Exam 2: Lecture 19 Hearing and balance Flashcards
where is the labyrinth embedded within the skull?
along the Petrous ridges of the temporal bone
labyrinth
(inner ear) the structure comprised of the cochlea, vestibule (utricle and saccule) and semicircular canals
cochlea
(hearing) spiral tube shaped like a snail shell as the organ that transduces sound into nerve impulses ⇒ part of the labyrinth
semicircular canals: what they do and where they connect
(balance) organs that transduce angular acceleration (rotation) into nerve impulses
- connecting at the vestibule
vestibule components
- utricle and saccule)
- (balance) organs that sense linear acceleration, including gravity
external ear components (2)
- Air filled; open chamber
- Pressure from sound moves the ear drum
middle ear
ossicles
ossicles
transmit pressure exerted by sound to the cochlea
- maleus, incus, stapes
inner ear
cochlea
- Sound vibrations are transmitted to liquid filled, closed chamber
- Basilar membrane: floor of chamber vibrates in response to sound
- On the anterior medial side of the labyrinth
oval window
how the sound gets transmitted to the cochlea
- Footplate of the stapes ⇒ movements can move fluid
- Fluid flows through the tube to the apex and then out at the round window
spiral ganglion
auditory primary afferents for hearing that contains the cell bodies responding to sound by hair cell vibration
- includes the cochlear nerve
basilar membrane
hair cells sit on here and are innervated by the spiral ganglion
hair cells
separate cell that communicates with the spiral ganglion neurons
- Acting as receptor cells (innervate) to sense vibrations and transmit that to the spiral ganglion
what effect does sound have?
when sound hits the eardrum there is compression of the tympanic membrane which compresses the fluid in the cochlea
- Displaces the basilar membrane
compression
downward movement of the basilar membrane
rarefaction
upward movement of the basilar membrane
how are the base and apex of the basilar membrane different?
Base: narrow, thick, tense ⇒ cross section is small
- Responds to high frequency sounds
Apex: wide, thin, flaccid ⇒ cross section is wider
- Responds to low frequency sounds
what resonant frequency does the round window have?
high frequency
low frequency would be Xhz and high frequency would by Yhz
low = 100; high = 10,000
what kind of mathematical property does the basilar membrane have?
logarithmic organization
how do hair cells work?
- cell has a nucleus and from one end of the cell there are fibrous hairs at different length
- the longest hair bending causes depolarization which excites the cell to release a neurotransmitter onto the spiral ganglion neuron = on
- vice versa
regions involved in processing sounds (5)
- cochlear nuclei
- superior olivary nuclei
- inferior colliculus
- medial geniculate nucleus
- auditory cortex
cochlear nuclei
sound localization and identification (medulla)
superior olivary nuclei
more involved in sound localization and volume control (pons)
inferior colliculus
identification of and reflexive responses to sounds (midbrain)
medial geniculate nucleus
thalamic relay nucleus (relays audition to our primary auditory cortex right on top of the temporal lobe)
auditory cortex
tonotopic organization and sound identification
tonotopic organization
different areas of the top of the temporal lobe respond to different frequencies of sound
pitch
a single frequency
conducting deafness
ear wax or issues with ossicles (bone growths; arthritis)
- Easiest to treat
- Arthritis prevents the bones form moving
sensorineural
result from exposure to loud noises or age related loss of high frequency hearing ⇒ treated with hearing aids
- Most common form of deafness
tinnitus
ringing in ears
- Common and associated with hearing loss
endolymph
the name of the fluid inside the ear ⇒ exerts a force at the cupula base of the semicircular canal
cupula
has hair cells embedded in it and depending on the motion of the fluid the cells are hyperpolarized or depolarized
- at the base of the semicircular canals
excitation
includes depolarization of the hair cell and increased impulse frequency
inhibition
includes hyperpolarization of the hair cells and decreased impulse frequency
what do the semicircular canals vs the vestibule sense?
rotation vs linear acceleration
utricle
hair cells in the horizontal sheet (side ways too)
- Detects acceleration front-back; left-right
saccule
hair cells in the vertical sheet
- Mid Sagittal vertical plane detecting acceleration front-back; up-down
flocculondular lobe
part of the cerebellum involved in balance
where do the central vestibular apparatus project axons to?
the vestibular nuclei in caudal pons and flocculonodular lobe
where do the vestibular nuclei project axons to? (3)
- Spinal cord (for when we sense balance is changing)
- Cerebellum
- Cranial nerve nuclei controlling eye movements ⇒ oculomotor (3), trochlear (4), abducens (6)
functions of the vestibular nuclei (3)
- projections to spinal cord
- cerebellum
- projections to nuclei innervating extra ocular muscle
what do projections to the spinal cord and cerebellum do?
- Coordinate eye movements with head and neck movements
- Coordinate vestibular input with anti-gravity muscles such as reflex
what do projections to nuclei innervating the extra ocular muscle do
Track object while turning your head
what are the 3 input systems to tell us how our body is oriented?
- vestibular => balance
- proprioception => feet and floor
- vision
vertigo
sensation of turning in the absence of motion
Menderes disease
disorder of entire inner ear ⇒ hearing + balance (type of vertigo)
nystagmus
repetitive tracking eye movements in the absence of movement
motion sickness
vestibular input to reticular formation => autonomic centers
