Lecture 10: Vestibular System and Cerebellum Flashcards
What kind of fibers are carried by the Inferior Cerebellar Peduncle?
Afferents to the cerebellum from spinal cord and brainstem
What kind of fibers does the Middle Cerebellar Peduncle carry?
Afferents to the cerebellum from the contralateral pontine nuclei
What kind of fibers are carried by the Superior Cerebellar nuclei and where are they distributed to?
Predominantly EFFERENTS from cerebellar nuclei; distributed to diencephalon and brainstem
What are the 3 deep cerebellar nuclei; what are their function?
- Dentate nucleus
- Interposed nucleus
- Fastigal nucleus
- Are the output/efferents of the cerebellum
What are the 3 layers of the Cerebellar Cortex from inner to outer?
- Granule cell layer: cell-dense inner region, adjacent to white matter
- Purkinje cell layer: sandwiched btwen the granular layer
- Molecular layer: outer pale layer, w/ few cells but high number of processes
Which cells are the only efferent neurons of the cerebellum?
- Purkinje cells
- All info entering the cerebellar cortex eventually converges upon the Purkinje cells
- Purkinje cell axon is the ONLY efferent from cerebellar cortex; most them terminate in the deep cerebellar nuclei
Which cells of the cerebellum are excitatory neurons that synapse w/ Purkinje cells and the molecular layer?
Granule cells
Which cells of the cerebellum are inhibitory cells w/n granular layer, extend dendrites into molecular layer?
Golgi cell
What are the inhibitory cells in the molecular layer of the cerebellum?
Basket and Stellate cells
What are the Mossy Fibers of the cerebellar cortex and what do they form?
- Cerebellar afferent axons that originate from cerebellar nuclei and other nuclei in the SC, medulla, and pons
- Branch profusely in granular layer and contact other cells at irregular intervals, form the mossy fiber rosette
- Excitatory to Granule cell and Golgi cell dendrites
What is the significance of Olivocerebellar fibers, where do they originate and what do they terminate as?
- Represent largest bundle of AFFERENTS and come from the inferior olivary nucleus
- Terminate as climbing fibers in the contralateral cerebellar hemisphere, which wrap around dendritic trees of purkinje fibers
- Each Purkinje fiber innervated by a single climbing fiber and they EXCITE Purkinje cells
What are the sources of Multilayered (monoaminergic) fibers of the cerebellum?
- Locus ceruleus (nonadrenergic)
- Raphe nuclei (serotoninergic)
- Hypothalamus
What is the function of the Multilayered (monoaminergic) fibers of the cerebellum in regards to the cells of the Cerebellar cortex, including Purkinje fibers?
Decreasing spontaneous discharge rates and alter the responsiveness of Purkinje fibers
What are the 3 functional subdivisions of the Cerebellum?
1) Pontocerebellum
2) Vestibulocerebellum
3) Spinocerebellum
The Vestibulocerebellum is equated with what lobe and nuclei; primary function?
- Flocculonodular lobe and fastigial nuclei
- Maintenance of balance/equilibrium
The Vestibulocerebellum has connections with what nuclei of brainstem and information is relayed to what lobe?
- Vestibular and reticular nuclei of the brainstem (via inferior cerebellar peduncle)
- Information relayed to ipsilateral FLOCCULO-NODULAR lobe
What is the path of cortical efferent fibers from the Vestibulocerebellum?
Cortical efferent fibers –> Fastigal nucleus –> Vestibular nuclei and Reticular formation
LMN output of the Vestibulocerebellum is _______ via ________ and ________ projections
LMN output of the Vestibulocerebellum is bilateral via vestibulospinal and reticulospinal projections
The Spinocerebellum influences what; which tracts are the afferents from; and via what cerebellar penduncles?
- Influences muscle tone and posture
- Afferents from spinocerebellar and cuneocerebellar tracts
- Via the inferior and superior peduncles
Which parts of the Spinocerebellum specifically control axial and limb musculature; describe both pathways?
- Vermal cortex and fastigial efferents (axial) —> vestibular and reticular nuclei
- Globose and emboliform nuclei (limb) —> superior cerebellar peduncle —> red nucleus and thalamus
The Ponto(NEO)cerebellum is concerned with what movement; comprised the majority of which hemisphere and nuclei?
- Muscular coordination, including trajectory, speed and force of movements, FINE movements
- Comprises the majority of the cerebellar hemisphere and DENTATE nuclei
Ponto(NEO)cerebellar fibers are principal afferents, describe their route on the way to the cerebellar hemisphere?
