Cerebellum Ekman-Ch 15 PDF

Cerebellum Ekman-Ch 15 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah CONTENTS Anatomy Neural connections Function Lesion Anatomy  Anatomy It is divided (by 2 fissures; 1ry and po...

Cerebellum Ekman-Ch 15 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah CONTENTS Anatomy Neural connections Function Lesion Anatomy  Anatomy It is divided (by 2 fissures; 1ry and posterolateral fissure) into 3 prominent anatomical lobes: A.The anterior lobe. B.The posterior lobe. C.The flocculonodular lobe. The anterior and posterior lobes are divided into longitudinal zones; a) Vermal zone → occupies the vermis. b) Intermediate (or paravermal) zone → lying on each side of the vermis, occupying the medial regions of the cerebellar hemispheres. c) Lateral zone of the cerebellar hemisphere → lying just lateral to the intermediate zone.  Anatomy 3 major functional divisions 1.Vestibulocerebellum→ composed of the "flocculonodular lobe“ 2.Spinocerebellum → composed of the vermis and paravermal zone. 3.Cerebrocerebellum→ composed of lateral zones of the cerebellar hemispheres. The cerebellum is attached to the brain stem by 3 pairs of tracts called Cerebellar Peduncles: connect the cerebellum to the brainstem; each pair of peduncles connects the cerebellum to a separate division of the brainstem. Inferior cerebellar peduncle- afferents (input) spinocerebellars (Posterior), cuneocerebellars, vestibulocerebellars, and olivocerebellars Middle cerebellar peduncle- afferent, pontocerebellars Superior cerebellar peduncle- primarily efferent (output) cerebellorubrals (to red nucleus) and cerebellothalamics (to VL nucleus of thalamus) The cerebellar cortex contains three layers: molecular, Purkinje cell, and granular layers Molecular layer - inhibitory interneurons (GABA-erg): stellate cells, basket cells - flattened dendritic trees of Purkinje cells - fibers: parallel fibers originating from granule cells Purkinje cell layer - cell bodies of Purkinje cells Granular layer - axons rises vertically to molecular layer - split in two, traveling horizontally to form: parallel fiber (a distinctive "T" shape) from Granule cell - parallel fibers pass through the dendritic trees of Purkinje cells - granule cells use glutamate exerting excitatory effects - fibers: - terminating mossy fibers - traversing climbing fibers - Golgi cell : inhibitory  Intrinsic Cerebellar Cortex Connections IMPORTANT! Granule cells give rise to parallel Purkinje fibers cells Mossy fibers terminate on granule cells Purkinje cells project to Climbing deep cerebellar fibers nuclei terminate on Purkinje cells Neural Connections Nuclei of cerebellum The cerebellar nuclei comprise 4 paired deep grey matter nuclei deep within the cerebellum near the fourth ventricle. They are arranged in the following order, from lateral to medial: dentate nuclei (the largest and most lateral) emboliform nuclei, globose nuclei, and fastigial nuclei (most medial) Vestibulocerebellum (Archicerebellum) functions in maintaining balance and controlling head and eye movements. located in flocculonodular lobe. projects to vestibular nuclei. it is involved in vestibular reflexes (such as the vestibuloocular reflex) and in postural maintenance. Afferent input: vestibular nerve and vestibular nuclei. Efferent path: vestibular nuclei Spinocerebellum (Paleocerebellum) comprises the vermis + intermediate hemisphere of the cerebellar cortex, as well as the fastigial and interposed nuclei. projects through fastigial and interposed nuclei. has a somatotropic organization. it receives major inputs from the spinocerebellar tracts. Its output projects to rubrospinal, vestibulospinal, and reticulospinal tracts It is involved in the integration of sensory input with motor commands to produce adaptive motor coordination controls posture and movement of trunk and limbs.  Spinocerebellum a)Afferents: From 2 main sources: 1) Brain and brainstem centers: such as cerebral cortex, red nucleus, vestibular nuclei, reticular formation, and inferior olivary nucleus. These afferents tells the spinocerebellum about the "plan" of the movement ordered by higher motor centers. 2) Peripheral receptors: via; i) Dorsal spinocerebellar tract: from ms. spindles, GTOs, joint and pressure receptors→ terminate ipsilaterally in the vermis and paravermal intermediate zone. These signals inform the cerebellum about the position and movements of the different parts of body (Fine mov’t). ii) Ventral spinocerebellar tract: quickly returns to the spinocerebellum copies of the motor commands (Gross mov’t)  Spinocerebellum b) Efferents: 1) From the vermis: → to the "fastigial" nucleus → then projects to the vestibular nuclei and RF of the brain stem (which tracts?)→ to axial ms. 2) From the intermediate Zone: → to the interposed nucleus → via the superior peduncle, they project to: (i) Contralateral thalamus → to the cerebral cortical motor areas and BG. (ii) Contralateral red nucleus. (iii) RF of the brain stem. They connect with the corticospinal and rubrospinal tracts → control of the "distal ms" of the limbs. Cerebrocerebellum (Neocerebellum) participates in the planning of movement located in the lateral hemisphere projects to the dentate nucleus Corticopontocerebellar pathway: from its extensive connections with the cerebral cortex, via the pontine nuclei (afferents) and the VL thalamus (efferents). It is involved in the planning, timing of movements, coordination. -- Afferent input : from entire contralateral cerebral cortex -- Efferent pathway : thalamus  Cerebrocerebellum a) Afferents: Almost all the afferents to the cerebrocerebellum originate in the cerebral cortex (CC) via the pontine nuclei. The cerebral cortical projections provide it with; i) Motor information → about the motor commands from motor areas. ii) Sensory information →about the present postural state of the body, from the somatic sensory areas.  