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Vestibular N

-enters brainstem in Pontomedullary sulcus
-courses below restiform body
-terminate in one or more of 4 vestibular nuclei--vestibular nuclei, fastigial nuclei, flocculonodular lobe


Medial longitudinal fasciculations

-fibers from vestibular nuclei and paramedian pontine reticular formation (PPRF) decussation in pons and ascend into the MLF and descend into the medial vestibuli spinal tract
-most fibers in MLF are crossed and originate from opposite side
-terminates in Oculomotor, Trochlear, and Abducens nuclei


Vestibulo-ocular pathway

-MLF terminates in Oculomotor, Trochlear, and Abducens
-Oculomotor system: role in coordinated, synchronized eye movements, and horizontal gaze
-horizontal gaze involves coordinated contractions of lateral rectus of one eye and medial rectus of other eye


Paramedian pontine reticular formation

-critical center for horizontal gaze

-staging and coordinating area for Oculomotor system

-sends fibers to Abducens nucleus of same side for influencing the ipsilateral lateral rectus
-also sends fibers to the contralateral MLF to the contralateral Oculomotor nucleus that innervates the medial rectus


Medial vestibulospinal tract

-descending continuation of Medial Longitudinal Fasciculus in SC
-primarily an uncrossed descending tract
-influences the Ms of neck, upper back, and proximal upper limbs
-key link in coordinating the positioning of head relative to eye movements


Lateral Vestibulospinal Tract

-originates from lateral vestibular nucleus-->descends in lateral funiculus-->terminates ipsilateral intermediate gray
-facilitates extensor tone and reflexes of antigravity axial and appendicular musculature


Reticular formation

-strong, bilateral projections from vestibular nuclei
-connections affect the somatic motor system (postural tone)
-provides a mechanism for visceral autonomic effects or disturbances (vertigo, nausea, vomiting)


Juxtarestiform body

-vestibular connection to the cerebellum courses thru the medial portion of the inferior cerebellar peduncle



-vestibular system and cerebellum are linked by the flocculo-nodular lobe and its deep cerebellar nucleus, fastigii


Flocculo-nodular lobe

Receives input from vestibular nuclei and reticular formation
-output from cortex is directly to fastigial nucleus


Direct fastigiobulbar tract

-fibers originate in fastigial nucleus
-terminate in ipsilateral vestibular nuclei and RF


Indirect fastigiobulbar tract

-fibers originating in fastigial nucleus
-decussation in cerebellar commissure
-bifurcate ascending and descending limbs


Connection of the vestibular system with the extra pyramidal system

Flocculonodular lobe-->fastigial nucleusvestibular nuclei-->MVST and LVST for axial musculature

The fastigial nucleus sends info to the ventral lateral nucleus and then to the primary motor cortex and the anterior corticospinal tract which works on axial musculature


Doll's Eyes Maneuver

-in an unconscious pt without cervical injury, side to side movement of head results in horizontal movement of eyes in opposite direction

Head turns right
Horizontal gaze to left-->normal finding
Right addicts, left neutral-->left VI palsy
R neutral, left abducts-->right III palsy
No response-->midbrain damage

Head turns left
Horizontal gaze to right-->normal finding
L neutral, R abduct-->left III palsy
L adducts, R neutral-->right IV palsy
No response: midbrain damage


Oculocaloric Testing

-in an unconscious pt, injection of cold water into the ext. auditory meatus results in horizontal gaze toward side of stimulus

Ex: testing R ear
1. R eye abducts, L eye adducts--normal
2. R eye abducts, L eye no response--left III N palsy
3. R eye no response, L eye adducts--R VI N palsy
4. R eye no response, L eye no response--R VIII N palsy, midbrain damage


S/S of unilateral lesion of vestibular system

-postural impairment
-eyes, head, body turn towards side of lesion
-pt tends to fall toward side of lesion
-nystagmus--directed toward side of lesion
-vertigo--opposite of lesion


Lesion of paramedian pontine reticular formation

-PPRF has lateral gaze center
-unilateral lesion of PPRF results in paresis or paralysis of horizontal gaze toward the SAME side of lesion and a gaze preference away from side of lesion
-deficit due to destruction of fibers that course from PPRF to ipsilateral Abducens nucleus and contralateral Oculomotor nucleus

Ex: lesion of the right PPRF would result in pt's inability to move both eye in conjugate horizontal gaze to R, so gaze preference to left



-newest addition to cerebellum
-posterior lobes
-assoc with precise coordination of skilled limb movements


Fastigial nucleus

-medial most nucleus of the 4 nuclei in the deep cerebellum
-has vestibular connections and function
-acts to send vestibular efferents in ICP


Dentate Nucleus

-large convoluted cup shaped nucleus gives rise to efferents thru the SCP
-most efferents are described as dentato---dentato-rubral fibers originate in dentate and terminate in red nucleus


Dorsal spinocerebellar tract (DSCT)

-conveys unconscious precise proprioception from lower 1/2 of body and lower extremities
-originates in nucleus dorsalis-->ipsilateral ICP-->anterior vermis


Cuneocerebellar tract

-conveys unconscious precise proprioceptive info from upper 1/2 of body and upper extremities
-originate in accessory cuneate nucleus-->vermis


Trigeminocerebellar tract

-one of 2 unconscious sensory tracts from face
-from sub nucleus rostralis and interpolaris of descending nucleus of V and project to anterior vermis


Olivocerebllar fibers

-originate in inferior Oliver's nucleus (ION) and terminate as climbing climbing fibers in contralateral cerebellar hemisphere
-important processing and relay center for sensory info from spinal cord and motor info from reticular formation and extrapyramidal system
-receives input from central tegmental fasciculus and spinoolivary tract


Central tegmental fasciculus (CTF)

-ascending and descending fibers from medial group of reticular nuclei
-located in center of tegmental reticular formation
-originates in red nucleus, central periaqueductal gray, and midbrain tegmentum
-critical link b/w extrapyramidal system and cerebellum


Pontocerebellar fibers

-form all of middle cerebellar peduncle
-terminate in ipsilateral pontine nuclei which project to contralateral cerebellar hemispheres
-form part of feedback loop b/w motor cortex and cerebellum


Ventral spinocerebellar tract

-conveys unconscious, proprioceptive info from lumbosacral levels of cerebellum
-originates in dorsal horn and IG and decussation in AWC and ascends in lateral funiculus
-passes thru SCP and anterior vermis of cerebellum


Trigeminocerebellar tract

-derived from main sensory nucleus of V
-projects to anterior vermis of cerebellum via SCP
-conveys precise info from head to cerebellum


Dentato-rubro-thalamic pathway

Dentate nucleus
-->VL nucleus-->primary motor cortex
-->red nucleus-->VA nucleus-->pre motor cortex-->red nucleus by way of corticorubral fibers-->reticular formation and rubrobulbar and rubrospinal tracts in brainstem


Purkinje Cell Layer

-middle layer of cortex of cerebellum
-large inhibitory neurons
-100000 synapses on a single cell
-example of principles of convergence, temporal, and spatial summation, and synaptic excitation/inhibition

-all info entering cerebellar cortex converges on Purkinje cells and the Purkinje cell axon is ONLY efferent from cerebellar cortex
-most terminate in deep cerebellar nuclei