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7.6 - Vestibulocochlear nerve

Terms in this set (34)

function of vestibulocochlear nerve
transmits information about sound and equilibrium from inner ear to the brain
receptor organ of vestibular part of CN VIII
labyrinth, consisting of 3 semicircular canals (posterior, superior, horizontal), utricle + saccule
- receptor cells are located in the ampullar crista of each semicircular canal and in the macular crista of utricle and saccule

- ampulla has otoliths which move to activate the afferent nerve fibers
- macula has hair cells in a cupula which move to activate the afferent nerve fibers
explain pathway of signals from inner ear to CNS
1) movement of head moves otoliths in ampulla and cupula in macula to activate the afferent nerve fibers
2) Signal travels via vestibular nerve to vestibular ncl in brainstem (pons)
3) Several pathways form here:
- vestibulospinal tract --> motor neurons
- reticular formation
- cerebellum
- ncl of CN III
- to cortex via thalamus
most common symptom of lesion affecting the vestibular system
vertigo
4 main symptoms of vestibular lesions + their definitions
1) Vertigo = illusion of movement of patient of patient's surroundings (always worse during head movement), always rotatory/spinning
2) Nystagmus = involuntary biphasic rhytmic ocular oscillations
3) Tonic deviation of extremities and trunk (cannot maintain extremities straight)
4) Vestibular ataxia (not straight gait, esp. with closed eyes)
what other symptoms often occur together with vertigo?
autonomic disorders; nausea, vomiting, sweating
- vertigo is ALWAYS worse during head movement!!
Two clinical forms of nystagmus + causes
1) Pendular; both phases are slow, mostly congenital
2) Jerk; one slow and one fast/saccadic phase (slow phase is abnormal, fast phase is the correction) --> dysfunction of vestibular system, brainstem or cerebellum

Jerk nystagmus is named according to the direction of the fast phase
3 types of nystagmus according to direction of movement
1) Horizontal
2) Vertical
3) Rotatory
3 grades of horizontal nystagmus
1) First degree: nystagmus only during gaze in direction of rapid phase
2) Second degree: nystagmus during gaze straight ahead
3) Third degree: nystagmus also during gaze in direction of the slow phase
3 tests to detect tonic deviations of extremities due to vestibular damage
1) Hautant's sign: patient sits and lifts both arms forward with eyes closed, conjugate deviation of borth arms to one side indicated ipsilateral lesion of the labyrinth
2) Romberg's sign: Both arms lifted while standing, head turned to one side, patient deviates to side of head rotation, or falls over when eyes close
3) Unterberger's sign: patient is asked to walk on the spot with eyes closed and both arms lifted forward, rotation to one side indicates vestibular damage on the side which the patient rotates towards
what is vestibular ataxia?
deviation from straight direction during walking, esp with eyes closed (severe states --> patient cannot walk at all)
Peripheral vestibular syndrome
- affected structures
- symptoms
- harmonic or disharmonic?
- correlation between nystagmus and vertigo
- causes
- due to damage to the labyrinth or vestibular nerve
- rotatory vertigo, horizontal nystagmus (grade 2-3) with slow phase toward side of lesion, tonic deviations to same side as lesion --> HARMONIC (NB: nystagmus is defined according to direction of fast phase, and is therefore in the opposite direction of the lesion)
- positive correlation between intensity of vertigo and nystagmus (always occur together)
- Menier's disease, vestibular neuritis, acute labyrinthitis, benign paroxysmal (positional) vertigo, zoster oticus, toxic affections of CN VIII (aminoglycosides; streptomycin, gentamycin)
what is zoster oticus?
- triad of symptoms
- Tx
reactivation of previous varicella infection in geniculate ganglion
- symptoms; ipsilateral facial nerve paralysis, ear pain, vesicules in auditory canal
- Tx = antivirotics
Menier's disease (wiki)
- disorder of the inner ear, characterized by episodes of rotatory vertigo, tinnitus, hearing loss and sensation of fullness/pressure in the ear
- relate to endolymphatic hydrops (too much endolymph)
- no real cure excists (betahistidine and corticosteroids for symptomatic treatment)
Endolymph and perilymph
Membranous and bony labyrinths of the inner ear

special composition of endolymph?
Membranous labyrinths are located inside the bony labyrinths, membranous labyrinths contain the receptor organs for equilirbium and hearing
- perilymph lies between the membranous and the bony labyrinths
- endolymph lies within the membranous labyrinths