- Cross to the opposite side of brainstem
- Enter via middle cerebellar peduncle
- Terminate predominantly in the lateral parts of the cerebellar hemisphere
Output from the Ponto(NEO)cerebellum is directed to what nucleus, which then projects where (describe the route up to motor cortex)?
- Dentate nucleus —> contralateral Red nucleus and Ventral Lateral nucleus of the thalamus (via superior cerebellar peduncle)
- VLN (thalamus) projects to the motor cortex
Action by Ponto(NEO)cerebellum on cerebral cortical areas gives rise to what descending paths?
- Corticospinal
- Corticobulbar
Lesions of the lateral cerebellum result in what deficits?
- Deterioration of coordinated movement (dyssynergia)
- May also be a decrease in muscle tone (hypotonia) and DTR’s
- Ataxia involving extremities
- May also have an unsteady gait w/ tendency to lean to side of lesion
- Dysmetria (past-pointing)
- Tremors
What are 2 common types of tremors seen in patients with lateral cerebellar lesions?
- Kinetic tremor (intention tremor): when pt performs voluntary movement, most obvious as the end-point is approached
- Static tremor: mainfested when the pt stands with UE’s extended (muscles contracted against gravity)
What are the 4 vestibular nuclei?
- Superior vestibular nucleus
- Medial vestibular nucleus
- Lateral vestibular nucleus
- Inferior vestibular nucleus
Afferents of which subdivisions of the cerebellum pass through the inferior cerebellar peduncle?
- Vestibulocerebellum
- Spinocerebellum
Describe the clinical manifestations of alcohol cerebellar degeneration, what structures affected, and what do patients present with?
- Chronic ingestion can cause atrophy of cortex of anterior lobe of the cerebellum
- Can also atrophy pontocerebellum and dentate nucleus
- Pt presents w/ severe ataxia of the LE’s and trunk, w/ minor involvement of UE’s
Alcohol degeneration of the cerebellum may also be seen with what other condition?
- Korsakoff’s syndrome
- Chronic memory disorder caused by severe thiamine deficiency
Describe the clinical manifestations of Friedreich’s Ataxia; ineritance patter; what structures affected?
- Autosomal recessive
- Manifests in initial symptoms of poor coordination such as gait disturbance, but does not affect cognitive function
- Progressive neuronal necrosis and demyelination of proprioceptive neurons in the dorsal roots, posterior columns, medial lemniscus, spinocerebellar tracts, and corticospinal tracts
- Causes degeneration of Purkinje cells, dentate nucleus, and superior cerebellar peduncle
Afferent fibers for which part of cerebellum cross through middle cerebellar peduncle?
Pontocerebellum
Vestibular afferents from the semicircular canals primarily project to what 2 vestibular nuclei?
1) Superior vestibular nuclei
2) Medial vestibular nuclei
Vestibular afferents from Otolith organs primarily project to what 3 vestibular nuclei?
1) Lateral vestibular nuclei
2) Medial vestibular nuclei
3) Inferior vestibular nuclei
Saccular afferents project to neurons in which nucleus, and influence which eye movements?
- Contralateral oculomotor nucleus
- Influence vertical eye movements
What is the vestibuloocular reflex; what does it allow us to do?
- Keep a fixed gaze on an object while the head is moving
- Stabilizing eye movements, which are compensatory, due to being equal in magnitude and opposite in direction to the head movement perceived
- Can also be suppressed at will to focus on moving target
Primary afferents from the horizontal semicircular canals send axons to which fasciculus and nucleus; how does abducens nucleus contribute to the movement of both eyes?
- Send axons through medial longitudinal fasciculus (MLF) to contralateral abducens nucleus
- Abducens motor nucleus send excitatory impulses via CN VI to ipsilateral lateral rectus m.
- Abducens interneurons send excitatory impulses to contralateral oculomotor nucleus, which innervates medial rectus m.
Explain what happens with compensatory eye movement when you turn your head to the left, how do the semicircular canals contribute?
- Excitatory signals from left horizontal semicircular canal afferents increase firing rate of neurons in left vestibular nuclei
- Inhibitory signals from right vestibular nuclei are decreased
- Neurons in left vestibular nuclei excite both the contralateral abucens motor neurons and interneurons
- Contraction on right lateral rectus and left medial rectus, resulting in rightward eye movement
What is Nystagmus and describe the 2 phases?
