Cns 9


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Cns 9

  1. 1. The Cerebellum <ul><li>The cerebellum is located dorsal to the pons and medulla under the occipital lobe of the cerebral hemispheres </li></ul>Cerebellum
  2. 2. The Cerebellum <ul><li>It is separated from the occipital lobe by the transverse fissure </li></ul><ul><li>It rests in the posterior cranial fossa of the skull </li></ul>
  3. 3. Cerebellum: Gross Anatomy <ul><li>It consists of cerebellar cortex and and deep cerebellar nuclei, with white medulla in between </li></ul><ul><li>Cerebellum is uninterrupted across the midline </li></ul><ul><li>The cortex consists of ridges called folia. </li></ul><ul><li>The cerebellum consists of three parts: </li></ul><ul><ul><li>A small inferior part …Flocculonodular lobe (floccular, means a tuft of wool); </li></ul></ul><ul><ul><li>A narrow central vermis (worm shaped) </li></ul></ul><ul><ul><li>Two large lateral hemispheres </li></ul></ul>nodulus flocculus tonsil Ventral View
  4. 4. Anatomy of the Cerebellum 2 symmetrical hemispheres connected medially by the Vermis Folia: Transversely oriented gyri 3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN) Neural arrangement: Gray matter (Cortex), White matter (Internal), Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial Arbor vitae (tree of life): distinctive treelike pattern of the white matter Folium
  5. 5. Divisions of the Cerebellum nodulus flocculus Ant Lobe Ant Lobe Post Lobe Post Lobe tonsil Ventral View Superior Surface vermis hemisphere Ant Lobe Post Lobe nodulus flocculus Schematic
  6. 6. Cerebellum Regulation of muscle tone, coordination of skilled voluntary movement Planning of voluntary activity Maintenance of balance, control of eye movements Anterior Lobe Posterior Lobe Flocculo-Nodular Lobe (FN lobe) Folia Primary fissure Vestibulocerebellum Spinocerebellum Cerebrocerebelum
  7. 7. Cerebellar Subdivisions <ul><li>Multiple nomenclatures have been used to describe the various lobules </li></ul><ul><ul><li>Larsell (1952) used Roman Numerals I-X (anterior to posterior) </li></ul></ul>Archicerebellum-vestibulocerebellum Paleocerebellum-spinocerebellum Neocerebellum-pontocerebellum/cerebrocerebellum
  8. 8. Cerebellar Peduncles Medulla Inferior (ICP) Pons Middle (MCP) Midbrain Superior (SCP) Connects to Peduncle SCP SCP SCP MCP MCP MCP ICP ICP ICP
  9. 9. The Macroscopic Anatomy of the Cerebellum <ul><li>Gross anatomical divisions </li></ul><ul><ul><li>Anterior lobe </li></ul></ul><ul><ul><li>Posterior lobe </li></ul></ul><ul><ul><li>Flocculonodular lobe </li></ul></ul>
  10. 10. The Evolutionary & Functional Division of the Cerebellum <ul><li>The cerebellum can be divided by </li></ul><ul><ul><li>Evolutionary age </li></ul></ul><ul><ul><li>Function </li></ul></ul>
  11. 11. Cerebellar Subdivisions <ul><li>Multiple nomenclatures have been used to describe the various lobules </li></ul><ul><ul><li>Larsell (1952) used Roman Numerals I-X (anterior to posterior) </li></ul></ul>Archicerebellum-vestibulocerebellum Paleocerebellum-spinocerebellum Neocerebellum-pontocerebellum/cerebrocerebellum
  12. 12. The Evolutionary Division of the Cerebellum <ul><li>Three phylogenetic divisions within the cerebellum – according to evolutionary age </li></ul><ul><ul><li>The flocculonodular lobes (archicerebellum) </li></ul></ul><ul><ul><li>The anterior lobes (paleocerebellum) </li></ul></ul><ul><ul><li>The posterior lobes (neocerebellum) </li></ul></ul>
  13. 13. Functional Division of the Cerebellum <ul><li>Three functional divisions run perpendicular to the phylogenetical divisions </li></ul><ul><li>Align from the midline outwards toward the sides of the body </li></ul>
  14. 14. The Archicerebellum <ul><li>Associated with the flocculonodular lobe </li></ul><ul><li>Functions </li></ul><ul><ul><li>Balance (vestibular function) </li></ul></ul><ul><ul><ul><li>Receives input from the inferior and medial vestibular nuclei </li></ul></ul></ul><ul><ul><ul><li>Sends fibers back to the vestibular nuclei </li></ul></ul></ul><ul><ul><ul><li>Creates a feedback loop that allows for the constant maintenance of balance </li></ul></ul></ul><ul><ul><li>Eye movement </li></ul></ul>
