[NEURO]LEC_207_CEREBELLUM_AND_ITS_CONNECTIONS.pdf

(007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021...

(007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 OUTLINE THE CEREBELLUM A. Dural Partitions B. Dorsal View C. Functions D. Gross Anatomy E. Gross anatomical Organization F. Internal Anatomy  Cortical layers  5 cell types WHITE MATTER OF THE CEREBELLUM A. 3 types of Fibers B. Cerebellar Cortical Mechanisms AFFERENT CEREBELLAR PATHWAY Figure 3. Posterior cranial fossa (black line) EFFERENT CEREBELLAR PATHWAY A. Major Cerebellar Outputs B. Cerebellar Nuclei and Regions of the Cortex from which they receive projections C. Cerebellar Efferent Fibers CLINICAL ABNORMLITIES A. Cerebellar Damage B. Functional Areas of the Cerebellum C. Application D. Ataxia E. Cases TEST YOUR KNOWLEDGE REFERENCES Figure 4. Sagittal view of cerebellum THE CEREBELLUM A. DURAL PARTITIONS - literally means “little brain” Figure 1 & 2. Cerebellum (encircled) LOCATION:  dorsal to the brain stem - connected to the brainstem by 3 pairs of cerebellar peduncles  Posterior cranial fossa and covered superiorly by the tentorium cerebelli  Largest part of the hindbrain and lies posterior to the 4th ventricle, pons and the medulla Figure 5 & 6. Dural partitions Page 1 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021  Maintenance of Equilibrium/ balance (in conjunction Tentorium with the vestibular system) Separates cerebellum from cerebrum cerebelli  Regulation of Muscle Tone: modulates spinal cord and Falx Separates cerebellum into 2 hemispheres brain stem mechanisms involved in postural control. cerebelli (right and left) o Note: Tone- maintenance of partial contraction of a muscle o Controlled by: muscle spindles- receptors measuring muscle stretch/ length (muscle B. DORSAL VIEW OF THE CEREBELLUM spindles: received by dorsal column and Cerebellum: ovoid-shaped spinocerebellar tract)  Speech/ eye modulation (fine-tune only- does not control it voluntary)  Some role in cognition (cerebellum has several connections with cerebral cortex. Cerebellar damage: you may lose some of the cognitive function) D. GROSS ANATOMY OF THE CEREBELLUM Figure 7. Dorsal view of cerebellum  Has vermis: middle  2 hemispheres: lateral  anterior to the cerebellum: brain stem and 4th ventricle Figure 9. Anatomical division of cerebellum I. DIVISIONS o Superior view  2 lateral hemispheres  1 vermis II. TWO SURFACES Figure 8. MRI (cerebellum) Figure 10. Dorsal view of cerebellum C. FUNCTIONS OF THE CEREBELLUM o Superior or dorsal: no distinction between vermis and  Coordination and Movement: the cerebellum controls hemisphere the timing and pattern of muscle activation during movement Page 2 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021  White matter- internal o Embedded within white matter: 4 deep cerebellar nuclei (like in thalamus, nuclei act as relay stations) Figure 11. Ventral view of cerebellum o inferior or ventral view: inferior surface vermis lies in depth of vallecula Figure 14. Coronal section, posterior view of cerebellum III. 2 MAJOR FISSURES I. Internal structures of the cerebellum o Primary fissure- separates anterior lobe from the  Cortical gray matter: folded into transverse folds known posterior (middle) lobe on the superior surface as “folia”; each fold/ folium has a core of white matter and o Dorso/ posterolateral fissure- separates the covered superficially by gray matter posterior (middle) lobe from the flocculonodular lobe  Medullary core of white matter on the inferior surface  4 deep cerebellar nuclei within the white matter o Arbor vitae: “tree of life” (tree-like outline of the white matter) Figure 15. Arbor vitae of cerebellum Figure 12. Fissures and lobes of cerebellum II. Longitudinal or “Functional” Zones E. GROSS ANATOMICAL ORGANIZATION  Internal organization (similar to cerebral hemisphere)  Cerebellar cortex o Surface: gray matter (has nerve cell bodies) o Sulci o Folia: deeply folded together, tree like structure (rather Figure 16. Superior view of an “unrolled” cerebellum, placing than gyri: cerebrum) the vermis in one plane Figure 13. Cortex, sulci and 1. Cortex of the vermis white matter of cerebellum  Most medial portion of cerebellum Page 3 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021  Associated with the fastigial nucleus (of the deep III. Cerebellar lobes cerebellar nucleus)  Concerned with regulation of muscle tone for posture and locomotion  Movement of the long axis of the body(trunk) namely, neck, shoulders, thorax, abdomen and hips 2. Paravermis or intermediate zone  Part of the cerebellum associated with the interpositus nucleus of the deep cerebellar nuclei)  Participate in the control of an evolving movement by utilizing proprioceptive sensory information generated by the movement itself to correct errors in the movement  Control the muscled of distal part of the limbs especially the hands and feet (fine-tune only)  Receives proprioceptive info from muscle spindles Figure 18. Fissures and lobes of cerebellum  It also has connection with spinal cord 1. Anterior lobe: spinocerebellum (paleocerebellum) 3. Lateral Zone of the Cerebellar Hemisphere  Relatated to spinal cord postural tone (Cerebrocerebellum)  Connections are spinocerebellar tracts. Controls tone,  The largest and most lateral part of the cerebellum posture, and crude movement of limbs (e.g: swinging  Associated with the dentate nucleus (of the