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Hearing and balance
The 3 parts of the ear
Inner, outer and middle
The parts of the ear involved with hearing
Outer and middle
Hearing and equillibrium
Receptors for hearing and balance
respond to separate stimuli, are activated independently
Components of the Outer Ear
External auditory canal
Tympanic Membrane (eardrum)
Auricle is composed of
The helix (rim)
External auditory canal
short, curved tube filled with ceruminous glands
This is the thin connective tissue membrane that vibrates in response to sound
Transfers sound energy to the middle ear ossicles
Boundary between outer and middle ears
Small, air filled, mucosa-line cavity
The tympanic cavity (middle ear) is flanked laterally by what?
By the tympanic membrane
The tympanic cavity (middle ear) is flanked medially by what?
Oval and round windows
Connects the middle ear to the nasopharynx
Function of the pharyngotympanic tube
Equalizes pressure in the middle ear cavity with the external air pressure
The 3 bones of the tympanic cavity, lateral to medial.
Tensor Tympani is suppled by which nerve
Stapedius supplied by which nerve
Function of the small bones in the tympanic cavity
Transmits vibratory motion of the tympanic membrane to the OVAL window dampened by the tensor tympani and stapedius muscles.
How to remember the 3 bones of the tympanic cavity
Lateral to Medial you never miss NIS
part of the inner ear. Tortuous channels worming their way through the temporal bone. Contains the vestibule, the cochlea and the semicircular canals.
What is the bony labrynth filled with?
Filled with PERILYMPH
What is Perilymph very low in
Very low in potassium
Par of inner ear. Series of membranous sacs within the bony labyrinth.
What is the membranous labyrinth filled with?
Filled with potassium rich fluid ENDOLYMPH
spiral, conical bony chamber
where does the cochlea extend from
extends from the anterior vestibule
What does the cochlea coil around
coils around a bony pillar called the MODIOLUS
the cochlear duct, which ends at the cochlear apex.
The Organ of Corti is in what
3 chambers of the cochlea
1) Scala Vestibuli
2) Scala Media (cochlear duct
Which of the 3 chambers of the cochlea contain the hearing receptor?
Scala tympani terminates at
the round window
Scalas tympani and vestibuli are both filled with
The scala tympani and vestibuli are continuous with eachother via the
Scala media is filled with
The "floor" of the cochlear duct is composed of
the bony spiral lamina and the basilar membrane which supports the organ of corti
Cochlear branch of which nerve runs from the organ of corti to the brain?
Sound vibrations beat against what membrane
the tympanic membrane
How the tympanic membrane works
Pushes the ossicles, which presses fluids in the inner ear against the oval and round windows
The movement of what sets up shearing forces that pull on mechanosensitive hair cells
The route of sound to the inner ear: Outer Ear
Pinnea, external auditory canal, tympanic membrane
The route of sound to the inner ear: Middle ear
Malleus, incus and stapes to the oval window
The route of sound to the inner ear: Inner Ear
Scalas vestibuli and tympani to the cochlear duct.
Mechanically gated ion channels are found where
found where the hair meets the cell
Transmission of sound to the inner ear needs
stimulation of the organ of corti and generation of impulses in the cochlear nerve
Audible sound waves
penetrate through the cochlear duct.
Vibrate the basilar membrane
The audible sound waves excites specific hair cells according to what
According to the FREQUENCY of sound
This is composed of supporting cells and outer and inner hair cells
The Organ of Corti
In the organ of corti, afferent fibers of the cochlear nerve attach
to the base of hair cells
In the organ of corti, the stereocilia (hairs) touch
the tectorial membrane
during the bending of stereocilia, when it opens MECHANICALLY GATED ion channels found where the stereocilia meet the hair cell.
Bending stereocilia causes
causes a graded potential and the release of a neurotransmitter: termed Mechanotransduction
The neurotransmitter released by mechanotransduction causes
cochlear fibers to transmit impulses to the brain, where sound is perceived
Impulses from the cochlea pass via the spiral ganglion to
the cochlear nuclei
Impulses from the cochlear nuclei are sent
to the superior olivary nucleus.
Inferior colliculus (auditory reflex center)
Pitch is perceived by
The primary auditory cortex
Loudness is perceived by
Varying thresholds of cochlear cells
the number of cells stimulated
4 types of deafness
1) conduction deafness
2) Sensorineural deafness
4) Meniere's syndrome
something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles)
More common. Results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
Ringing or clicking sound in the ears in the absence of auditory stimuli
Labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea and vomiting. Also Progressive hearing loss.
2 parts of a balance vestibule
The saccule and the utricle each contain
each contain a macula (sensory receptor)
Vestibular receptors monitor
Vestibular receptors respond to
gravity and changes in the position of the head
What is the maculae
The sensory receptors for static equillibrium
contain supporting cells and hair cells
Each hair cell of the maculae has
has stereocilia and kinocilium embedded in the otolithic membrane
Jellylike mass studded with tinny CaCO3 stones called Otoliths
Utricular hairs respond to
Saccular hairs respond to
Otolithic movement in the direction of kinocilia:
depolarizes vestibular nerve fibers
increases the number of action potentials generated
Otolithic movement in the opposite direction:
Hyperpolarizes vestibular nerve fibers
Reduces the rate of impulse propagation
DO the vestibular neurons have a constant signal?
Stereocilia move TOWARDS the kinocilium and what happens
and the signal increases in frequency (depolarization) compared to the normal tonic level
Stereocilia move AWAY from the kinocilium and what happens
and the signal decreases in frequency (hyperpolarization) compared to the normal tonic level.
cover three planes of space (x,y,z)
Single swollen end of each canal in the semicircular canals
Where is the crista ampullaris (equilibrium receptors)?
In the ampulla
Semicircular canal receptors respond to what
angular movements of the head (Dynamic Equillibrium)
Each crista contains what
Has support cells and hair cells that extend into a gel-like mass called the cupula
Vestibular nerve fibers innervate what
innervate hair cells
Cristae respond to changes in what
changes in velocity of rotatory movements of the head
Directional bending of hair cells in the cristae causes:
1) depolarizations, and rapid impulses reach the brain at a faster rate
2) Hyperpolarizations and fewer impulses reach the brain.
What is the result of the directional bending of hair cells in the cristae
result is that the brain is informed of rotational movements of the head
Depolarization occurs in the SAME direction as the head movement. (Left head turn produces depolarization in the LEFT horizontal canal)
Anterior and Posterior Canals
Depolarization occurs in the OPPOSITE direction as the head movement (FORWARD head tilt produces depolarization of the POSTERIOR canals)
Components of the Vestibule
Saccule and Urticle
Receptor of the Vestibule
Dampening element of the Vestibule
Modality of the Vestibule
Components of the Semicircular canals
Horizontal (lateral) canal
Receptor of the semicurcular canals
Dampening element of the semicurcular canals
Modality of the semicurcular canals
When both Ampulla are working together
One side excited and the other inhibited
Ordinarily the head movement implied by the visual and vestibular signals are equal but there can be conflict resulting in a) motion sickness b) vertigo
Nausea and vomiting. Occurs when the visual and vestibular signals are unequal
A perception of head motion when the head is still. Part of motion sickness
Benign Paroxysmal Positional Vertigo (BPPV)
One of the most common causes of vertigo. Otoliths from the utricle dislodge and float into the posterior canal, causing interference with cupula function.
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