Vestibular System And Cerebellum Flashcards
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
Vestibulo-cerebellum
-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
- R eye abducts, L eye adducts–normal
- R eye abducts, L eye no response–left III N palsy
- R eye no response, L eye adducts–R VI N palsy
- 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
Neocerebellum
- 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
S/S of Cerebellar Dysfunction
- unilateral lesions of cerebellum result in IPSILATERAL deficits b/c of extensive crossing and recrossing of tracts
- midline lesion of vermis affect axial musculature
- ataxia–staggering gait
- dysdiadochokinesia–inability to perform rapidly alternating movements
- intention tremor–lesion in SCP or dent ate nucleus
- decomposition of mvmt–breakdown of fluid, multi joint movement
- slurred or scanning speech
- asthenia–weakness of limb/axial Ms
- nystagmus
- hypotonia/hyporeflexia
Alcohol degeneration of cerebellum
- chronic ingestion of ethanol causes cortical atrophy of anterior lobe of cerebellum, and possibly Neocerebellum and dentate nucleus
- in the later stages of dz, pts with severe ataxia of lower limbs and trunk and a minor involvement of upper limbs
Friedreich’s Ataxia
- autosomal recessive degenerative dz of adolescence and adulthood
- progressive neuronal necrosis and demyelination of proprioceptive neurons in dorsal roots, posterior columns, ML, spino cerebellar tracts, and CST
- also get degeneration of Purkinje fibers, dentate nucleus, and SCP
- ataxia is initial and in lower limbs then moves to upper limbs
- dysdiadochokinesia, dysmetrai, nystagmus, and intention tremor
- wide based gait and spasticity
- optic atrophy, hearing loss, dysarthric speech
- dementia
-death in 10-20 yrs due to cardiac or pulmonary complications
Vestibular Rs
Innervated by short peripheral processes/ dendrites of bipolar neurons that form the vestibular N
