Neurology:: Ears
what is the chorda tympani?
chorda tympani is part of the facial nerve that travels through the ear. it innervates the taste buds in the anterior 2/3s of the ear
what would a tympanogram look like if you had eustachian tube dysfunction?
negative pressure in the ear --> compliance is maximal at a negative pressure because the eustachian tube is pulling the tympanic membrane in
how does the cerebellum process vestibular information?
CN 8 nucleus in the pons --> cerebellum (ipsilateral via inferior cerebellar peduncle) cerebellum --> back to vestibular nucleus and reticular formation --> spinal cord (ventral/lateral vestibulospinal tracts) and medial longitudinal fasciculus to control eye movements
what is the nomenclature for genetic deafness?
DFN = deafness, nonsyndromic locus A = autosomal dominant B = autosomal recessive no letter = x-linked
what is GJB2 mutation?
GJB2 mutation is the most common cause of non-syndromic congenital deafness.
what lesion would cause loss of vision from the right visual field with sparing of the macula?
PCAinfarct, damage to the occipital lobe (opposite side, so right visual field = left occipital lobe)
what is the vestibular system?
The vestibular system is how we tell where our head is in space. the vestibular system is made up of the saccule and utricle, the ampulla/cupula, and the semicircular canals. the saccule (vertical) and utricle (horizontal) sense lateral, linear movements. the semicircular canals sense rotational movements. the ampulla are swellings at the base of each semicircular canal, which contain hair cells. these are bent by fluid movements, which create nervous system signals to inform our brain of head positioning
what is labyrinthitis?
acute onset vertigo from viral vestibular insult. inflammation of the labyrinthine structure (bony supports of ear)
what drugs cause hearing loss ?
aminoglycosides
what drugs cause tinnitis?
aminoglycosides (gentamycin, streptomycin) quinidine/quinine (class 1a sodium channel blockers) aspirin
what is argyll-robertson pupil?
argyll-robertson is when your pupil accommodates to someone bringing their finger up to your nose but doesn't react to light. this is usually caused by tertiary treponema pallidum infection associated with tabes dorsalis (sensory ataxia, impaired proprioception)
where are low frequency sounds registered in the cochlea?
at the apex of the cochlea near the helicotrema. this part of the cohclea is wide and more flexible.
where are high frequency sounds registered in the cochlea?
at the base of the cochlea (nearest the oval window). this part of the cochlea is thin and rigid.
who gets otosclerosis?
autosomal dominant risk factors for getting it. usually caused by a viral infection. often made worse by pregnancy, seen in middle aged white women
what is DFNB1/DFNA3?
congenital deafness leading to pre-lingual (before you can speak) being deaf. no inner ear or vestibular abnormalities. caused by GJB2, GJB6 mutations GJB2 mutations are common in SE asians, ashkenzi jews, and white people (gap junction proteins)
what congenital infections causes deafness?
cytomegalovirus (also causes blueberry muffin rash, petechiae, microcephaly deafness comes later, sensoryneural) toxoplasmosis, rubella, herpes
what is bell's palsy?
damage to cranial nerve 7 leads to facial paralysis on one side of the face
what lesion would cause loss of vision from the left eye?
damage to left optic nerve
what lesion would cause loss of vision from the periphery on both eyes?
damage to optic chiasm
what lesion would cause loss of vision from one hemisphere of sight?
damage to optic tract after optic chiasm on one side of the brain
which direction of hair cell movement causes depolarization vs hyperpolarization?
depolarization is caused by movement towards the kinocilia (big hair) hyperpolarization is caused by movement away from the kinocilia (big hair)
what is the anatomy of the vestibular apparatus?
each of the semicircular canals are oriented at 90 degrees from one another so that they are able to sense all of the possible movements of the head within the utricle and saccule and semicircular canals are hair cells, which depolarize (K+ floods into cell, remember endolymph has high K+ and low Na+) when the stereocilia are directed towards the kinocilia (big hair). hair cells are made from neuroectoderm. depolarization causes opening of voltage-gated calcium channels, which cause an influx of calcium and ultimately neurotransmitter release to the brain the main difference between the vestibular apparatus and cochlea is the mechanism of stimulation. the cochlea is receiving sound as an input, but the vestibular apparatus needs something else. There are *otoliths*, small calcium carbonate crystals embedded in a gel that surrounds the vestibular hair cells. as the head rotates or moves, the weight of the otoliths causes an inertial force, pulling the hair cells in the opposite direction of movement. this causes depolarization or hyperpolarization, and allows us to know where we are.
how do you treat benign positional paroxysmal vertigo?
epley maneuver!
what innervates the stapedius muscle?
facial nerve
describe hair cells of the cochlea
hair cells of the cochlea are found within the organ of corti. they're surrounded by endolymph. when sound reaches the oval window, the basement membrane of the cochlea vibrates, causing movement of the stereocilia of hair cells. if they move towards the kinocilia (biggest hair), the cell depolarizes through influx of K+. if they move away from the kinocilia, the cell repolarizes through efflux of na+
what are complications of cholesteatoma?
