Chapters 12 Motor System Cerebellum

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Chapters 12 Motor System Cerebellum

• Chris Rorden
• University of South Carolina
• Norman J. Arnold School of Public Health
• Department of Communication Sciences and
  Disorders
• University of South Carolina

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Function of Cerebellum

• Error Control Device - Monitor, Quality Control
• Monitors outputs to muscles from motor cortex and
  sensory signals from receptors
• Compares the efferent project plan with execution
  at motor action site
• Considers related factors and makes adjustments

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Cerebellum

• 50 of brains neurons, 10 of volume
• Can change movements as necessary
• E.G. Walking or talking
• Does not reach conscious awareness
• Muscle synergy or coordination monitored
• Important in running, speaking - all fluid
  movements

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tentorium cerebelli

• "tent of the cerebellum"
• dura mater that separates the cerebellum from the
  inferior portion of the occipital lobes.

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Posterior Cranial Fossa

• Fossa is a depression or cavity in the bone
• Cerebellum, pons, and medulla oblongata sit in
  the Posterior cranial fossa

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Cerebellar Anatomy
Seen from feet

• Located dorsal to pons and medulla
• In posterior fossa under tentorium cerebelli
• Lobes
• Floccular Nodular(small fluffy mass)
• Anterior
• Posterior

Anterior lobe (H)
Posterior lobe (I)
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Flattened Cerebellum

• Longitudinally separated into hemispheres and
  cortices
• Median (Vermal)
• Vermisworm
• Paramedian (Paravermal
• Lateral

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Cerebellum
Paramedian
Primary Fissure
Median
Posterior Superior Fissure
Horizontal Fissure
Prepyramidal Fissure
Posterolateral Fissure
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Cerebellar Nuclei (Nuclei deep cluster of
neurons)

• Dentate nucleus
• Largest, communicates through cerebellar peduncle
  
• Carries information important for coordination of
  limb movements (along with the motor cortex and
  basal ganglia)
• Emboliform nucleus (medial side of the nucleus
  dentatus)
• Regulates movements of ipsilateral extremity
• Globose nucleus
• Regulates movements of ipsilateral extremity
• Fastigial nucleus
• Regulates body posture
• Is related to the flocculo nodular lobe

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Dentate Nucleus
Dentate Nucleus
Pontine Projections
Superior Cerebellar Peduncle
Pons
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Somatotopic Organization

• Tactile information
• Ipsilateral anterior lobule
• Bilateral paramedian lobules
• Cerebral Cortex and Cerebellum have similar
  representations
• Motor representation
• Same area as sensory mapping
• May have auditory and visual processing

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Transverse Cerebellar Regions

• Floccular nodular lobe (Archicerebellum )
• Oldest, related to vestibular part of VIII
• Regulates equilibrium through vestibulospinal
  tract
• Anterior lobe (Paleocerebellum)
• Rostral to Primary Fissure
• General Sensory Receptors
• Concerned with muscle tone and walking
• Posterior lobe (Neocerebellum)
• Newest and Largest, Receives afferent projections
  from contralateral sensorimotor cortex
• Projects to contralateral motor cortex
• Functions in coordination of fine and skilled
  movements

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Longitudinal Cerebellar Regions

• Vermis
• Contributes to body posture
• Paravermal region
• Regulates movements of ipsilateral extremities
  (e.g. walking)
• Lateral Zone
• Regulates skilled movements of ipsilateral
  extremity (e.g. tying your shoe)

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Cerebellar Connection

• Three Peduncles
• Inferior afferent mediate sensorimotor input
  to the cerebellum
• Middle afferent same as above
• Superior efferent transmit output from the
  cerebellum to the brainstem and on to the
  thalamus, motor cortex, and spinal cord
• Varied afferents to Cerebellum
• spinal cord
• brainstem
• motor cortex
• AfferenetEfferent Ratio 401
• For each going from cerebellum to body, 40 coming
  in

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Afferent Pathways (Inferior)

• Vestibulocerebellar Tract
• Info From Semicircular Canals Through Inferior
  Peduncle
• Maintains Upright Posture
• Dorsal Spinocerebellar Tract
• Info From Reticular Nuclei (involved in
  regulation of sleep, respiration, heartbeat,
  etc.)
• Unconscious Proprioception From Muscle Spindles,
  Golgi Tendons and Tactile Receptors

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Afferent Pathways (Inferior 2)

• Reticulocerebellar Tract
• Info From Cerebral Cortices, Spinal Cord,
  Vestibular Complex, and Red Nucleus
• Olivocerebellar Tract
• Info From Spinal Cord Through Olivary N to
  Contralateral Cerebellar Hemisphere
• Source of Climbing Fibers for Direct Input to
  Cerebellum
• Cuneocerebellar Tract
• Mediate Proprioception From Upper Limbs and Neck

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Afferent and Efferent Projections
Thalamus
Red nucleus
Superior Cerebellar Peduncle
Middle Cerebellar Peduncle (pontocerebellar
fibers)
Inferior Cerebellar Nucleus (olivocerebellar
fibers)
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Afferent Pathways (Middle)

• Info From Pontine Nuclei From Opposite Cerebral
  Cortex, Visual and Auditory Inputs
• To Opposite Cerebellar Hemisphere

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Efferent Pathways

• Arise From Cerebellar Nuclei
• Dentate nucleus
• Emboliform nucleus
• Globose Nucleus
• Through Superior Cerebellar Peduncle to
• Red Nucleus (Brainstem)
• Thalamus
• Motor Cortex

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Cerebellar Cortex

• Structured in Three Parallel Layers
• Molecular
• Purkinje
• Connecting Surface and Deep Cerebellar Nuclei
• Source of All Efferent Fibers
• Cerebellar Cortex
• Granular
• Have Mossy Fiber Axons to Purkinje Axons

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Clinical Considerations

• Signs of Dysfunction
• Impaired Muscle Synergy
• Reduced Muscle Tone
• Evident in Skilled Tasks
• Ataxia
• Lack of Order and Coordination in Activities
• Slow Movement (Bradykinesia)
• Mild Muscular Weakness (Asthenia)
• Asynergia
• Speech difficulties (Ataxic Dysarthria)
• affects respiration, phonation, resonance and
  articulation, but most pronounced in articulation
  and prosody.

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Clinical Considerations 2

• Dysdiadochokinesia
• Clumsiness in Alternating Movements
• Tapping, Speech Sound
• Dysarthria
• Ataxic Dysarthria
• Scanning Speech
• Slurred and Disjointed Speech
• Dysmetria
• Error in Judgment of Range and Distance of Target
• Undershooting or Overshooting

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Clinical Considerations 3

• Intentional Tremor
• Accessory Movement During Volitional Task
• vs. Parkinsons Disease Where Tremor Lessens
  During Volitional Movement
• Hypotonia
• Reduced Resistance to Passive Stretch
• Rebounding
• Inability to Predict Movement
• Cannot Hold Back Movement
• Disequilibrium
• Unsteady Gait, Body Wavering

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Cerebellar Pathologies

• Cerebrovascular Accident (CVA)
• Thrombotic, embolic or hemorrhagic
• Vertebrobasilar Artery
• Toxicity
• Chronic Alcoholism
• Progressive Cerebellar Degeneration
• Friedrich's Ataxia Autosomal Recessive Heredity
  Degenerative Condition
• Combined Sensory and Motor Dysfunctions