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59 Cards in this Set

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Note petrous temporal bone.
Three ossicle bones
Malleus, incus, stapes; transmits energy into the oval window -> scala vestibuli -> helicotroma -> scala tympani -> round window
The stapes then causes the oval window to
vibrate. Realize that considerable amplification of sound occurs between the tympanic
Membrane the the footplate of the stapes.
Through what opening does CN VII, VIII and nervus intermedius run through?
What info does the nervous intermedius carry?
The nervus intermedius carries fibers for taste to the anterior two-thirds of the tongue and preganglionic parasympathetics. The labyrinthine artery and vein also enter the canal (acoustic auditory meatus)
Name of the bony core around which the cochlea is covered?
Modiolus; contains the ganglion cells o fthe cochlear portion of the vestibulo cochlear nerves; edges of modiolus form the spiral lamina
Where is perilymph vs endolymph located?
The scala vestibuli and scala
tympani contain perilymph, whereas the cochlear duct contains endolymph. The scala
vestibuli and scala tympani are connected at the apex by the helicotrema. The cochlear
duct ends blindly at the apex of the modiolus.
What membranes separate the scala vestibuli from the cochlear duct and the scala tyampni from the cochlear duct?
The cochlear duct is separated from the scala vestibuli by the vestibular mem-
brane of Reissner and from the scala tympani by the basilar membrane.
The scala vestibuli makes a V (with Reissner’s
vestibular membrane and the basilar
membrane).

The scala tympani has no organ of Corti,
so its shape resembles that of a tympanum
(kettle drum).
Worst memory trick ever
Relationship of frequency to wavelength on the basilar membrane
Realize that high frequencies are registered nearer the beginning of the basilar membrane, and low frequencies nearer the end. This is because
the fibers at the beginning of the membrane are short, and those at the
end of the membrane are long. Wavelength is inversely related to frequency. Thus, the higher the frequency, the shorter the wavelength.
The lower the frequency, the longer the wavelength. This is why low
frequency sound waves (longer wavelength) sound waves require a longer portion of the basilar membrane than higher frequency (lower wavelength) waves.
Inner vs outer hair cells
Inner: Transform sound vibrations in the cochlea into electrical signals relayed via auditory nerve to brainstem; articulates with multiple fibers

Outer: Amplify sound via stereocilia or mechanical motility

Outer hair cells outnumber inner cells three to one
Membrane deflection
The deflection of the hair cell stereocilia opens mechanically gated ion channels that
allow any small, positively charged ion (primarily potassium and calcium) to enter the
cell. The influx of positive ions from the endolymph in the cochlear duct) depolarizes the
cell, resulting in a receptor potential. This receptor potential opens voltage-gated
calcium channels. Calcium ions then enter the cell, and trigger the release of
neurotransmitters (glutamate) at the base of the cell. Glutamate diffuses across the
space between the hair cell and the nerve terminal, where binding to receptors results
in the generation of an action potential.
spiral ganglion bipolar cells
BIPOLAR CELLS OF THE SPIRAL (COCHLEAR) GANGLION. These are bipolar
neurons. They project centrally as the cochlear nerve to the dorsal and ventral cochlear nuclei. Some bipolar cells also project peripherally to the hair cells of the organ of Corti.
Where does VIII enter the brainstem
Note the vestibulocochlear nerve entering the brainstem at the cerebellopontine angle. Note the dorsal (posterior) cochlear
nucleus and the ventral (anterior) cochlear nucleus.
Where does VIII enter the brainstem
Note the vestibulocochlear nerve entering the brainstem at the cerebellopontine angle. Note the dorsal (posterior) cochlear
nucleus and the ventral (anterior) cochlear nucleus.
Dorsal cochlear nucleus -> lateral lemniscus
Where does anterior cochlear nucleus synapse?
Note axons from the spiral ganglion entering the ventral
(anterior) cochlear nucleus. Note axons from cells in this nucleus entering the
ipsilateral lateral lemniscus. Note other axons synapsing on the nucleus of the trapezoid
body. Cells located in this nucleus then project to the contralateral lateral lemniscus.
Note other axons from this the ventral cochlear nucleus synapsing in the superior
olivary nucleus. Axons from the cells of this nucleus then synapse on the contralateral
superior olivary nucleus . Axons from these neurons then enter the contralateral lateral
lemniscus.
Projections of the lateral lemniscus
AUDITORY PATHWAY 2. Note the crossing of axons from cells in the nucleus of the
lateral lemniscus and the nucleus of the inferior colliculus (via the commissure of the
inferior colliculi).
Cochlear nerve ->

