Chapters 12 Motor System Cerebellum l Chris Rorden

Chapters 12 Motor System – Cerebellum l Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders University of South Carolina 1

Function of Cerebellum l 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 2

Cerebellum 50% of brain’s neurons, 10% of volume l Can change movements as necessary l – E. G. Walking or talking Does not reach conscious awareness l Muscle synergy or coordination monitored l Important in running, speaking - all fluid movements l 3

tentorium cerebelli "tent of the cerebellum" l dura mater that separates the cerebellum from the inferior portion of the occipital lobes. l 4

Posterior Cranial Fossa is a depression or cavity in the bone l Cerebellum, pons, and medulla oblongata sit in the Posterior cranial fossa l 5

Cerebellar Anatomy Seen from feet Located dorsal to pons and medulla l In posterior fossa under tentorium cerebelli l Lobes l – – – Floccular Nodular(small fluffy mass) Anterior Posterior Anterior lobe (H) Posterior lobe (I) 6

Flattened Cerebellum l Longitudinally separated into hemispheres and cortices – Median (Vermal) Vermis=worm – – Paramedian (Paravermal Lateral 7

Cerebellum Median Prepyramidal Fissure Posterolateral Fissure Paramedian Primary Fissure Posterior Superior Fissure Horizontal Fissure 8

Cerebellar Nuclei (Nuclei = deep cluster of neurons) l Dentate nucleus – – l Emboliform nucleus (medial side of the nucleus dentatus) – l Regulates movements of ipsilateral extremity Globose nucleus – l Largest, communicates through cerebellar peduncle Carries information important for coordination of limb movements (along with the motor cortex and basal ganglia) Regulates movements of ipsilateral extremity Fastigial nucleus – – Regulates body posture Is related to the flocculo nodular lobe 9

Dentate Nucleus Pontine Projections Pons Dentate Nucleus Superior Cerebellar Peduncle 10

Somatotopic Organization l Tactile information – – – l 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 11

Transverse Cerebellar Regions 1. Floccular nodular lobe (Archicerebellum ) – – 2. Anterior lobe (Paleocerebellum) – – – 3. Oldest, related to vestibular part of VIII Regulates equilibrium through vestibulospinal tract 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 12

Longitudinal Cerebellar Regions l Vermis – l Paravermal region – l Contributes to body posture Regulates movements of ipsilateral extremities (e. g. walking) Lateral Zone – Regulates skilled movements of ipsilateral extremity (e. g. tying your shoe) 13

Cerebellar Connection l Three Peduncles 1. 2. 3. l Varied afferents to Cerebellum : – – – l 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 brainstem motor cortex Afferenet: Efferent Ratio = 40: 1 – For each going from cerebellum to body, 40 coming in 14

Afferent Pathways (Inferior) l Vestibulocerebellar Tract – – l 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 15

Afferent Pathways (Inferior 2) l Reticulocerebellar Tract – l Olivocerebellar Tract – – l Info From Cerebral Cortices, Spinal Cord, Vestibular Complex, and Red Nucleus 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 16

Afferent and Efferent Projections Thalamus Red nucleus Superior Cerebellar Peduncle Middle Cerebellar Peduncle (pontocerebellar fibers) Inferior Cerebellar Nucleus (olivocerebellar fibers) 17

Afferent Pathways (Middle) Info From Pontine Nuclei From Opposite Cerebral Cortex, Visual and Auditory Inputs l To Opposite Cerebellar Hemisphere l 18

Efferent Pathways l Arise From Cerebellar Nuclei – – – l Dentate nucleus Emboliform nucleus Globose Nucleus Through Superior Cerebellar Peduncle to – – – Red Nucleus (Brainstem) Thalamus Motor Cortex 19

Cerebellar Cortex l Structured in Three Parallel Layers – – Molecular Purkinje l Connecting Surface and Deep Cerebellar Nuclei l Source of All Efferent Fibers l Cerebellar Cortex – Granular l Have Mossy Fiber Axons to Purkinje Axons 20

Clinical Considerations l Signs of Dysfunction – – Impaired Muscle Synergy Reduced Muscle Tone Evident in Skilled Tasks Ataxia l Lack of Order and Coordination in Activities l Slow Movement (Bradykinesia) l Mild Muscular Weakness (Asthenia) l Asynergia l Speech difficulties (Ataxic Dysarthria) – affects respiration, phonation, resonance and articulation, but most pronounced in articulation and prosody. 21

Clinical Considerations 2 l Dysdiadochokinesia – – l Dysarthria – – – l Clumsiness in Alternating Movements Tapping, Speech Sound Ataxic Dysarthria Scanning Speech Slurred and Disjointed Speech Dysmetria – – Error in Judgment of Range and Distance of Target Undershooting or Overshooting 22

Clinical Considerations 3 l Intentional Tremor – – l Hypotonia – l Reduced Resistance to Passive Stretch Rebounding – – l Accessory Movement During Volitional Task vs. Parkinson’s Disease Where Tremor Lessens During Volitional Movement Inability to Predict Movement Cannot Hold Back Movement Disequilibrium – Unsteady Gait, Body Wavering 23

Cerebellar Pathologies l Cerebrovascular Accident (CVA) – – l Toxicity – l Thrombotic, embolic or hemorrhagic Vertebrobasilar Artery Chronic Alcoholism Progressive Cerebellar Degeneration – – Friedrich's Ataxia: Autosomal Recessive Heredity Degenerative Condition Combined Sensory and Motor Dysfunctions 24