deep of arms while walking) cerebellar nuclei)  Damage: forelimb hyperextension and hindlimb hip  Receives inputs from the cerebral cortex and flexion pontine nuclei  Sends outputs to the thalamus and red nucleus 2. Posterior lobe: cerebrocerebellum (neocerebellum):  Influences the output to the motor cortex and middle lobe permits fine delicate adjustments in muscle tone ->  Corticocerebellar in connections (cerebral cortex) skilled movement (e.g. surgery, writing, painting)  Concerned with regulation of fine (or skilled)  Is concerned with the planning of sequential movements of limbs movements of the entire body and is involved with  Damage: hypotonia, hypermetria (inability to assess the conscious assessment of movement errors distance) and intention tremor  Cognitive functions 3. Flocculonodular Lobe = Vestibulocerebellum  Oldest part  Chiefly vestibular in connection (CN VIII vestibular nuclei)  Controls the axial musculature & bilateral movement used for locomotion (extremities) & maintenance of equilibrium (vestibule).  Associated with the vestibular system (Equilibrium, eye movement)  Damage results in disequilibrium (problem with balance; eg. Damage to the Right Flocculonodular Lobe = tendency to lose balance and fall towards the right side), wide based gait and nystagmus (flickering of eye) Figure 17. Longitudinal Zones in transverse section Page 4 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 IV. Other Important Structures Traumatic Subdural Hematoma in the figure pushes the brain 1. Cerebellar Tonsils downward, that compression of the brain may also push the cerebellar tonsils down towards the foramen magnum – Tonsillar Herniation, this downward herniation of tonsils towards the foramen magnum may compress the medulla oblongata that may lead to sudden death. Figure 19: Inferior view of the Cerebellum showing the Cerebellar Tonsil  Relations:  Medial: Uvula of the Vermis  Superior: Flocculonodular lobe Figure 21: Chiari Type 1 Malformation  Anterior: Posterior surface of the Medulla and the Cerebellomedullary fissure Cerebellar Tonsils are well below the foramen magnum; more than  Posteroinferior: Cisterna Magna 5mm downward herniation of cerebellar tonsils in the foramen magnum.  Related Pathology:  Cerebellar Tonsillar Ectopia o Arnold-Chiari Phenomenon  Tonsillar herniation The Arnold-Chiari malformation ls a congenital anomaly in  Chiari type I malformation which there ls a herniation of the tonsils of the cerebellum and the medulla oblongata through the foramen magnum into the vertebral canal. This results in the blockage of the exits in the roof of the fourth ventricle to the CSF, causing internal hydrocephalus. It is commonly associated with craniovertebral anomalies or various forms of spina bifida. Signs and symptoms related to pressure on the cerebellum and medulla oblongata and involvement of the last four CNs are associated with this condition. 2. Cerebellar Peduncles  “Bridges”  Made up of fibers/axons (White matter fiber tracts)  One of the structures that connects the cerebellum to the brainstem (cerebellum is intimately related to the brainstem); most of the fibers will pass through the brainstem before going to the cerebellum and on the other hand, the cerebellum will also send information towards the brainstem before it reaches the cerebrum or extremities. Figure 20: Traumatic Subdural Hematoma o Brainstem acts as a relay station for information that goes into and from the Cerebellum, which Page 5 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 means if there is a problem with the Brainstem, symptoms that are similar to lesions of Cerebellum might also manifest.  3 Symmetrical Bundle of Fibers/Axons  Superior cerebellar peduncles - Connects cerebellum with the midbrain - It is predominantly Efferent axons (Axons Goes away from cerebellum) - Contains mostly efferent tracts fromm the deep cerebellar nuclei - Some tracts cross in the decussation of the superior peduncle, then divide into a Figure 23: Coronal section of the cerebellum showing the White descending limb (to the pons) and the and Gray matter. ascending limb (to the midbrain and thalamus)  Cortical layers of the cerebellum (Grey matter)  Middle cerebellar peduncles  Molecular layer: Superficial - Connects the cerebellum with the pons - 2 types of neurons: - Contains only Afferent axons from Pontine o Outer Stellate Cells nuclei o Inner Basket Cells - Contains only afferent tracts (Towards the - Neuroglial cells present. cerebellum) - Consists of predominantly of unmyelinated nerve  Inferior cerebellar peduncles fibers from the axons of granule cells, axon of stellate - Connects the cerebellum with the medulla and basket cells, sensory climbing fibers, dendrites of - Contains both Afferent and Efferent axons purkinje and Golgi cells. - Largely a synaptic layer - These neurons are scattered among dendritic arborizations and numerous thin axons that run parallel to the long axis of the folia. Neuroglial cells are found between these structures.  