1. Ventral cochlear nucleus -> trapezoid body -> superior olivary nucleus -> contrallateral lateral lemniscus
2. dorsal cochlear nucleus -> ipsilateral lateral lemniscus
Neural acoustic pathways
Where is the primary auditory cortex?
THEPRIMARY AUDITORY CORTEX IS THE TRANSVERSE TEMPORAL
GYRUS OF HESCHL, WITHIN THE LATERAL SULCUS. THIS CONTAINS
BRODMANN AREAS 41 AND 42.
Loss of the corneal blink reflex
Schwannoma: early sign of distortion of the trigeminal nerve by
a tumor emerging from the internal acoustic meatus into the posterior cranial fossa.
Weakness of the muscles of mastication (temporalis, masseter, medial and lateral
pterygoids)
schwannoma: is a later sign of trigeminal involvement. The masseter and temporalis
may be tested by having the patient clench the jaws while palpating the muscle. Further-
more, wasting of the masseter and temporalis may be determined by palpation. For the
lateral pterygoid, the jaw deviates towards the affected side when the mouth is opened,
because the normal lateral pterygoid muscle Is now unopposed by the damaged lateral
pterygoid. Remember the lateral pterygoid muscle draws the jaw forwards. The two lateral pterygoids balance each other.
Weakness of the entire hemiface with atrophy
schwannoma: may occur as the facial nerve becomes
stretched by the tumor. Remember that a lower motor neuron VII lesion involves the
entire hemiface. An upper motor neuron lesion spares the upper face due to its bilateral
innervation from the facial nuclei.
Anesthesia of the posterior third of the tongue, oropharynx and nasopharynx
schwannoma: denote
involvement of the glossopharyngeal nerve.
Ipsilateral cerebellar signs (ataxia, pendular reflexes, intention tremor) in the arm and
leg
schwannoma: appear when the cerebellum is compressed
hypertonia, hyperreflexia, Babinski
UMN signs in the limbs = compression of brainstem in schwannoma
headache, drowsiness, papilledema, abducent palsy
increased intracranial pressure signs = obstruction o fthe circulation of CSF inside or around the brainstem
Which nerves would be compromised first/early/late symptoms of acoustic neuroma?
ACOUSTIC NEUROMA. Note the
tumor developing from the
vestibular nerve (a branch of
the vestibulocochlear nerve)
within the internal auditory
meatus (canal). Note the
proximity of the facial nerve
(CN VII) and both divisions of
the vestibulocochlear nerve
(VN VIII) as well as the nervus
intermedius. Note that further
expansion endangers the
glossopharyngeal nerve (CN IX),
vagus (CN X) and the trigeminal
(CN V). If the tumor becomes
sufficiently large, the abducent
nerve may also be damaged,
although it is usually the last
of these to be involved, as it is
placed on the apex of the
petrous temporal bone.
Bilateral acoustic neuromas; left vestibulocochlear nerve tumor has a meningioma also associated with it
Sound reaches threshold; VIII -> superior olivary nucleus -> VII -> stapedius muscle contraction bilaterally


It can be tested by placing A sonic
probe into the ear canal and presenting a test noise to the tympanic membrane. When
the sound volume reaches threshold, the stapedius contracts, stiffening the tympanic
membrane. The change in the resistance of the tympanic membrane is then measured
and recorded.
From what nucleus is the tensor tympani innervated by?
The
tensor tympani is innervated
by neurons in the motor
nucleus. When stimulated,
it dampens the vibrations of
the ossicles, preventing
nerve damage.
TYMPANIC CAVITY. Note the insertion of the tendon of the tensor tympani (red
arrow) onto the handle of the malleus. When stimulated by loud noises, the muscle
contracts to dampen the vibration of the ossicles and prevent nerve damage. The
muscle is innervated by neurons in the motor nucleus of the trigeminal. Its function is
similar to that of the stapedius, which attached to the stapes.
Olivocochlear efferents function?
When stimulated, the outer hair cells can actively amplify the travelling wave. The olivocochlear fibers are concerned with the active preprocessing of sound (“cochlear amplifier”), and acoustic protection.
Where can inner ear infections spread?
The tympanic cavity is the site of a middle ear infection (otitis media). The anatomical
relationships are particularly important in treating chronic suppurative otitis media.
They may invade the adjacent sigmoid dural venous sinus to produce a sinus
thrombosis. They may pass through the air cells of the apex of the petrous
temporal bone to enter the CSF space, causing abducent paralysis, trigeminal
nerve irritation, or visual disturbances. This latter combination constitutes
Gradenigo syndrome, an inflammation of the apex of the petrous temporal bone.
They may also invade the facial canal, causing a peripheral facial palsy (Bell’s
palsy).

Pathogenic bacteria may spread to adjacent regions. They may spread upwards
through the tegmen tympani (the roof the tympanic cavity) into the middle cranial
fossa to produce meningitis or a cerebral abscess (especially of the temporal lobe).
They may invade air cells of the mastoid process (red arrow) to produce mastoiditis.
Gradenigo Syndrome
Bacteria passes through the air cells of the apex of the petrous
temporal bone to enter the CSF space, causing abducent paralysis, trigeminal
nerve irritation, or visual disturbances. This latter combination constitutes
Gradenigo syndrome, an inflammation of the apex of the petrous temporal bone
The WEBER TEST. When a vibrating tuning fork is placed on the center of the forehead,
the normal response is for the sound to be heard in the center, without lateralization to
either side. A. In conductive hearing loss, the sound is heard on the side of the conduc-
tive hearing loss. B. In sensorineural hearing loss, the sound is heard better on the
opposite, unaffected side.


