is cartilage, medial 1/3 is temporal bone, goes from auricle to tympanic membrane
*contains ceruminous glands that secrete waxy material, and debris trapping hairs
Tympanic Membrane
Separates the external and middle ear, vibrates in response to incoming sound waves
Middle Ear (5)
- Tympanic membrane
- Auditory ossicles- 3 bones- malleus, incus and stapes- which connect tympanic membrane with internal ear (oval window)
- Eustachian tube (pharyngotympanic tube)- makes pressure equal b/t middle ear and outside (otitis media= middle ear infection that causes redness, swelling and pain)
- Tensor tympani and stapedius muscles
- Oval and round windows
*middle ear collects and amplifies sound waves, and transmits sound to internal ear
Muscles of Middle Ear
- Tensor tympani- pulls on malleus (bone of tympanic membrane) to increase stiffness and limit movement
- Stapedius- pulls on stapes to restrict movement at oval window
*prevents excessive vibration of bony ossicles
Oval and Round Windows
Oval Window:
-Stapes pushes against oval window to transmit sound waves to internal ear
Round Window:
-Helps sound waves travel through internal ear
Internal Ear
-Innermost compartment encased in temporal bone
-Involved in hearing and balance
1.Bony labyrinth
2. Membranous labyrinth (within bony)
*Perilymph= fluid between bony and membranous, endolymph= fluid within membranous (tube)
Bony Labyrinth Components (3)
- Cochlea
- Vestibule
- 3 Semicircular Canals
Cochlea
-Sensory organ for hearing
-Sound travels through fluid in pressure waves and sends sound information to brain
-Sound enters through oval window to Scala Vestibuli, passes cochlear duct to Scala Tympani after signal transmitted
-Apex of cochlea= helicotrema *where scala vestibuli and tympani meet
-Contains organ of corti
*cochlear duct (scala media) within membranous labyrinth
Vestibule
Utricle and saccule within membranous labyrinth
-Detects head position, gravity and linear acceleration
-Maintains stability and posture
*balance and equilibrium
Semicircular Canals
3 semicircular canals, semicircular ducts within membranous labyrinth
-Detects rotational motion in 3 different planes
-Maintains balance
Anterior= nodding yes
Posterior= side to side “roll”
Lateral= shaking head no
Sensory Hair Cells
-Cells with hair-like projections (called stereocilia)
-Detects motion
-Involved in hearing and balance
*external stimuli bends hairs one way or another which sends signal through nerve to determine motion
*volume determined by how many hair cells are stimulated
Sound Transmission Review (3)
- Sound waves transmitted through external ear to tympanic membrane
- Vibrations pass through ossicles of middle ear, which amplify sound
- Stapes pushes against oval window and sound waves are transmitted to cochlea
Organ of Corti
Also called spiral organ, contains basilar membrane (bottom) and tectorial membrane (top) with hair cells in between
-Waves in perilymph move basilar membrane up and down
-Stereocilia of hair cells are pushed against and pulled away from tectorial membrane
-Greater displacement= more neurotransmitter release
OVERALL Process of Hearing (6)
- Sound waves travel through external acoustic meatus to tympanic membrane causing vibration
- This vibrates the ossicles which amplifies the sound
- Stapes pushes against oval window which causes waves in perilymph, and sound travels through scala vestibuli
- Waves of perilymph push against basilar membrane as they travel
- Hair cells push against tectorial membrane and bend, which causes neural signal to be transmitted
- Impulses travel to CNS via cochlear branch of CN VIII
*higher pitch sounds= shorter hairs can pick up, goes through scala tympani to exit through round window
*lower pitch sounds= picked up by longer hair cells, travels further (towards helicotrema) before going to scala tympani