- With large head rotations (360°), vestbuloocular reflex directs eyes slowly in the direction opposite head motion = slow phase
- Eye reaches limit –> spring back rapidly to central position, moving in same direction as head = fast phase
- Another slow phase then begins
*Slow phase relies on connections from vestibular nuclei to CN III, IV, VI nuclei
What is Oculocaloric Testing for Vestibuloocular response; which direction do eyes move?
- In a concious patient, ice water injected in ear creates a convection current in endolymph in lateral semicircular duct.
- Patient with intact brainstem, ice water causes eye to INITIALLY turn TOWARD the stimulus, and then horizontal nystagmus will be to the non-stimulated ear
- Warm water place in ear will initially cause eye to turn AWAY from the stimulus, and then horizontal nystagmus will be toward the stimulated ear
For nystagmus during this test = COWS
What are the clinical implications from ice water caloric testing if the eye fails to abduct or adduct?
- Failure to abduct = CN VI nerve palsy
- Failure to adduct = CN III nerve palsy
The vestibular nerve has direct connections to which of the following?
A. Dentate nucleus
B. Flocculo-nodular lobe
C. Paramedian pontine RF
D. Abducens nucleus
B. Flocculo-nodular lobe = Vestibulocerebellum - Strongly influenced by CN VIII
The secondary connection from the vestibular nuclei controlling head position is what?
Medial longitudinal fasciculus
In a patient with an intact brainstem, what is the normal response for when cold fluid is poured into the ear (i.e., right ear for example)?
- Right eye will abduct (toward the stimulus), left eye will adduct (toward the stimulus)
- Nystagmus will cause both eyes to move toward the opposite direction, back towards center, away from stimulus
The Doll’s eyes manuever is CONTRAINDICATED in which patients?
Suspected or confirmed C-spine injury
In the unconcious patient w/o cervical injury and INTACT brainstem, side-to-side movement of the head results in what movement of the eyes?
- Movement of the head to the right, causes horizontal gaze of the eyes to the left, and vice versa
- These are called doll’s eyes movements (Oculoclonic reflex)
What controls the slow phase and fast phase during the oculoclonic reflex?
Slow phase: CN III, IV, and VI nuclei
Fast phase: signals that originate from the reticular formation (RF)
Unilateral lesions of the vestibular system cause _______ signs and symptoms
ipsilateral
Lesions of the MLF result in a characteristic disturbance of horizontal gaze called what; abnormal gaze response is in what direction related to lesions and how the disturbance named?
- Internuclear opthalmoplegia (syndrome of MLF)
- Pt w/ an INO have an abnormal response to horizontal gaze in the direction opposite the side of lesion
- INO is named according to the side of oculomotor impairment
When attempting horizontal gaze to the left, the right eye does not adduct; the left eye exhibits nystagmus, how would you name this INO and where is lesion?
Right INO due to a lesion of the right MLF
How is accomodation affected by internuclear ophthalmoplegia?
Accomodation does not use the MLF and is unaffected by INO
The PPRF is a critical center for what kind of gaze and where does it send fibers?
- Critical center for horizontal gaze
- Sends fibers to ipsilateral abducens nucleus to influence ipsilateral lateral rectus m.
- Sends fibers to contralateral oculomotor nucleus to influences contralateral medial rectus m.
A unilateral lesions of the PPRF results in what?
- Paresis or paralysis of horizontal gaze toward the same side of the lesion
- Deficit due to destruction of fibers to the ipsilateral abducens nucleus and contralateral oculomotor nucleus
i. e., lesion of the right PPRF would cause inability to perform horizontal gaze to the right.
What tract is the critical link between the extrapyramidal system and cerebellum?
Central Tegmental Fasciculus
Which nucleus is responsible for planning, execution, and FINE tuning our movements?
Dentate nucleus
The vestibular nuclei projects to influence 4 principal tracts or areas, what are they and what are their functions?
- MLF - Eyes turn to side of stimulus
- MVST - Head turn to side of stimulus
- LVST - Body turns to side of stimulus
- RF - Nausea/Vertigo/Visceral Disturbances
What are the 6 afferents through the inferior cerebellar peduncle (hint: there is a mnemonic)?
1) Dorsal spinocerebellar tract - unconcious, precise propriocpeptive info from lower 1/2 body
2) Cuneocerebellar tract - unconcious, precise, proprioceptive info from upper 1/2 body
3) Trigeminocerebellar tract - info from head/face
4) Arcuocerebellar fibers
5) Reticulocerebellar fibers
6) Olivocerebellar tract - largest bundle of afferents that become climbing fiber —> Purkinje cells