Purkinje layer: Intermediate - Intermediate layer - Consists of a single row of Purkinje cell bodies (30 million cells) o Functional unit of cerebellum o Multipolar (Structural type) or Golgi type 1 neurons (large) o Classic type of neuron - Dendrites of Purkinje neurons extend into the molecular layer and axons synapses with the deep Figure 22: Sagittal section through the Vermis of the Cerebellum cerebellar nuclei. showing the location of the Three Cerebellar Peduncles - They are flask shaped and are arranged in a single layer. In a plane transverse to the folium, the dendrites F. INTERNAL ANATOMY OF THE CEREBELLUM of these cells are seen to pass into the molecular The cerebellum consists of: layer, where they undergo profuse branching. The I. Cortex/Gray matter: Outer Area primary and secondary branches are smooth, and A. Molecular Layer – external layer subsequent branches are covered by short, thick B. Purkinje cell layer – middle layer dendritic spines. It has been shown that the spines C. Granular layer – internal layer form synaptic contacts with the parallel fibers derived II. White matter: Medullary core/Inner volume from the granule cell axons. A. Axons - At the base of the Purklnje cell, the axon arises and B. Four pairs of deep cerebellar nuclei passes through the granular layer to enter the white embedded in the medullary core matter. On entering the white matter, the axon Page 6 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 acquires a myelin sheath, and it terminates by synapsing with cells of one of the intracerebellar - nuclei. Collateral branches of the Purkinje axon make synaptic contacts with the dendrites of basket and stellate cells of the granular layer in the same area or in distant folia. A few of the Purkinje cell axons pass directly to end in the vestibular nuclei of the brainstem.  Granular layer: Deep - Consists of densely packed neurons that send axonal projections into the molecular layer. - Composed of Granular cells (30 to 50 billion cells) - Packed with small cells with densely staining nuclei Figure 25: Cells found in the Cerebellar Cortex (Gray Matter) and scanty cytoplasm. Each cell gives rise to four or five dendrites, which make claw-like endings and have A. PURKINJE CELLS synaptic contact with mossy fiber input. The axon of each granule cell passes into the molecular layer, where it bifurcates at a T-junction, the branches  Functional unit of the cerebellum (Multipolar or Golgi type running parallel to the long axis of the cerebellar 1 neuron) folium. These fibers, known as parallel fibers, run at  Largest cells compared to other cells in the CNS (cell right angles to the dendritic processes of the Purkinje body = 60-90 um in diameter), even larger than the cells. Most of the parallel fibers make synaptic pyramidal cells in the cerebral cortex contacts with the spinous processes of the dendrites  Cell body: In Purkinje cell layer of the Purkinje cells. Neuroglial cells are found  Dendrite: In molecular cell layer throughout this layer. Scattered throughout the - where they undergo profuse branching granular layer are Golgi cells. Their dendrites ramify.  Axon: The only projections that exit the cerebellar cortex In the molecular layer, and their axons terminate by (Only axon that will exit the cerebellar cortex). splitting up into branches that synapse with the - Purkinje axon make synaptic contacts with the dendrites of the granular cells. dendrites of basket and stellate cells of the granular layer in the same area or in distant folia.  Receives inhibitory synapse (GABA) from basket cells Figure 24: Microscopic view of the Gray Matter showing the different layers. 5 CELL TYPES Figure 26. Synaptic transmissions between the cells within  Stellate cells – Inhibitory neuron the cerebellum.  Basket cells – Inhibitory neuron  Receives inhibitory synapse (GABA & taurine ) from  Purkinje cells – Inhibitory neuron stellate cells (it occurs in the molecular layer)  Golgi cells – Inhibitory neuron Receives Excitatory synapse (aspartate) from a single  Granule cells – Excitatory neuron climbing fiber granular.  Unipolar Brush cells – Floculonodular lobe/Vermis –  Excitatory synapses (glutamate) from granular Excitatory neuron cells/parallel fibers. Over 200,000 mossy fibers indirectly Page 7 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 through Golgi cell, then granule cell excites each Purkinje  Dendrites: Oriented in rostrocaudal plane (perpendicular cell. to folia)  Mostly project to deep cerebellar nuclei (to all four); some  Receive excitatory stimuli (glutamate from granule cells’ fibers project to vestibular nuclei in brainstem parallel fibers Often also releases a peptide cotransmitter.  Axons: Oriented in rostrocaudal plane (perpendicular to  The primary and secondary branches are smooth,and folia) subsequent branches are covered by short, thick dendritic  Projects from the molecular layer to Purkinje cell layer spines.  Forms inhibitory synapses (GABA) with Purkinje cell  They are flask shaped and are arranged in a single layer body where they undergo profuse branching.  They are interconnecting with each other either inhibitory or excitatory B. GRANULAR CELLS  They serve as inhibitory interneurons  1x1011 granule cells (more neurons than entire cerebral cortex) E. STELLATE CELLS  Cell body: Located in granule cell layer  Interneuron  Axon: Projects from granule cell layer, through Purkinje  Cell body located in molecular layer cell layer, up to molecular layer where it forms parallel  Dendrites: Oriented in rostrocaudal plane (perpendicular fibers (which are oriented in a horizontal plane, parallel to folia). to the cerebellar folia - Cells have multiple branching dendrites and a  Receives Inhibitory synapse (GABA) from Golgi cells. relatively short axon,which terminates on a  Forms excitatory synapses (glutamate) on Golgi basket nearby neuron. and stellate cell projecting to the molecular cell layer.  