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Chapters 12 Motor System – Cerebellum

Chris RordenUniversity of South CarolinaNorman J. Arnold School of Public HealthDepartment of Communication Sciences and DisordersUniversity 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 brain’s neurons, 10% of volumeCan change movements as necessary

– E.G. Walking or talkingDoes not reach conscious awarenessMuscle 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

Located dorsal to pons and medulla

In posterior fossa under tentorium cerebelli

Lobes– Floccular Nodular(small

fluffy mass)– Anterior– Posterior

Seen from feet

Posterior lobe (I)

Anterior lobe (H)

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Flattened Cerebellum

Longitudinally separated into hemispheres and cortices– Median (Vermal)

Vermis=worm– Paramedian

(Paravermal)– Lateral

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Cerebellum

Median Paramedian PrimaryFissure

PosteriorSuperiorFissure

HorizontalFissure

Posterolateral Fissure

Prepyramidal 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

Pons

PontineProjections

DentateNucleus

SuperiorCerebellarPeduncle

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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

1. Floccular nodular lobe (Archicerebellum )– Oldest, related to vestibular part of CN VIII– Regulates equilibrium through vestibulospinal tract

2. Anterior lobe (Paleocerebellum)– Rostral to Primary Fissure– General Sensory Receptors– Concerned with muscle tone and walking

3. 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

1. Inferior – afferent: mediate sensorimotor input to the cerebellum2. Middle – afferent: same as above3. 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

Afferenet:Efferent Ratio = 40:1– 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

Superior CerebellarPeduncle

Red nucleus

Thalamus

Middle CerebellarPeduncle (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 (Poor coordination of muscles: Dysdiadochokinesia) 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

Switching between supination and pronation – e.g. screwing in a light buld

– Tapping, Speech Sound Dysarthria

– Ataxic Dysarthria– Poor articulation: 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. Parkinson’s 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

Poor coordination of Gait and speech