Lecture 8 - The Ear Flashcards
What are the three divions of the ear?
- external
- middle
- internal
Functions of external ear
- collects and directs sounds waves
- protects
Functions of middle ear
- amplify and transmit sound waves
- transmits sound to internal ear
Functions of internal ear
structures of the external ear
- auricle
- external acoustic meatus
(the auricle protects the external acoustic meatus)
Auricle
- cartilage
- captures waves and sounds
external acoustic meatus
- from auricle to tympanic membrane (eardrums)
- lateral 2/3 = cartilage
- medial 1/3 = temporal bone
- directs sound wave into the ear
- ceruminous glands (create cerumon (earwax))
- debris trapping hairs (prevent things from entering more)
Bony component of external ear
temporal bone
tympanic membrane
- seperates external and middle ear
- vibrates in response to incoming sound waves
- can rupture (from object like a q-tip or infection, etc)
Pharyngotympanic tube and eustachian tube (part of pharyngotympaic tube)
- makes pressure even (ears and nose)
- direct tube from nose to ear
Auditory ossicles
- three bones
- malleus
- incus
- stapes
- bony ossicles
- connect tympanic membrane and internal ear
Malleus
hammer shaped
incus
attached malleus and stapes
stapes
- smallest bone in body
- connects incus to internal ear? via oval window
muscles og middle ear
- tensor tympani
- stapedius
they prevent excessive vibration of the bony ossicles
what does th tensor tympani do?
pulls on malleus, restricts movement at … ?
what does th estapedius do?
pulls on stapes, restricts movement at oval window
oval window
stapes pushes agasint oval window to transmit sound waves to internal ear
round window
helps sound waves travel through internal ear
features of internal ear
- innermost compartment
- encased in temporal bone
- sensations of hearing and balance
internal ear is composed of…
- bony labyrinth
- membranous labyrinth
- perilymph (fluid between bony labyrinth and membranous labyrinth
- endolymph (fluid inside membraneous labyrinth
bony labyrinth
- cochlea
- vestibule
- 3 semicircular canals
membranous labyrinth
- cochlea (cochlear duct)
- vestivule (utricle and saccule)
- 3 semicircular canals (semicircular ducts)
cohclea
- sensory organ for hearing (mechanical)
- sound travels through fluid (pressure)
- sends sound info to brain
vestibule
- utricle and saccule
- detects: head position, gravity, linear aceleration
- maintains stabilty and posture
3 semicircular canals
- semicircular ducts
- detects rational motion in 3 diff planes
- maintains balance
sensory hair cells
- cells with hair-like projections (stereocilia)
- detects motion (when hair cells are bent)
- hearing and balance
Amplitude
- higher = louder
- height of sound waves
- colume of osund
- decibels (dB)
Frequency
- how close together wave are
- pitch of sound
- hertz (Hz)
- closer the waves = higher the pitch
sound transmition review
- sound waves transmitted through external ear to tympanic membrane
- vibrations pass thrugh ossicles of middle ear
- stapes pushes agasint oval window and sound waves are transmitted to cochlea
What are the structures of the cohclea
- sala vestibuli
- helicotrema
- scla tympani
- cohclear duct (scala media)
How is pitch determined?
how far it travels in the cochlear duct, the further = and the least far it travels =
In what areas of the cohclea contaisn endolymph vs perilymph?
- cochlear duct = endolymph
- scala vestibuli and scala tympani = perilymph
What is the sensory organ of corti?
- aka spiral organ
- on cochlea
structures of organ of corti
- tectorial membrane
- basilar membrane
- hair cell
function of organ of corti
- waves in perilymph move basilar membrane up and down
- stereocilia of hair cells are pushed agasint and pulled away from tectorial membrane to eliciate a repsonse
Innervation
- CN VIII (vestibulocochlear nerve)/cochlear branches of CN VIII
Process of hearing
- sound waves cause vibration of the tympanic membrane
- movement of tympanic membrane vibrates ossicles (amplify sound)
- stapes pushing agasint oval window causes waves in perilymph
- Waves in perilymph push agasint basilar membrane as they travel through the cohclea
- Hair cells push agasint tectorial membrane and when they bend a neural signal is transmitted
- Impulses travel to CNS via cochlear branch of CN VIII (vestibulocochlear nerve)
Hearing loss: conductive
- external or middle ear
- usually temporal
- usually from blockage
- ex: cerum (earwax) build-up or punctuered tympanic membrane)
Hearing loss: sensorineural
- internal ear/nerve pathway
- usually permanent
- ex: cochlear nerve degeneration caused by againg or trauma induced sensory cell damage
Vestibular apparatus stuctures (2)
- vestibule
- semicircular canals
Vestibule
- utricle and saccule
- detects head position, gravity, linear acceleration
- maintains stability and posture
Semincircular canals
- Semincircular ducts
- detects rotational movement
- maintains balance
Equilibrium types (2)
- dynamic
- static
Dynamic Equilibrium
- mainainting balance when head and body are moved suddenly
- semiciruclar ducts
Static Equilibrium
- maintains posture and stability when body is motionless
- saccule and utricle
Semicircluar canals movement detection
- posterior: side to side
- anterior: nodding “yes”
- lateral: shakign head “no”
Rotational movement
- Posterior: roll
- Anterior: pitch
- Lateral: yaw
Semicircluar canals features
- membranous labyrinth filled with endolymph (each duct is continuous with utricle)
- each duct contains an ampulla (swollen region containing sensory receptors)
- hair cells are clisterred together on patys of tje ampulla (crista(e) ampullaris)
- sensory hair cells embedded in gelatinous mass (cupula)
Sensing rotational movement
- Head rotates and causes movement of endolymph
- Semicircular canal rotates with the head and endolymph sloshes agasint cupula
- Displacement of cupula distorst the sensory hair cells
- Nerve impulses are yyransmitted during this dispalcement/movement
Vestibule - saccule and utricle features
- membranous sacs filled with endolymph
- each sac contains a macula (hair cells in macula(e)
- utricle: horizontal acceleration
- saccule: vertical acceleration
Macula structures
- otoliths (little crystal things)
- gelatinous mass
- hair cells
Otoliths
- crystals are heavy and lag behind
- gravity and velocity
- movement of them stimulate hair cells which release neurotransmitters and send neural signals
Innervation
- CN VIII (vestibulocochlear nerve)
What is the vestibular systrem?
balance and equilibrium