Receive excitatory stimuli (glutamate) from granule cell’s  Most numerous neuron found in CNS, even more parallel fibers) numerous than entire cerebral cortex.  Axons: project within the molecular layer  Their dendrites ramify in the molecular layer, and their  Forms inhibitory synapses (GABA and taurine) on axons terminate by splitting up into branches that Purkinje cell dendrites synapse with the dendrites of the granular cells.  Both basket cells and stellate cells form inhibitory  Most of the parallel fibers make synaptic contacts with synapses with purkinje cells in the molecular cell layer. the spinous processes of the dendrites of the Purkinje  Sometimes called granule cells because of their small cells. size,are polygonal in shape.  Cell bodies measure about 8m in diameter C. GOLGI CELLS  They serve as inhibitory interneurons  Interneuron  Acts as interneurons that are found between your sensory and motor cortex  Cell body located in granule cell layer  Dendrites in all three layers, receiving excitatory stimuli (from molecular to purkinje to granular cell layer)  Granule cells’ parallel fibers from excitatory synapses (glutamate) in molecular layer  Climbing fibers ( from inferior olivary nucleus) form excitatory synapses (aspartate) in molecular layer  They serve as inhibitory interneurons D. BASKET CELLS  Interneuron  Cell body located in molecular layer  Name derives from the fact that its axons form “basket- Figure 27. Summary of the 5 cell types of the cerebellum. like” terminal arbors around soma/body of Purkinje cells Page 8 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 - passes through the granular layer of the cortex, WHITE MATTER OF THE CEREBELLUM terminate in the molecular layer by dividing repeatedly. - wraps around and synapse with the dendrites of Purkinje fibers (1 climbing fiber: 10 Purkinje neurons; 1 Purkinje neuron: 1 climbing fiber). Neurotransmitter: Aspartate Excites: Purkinje cell and other cerebellar nuclear neurons on which their collateral terminate B. Mossy fibers - are the terminal fibers of all other cerebellar afferent tracts - have multiple branches and exert a much more diffuse excitatory effect (1 mossy fiber: thousands of Purkinje cells). Neurotransmitter: glutamate Excites: Granule cell, Golgi cell dendrites, and other Figure 28: Cerebellum. Coronal section, posterior view cerebellar nuclear neurons on which their collateral terminate A. 3 TYPES OF FIBERS B. INTRACEREBELLAR NUCLEAR MECHANISMS I. INTRINSIC (COMMISURAL) FIBERS The deep cerebellar nuclei receive afferent nervous information from two sources: - connects neurons on the same side 1. Inhibitory axons from Purkinje cells - connects right and left cerebellar hemispheres 2. The excitatory axons that are branches of the afferent II. AFFERENT FIBERS climbing and mossy fibers - towards the cerebellar cortex thru cerebellar peduncles AFFERENT CEREBELLAR PATHWAY - Example: Spinocerebellar / Cuneocerebellar tract NOTE: These are the pathways highlighted in Dr. Viado’s PPT, refer to o Cuneo – comes from nucleus cuneatus of Table 1 for the summary of all the afferent fibers/pathway. Thank you. the dorsal column of spinal cord o Spinocerebellar/Cuneocerebellar tract I. Cortico-Olivocerebellar fibers - carries proprioceptive information from - arise from the cerebral cortex to the inferior olivary nucleus extremities through the internal capsule and corona radiata (bilateral III. EFFERENT FIBERS termination) - axons from the purkinje cells - Then, the inferior olivary nucleus of caudal medulla gives rise - axons leave the cerebellum through the cerebellar to fibers that cross the midline and enter the opposite peduncles cerebellar hemisphere through the inferior cerebellar peduncle o Purkinje cells – only type of neuron (refer to fig. 29 for visual details, labeled there as Cortico-olivary whose axon will project away/out of the cerebellar pathway) cerebellum - terminate as climbing fibers in the cerebellar cortex. NOTE: Cerebellar peduncles are the entrance and exit of - arise exclusively from the Inferior Olivary Nucleus of caudal afferent and efferent fibers; bridge between cerebellum and medulla. brainstem - have a powerful excitatory effect on Purkinje cells upon which they synapse. CEREBELLAR CORTICAL MECHANISMS - known to coordinate signals to the cerebellum to regulate motor TWO MAIN LINES OF INPUT TO THE CORTEX AND ARE coordination and learning EXCITATORY TO THE PURKINJE CELLS: A. Climbing fibers - are the terminal fibers of the olivocerebellar tracts. Page 9 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 - project to flocculonodular lobe via fastigial nucleus of the deep cerebellar nuclei (pass through inferior cerebellar peduncle) - functions to convey information concerning the position of head and body in space as well as information useful in orienting the eyes during movements (coordinate head and eye movement). III. Cerebropontocerebellar fibers - arise from pyramidal/Betz cells in the cerebral cortex, synapse on the pontine nuclei which send their axons to the contralateral cerebellar cortex via pontocerebellar fibers (thru middle cerebellar peduncle) (refer to Fig. 29). Inferior Olivary nucleus  Olivocerebellar pathway  cerebellar peduncle  cerebellum - alerts cerebellum regarding anticipated