Cerebrocerebellum b) Efferents: -From the cortex of the cerebrocerebellum → to the "dentate" nucleus→ through the superior peduncle to terminate mainly in the VL nucleus of the contralateral thalamus→ finally projects to the motor areas of the CC. -The "cerebello - dentato - thalamo- cerebral" pathway mediates the role of the cerebrocerebellum in adjusting the plan of the motor command before being discharged from the CC motor areas to the lower MNs.  Cerebellar Connections: Principle of Lateralization Spinocerebellar and Vestibulocerebellar Inputs are primarily ipsilateral (conveying information about the same side of the body) Cerebellar efferents project to the contralateral VL nucleus of the thalamus and motor cortex. Corticopontines project to basilar pons, and pontocerebellar afferents cross back to the original side. Hence, clinical deficits resulting from cerebellar lesions are expressed ipsilaterally. Functions  1) Regulation of Equilibrium When the equilibrium is disturbed or exposed to acceleration→ ++ the vestibular receptors→ send sensory signals to Vestibulocerebellum which initiate immediate corrective signals that are sent to:- i) The vestibular nuclei, and RF → adjust the tone and contractility of the axial and proximal limb ms. This helps to maintain equilibrium during the change in head position, and during exposure to acceleration or active movements of the body. ii) The superior colliculus → to coordinate eye movements with head movements during exposure to acceleration→ to maintain clear vision which is important for keeping equilibrium during head movements. 2) Regulation of Posture The vermis is the principal region of the cerebellum concerned with postural adjustment. It to receive sensory information from ms and joint proprioceptors (particularly from the axial regions), concerning "position" of the body. Its output controls the vestibulospinal and reticulospinal tracts that regulate the tone and contraction of the axial and proximal limb ms. 3) Regulation (or Coordination) of Voluntary Movements Coordination of movements means one's ability to proceed smoothly and precisely from one movement to the next in proper succession. The cerebellar role in coordination of movements is carried out by a No. of mechanisms, including:-  Coordination a) Comparator and Error- Correction Mechanism When the motor areas of the CC send motor commands to ms for performance of a voluntary movement, the spinocereb ellum receives immediately an "efference copy" of the inten ded motor command through; 1. Cortico- ponto-cerebellar pathway (cerebrocerebellum) 2. Ventral spinocerebellar tract As the movement proceeds, the spinocerebellum receives pro prioceptive signals about the actual motor performance via spinocerebellar tract  Coordination a) Comparator and Error- Correction Mechanism The intermediate zone of the spinocerebellum essentially acts as a "comparator" that compares the motor intentions of the higher centers with the actual performance of the involved ms. When there is any "error" in performance or "deviation" from the original plan of the intended voluntary motor act, then the intermediate zone and the interposed nucleus send 'corrective signals" back to the motor areas of the CC and the red nucleus, which give origin to the descending motor tracts innervating mainly the lower motor neurons of the distal limb ms. 4) Role of the Cerebellum in Motor learning When a person first performs a complex motor act, the degree of cerebellar adjustment of the "onset" and "termination" of the successive ms contractions involved in the movements is almost always inaccurate, then cerebellar neuronal circuits learn to make more accurate movement the next time. Thus, after the motor act has been repeated many times (motor training), the successive steps of the motor act become gradually more precise. Once the cerebellum has perfectly learned its role in different patterns of movements, it establishes a specific "stored program" for each of the learned movements. 5) Role of the Cerebellum in Rapid and Ballistic Movements These movements include writing, typing, talking, running, and many other athletic and professional motor skills. These movements occur so rapidly that it is almost impossible to depend for their control on the sensory feed-back information from the periphery, because the movement would be over before such information reaches the cerebellum and the cerebral cortex. These movements are referred to as "ballistic" movements (ballistic is a word meaning "thrown"), because once the movement goes on there is no way to modify its present course by any sensory feed-back control mechanism (Spinocerebellum). Cerebellar Lesions: deficits expressed ipsilaterally Ataxia- tendency to fall toward side of lesion Intention Tremor (Action Tremor) Dysdiadokinesia- inability to produce alternating antagonistic actions Past-pointing Nystagmus- flocculonodular lobe lesion Cerebellar Signs Hypometria & Response delays Ataxia Incoordination/ rapid alternating movements (disdiadocho- kinesia) Any questions?