hearing loss (conductive) meningitis
what is klein-waardenburg syndrome?
hearing loss (congenital or can be post-lingual) pigmentary abnormalities (white forelock, hair hypopigmentation, early greying, heterochromia or bicolored iris) telecanthus (large separation between eyes) limb length abnormalities caused by PAX3 (messed up homeodomain stuff) mechanism: messed up melanocyte development, decreased control of neural crest development
what is presbycusis?
hearing loss related to being old. you lose higher frequency sounds first (at base of cochlea) caused by destruction of hair cells in rigid base of cochlea
what causes horner syndrome?
horner syndrome = loss of sympathetic innervation to the face symptoms: ptosis, anhidrosis, miosis associated with spinal cord lesions above T1 or the stellate ganglion alongside the spinal cord (pancoast) 1st neuron is in spinal cord c2-t1 second neuron is in superior cervical ganglion third neuron is messed up by external carotid artery dissection.
what are the semicircular canals?
in each ear we have 3 semicircular canals, oriented 90 degrees apart from one another. the semicircular canals allow our brain to know about rotational movements of our head. each semicircular canal contains a swelling at its base, called the ampulla. within the ampulla lies the cupula, a gelatinous mass that contains sterocilia from specialized hair cells.
where are the oculomotor and edinger wesphal nuclei located?
in the midbrain, by the superior colliculus!
describe hair cells of the vestibular apparatus
in the vestibular apparatus, a layer of otolith (calcium carbonate crystals) provides weight, resting above the hair cells in the utricle and saccule. linear movements of the head (horizontal or vertical) create inertial forces, pulling stereocilia beneath the otolith layer in the opposite direction of movement. the hair cells depolarize and send a signal to the brainstem. the ampulla of the ear contains the cupula, a large gelatinous accumulation of sterocilia. the cupula moves in response to rotation of the head or body, and helps provide our brain with positional information via CN 8. hair cells are oriented in polar opposite directions across the ears (your left ear depolarizes but your right ear hyperpolarizes. this is different than the cochlea, where we're able to determine which side sound comes from based on timing of the stimulus)
describe the pupillary light reflex
light sent to one eye sends isgnal to pretectal nucleus in midbrain. from there, the ciliary ganglion on both sides of the head are stimulated. both eyes will respond by constricting the pupillary sphincter muscles. a health response has light in one eye causing bilateral pupillary constriction
what lesion would cause loss of vision from the upper half of a hemisphere of sight?
loss of meyer's loop on one side of the brain
what lesion would cause loss of central vision?
macular degeneration (central scotoma)
what is branchio-oto-renal syndrome?
malformation of the middle/inner/outer ear, hearing loss, branchial fistulae, and renal malformations Branchio-oto-renal syndrome is often caused by the EYA1 gene mutation, a gene expressed in the inner ear, head mesenchyme and kidneys associated with normal embryological development
what is meniere's disease?
meniere's disease = endolymphatic hydrops =intermittent long vertigo spells. you can localize symptoms of fullness/pressure/tinnitus to one ear during a vertigo spell symptoms: low frequency hearing loss (normally you lose high frequency sounds), tinnitus, episodic vertigo treatment: diuretic, low salt diet
what is nystagmus?
nystagmus is involuntary motion of eyes due to inappropriate stimulation of the vestibular system. nystagmus has two phases: slow incorrect movement and fast corrective saccade. for example, if you damage the right ear's vestibular system, the body thinks the head is slowly turning to the left. the eyes will drift right in response, and then snap back into position. nystagmus is made worse when you try to look laterally
what are the otolith organs?
otolith are calcium carbonate crystals suspended in a gel resting above the hair cells of the utricle and saccule. otolith provide the stimulus to our horizontal/vertical vestibular system. the otolith are heavy and respond slowly to acceleration. the inertia they create pulls on the underlying hair cells and causes depolarization/hyperpolarization
what is cholesteatoma?
overgrowth of desquamated keratin debris within the middle ear space. can erode the ossicles and mastoid air cells symptoms: conductive hearing loss, otorrhea
what ion flows into hair cells in response to stereocilia being pushed in the direction of the kinocilia?
potassium! remember that stereocilia are surrounded by endolymph, which is most like intracellular fluid (high in k+ low in na+). so this is one of the few neurons/nerves that will be depolarized by potassium influx
describe transmission of sound through the cochlea
pressure waves in air --> tympanic membrane vibrations --> maleus --> incus --> stapes (modulated by stapedius muscle from CN 7) --> oval window vibration --> perilymph vibrations --> endolymph vibrations --> hair cell depolarization in organ of corti
what is otosclerosis?
sclerosis of ear bones --> they no longer vibrate like they're supposed to and you have conductive hearing loss
what is the vestibular apparatus?