movements (skilled, conscious movements, planning and timing of movements, Figure 28: Olivocerebellar fibers cognitive function) IV. Spinocerebellar fibers - arise from spinal cord towards the rostral lobe via spinocerebellar tracts - makes cerebellum aware of ongoing movements via proprioceptive input from muscle spindles and joint receptors (involve in adaptive motor coordination) Figure 29. Cerebellar afferent fibers from the cerebral cortex. The cerebellar peduncles are shown as ovoid dotted lines. II. Vestibulocerebellar fibers - arise mainly from the vestibular nerve and vestibular nuclei which receives information about motion (semicircular canals) and position relative to gravity (utricle and saccule) - Then, afferent fibers are sent by vestibular nerve; Figure 30. Cerebellar afferent fibers from the spinal cord and internal passes through inferior cerebellar peduncle on the same side ear. The cerebellar peduncles are shown as ovoid dotted lines (ipsilateral) (refer to Fig. 30) - terminate as mossy fibers in the flocculonodular lobe of the cerebellum. Page 10 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 1 EFFERENT CEREBELLAR PATHWAY They only receive one axon coming from purkinje cell. The purkinje cell dendrites are projecting towards the molecular layer - Axonal fibers going out of the cerebellum but their axons will only project in the white matter towards the deep A. MAJOR CEREBELLAR EFFERENT OUTPUTS cerebellar nuclei. They have a synapse with the nerve cell bodies Major Cerebellar Efferent Outputs - arise exclusively from in the deep cerebellar nuclei and from deep cerebellar nuclei, it will Purkinje cells, projecting to neurons in deep cerebellar nuclei. send another fiber outside of cerebellum. *Purkinje cells - functional unit of the cerebellum. Its information is being relayed to outside through the deep cerebellar nuclei. The axons of the neurons that form the cerebellar nuclei constitute the efferent outflow from the cerebellum.  A few Purkinje cell axons pass directly out of the cerebellum to the lateral vestibular nucleus.  The efferent fibers from the cerebellum connect with the red nucleus (globose-emboliform-rubral), thalamus (dentatothalamic), vestibular complex (fastigial vestibular), and reticular formation (fastigial reticular). I, DEEP CEREBELLAR NUCLEI Pairs of nuclei (nerve cell bodies) embedded in the cerebellar white matter. a) Fastigial Nucleus b) Interposed (Interpositus) Nuclei - interposed between Figure 31. Deep cerebellar nuclei: Fastigial, globose, emboliform and dentate nuclei fastigial nucleus and dentate nucleus 1. Globose Nucleus 2. Emboliform Nucleus c) Dentate Nucleus Page 11 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 II. LOCATION CEREBELLAR EFFERENT FIBERS SYNAPSE LOCATION Medially - Fastigial Nucleus Entire output is thru the axons of the Purkinje cells passing Laterally - Globose Nucleus & Emboliform thru the deep cerebellar nuclei. Nucleus Connect (Synapse) with the Most Lateral - Dentate Nucleus  Red Nucleus (globose-emboliform-rubral pathway)  Thalamus (dentatothalamic pathway) III. FROM LATERAL-MEDIAL EXIT  Vestibular Complex (fastigial vestibular pathway) A. Axons that leave thru the superior cerebellar peduncle  Reticular Formation (fastigial reticular pathway)  Dentate Nucleus  Emboliform Nucleus  Globose Nucleus C. EFFERENT CEREBELLAR PATHWAYS B. Axons that exit thru the inferior cerebellar peduncle (to A. Globose-Emboliform-Rubral Pathway enter brainstem) Axons of neurons in the globose and emboliform nuclei travel  Fastigial Nucleus through the superior cerebellar peduncle and cross the midline to *None exits thru the middle cerebellar peduncle the opposite side in the decussation of the superior cerebellar peduncles. IV. INPUT TO CERBELLAR NUCLEI (derived from two sources) The fibers end by synapsing with cells of the contralateral red 1. Excitatory Input nucleus, which give rise to axons of the rubrospinal tract. - derived from fibers that originate in cells that lie outside the Thus, this pathway crosses twice, once in the decussation of the cerebellum superior cerebellar peduncle and again In the rubrospinal tract - (Afferent fibers eg: Vestibulocerebellar fibers towards the close to Its origin. By this means, the globose and emboliform Fastigial Nucleus) nuclei influence motor activity on the same side of the body. - The information coming from the afferent fibers are EXCITATORY A. Dentatothalamic Pathway 2. Inhibitory Input - derived from fibers that arise from the Purkinje cells of the Axons of neurons in the dentate nucleus travel through the cortex superior cerebellar peduncle and cross the midline to the opposite - fibers are INHIBITORY side in the decussation of the superior cerebellar peduncle. The fibers end by synapsing with cells in the contralateral ventrolateral B. CEREBELLAR NUCLEI & REGIONS OF THE CORTEX nucleus of the thalamus. The axons of the thalamic neurons FROM WHICH THEY RECEIVE PROJECTIONS ascend through the internal capsule and corona radiata and terminate in the primary motor area of the cerebral cortex. By this REGION OF THE pathway, the dentate nucleus can influence motor activity by acting CEREBELLAR on the motor neurons of the opposite cerebral cortex; impulses CEREBELLAR SYNONYMS CORTEX THAT SENDS from the motor cortex are transmitted to spinal segmental levels NUCLEUS AXONS TO THE through the corticospinal tract. NUCLEUS *Remember that