Vestibular System And Cerebellum

Question 1

Vestibular N

Answer 1

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

Question 2

Medial longitudinal fasciculations

Answer 2

• 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

Question 3

Vestibulo-ocular pathway

Answer 3

• 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

Question 4

Paramedian pontine reticular formation

Answer 4

• 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

Question 5

Medial vestibulospinal tract

Answer 5

• 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

Question 6

Lateral Vestibulospinal Tract

Answer 6

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

Question 7

Reticular formation

Answer 7

• 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)

Question 8

Juxtarestiform body

Answer 8

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

Question 9

Vestibulo-cerebellum

Answer 9

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

Question 10

Flocculo-nodular lobe

Answer 10

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

Question 11

Direct fastigiobulbar tract

Answer 11

• fibers originate in fastigial nucleus

- terminate in ipsilateral vestibular nuclei and RF

Question 12

Indirect fastigiobulbar tract

Answer 12

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

Question 13

Connection of the vestibular system with the extra pyramidal system

Answer 13

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

Question 14

Doll’s Eyes Maneuver

Answer 14

-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

Question 15

Oculocaloric Testing

Answer 15

-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

Question 16

S/S of unilateral lesion of vestibular system

Answer 16

• 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

Question 17

Lesion of paramedian pontine reticular formation

Answer 17

• 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

Question 18

Neocerebellum

Answer 18

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

Question 19

Fastigial nucleus

Answer 19

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

Question 20

Dentate Nucleus

Answer 20

• 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

Question 21

Dorsal spinocerebellar tract (DSCT)

Answer 21

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

Question 22

Cuneocerebellar tract

Answer 22

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

Question 23

Trigeminocerebellar tract

Answer 23

• one of 2 unconscious sensory tracts from face

- from sub nucleus rostralis and interpolaris of descending nucleus of V and project to anterior vermis

Question 24

Olivocerebllar fibers

Answer 24

• 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

Question 25

Central tegmental fasciculus (CTF)

Answer 25

- 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

Question 26

Pontocerebellar fibers

Answer 26

- 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

Question 27

Ventral spinocerebellar tract

Answer 27

- 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

Question 28

Trigeminocerebellar tract

Answer 28

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

Question 29

Dentato-rubro-thalamic pathway

Answer 29

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

Question 30

Purkinje Cell Layer

Answer 30

- 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

Question 31

S/S of Cerebellar Dysfunction

Answer 31

- 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

Question 32

Alcohol degeneration of cerebellum

Answer 32

- 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

Question 33

Friedreich's Ataxia

Answer 33

- 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

Question 34

Vestibular Rs

Answer 34

Innervated by short peripheral processes/ dendrites of bipolar neurons that form the vestibular N