NB: endolymph contains a high concentration of K+, so influx of K+ is responsible for depolarization of the receptor cells (not Na+!)
Central vestibular syndrome
- affected structures
- correlation between nystagmus, tonic deviations and vertigo
- vestibular ncl or pathway
- vertigo, nystagmus (horizontal, vertical, rotatory)
- no correlation between the direction of nystagmus and the tonic deviations, nor the instensity of nystagmus and vertigo --> DISHARMONIC
- caused by lesions in brainstem, mostly vascular-ischemic lesions (vertebral or basilary artery), inflammation or tumors
4 most common causes of vestibular disorder
1) Vestibular neuronitis (acute peripheral vestibulopathy)
2) Acute posttraumatic vertigo
3) Benign paroxysmal positional vertigo
4) Meniere's disease
Vestibular neruonitis
- what?
- signs and symptoms
- most affected ppl
- cause
- treatment
- result of vestibular examination
- sudden attack of vertigo (rotatory), nausea, vomiting and disequilibium --> patient stays motionless in bed
- spontanous nystagmus with slow phase towards side of lesion
- hearing is impaired, but tinnitus may occur
- mostly in adults between 30-60 years of age
- benign condition, lasts some days, can be spontanoues recovery
- unknown cause, can be viral
- vetibular examination reveals unilateral vestibular areflexia
Acute posttraumatic vertigo
- what?
- signs and symptoms
- treatment
- vertigo occuring after concussion of the labyrinth (head injury)
- (in case of blood in external auditory canal --> fracture of temporal bone)
- persistent vertigo, loss of balance, spontaneous nystagmus (fast phase away from lesion),
- spontaenous reveal of symptoms after some days, then gradual recovery
Benign paroxysmal positional vertigo
- what?
- signs and symptoms
- causes
- diagnosis and treatment
- vertigo and nystagmus only occur when head is in a certain position or certain headmovements
- severe rotational vertigo for some seconds (never more than 1 min)
- posttraumatic, viral, ischemic , but mostly due to canalolithiasis (otholitic stones move freely within the semicircular canals during head movement, typically posterior canal)
- Diagnosis and treatment; Dix-Hallpike and Epley maneuvers ---> NB: can heal spontaneously
Meniere's disease (book)
- recurrent attacks of intense vertigo, lasting for minutes to hours (preceeded by tinnitus and hearing loss) --> typically episodes of remission and relapses
- caused by too much endolymph (endolymphatic hydrops), maybe due to insufficient resoprtion in the endolymphatic sac
duration of vertigo in:
- Vestibular neuronitis
- Acute posttraumatic vertigo
- Benign paroxysmal positional vertigo
- Meniere's disease
- VN: acute attack
- APTV: continous
- BPPV: several seconds, no more than 1 min
- Meniere's: min--> hours
treatment of acute vertigo
- thiethylperazine (antiemetic) or diazepam (hypnotic, benzodiasepine)
- antihistamines (embramine, promethazine)
- betahistidine (antihistamine) can prevent attacks of Meniere's disease
other causes of central vertigo
- multiple sclerosis
- tumors of posterior fossa
most common symptoms and signs in patients with transient ischemia in vertebrobasilar distribution (3)
- vertigo
- nystagmus
- disequilibrium
first step in evaluation of patient complaining of dizziness
- find accurate description of symptoms!! ---> dizziness is a very wide term
4 differential diagnosis causing dizziness
1) Vertigo
- often also nausea, vomiting, disequiliribum/imbalance, nystagmus
- damgage to vestibular system
2) Syncope or presyncope
- decreased cerebral perfusion
3) Disequilirium (sence of imbalance)
- inpaired inputs of spatial orientation (proprioception, cerebellum, extrapyramidal pathway, visual system)
4) Psychogenic dizziness (anxiety nerosis, conversion disorders, depression) --> dizziness does not fit into any other recognizable condition (no vertigo, nystagmis, syncope, disequilibrium), more continous than episodix
causes of disquilibrium causing a feeling of dizziness
- loss of proprioception --> worsens without visual input (peripheral polyneuropathy disorders of posterior columns (vit B12 deficiency, tabes dorsalis, myelopathies)
- cerebellar disorders (tumors, infarcts, alcoholic degeneration)
- extrapyramidal diseases (parkinsonism)
Explain the pathway of auditory nerve
receptor cell in organ of Corti in cochlea --> first order neurons in spiral ganglion --> cochlear nerve --> coclear ncl in brainstem --> second order neurons (some axons cross, some stay ipsilaterally) --> lateral leminiscus --> inferior colliculus + medial geniculate body --> third order neurons --> auditory cortex in temporal lobe
Most common cause of acute, bilateral hearing loss
mostly viral or bacterial meningitis
most common cause of progressive, bilateral hearing loss
carcinomatous meningitis, basilar meningitis (TBC), syphilis, toxoplasmosis, intoxication
why is central hearing loss so rare?
partial crossing of fibers of acoustic pathway
causes of acoustic hallucinations
irritation of temporal lobe in transverse temporal gyri (whistles, ringing) or surrounding areas (more complex sounds)
cause of hearing loss in general?
1) impaired conduction of sound (disorder of middle ear or obstruction of external auditory canal)
2) Sensorineural deficit (Meniere's disease, disorders of cochlea of cochlear part of CN VIII (acoustic neuroma, meningioma in cerebellopontine angle)
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