most of the fibers of the corticospinal tract cross to the opposite side in the decussation of the pyramids or Dentate Lateral Lateral portions of the later at the spinal segmental levels. Thus, the dentate nucleus is Nucleus cerebellar cerebellar hemisphere able to coordinate muscle activity on the same side of the body. nucleus Emboliform Anterior Intermediate part B. Fastigial Vestibular Pathway Nucleus interpositus The axons of neurons in the fastigial nucleus travel through the nucleus inferior cerebellar peduncle and end by projecting on the neurons Globose Nuclei Posterior Intermediate part of the lateral vestibular nucleus on both sides. interpositus *Remember that some Purkinje cell axons project directly to the nucleus lateral vestibular nucleus. The neurons of the lateral vestibular nucleus form the vestibulospinal tract. The fastigial nucleus exerts Fastigial Medial cerebellar Median part/Vermis a facilitatory influence mainly on the ipsilateral extensor muscle Nucleus nucleus tone Page 12 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 C. Fastigial Reticular Pathway 1. PRESENTATION OF CEREBELLAR DAMAGE NOTE: NO WEAKNESS The axons of neurons In the fastigial nucleus travel through the a. Ataxia (Cerebellar ataxia: Trunkal (AXIAL- thorax, inferior cerebellar peduncle and end by synapsing with neurons of abdomen, hips) vs Appendicular (extremities) the reticular formation. Axons of these neurons influence spinal segmental motor activity through the reticulospinal tract. b. Wide based gait- The patient may stand with feet farther apart than usual in an effort to maintain balance. TRUNKAL/GAIT ATAXIA: VERMIAN SYNDROME -feet separation, wide based, low stooping - Since the vermis is unpaired and Influences midline structures, muscle incoordination involves the head and trunk: and not the limbs. There is a tendency to fall forward or backward. There Is difficulty ln holding the head steady and in an upright position. There also may be difficulty in holding the trunk erect. c. Proprioception problems d. Incoordination (Dysdiadochokinesia) -abnormal repeated (Alternating) movements – Hemisphere syndrome - inability to perform alternating movements regularly and rapidly. Ask the patient to pronate and supinate the forearms rapidly. On the side of the cerebellar lesion, the movements are slow, jerky, and incomplete. Figure 32. Cerebellar efferent fibers. The cerebellar peduncles e. Dysmetria (Distance Overshooting) -you cannot calculate are shown as ovoid dotted fines. the distance; “sumosobra”; instead of touching the nose, you might ne touching your eyes. CLINICAL ABNORMALITIES - (also called past-pointing) is apparent in patients when (LESION TO THE CEREBELLUM they attempt to point accurately or rapidly to moving or stationary targets. The patient may reach past the target A. CEREBELLAR DAMAGE (hypermetria) or fall short of the target (hypometria). Each cerebellar hemisphere is connected by nervous pathways, f. Intention tremors principally, on the same side of the body. Thus, a lesion of a - Tremor is a consistent finding in patients with lateral cerebellar hemisphere will be limited to the ipsilateral side. cerebellar lesions. A kinetic tremor, commonly called an intention tremor, is evident when the patient performs a Ex: there’s a lesion on the RIGHT cerebellum, the presentation voluntary movement and is most obvious as the end- would be on your RIGHT SIDE. point, or target, is approached. This deficit is commonly seen when the patient extends the upper extremity and Page 13 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 then attempts to touch the index finger to the nose. At rest there is little or no tremor, but as the finger C. APPLICATION approaches the nose, the tremor is markedly 1. Unilateral cerebellar hemisphere syndrome accentuated. o Unilateral limb incoordination; ipsilateral - opposite to that seen in patients with Parkinson disease, cerebellar syndrome (Side of the lesion) whose tremor is evident at rest (resting tremor) but o Loss of limb motor coordination of the same side largely diminishes during a voluntary movement. (Dysdiadochokinesia) 2. Bilateral Cerebellar Hemisphere syndrome o Bilateral limb incoordination 3. Vermis syndrome (midline cerebellar vermis lesion) o Vermis is unpaired o Trunkal ataxia or gait ataxia w/o limb incoordination o Affects the head and trunk (neck, shoulders, thorax, abdomen and the hips) o Does not affect the limbs/extremities 4. Flocculonodular lobe – related to vestibular functions o Vestibule S/S: Disequilibrium (Balance problem) g. Pendular nystagmus -eyes swinging back and forth / Nystagmus (eye problem) - rhythmic oscillation of the eyes may be of the same rate in both directions D. ATAXIA h. Hypotonia – loss of influence of the stretch reflex; 1. CEREBELLAR- involves only the cerebellum “nanlalambot” a. Trunkal/Gait Ataxia – Vermis Syndrome - The muscles lose resilience to palpation. There ls b. Appendicular Ataxia – Hemispheric syndrome diminished resistance to passive movements of joints.  Dysdiadochokinesia, Dysmetria (Finger to nose Shaking the limb produces excessive movements at the test), Intention tremor, abnormal heel to shin test terminal joints. The condition is attributable to loss of cerebellar influence on the simple stretch reflex.  