1 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

2 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

3 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

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

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

6 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)

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

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

9 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

10 Dentate Nucleus Pons Pontine Projections Dentate Nucleus Superior Cerebellar Peduncle

11 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

12 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

13 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)

14 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

15 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

16 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

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

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

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

20 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

21 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.

22 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

23 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

24 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