Cerebellum - Ekman-Ch 15 PDF

Cerebellum Ekman-Ch 15 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah CONTENTS Anatomy Neural connections closely connected to anatomy Function Lesion Anatomy  nicknamed “small brain” cerebellum has more fine wrinkles because the...

Cerebellum Ekman-Ch 15 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah CONTENTS Anatomy Neural connections closely connected to anatomy Function Lesion Anatomy  nicknamed “small brain” cerebellum has more fine wrinkles because they want to contain more information cerebellum is control addict 3 divisions  Anatomy primary It is divided (by 2 fissures; 1ry and posterolateral fissure) into 3 prominent anatomical lobes: posterolateral fissure divides flocculondular lobe A.The anterior lobe. B.The posterior lobe. “chopstick” dividing into ant and post C.The flocculonodular lobe. 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.  the one who has Anatomy most information from spinocerebellar 3 major functional divisions tract functional division is important!! and its location 1.Vestibulocerebellum→ composed of the "flocculonodular lobe“ function: balance receives info from spinocerebellar tract 2.Spinocerebellum → composed of the vermis and paravermal zone. medial function: motor execution spinocerebellar - unconscious proprioception 3.Cerebrocerebellum→ composed of lateral zones of the cerebellar hemispheres. function: planning connects to cerebral cortex motor planning has connection to cortex horizontal connected to vestibular nuclei function: balance The cerebellum is attached to the brain stem by 3 pairs of tracts called Cerebellar Peduncles: no need to memorize everything just know there are 3 peduncles and which tract is in which peduncle connect the cerebellum to the brainstem; each pair of peduncles connects the cerebellum to a separate division of the brainstem. 3 pairs remember the tracts that are mentioned * from ascending tracts 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) has anterior spinal tract  cerebrocortex - 6 layers The cerebellar cortex contains three layers: molecular, Purkinje cell, and granular layers middle innermost outermost middle layer has purkinje cells Molecular layer input; outermost layer connection to dendrites - inhibitory interneurons (GABA-erg): stellate cells, basket cells - flattened dendritic trees of Purkinje cells - fibers: parallel fibers originating from granule cells --> from the innermost layer connected to dendrites of purkinje cells middle goes into the outer (molecular) Purkinje cell layer at the end of granule cells the one exit point output layer; - cell bodies of Purkinje cells sending information out of the cortex from this mossy fibers are connected "faster" Granular layer input rememeber: - axons rises vertically to molecular layer which cell is in which layer? where is the entry point to cortex and where is exit point - split in two, traveling horizontally to form: parallel fiber (a distinctive "T" shape) from Granule cell mossy + climing fibers -> the input layers for - parallel fibers pass through the dendritic trees of Purkinje cells cerebellar cortex - granule cells use glutamate exerting excitatory effects - fibers: source of information going into cortex - terminating mossy fibers end at dendrite of granule cell - traversing climbing fibers connect to dendrite of purkinje - Golgi cell : inhibitory climbing hugging (less connections) with purkinje cell mossy high five  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 max 10 purkinje cell Neural Connections Nuclei of cerebellum they are pairs 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) remember the pairs of cerebellum nuclei in order (location) they are connected to particular areas of the cerebellum all connect to functional division inside vermis outside vermis from centre lateral most - outside nucleus Vestibulocerebellum (Archicerebellum) remember: name, function, location, connection *! has no connection with cerebellar nuclei has connection to outside of cerebellum (vestibular nuclei) 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. connection with vestibular nuclei Afferent input: vestibular nerve and vestibular nuclei. Efferent path: vestibular nuclei remember input and output of each !!  Spinocerebellum middle part of cerebellum (Paleocerebellum) each part of cerebellum has particular input and output area location comprises the vermis + intermediate hemisphere of the cerebellar cortex, as well as the fastigial and interposed nuclei. spinocerebellar tract projects through fastigial and interposed nuclei. react faster because their pathway is short has a somatotropic organization. - ballistic movt function: unconcious proprioception it receives major inputs from the spinocerebellar tracts. works for posture and limb control Its output projects to rubrospinal, vestibulospinal, and reticulospinal tracts centermost - central nuclei posture lateral - lateral nuclei 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. remember input and output of each !!  Spinocerebellum a)Afferents: mostly from spinocerebellar tract 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 function - motor planning lateral (Neocerebellum) most important connection 1 lat part -> dentate nucleus -> thalamus -> cortex remember the structure/order participates in the planning of movement 2 located in the lateral hemisphere 5 projects to the dentate nucleus most important connection 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 3 4  right cerebellum information goes to left cortex Cerebrocerebellum where is decussation!* 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. info in --> MCP (medial cerebral peduncle) info out --> SCP (superior cerebral peduncle)  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  know function, which part of cerebellum is related to the function 1) Regulation of Equilibrium which functional part of cerebellum is invloved 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:- remember which part is involved 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 spinocerebellum - unconscious proprioception vermis is in spinocerebellar 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 paravermis -> connected to red nucleus - responsible for voluntary movt = "UL" spinocerebellum 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:- related to spinocellebrlar esp  coordination --> error detect + compare Coordination coordination through this mechanism 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 main area of error correction 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.  basal ganglia -> pro, autopilot, feed forward cerebellum -> noob, error detection, feedback motor learning - 2 situations -> when start to learning motor skills (cerebellum) and when we are skillful (basal ganglia) 4) Role of the Cerebellum in Motor learning day 1 of learning: cerebellum (error detection) 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. feed back correcting mechanism’ 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. know difference btw BG and cerebellum cerebellum: feedback mechanism - after action BG: before action coordination: spinocellebellar (but has input to compare) 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 leads to incoordination Ataxia- tendency to fall toward side of lesion Intention Tremor (Action Tremor) Dysdiadokinesia- inability to produce there is incoordination - not able to correct the error alternating antagonistic actions Past-pointing Nystagmus- flocculonodular lobe lesion Cerebellar Signs Hypometria & delayed response Response delays coordination issues Ataxia Incoordination/ rapid alternating movements (disdiadocho- kinesia) Any questions?