  15. 15. The Paleocerebellum <ul><li>Separated from the anterior lobes by the primary fissure </li></ul><ul><li>Separated from the flocculonodular lobes by the posterolateral fissure </li></ul>
  16. 16. The Paleocerebellum <ul><li>Function </li></ul><ul><ul><li>Controls proprioception related to muscle tone </li></ul></ul><ul><ul><ul><li>Receives inputs from muscle stretch receptors via the inferior olive (in the medulla) </li></ul></ul></ul><ul><ul><ul><ul><li>Send out put to the inferior cerebellar peduncle </li></ul></ul></ul></ul><ul><ul><ul><li>Receives inputs from the dorsal and ventral spinocerebellar tracts </li></ul></ul></ul><ul><ul><ul><ul><li>Carries information about the position and forces acting on the legs </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sends axonal projections to the deep cerebellar nuclei </li></ul></ul></ul></ul>
  17. 17. The Neocerebellum <ul><li>Receives input from the pontocerebellar tract </li></ul><ul><ul><li>From the cerebral cortex (motor) via the pontine nuclei in the base of the skull </li></ul></ul><ul><li>Axons project to the deep cerebellar nuclei through the middle cerebellar peduncles </li></ul><ul><li>The major output tract of the cerebellum is the superior cerebellar peduncle </li></ul><ul><ul><li>Sends signals to the motor cortex and the supplementary motor area </li></ul></ul>
  18. 18. The Neocerebellum <ul><li>Function </li></ul><ul><ul><li>Control motor function </li></ul></ul><ul><ul><ul><li>Coordinate fine finger movements </li></ul></ul></ul><ul><ul><li>Feed-forward </li></ul></ul><ul><ul><li>Feed-back </li></ul></ul>
  19. 19. Longitudinal Cerebellar Regions <ul><li>Vermis </li></ul><ul><ul><li>Contributes to body posture </li></ul></ul><ul><li>Paravermal region </li></ul><ul><ul><li>Regulates movements of ipsilateral extremities (e.g. walking) </li></ul></ul><ul><li>Lateral Zone </li></ul><ul><ul><li>Regulates skilled movements of ipsilateral extremity (e.g. tying your shoe) </li></ul></ul>
  20. 20. Deep Cerebellar nuclei <ul><ul><ul><li>Dentate </li></ul></ul></ul><ul><ul><ul><li>Emboliform </li></ul></ul></ul><ul><ul><ul><li>Globose </li></ul></ul></ul><ul><ul><ul><li>Fastigial </li></ul></ul></ul>Interposed Fast G E Dent
  21. 21. Simplified Cerebellar Circuitry Spinal Cord, Cerebral Cortex (via pontine nuclei), Vestibular System Cerebellar Cortex Inferior Olive Deep Cerebellar Nuclei Brainstem, thalamus, midbrain Mossy Fibers Climbing Fibers Spinal cord, Cerebral Cortex + - + INPUT
  22. 22. Microscopic Sections Cortex Mol Gr WM Purkinje Molecular Granular Inner Middle Outer Granular layer Purkinje cell layer Molecular layer Granule cells, Golgi cells Purkinje cells Stellate cells, Basket cells
  23. 23. Major Cell Types <ul><li>Granule cells </li></ul><ul><li>Purkinje cells </li></ul><ul><li>Golgi cells </li></ul><ul><li>Stellate cells </li></ul><ul><li>Basket cells </li></ul>***The Purkinje cell is the only output of the cerebellar cortex Glutamate GABA GABA GABA GABA
  24. 24. 5 cell types Stellate (inhibitory) Basket (inhibitory) (molecular layer) Purkinje (inhibitory) (Purkinje layer) Golgi (inhibitory) Granule (excitatory) (Granular layer) Microcircuitry of cerebellum
  25. 25. <ul><li>Inputs : </li></ul><ul><li>Climbing fiber (“+”, excitatory, from inferior olive nucleus) </li></ul><ul><li>Mossy fiber (+, from spinal cord & brain stem) </li></ul><ul><li>Output : </li></ul><ul><li>Purkinje cell axon (“-”, inhibitory) </li></ul>
  26. 26. Internal circuitry <ul><li>Organization of cortex is uniform across different subdivisions </li></ul><ul><li>AFFERENT pathways to the cerebellar cortex excite Purkinje cells. </li></ul><ul><li>Basket, stellate and Golgi cells regulate Purkinje cell activity. </li></ul><ul><li>EFFERENT pathways from the cortex originate from Purkinje cells. </li></ul>
  27. 27. Purkinje Cell Recieves + inputs from parallel fibers and climbing fibers Recieves - inputs from basket cells, Golgi cells, stellate cells Heavily invested with glial processes
  28. 28. <ul><li>First direct pathway : </li></ul><ul><li>climbing fiber (+)  Purkinje cells (-)  deep nuclei </li></ul><ul><li>each climbing fiber projects to 1-10 Purkinje cells </li></ul><ul><li>each Purkinje cell receives input from a single climbing fiber </li></ul><ul><li>Powerful excitatory connection, each climbing fiber spike cause a burst of spikes in Purkinje cell (called a “complex spike”) </li></ul>complex spike
