Download chapter 12 - cerebellum

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 brain’s 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) 6
Flattened Cerebellum
Longitudinally
separated into
hemispheres and
cortices
– Median (Vermal)
Vermis=worm
– Paramedian
(Paravermal
– Lateral
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Cerebellum
Median
Prepyramidal Fissure
Posterolateral Fissure
Paramedian
Primary
Fissure
Posterior
Superior
Fissure
Horizontal
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
Pontine
Projections
Pons
Dentate
Nucleus
Superior
Cerebellar
Peduncle
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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 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
cerebellum
2. Middle – afferent: same as above
3. 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
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. 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
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