12 Vestibular System and Cerebellum - Β Flashcards
The deep indentations of the cerebellum are ___________ while the smaller creases are called ________
Fissures; folia
Fissures divide the cerebellum into
Lobes and lobules
*The two hemispheres of the cerebellum are joined midline by the
Vermis
What are the main lobes of the cerebellum
Posterior, anterior, flocculonodular
What defines the flocculus and vermis (the nodule) to form the flocculonodular lobe
Posterolateral fissure
*The inferior cerebellar peduncle does what
Afferents to the cerebellum from the spinal cord and brainstem
*What is composed of recipricol fibers b/n the cerebellum and vestibular structures
Juxtarestiform body (wall of 4th ventricle)
*What part of the cerebellum has fibers arising in SC or medulla
Restiform body
*What is the largest cerebellar peduncle? What does it do?
Middle; emerges laterally from the basal pons and is composed of afferents to the cerebellum from the contralateral pontine nuclei
*What is unique about the superior cerebellar peduncle
It is most efferent fibers from the cerebellar nuclei and is distributed to the diencephalon and brainstem
What are the primary afferents of the cerebellum
Deep cerebellar nuclei
What are the main deep cerebellar nuclei
- Dentate
- Interposed comprised of emboliform (anterior interposed) and globose (posterior interposed)
- Fastigial
*Each folium of the the cerebellum has a superficial layer ___________ and a core of myelinated fibers ___________
Cerebellar cortex; arbor vitae
What are the layers of the cerebellar cortex
-purkinje -granule cell -molecular
The granule cell layer is composed of
Cell-dense inner region immediately adjacent to white mayyer core
*What are the purkinje cells
Only efferent neurons of the cerbellum
What are the granule cells
Excitatory neurons that synapse w/ purkinje cells and the molecular layer (basket and stellate cells) They extend parallel fibers
What are the golgi cells
Inhibitory cells within the granular layer, extend dendrites into molecular
*What are the basket and stellate cells
Inhibitory cells in the molecular layer
What are mossy fibers
Cerebellar afferent axons that originate from cerebellar nuclei and other nuclei in the SC, medulla, pons
The mossy fibers branch in granular layer to form
Mossy fiber rosette
What gives the mossy fibers their appearance
Cerebellar glomerulus
What are excitatory to granule cell and golgi cell dendrite
Mossy fibers
What are the afferent fibers to the cerebellar cortex
Climbing fibers and multilayered fibers
Climbing fibers arise from
Inferior olivary nuclei
What do olivocerebellar fibers do
Send collaterals to the appropriate cerebellar nucleus that corresponds to the overlying cortical zone
What is the function of the climbing fibers
Exciting purkinje cells
Where are multilayered cells from
Locus ceruleus (noradrenergic) Raphe nuclei (serotinergic) Hypothalamus
The main function of the multilayered fibers are
Decreasing spontaneous discharge rates of purkinje cells
Which cerebellar fibers innervate all major cell types
Multilayered cells
*What are the functional subdivisions of the cerebellum
Pontocerebellum Vestibulocerebellum Spinocerebellum
*What is the pontocerebellum function
-comprises the majority of the cerebellar hemisphere and dentate nuclei -muscle coordination, speed/force/trajectory of movements
What is the function of the vestibulocerebellum
- Equated with flocculonodular lobe and fastigial nuclei
- maintenance of balance/EQ
What is the function of the spinocerebellum
- approximates the vermins and surrounding area with the globose and emboliform nuclei
- coordinates muscle tone/posture
The vestibulocerebellum LMN output is
B/l bia vestibulospinal and reticulospinal projections
What afferents does the spinocerebellum receive
-spinocerebellar and cuneocerebellar tracts -info from muscle, joint, and cutaneous receptors
Fibers of the spinocerebellum terminate
In the cortex of the ipsilateral vermis and adjacent paravermis
The output of the spinocerebellum is focused primarily on
Control of axial and limb musculature
What is the pathway for axial movements from the spinocerebellum
Vermal cortex and fastigial efferents —> vestibular and reticular nuclei
What is the limb pathway from the spinocerebellum
Globose and emboliform —> superior cerebellar peduncle —> red nucleus and thalamus
What are the principal afferents of pontocerebellum
Pontocerebellar fibers -they cross to the opposite side of the brainstem -enter via middle cerebellar peduncle -terminate predominantly in the lateral part of the cerebellar hemisphere