Heel-to-shin test or heel-to-knee-to-toe test i. Dysarthric speech (Slurred) – Due to ataxia of the muscles In a recumbent position the patient will find it difficult of the larynx to place the heel on the opposite knee and slide it - Articulation is jerky, and the syllables often are separated down the shin to the toe. In the compromised patient, from one another. Speech tends to be explosive, and the the heel will oscillate to the right and left off the shin syllables often are slurred. as the movement is made. Variations on this test may also be seen in patients with lesions of the posterior column– medial lemniscus system. B. IMPORTANT PARTS TO REMEMBER: FUNCTIONAL  Abnormal reflexes: Pendular Reflex AREAS OF THE CEREBELLUM occurs following tapping of the patellar tendon. 1. Vermis – influences the movement of the long axis Normally, the movement occurs and is self-limited (Trunk) of the body by the stretch reflexes of the agonists and o Neck, shoulders, thorax, abdomen, hips antagonists. In cerebellar disease, because of loss 2. Intermediate zone/Paravermis of Influence on the stretch reflexes, the movement o Immediately lateral to vermis continues as a series of flexion and extension o Control coordination of the distal parts of the movements at the knee joint; that is, the leg moves limbs (hands and feet) like a pendulum. 3. Lateral zone of the hemisphere (Cerebrocerebellum)  Depending on the side of the lesion (Right, left or o Largest Both)  Regulates coordination of muscle activation and is important in visually 2. PROPRIOCEPTIVE ATAXIA guided movements (vision is involved  Unrelated to the cerebellum not muscle activation)  Abnormal joint position sense  Conscious assessment of movement  Sensory ataxia – lesions in Proprioceptive pathways errors (In coordination with the  Abnormal Rombergs Test (Loss of balance in the dark Cerebral cortex) – Limb/ Extremities or when you close your eyes) and Pseudoatethosis (Abnormal writhing movements, usually the fingers) Page 14 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021  Causes: Peripheral Neuropathies, Dorsal column disorders of the spinal cord (carries proprioceptive  Dysarthria- ataxia of laryngeal muscles information) - (infection, autoimmune, metabolic, vascular etc) 3. VESTIBULAR ATAXIA - Vestibular nerve / or lesions in flocculonodular lobes  Disequilibrium / Balance-ipsilateral: if you have problem with your RIGHT ear, you will problem balancing yourself towards your right. -the patient will fall on the side of the lesion  Pendular Nystagmus – will occur in both eyes -ataxia of the ocular muscles 4. Cerebellar Medulloblastoma -Rhythmical oscillation of the eyes of the same rate in both directions -if you have middle ear lesion, your eye will not be affected. But if the problem involves the flocculonodular lobe, and because it innervates both R and L vestibular nuclei, it will occur in both eyes. E. CASES 1. Left Cerebellar Tumor that also involve the Cerebellar Vermis. -Left Hemispheric Lesion -Vermis Lesion 5. Pilocytic Astrocytoma Presentation: Trunkal (Vermis) + Left Appendicular  benign tumor (Hemisphere) Ataxia  4th ventricle is compressed; patient will have  Incoordination of the Hydrocephalus movement of extremities  Enlargement of 3rd and lateral ventricle  Left Dysdiadochokinesia  Left intention tremor  Left Dysmetria  Dysarthria  NO Nystagmus- will only appear if you have Flocculonodular lobe 2. Right Cerebellar Tumor Presentation: Appendicular Ataxia Right  All presentation will be on the right side 3. Vermian (Midline) Tumor with Floculonodular Lobe Involvement Presentation: Trunkal Ataxia + Vestibular Ataxia  Px will have imbalance/Disequilibrium  Abnormal Pendular reflexes Page 15 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 C. Parallel fibers TEST YOUR KNOWLEDGE D. Stellate cell 1. Fuctional zone that influences the output to the motor cortex and permits fine delicate movements. 11. These are the terminal fibers of the olivocerebellar tracts A. Lateral zone of cerebellar hemisphere B. Cerebocerebellum 12. These are fibers that project to flocculonodular lobe via C. Intermediate zone fastigial nucleus of the deep cerebellar nuclei D. A and B 2. True or False: Anterior lobe/ Spinocerebellum/ 13. These are fibers makes cerebellum aware of ongoing Paleocerebellum is responsible for crude movements of movements via proprioceptive input from muscle spindles limb. and joint receptors 3. Four (4) deep cerebellar nuclei is embedded within the 14. Ataxia is defined as: gray matter. A. Inability to perform rapidly alternating movements. 4. What provides excitatory input to the cerebellar Purkinje B. Error in the range of movement cells? C. Lack of continuity in the execution of movements A. Climbing fibers D. Error in the rate, force, and direction of movement B. Parallel fibers E. Muscle weakness C. Both A and B D. None of the choices 15. Tue or False: The clinical signs of cerebellar hemisphere disease generally occur on the same side as the lesion. 5. What connects the Cerebellum to the Medulla Oblangata? A 45-year-old man, who was an alcoholic, started to A. Superior Cerebellar Peduncle develop a lurching, staggering gait even when he was not B. Middle Cerebellar Peduncle C. Inferior Cerebellar Peduncle intoxicated. The condition became slowly worse over a period D. Cerebellar Tonsil of several weeks and then appeared to stabilize. Friends noticed that he had difficulty in walking in tandem with another 6. What are the structural and functional relations between person and tended to become unsteady on turning quickly. the cerebellar cortex and the deep, or central, nuclei? A. Deep nuclei receive input from Purkinje cells 16. A thorough physical examination of this patient revealed B. Deep nuclei receive input from mossy fibers. the following findings except: C. Deep nuclei receive input from climbing fibers. A. The patient exhibited Instability of trunk movements D. All of the above and incoordination of leg movements. 