Cerebellum Kiranmayi S.

50% of brain’s neurons, 10% of volume 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

THE CEREBELLUM AND BASAL GANGLIA COORDINATE MOVEMENTS THE CEREBELLUM IS INVOLVED IN PLANNING, COORDINATION, AND POSTURE ANTERIOR AND POSTERIOR LOBES INVOLVED IN LIMB MOVEMENT FLOCCULONODULAR LOBE IS INVOLVED IN EQUILIBRIUM AND POSTURE

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

Evolution 3 main stages based on the complexity of movement Archecerebellum – balance Paleocerebellum – posture, locomotion Neocerebellum – programming skilled and learned movement

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

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

Located dorsal to pons and medulla 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)

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

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

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

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)

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 Afferenet:Efferent Ratio = 40:1 For each going from cerebellum to body, 40 coming in

Globose & emboliform nuclei Cerebellar Nuclei Neocerebellum Dentate Nucleus Globose & emboliform nuclei Paleocerebellum Fastigeal Nucleus Vestibular Nucleus Archecerebellum

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 Fastigial nucleus Regulates body posture Is related to the flocculo nodular lobe

Dentate Nucleus Dentate Nucleus Pontine Projections Superior Cerebellar Peduncle Pons

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

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

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

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

Afferent Connections & Functions Equilibration – vestibular nuclei to archecerebellum through VIII nerve Subconscious Proprioception – anterior lobe is ipsilateral Feet – anterior, upper limbs posterior, head in located posteriorly in the superior vermis Motor Control Circuits – coordinates muscle groups, smoothes muscle action, adjusts muscle tone so that force and its direction and extent are appropriate and accurate

Efferent Pathways Cerebral cortex – dentato-rubro-thalamic route to the motor cortex Red nucleus – limb movements Reticular formation – muscle tone Vestibular nuclei – equilibrium

Structured in Three Parallel Layers 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

CELL TYPES AND CIRCUITS IN THE CEREBELLUM

Purkinje cells – very large Golgi type I neurons. Cerebellar Cortex Molecular layer – superficial, has few cells and many fibers run parallel to the folia and form granular cells of the deep layer. Satellite cells and Basket cell Purkinje cells – very large Golgi type I neurons. Large flask shaped cell bodies with profusely branched dendrites (400 000 synapses) Granular cells- vast numbers of small neurons with axons ascending into the molecular layer

PURKINJE CELLS ARE THE MOST PROMINENT OF ALL THE CEREBELLAR CELL TYPES TWO INPUTS: CLIMBING FIBERS (FROM OLIVARY NUCLEUS) AND PARALLEL FIBERS FROM GRANULE CELLS OUTPUT VARIES ACORDING TO INPUT: CLIMING FIBERS LEAD TO COMPLEX PATTERNS WHILE PARALLEL FIBERS GENERATE SIMPLE PATTERNS

CEREBELLAR LESIONS IPSILATERAL DISTURBANCES LATERAL LESIONS RESULT IN COORDINATION LOSS LESIONS IN THE VERMIS PRODUCE ATAXIA (LOSS OF COORDINATION) FLOCCULONODULAR LOBE LESIONS PRODUCE EQUILIBRIUM DISTURBANCE AND ATAXIA

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.

Overview of Hypothalamus Is very small Weighs only about 4 grams Brain=1400 grams Contains a variety of specialized structures.

Functions of Hypothalamus Autonomic nervous system regulation Hormone production Endocrine regulation Circadian rhythm regulation Limbic system interaction Various Temperature regulation Feeding

Regulates Mechanism by Receiving sensory information from all areas of the body. Comparing sensory information with biological set points. Adjusting the system to restore the body balance when deviations from biological set points occur. Example Set points Blood sugar, Hormone levels, Temperature, Sodium

Autonomic nervous system regulation Influences PSNS through projections to brainstem PSNS nuclei Posterior area influences SNS through projections to the lateral gray horn

Hormone Production Magnocellular regions of the supraoptic and paraventricular nuclei produce oxytocin and vassopressin (ADH) Transported via axonal transport systems (hypothalamohypophysial tract) to neurohypophysis􀁼 Released in circulation Damage to supraoptic n. ⇒ diabetes insipidus

Hormone Production Stimulating or inhibiting hormones are transported via the tuberoinfundibular tract and released in to the pituitary portal system and ultimately to the adenohypophysis

Cercadian rhythm regulation Input from retina to suprachiasmatic nucleus is then sent through poorly defined projections to the pineal gland

Temperature Feeding Posterior n. conserves heat Anterior n. dissipates heat Fever starts – sweating Fever ends – chills Feeding Lateral n. induces eating Ventromedial n. inhibits eating