The explanation for the Weber test is based on the masking effect of background
noise. In normal conditions, there is a considerable amount of background noise,
which reaches the tympanic membrane by air conduction. This tends to mask the
sound of the tuning fork heard by bone conduction. In an ear with a conductive
hearing loss, the air conduction is decreased, and the masking effect is therefore
diminished. Thus, the affected ear hears and feels the vibrating tuning fork better
than the normal ear.
Positive Rinne test
In the Rinne test, air conduction (AC) is greater than bone conduction (BC). Normal
patients are able to hear the tuning fork at the external auditory meatus after they
can no longer hear it on the tip of the mastoid process of the temporal bone.
This is a positive Rinne test (AC>BC).
Negative Rinne Test
Patients with a conductive hearing loss hear bone conduction better than air conduction.
(BC>AC). This is because the tympanic membrane-ossicular system is no longer func-
tional. However, bone conduction allows the sound wave to vibrate the footplate of the
stapes at the oval window, producing a travelling wave in the cochlea. This is termed a
negative Rinne test (BC>AC).
false negative rinne test
If there is total deafness in one ear, the patient may hear the tuning fork even when
It is placed on the mastoid process of the deaf ear. This is due to transmission of sound
vibrations by bone across the skull to the opposite side, where they are sensed by
the healthy ear. This is a false negative Rinne test.
What ganglion innervates the hair cells on the cupulae o fthe crista ampullares?
bipolar cells o fthe vestibular ganglion of Scarpa
What info does the macula of the utricle provide
Side to side movement
What info doe sthe macula of the saccule provide
Up and down movement
If you knocked out the maculae of the utricle nad saccule, what muscular effects would you observe
They are essential to the static, postural, tonic neck, and
righting reflexes.
Through what duct does perilymph communicate with the subarachnoid space
the perilymphatic duct of the cochlear canaliculus.
What structure secrtes endolymph
Stria vascularis of the cochlear duct
What structure absorbs endolymph
Endolymphatic sac
Mechano-electric transduction current
Potassium is the principal cation of the endolymph, which is secreted from the stria
vascularis. The high potassium content of the endolymph means that potassium, not
sodium, is carried as the depolarizing electrical current in the hair cells. This is known as
the mechano-electric transduction (MET) current. Endolymph has a high positive charge
(from 80-120 mV in the cochlea), mainly due to the presence of positively charged amino
acids. It is mainly this electrical gradient that allows potassium ions to flow into the
negatively-charged hair cells during mechanical stimulation of the hair bundle. Because the
hair cells are at a negative potential of about -50 mV, the electrical gradient from endo-
lymph to hair cell is on the order of 150 mV, which is the largest electrical potential found
in the body.
MLF fibers in balance
Coordinates head, neck and eye movements; contains fibers from medial vesti bular nucleus that terminate in cervical and uper thoracic levels
Lateral vestibulospinal tract
Begins in the ipsilateral lateral vestibular nucleus; found at all levels of spinal cod; facilitates extensor muscle tone in the antigravity muscles, thus maintaining upright posture
Efferent vestibular connections
Arise from vestibular nuclei; innervate hair cells in cristae ampullares and muculae of the utricle and saccule; thought to modulate spontaneous firing of the vestibular nerve fibers
A lesion where would produce dolls head eye movements?
lesion of the vestibular nuclei and MLF are present.
Left most picture
Normal brainstem
Middle picture
Bilateral MLF lesion; intranuclear opthalmoplegia
Right picture
Low brainstem lesion; neither eye moves when the head is turned
Post rotational nystagmus
Fast nystagmus component opposite direction of the turn, even after turning has stopped in pt with normal labryinths; pt will tend to fall to the right and experience a sensation of vertigo to the left
vestibuloochlear reflex; Excitatory pathways
in red, inhibitory pathways in
blue. Head is being spun to
the right (clockwise).
Note that the right lateral
semicircular canal is being
stimulated, activating the
right vestibular nerve and
vestibular nucleus. This
activates the left abducent
nucleus, stimulating the
left lateral rectus to contract,
moving the eyes to the left.
The MLF connections
to the right medial rectus
subnucleus of the oculomotor
nucleus to stimulate the right
medial rectus to contract,
preserving conjugate vision.
Note that hot water has the opposite effect
DIX-HALLPIKE TEST (NYLEN-BÁRÁNY TEST)
is a diagnostic maneuver used to identify
benign paroxysmal positional vertigo (BPPV).
(dislodged otoliths in psoterior semicircular canals)