7. What course do the axons follow in reaching these nuclei in B. While standing still, the patient stood with his feet the pons? together. A. Cortex-->internal capsule-->cerebral peduncle. C. He had no evidence of polyneuropathy. B. Cortex-->internal capsule-->red nucleus. D. The ataxia of the legs was confirmed by performing C. Cortex-->thalamus-->cerebellar peduncle the heel-to-shin test. D. Thalamus-->internal capsule-->cerebellar peduncle. E. Magnetic resonance Imaging showed evidence of 8.These are inhibitory neurons except: atrophy of the cerebellar vermis. A. Basket cells B. Golgi cells 17. The following additional abnormal signs might have been C. Granule cells observed In this patient except: D. Purkinje cells A. Nystagmus In both eyes B. Dysarthria 9.They are considered to be the largest cells compared to C. Tremor of the left hand when reaching for a cup other cells in the CNS and the axon of these cells exit the cerebellar cortex D. Paralysis of the right upper arm muscles A. Basket cells E. Dysdiadochokinesia B. Granule cells 18. Deep cerebellar nuclei axons that pass through the inferior C. Stellate cells cerebellar peduncle to the brain stem? D. Purkinje cells A. Emboliforn Nucleus 10.Most numerous neuron found in the CNS. B. Fastigial Nucleus A. Granule cells C. Dentate Nucleus B. Unipolar brush cell D. Globose Nucleus Page 16 of 17 CMED 1B  (007) THE CEREBELLUM AND ITS CONNECTIONS DR. A. VIADO | 01/20/2021 19. Emboliform Nucleus is also termed as: 9. D. A. Lateral Cerebellar Nucleus Rationale: Purkinje cells are the only cells whose axons exit B. Anterior Interpositus Nucleus the cerebellar cortex. They are also considered to be the C. Posterior Interpositus Nucleus largest because their cell body with 60-90um in diameter is D. Medial Cerebellar Nucleus larger that the pyramidal cells in the cerebral cortex. 10. A. 20. TRUE/FALSE. Fibers that arise from Purkinje cells of Rationale: There are approximately 1x1011 granule cells the cortex are EXCITATORY found in the CNS which is a lot more than the entire cerebral ANSWERS cortex. 11. Climbing fibers 1. D 12. Vestibulocerebellar fibers Rationale: Lateral zone is for planning of sequential 13. Spinocerebellar fibers movement of entire body. Cortex of the vermis is for the 14. D movement of long axis of the body. While, Paravermis or Rationale: Ataxia is a disorder caused by damage to the Intermediate Zone controls the muscle of distal part of limbs cerebellum and is defined as an error in the rate, force, and (hands and feet). direction of movement. 2. TRUE 15. TRUE Rationale: Anterior lobe/spinocerebellum/paleocerebellum Rationale: The cerebellar cortex indirectly projects to and controls tone, posture, and crude movement of limbs while receives information from the ipsilateral spinal cord. Posterior lobe: cerebrocerebellum (neocerebellum): middle Therefore, lesions affect the same side of the body. This old lobe is concerned with regulation of fine (or skilled) infarct is so small it was probably clinically silent. movements of limbs. 16. B 3. FALSE Rationale: Patients with cerebellar disease frequently exhibit Rationale: 4 deep cerebellar nuclei are embedded within the poor muscle tone, and to compensate for this, they stand stiff white matter (like in thalamus, nuclei act as relay stations). legged with their feet wide apart. 17. D 4. C Rationale: Although patients with cerebellar disease display Rationale: The Purkinje cells receive two types of excitatory disturbances of voluntary movement, none of the muscles input from outside of the cerebellum, one directly from a are paralyzed or show atrophy. single climbing fiber and the other indirectly via thousands of 18. B parallel fibers of the granule cells. 19. B 5. C 20. FALSE Rationale: Inferior Cerebellar Peduncle connects the Cerebellum with the Medulla Oblongata; Superior Cerebellar Peduncle connects Cerebellum with the Midbrain; Middle Cerebellar Peduncle connects the Cerebellum with the Pons; REFERENCES Cerebellar Tonsils are ovoid structures on the inferomedial surface of each cerebellar hemisphere. Faaa, F. P. D. H. E., & PhD, G. M. A. (2017). Fundamental 6. D Neuroscience for Basic and Clinical Applications Rationale: Purkinje cells synapse in one of the four deep (5th ed.). Elsevier. nuclei and have an inhibitory effect. The mossy and climbing fibers as they enter the cerebellum give off collaterals that Ph.D., S. R. (2018). Snell’s Clinical Neuroanatomy (8th excite the cells in the deep cerebellar nuclei. ed.). LWW. 7. A PPT-Doc Allan Viado Rationale: Axons from the cerebral cortex pass through the internal capsule and synapse in the ipsilateral pontine nuclei. The axons from the pontine nuclei then cross the midline and go to the opposite cerebellar hemisphere. 8. C. Rationale: Only granule cells are mainly excitatory neurons. Golgi and purkinje cells are both inhibitory and excitatory neurons while basket cells are mainly inhibitory neurons. Page 17 of 17 CMED 1B