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59 Cards in this Set
- Front
- Back
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Note petrous temporal bone.
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Three ossicle bones
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Malleus, incus, stapes; transmits energy into the oval window -> scala vestibuli -> helicotroma -> scala tympani -> round window
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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. |
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Through what opening does CN VII, VIII and nervus intermedius run through?
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What info does the nervous intermedius carry?
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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)
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Name of the bony core around which the cochlea is covered?
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Modiolus; contains the ganglion cells o fthe cochlear portion of the vestibulo cochlear nerves; edges of modiolus form the spiral lamina
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Where is perilymph vs endolymph located?
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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. |
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What membranes separate the scala vestibuli from the cochlear duct and the scala tyampni from the cochlear duct?
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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. |
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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
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Relationship of frequency to wavelength on the basilar membrane
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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. |
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Inner vs outer hair cells
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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 |
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Membrane deflection
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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. |
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spiral ganglion bipolar cells
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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. |
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Where does VIII enter the brainstem
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Note the vestibulocochlear nerve entering the brainstem at the cerebellopontine angle. Note the dorsal (posterior) cochlear
nucleus and the ventral (anterior) cochlear nucleus. |
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Where does VIII enter the brainstem
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Note the vestibulocochlear nerve entering the brainstem at the cerebellopontine angle. Note the dorsal (posterior) cochlear
nucleus and the ventral (anterior) cochlear nucleus. |
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Dorsal cochlear nucleus -> lateral lemniscus
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Where does anterior cochlear nucleus synapse?
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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. |
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Projections of the lateral lemniscus
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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). |
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Cochlear nerve ->
1. Ventral cochlear nucleus -> trapezoid body -> superior olivary nucleus -> contrallateral lateral lemniscus 2. dorsal cochlear nucleus -> ipsilateral lateral lemniscus |
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Neural acoustic pathways
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Where is the primary auditory cortex?
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THEPRIMARY AUDITORY CORTEX IS THE TRANSVERSE TEMPORAL
GYRUS OF HESCHL, WITHIN THE LATERAL SULCUS. THIS CONTAINS BRODMANN AREAS 41 AND 42. |
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Loss of the corneal blink reflex
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Schwannoma: early sign of distortion of the trigeminal nerve by
a tumor emerging from the internal acoustic meatus into the posterior cranial fossa. |
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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. |
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Weakness of the entire hemiface with atrophy
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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. |
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Anesthesia of the posterior third of the tongue, oropharynx and nasopharynx
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schwannoma: denote
involvement of the glossopharyngeal nerve. |
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Ipsilateral cerebellar signs (ataxia, pendular reflexes, intention tremor) in the arm and
leg |
schwannoma: appear when the cerebellum is compressed
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hypertonia, hyperreflexia, Babinski
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UMN signs in the limbs = compression of brainstem in schwannoma
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headache, drowsiness, papilledema, abducent palsy
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increased intracranial pressure signs = obstruction o fthe circulation of CSF inside or around the brainstem
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Which nerves would be compromised first/early/late symptoms of acoustic neuroma?
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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. |
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Bilateral acoustic neuromas; left vestibulocochlear nerve tumor has a meningioma also associated with it
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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. |
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From what nucleus is the tensor tympani innervated by?
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The
tensor tympani is innervated by neurons in the motor nucleus. When stimulated, it dampens the vibrations of the ossicles, preventing nerve damage. |
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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. |
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Olivocochlear efferents function?
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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.
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Where can inner ear infections spread?
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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. |
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Gradenigo Syndrome
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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 |
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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. |
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Positive Rinne test
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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). |
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Negative Rinne Test
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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). |
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false negative rinne test
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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. |
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What ganglion innervates the hair cells on the cupulae o fthe crista ampullares?
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bipolar cells o fthe vestibular ganglion of Scarpa
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What info does the macula of the utricle provide
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Side to side movement
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What info doe sthe macula of the saccule provide
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Up and down movement
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If you knocked out the maculae of the utricle nad saccule, what muscular effects would you observe
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They are essential to the static, postural, tonic neck, and
righting reflexes. |
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Through what duct does perilymph communicate with the subarachnoid space
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the perilymphatic duct of the cochlear canaliculus.
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What structure secrtes endolymph
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Stria vascularis of the cochlear duct
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What structure absorbs endolymph
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Endolymphatic sac
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Mechano-electric transduction current
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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. |
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MLF fibers in balance
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Coordinates head, neck and eye movements; contains fibers from medial vesti bular nucleus that terminate in cervical and uper thoracic levels
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Lateral vestibulospinal tract
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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
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Efferent vestibular connections
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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
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A lesion where would produce dolls head eye movements?
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lesion of the vestibular nuclei and MLF are present.
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Left most picture
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Normal brainstem
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Middle picture
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Bilateral MLF lesion; intranuclear opthalmoplegia
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Right picture
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Low brainstem lesion; neither eye moves when the head is turned
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Post rotational nystagmus
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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
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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. |
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Note that hot water has the opposite effect
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DIX-HALLPIKE TEST (NYLEN-BÁRÁNY TEST)
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is a diagnostic maneuver used to identify
benign paroxysmal positional vertigo (BPPV). (dislodged otoliths in psoterior semicircular canals) |