semicircular canals + ampula = rotational movement saccule = vertical movement utricle = horizontal movement
what is the vestibular nervous pathway?
sensation of movement by vestibular apparatus --> CN 8 vestibular nucleus in pons --> ipsilateral cerebellar hemisphere signal --> vestibular nucleus and reticular formation of brainstem receive correction signals from cerebellum --> motor command in pre-central cortex is modulated to maintain posture and steady gaze
what is miniere disease?
some kind of bad thing that happens to your ear causes perpheral vertigo symptoms: episodic vertigo, tinnitus, low frequency hearing loss
what is the dix-hallpike test?
test to confirm if somebody has BPPV. you twist them really quick and they get dizzy and you say "you have BPPV"
what is the ampulla?
the ampulla is the base of the semicircular canal. the ampulla contains the cupulla, a large gelatinous structure with stereocilia inside. the cupula bends with rotation of the head, signalling to our brain that our head is moving.
what is the caloric reflex test?
the caloric reflex test is a test for horizontal nystagmus. you put cold or warm water in the external auditory canal. the temperature difference between the water and body creates a current in the endolymph and cause horizontal nystagmus (in opposite directions based on temperature). hot water makes the eyes look to the opposite ear and nystagmus to the middle. cold water make the eyes look toward the ipsilateral ear and nystagmus to the middle. absent reactive eye movement = vestibular weakness COWS = cold opposite, warm same remember nystagmus is the slow movement/drift, not the initial shift/fast response
what is the cupula? what is the ampula?
the cupula is a specialized nerve cell in the base of the semicircular canals, at the swelling called the *ampulla*. the cupula is a gelatinous mass containing the stereocilia of a hair cell. during rotation of the head, the cupula is pushed back and forth by inertia, telling the body where our head is
what would atympanogram look like if you had destruction to part of the middle ear?
the ear is stiff and does not have a point of maximal compliance
inner ear (first aid)
the inner ear contains a snail-shaped, fluid-filled cochlea. the cochlea contains a basilar membrane that vibrates secondary to sound waves. vibration is transduced by specialized hair cells (depolarization via K+ influx from endolymph) , converted into a nervous system signal and sent to the CN 8 nucleus in the pons. low frequency vibrations are heard best at the apex near the helicotrema high frequency vibrations are heard
what is the lateral geniculate nucleus?
the lateral geniculate nucleus is a processing/sensory center for visual information. the lateral geniculate nucleus on one side of the brain takes in information from both eyes pertaining to the opposite visual field (left LGN gets signals about right visual field). from the lateral geniculate nucleus you have sensory information sent to the occipital lobe via meyer's loop (superior visual field, inferior pathway), or dorsal optic radiation (inferior visual field, superior pathway through internal capsule) all signals end up in occipital lobe, in the lingula (upper visual field) or cuneus (lower visual field)
what is the organ of corti?
the organ of corti is the sensory organ of the inner ear that allows us to pick up sound. it is surrounded by endolymph in the cochlea
what is the posterior commisure?
the posterior commissure is part of the brain involved in the pupillary light reflex. it's right on top of the cerebral aqueduct. the posterior commissure connects the pretectal nuclei from both hemispheres, creating the bilateral pupillary reflex
how does the vestibular system work?
the semicircular canals, utricle, and saccule sense head movements. their hair cells release information to the CN 8 nucleus in the pons. from there, the pons activates the cerebellum through the inferior cerebellar peduncle. the cerebellum then sends sensory and motor modulation signals up to the cortex.
what is benign positional paroxysmal vertigo?
this is a feeling of spinning with head position changes. benign positional paroxysmal vertigo is caused by malfunction of the posterior canal, from accumulation of debris in the canal. treatment = epley maneuver. you do slow movements of the head and body which shake up the accumulated debris and relieve symptoms
what are environmental causes of deafness?
toxoplasmosis, rubella, CMV, herpes, HIV meningitis, low birth weight hyperbilirubinemia ventilation *aminoglycosides*
what is the vestibulooccular reflex?
vestibulo-ocular reflex is when movement/rotation of your head causes compensatory stabilizing eye movement. when the head is pushed to the left, the eyes will move to the right to keep your vision central. damage to the vestibulo-ocular reflex causes nystagmus. the vestibulo-ocular reflex is controlled by signals from the vestibular apparatus of the inner ear.
what is the doll's head maneuver?
you hold the person's head and rotate it quickly to either side. if their eyes stay central, they have a healthy vestibulo-ocular reflex. if not, their eyes will follow the rotation and then slowly move back to an accommodated position. this is called saccade/nystagmus
what is a normal tympanogram?
you measure compliance. maximal compliance should be at zero pressure because the ear is exposed to atmospheric pressure. that's the peak in this graph.
what is superior canal dehiscense?
you're missing bone over the superior semicircular canal --> conductive hearing loss, sound/pressure cause momentary spinning + pulsatile tinnitis, autophony (your voice sounds loud)