What is the primary output of hte pontocerebellum
Dentate nucleus -projects to the contralateral red nucleus and ventral lateral nucleus of the thalamus via the superior cerebellar peduncle -VLN (thalamus) projects to motor cortex
Lesions of the lateral cerebellum
-Result in deterioration of coordinated movement (dyssynergia) -May also decrease muscle tone (hypotonia) and DTR -Ataxia involving extremities -May also have unsteady gait w/ tendency to lean toward side
Dysmetria can result from
Cerebellar lesions -this is past pointing and is apparent in patients when they attempt to point to objects
Tremors can result from
Lateral cerebellar lesions -can be kinetic (voluntary movements toward the end of the movement) or static (when they stand with upper extremities extended)
The semicircular canals record
Angular accelerations
The otolith organs record
Linear acceleration
Receptors in the vestibular organs are innervated by primary afferent fibers of
Vestibular ganglion (scarpa ganglion)
Central processes of the bipolar cells of the vestibules enter the brainstem and terminate
In the ipsilateral vestibular nuclei and cerebellum
The superior vestibular nucleus
Is superolateral in the central pons bordered by the restiform body and 4th ventricle
Where is the medial vestibular nucleus
Lateral floor of 4th ventricle throughout most of its rostrocaudal extent
Where is the lateral vestibular nucleus
Lies lateral to the medial vestibular nucleus and contains large neurons (Deiters cells)
Where is the inferior vestibular nucleus
Located lateral to the medial vestibular nucleus, extends through much of the medulla
The primary vestibular afferents enter the brainstem where
Pontomedullary junction -they transverse the restiform body and bifurcate into ascending and descending branches
Afferent fibers from the semicircular canals project where
Superior and medial vestibular nuclei
The otolith organs project primarily to
Lateral, medial, and inferior vestibular nuclei
Saccular afferents project to neurons in the
Contralateral oculomotor nucleus to influence vertical eye movements
Vestibular nuclei show what type of selectivity
Directional to cause certain head movements
Superior and medial vestibular nuclei receive information from
Otolith receptors and one semicircular canal pair (either horizontal or vertical)
Lateral and inferior vestibular nuclei receive information from
Several canal pairs and otolith receptors
What is the vestibuloocular reflex
Compensatory mechanism that allows you to track a fixed object while moving
What is the pathway for the vestibuloocular reflex
Axons through medial longitudinal fasiculus —> contralateral abducens nucleus —> abducens motor neurons send excitatory impulses via CN6 —>ipsilateral lateral rectus m + contralateral occulomotor nucleus (medial rectus m)
How is the vestibuloocular network modulated
-vestibular neurons send excitatory signals to ipsilateral oculomotor nucleus -vestibular neurons carry inhibitory signals to ipsilateral abducens nucleus
What is the slow phase of nystagmus
Eyes move opposite direction of head rotation
What is the fast phase of nystagmus
Eyes moving in the same direction as the head
How is nystagmus named
Direction of head rotation
Slow phase is dependent on what CN
3, 4, 6
What is caloric nystagmus
Warm water in the ear causes looking towards that side Cold water in the ear causes opposite eye movements
What is the oculoclonic reflex
Doll’s eyes movement Intact= both eyes looking in direction of fluid in ear
The slow phase of the oculoclonic reflex is mediated by
Vestibular nuclei (CN 3, 4, 6)
The fast phase of the oculoclonic reflex is mediated by
Signals that originate from the reticular formation
Lesioned RF but intact brainstem does what with oculoclonic reflex
Deviation of eyes in the direction of the slow phase
What is the name of the name of the brainstem circuitry that controls rapid eye movement
Saccades
What contains premotor neurons that project to the extraocular motor nuclei
Pontine reticular formation/paramedian pontine reticular formation
Lesions in the pontine reticular formation/paramedian pontine reticular formation cause
Horizontal gaze palsies -assuming the horizontal gaze center is involved
What are the cells of the pontine reticular formation that project to the extraocular motor neurons
Excitatory burst neurons Inhibitory burst neurons
When gaze shifts right what do the EBN and IBN do
EBN activate CN6 on the right IBN inhibit CN 6 on the left
What carries information about the direction that the eyes should move
MLF (medial longitudinal fasiculus)