  29. 29. <ul><li>Second direct pathway : </li></ul><ul><li>Mossy fiber (+)  granule cells (axon: parallel fibers, +)  Purkinje cells (-)  deep nuclei </li></ul><ul><li>each parallel fiber projects to thousands of Purkinje cells (high divergence) </li></ul><ul><li>each Purkinje cell receives input from ~200,000 parallel fibers (high convergence) </li></ul><ul><li>Weak excitatory connection, spatiotemporal summation of inputs from many parallel fibers causes a single spike in Purkinje cell (called a “simple spike”) </li></ul>glomeruli simple spikes
  30. 30. Inhibition: focusing in time and space <ul><li>Stellate, Golgi, basket cells also receive parallel fiber input and elaborate their dendrites in the molecular layer </li></ul><ul><li>Golgi cells project to granule cells </li></ul><ul><li>Feed forward inhibition </li></ul><ul><li>Stellate, basket cells tend to project laterally </li></ul><ul><li>Collaterals of Purkinje cells also contact nearby cells </li></ul>+ _ _
  31. 31. <ul><li>Lateral inhibition : </li></ul><ul><li>granule cells (axon: parallel fibers, +)  stellate and basket cells (-)  Purkinje cells in a different row </li></ul>
  32. 32. <ul><li>Negative feedback : </li></ul><ul><li>granule cells (axon: parallel fibers, +)  Golgi cells (-)  granule cells </li></ul>
  33. 33. Cerebellar Peduncles Superior peduncles (to the midbrain): Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus) Middle peduncles (to the pons): Cerebellum receives information advising it of voluntary motor activities initiated by motor cortex Inferior peduncles (to the medulla): Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord)
  34. 34. Somatotopic Organization <ul><li>Tactile information </li></ul><ul><ul><li>Ipsilateral anterior lobule </li></ul></ul><ul><ul><li>Bilateral paramedian lobules </li></ul></ul><ul><ul><li>Cerebral Cortex and Cerebellum have similar representations </li></ul></ul><ul><li>Motor representation </li></ul><ul><ul><li>Same area as sensory mapping </li></ul></ul><ul><ul><li>May have auditory and visual processing </li></ul></ul>
  35. 35. The Cerebellum <ul><li>Virtually all fibers entering and leaving the cerebellum are ipsilateral; from and to the same side of the body </li></ul>
  36. 36. Afferent Connections (1): 1. Inferior Cerebellar Peduncle Restiform Body Posterior Spinocerebellar Tract Olivocerebellar tract Cuneocerebellar Tract Reticulocerebellar Tract Juxtarestiform Body Vestibulocerebellar Tract Cerebellum Connections
  37. 37. Afferent Connections (2): 2. Middle Cerebellar Peduncle Pontocerebellar fiber Fibers from raphe nuclei 3. Superior Cerebellar Peduncle Anterior Spinocerebellar Tract Tecto-cerebellar tract Trigemino-cerebellar tract Fibres from locus coeruleus Cerebellum Connections
  38. 38. Efferent Connections : 1. Superior Cerebellar Peduncle Cerebellothalamic fiber - from 3 deep nuclei to VPLo, VLc, CL Cerebellorubral fiber - from nucleus interpositus and dentate nucleus both goes to cortex Cerebello-rubro-spinal tract Fibers to reticular formation and olivary complex 2. Inferior Cerebellar Peduncle Fastigiovestibular fiber Cerebello-reticular cerebello- olivary tract Cerebellum Connections
  39. 39. Outputs of the Cerebellum Dentate nuclei: project contralaterally through the superior cerebellar peduncle to neurons in the contralateral thalamus & from thalamus to motor cortex Func.: influence planning and initiation of voluntary movement Emboliform & Globose nuclei: project mainly to the contralateral red nuclei & a small group is projected to the motor cortex Red Nuclei  Rubrospinal Tract control of proximal limb muscles Fastigial nuclei: project to the vestibular nuclei & to the pontine and medullary reticular formation Vestibulospinal & Reticulospinal tracts Cerebellar nuclei: dentate, globose, emboliform, fastigial
  40. 41. MLF Main Connections of the Vestibulocerebellum lower motor neuron LMN vestibulospinal tract FASTIGIAL NUCLEUS Vestibular Organ Floculonodular Lobe Vermis ARCHICEREBELLUM VESTIBULAR NUCLEUS
  41. 42. Main Connections of the Paleocerebellum lower motor neuron SPINAL CORD rubrospinal tract NUCLEUS INTERPOSITUS Inferior Olivry Nucleus ANTERIOR LOBE PARAVERMAL ZONE PALEOCEREBELLUM RED NUCLEUS spinocerebellar tract
  42. 43. CEREBRAL CORTEX DENTATE NUCLEUS Main Connections of the Neocerebellum lower motor neuron LMN pyramidal tract POSTERIOR LOBE CEREBELLAR HEMISPHERE THALAMUS NEOCEREBELLUM Pontine Nucleus
  43. 44. upper motor neuron UMN BASAL GANGLIA Pyramidal Tract and Associated Circuits lower motor neuron UMN pyramidal tract Cerebellum
  44. 45. Reticular Formation CEREBELLUM Cerebellum and Automatic Motor Control Lower Motor Neuron (LMN) Motor Cortex Red Nucleus Vestibular Nucleus Proprioceptors
  45. 46. Olivocerebellar Connections Caudal portion of medial and dorsal accessory olivary nucleus ----------------- vermis of cerebellar cortex (A and B) fastigial nucleus vestibular nucleus Rostral portion of medial and dorsal accessory olivary nucleus ----------------- paravermal region (C 1 , C 2 , C 3 ) nucleus interpositus Principal Inferior Olivary Nucleus ----------------- cerebellar hemisphere (D 1 , D 2 ) dentate nucleus Cerebellum Connections
  46. 47. Cerebellum Function  Maintenance of Equilibrium - balance, posture, eye movement  Coordination of half-automatic movement of walking and posture maintenance - posture, gait  Adjustment of Muscle Tone  Motor Learning – Motor Skills  Cognitive Function
  47. 48. Cerebellum: Control of Voluntary Movement All three lobes of cerebellum work together- Comparator of a servo-mechanism <ul><li>Primary function: </li></ul><ul><li>To supplement & correlate the activities of other motor areas </li></ul><ul><li>Control of posture </li></ul><ul><li>Correction of rapid movements initiated by cerebral cortex </li></ul><ul><li>Motor learning Frequency of nerve impulses in the climbing fibers almost doubles when a monkey learns a new task </li></ul><ul><li>Movement Control: </li></ul><ul><li>Inputs from motor cortex inform the cerebellum of an intended movement before it is initiated </li></ul><ul><li>Sensory information is then received via the spinocerebellar tract </li></ul><ul><li>An error signal is generated and is fed back to the cortex </li></ul>
  48. 49. Cerebellum and Motor Learning <ul><li>Deficits in learning complex motor tasks after cerebellar lesions </li></ul><ul><li>fMRI studies : cerebellum active during learning of novel movements </li></ul><ul><li>Postulated that cerebellar nuclei store certain motor memories </li></ul><ul><li>May be involved in cognitive functions </li></ul><ul><li>Cerebellar Cognitive Function </li></ul><ul><li>Plays a role in language and problem solving </li></ul><ul><li>Recognizes and predicts sequences of events </li></ul>
  49. 50. Cerebellar Processing - 1 <ul><li>The frontal motor association areas of the cerebral cortex indicates its intents to initiate voluntary muscle contractions </li></ul><ul><li>Through collateral fibers of the pyramdial tracts, it notifies the cerebellum of its activity </li></ul>
  50. 51. Cerebellar Processing - 2 <ul><li>At the same time, the cerebellum receives information from the proprioceptors throughout the body </li></ul><ul><ul><li>Tension in muscles, tendons, and joint positions </li></ul></ul><ul><ul><li>From visual and equilibrium pathways </li></ul></ul><ul><li>This information enables the cerebellum to determine where the body is and where it is going </li></ul><ul><ul><li>More specifically where the parts of the body are located in space and how are they moving </li></ul></ul>
  51. 52. Cerebellar Processing - 3 <ul><li>The cerebellar cortex assesses this information and calculates the best way to coordinate the force, direction, and extent of muscle contraction </li></ul><ul><ul><li>Prevents overshoot </li></ul></ul><ul><ul><li>Maintains posture </li></ul></ul><ul><ul><li>Ensures smooth, coordinated movements </li></ul></ul>
  52. 53. Cerebellar Processing - 4 <ul><li>Via the superior peduncles, the cerebellum dispatches its “blueprint” for coordination to the cerebral motor cortex which makes appropriate adjustments in its motor plan </li></ul><ul><li>Cerebellar fibers also flow to brain stem nuclei, such as the red nuclei of the midbrain, which in turn project to motor neurons of the spinal cord </li></ul>
  53. 54. The Cerebellum <ul><li>The cerebellum continually compares the higher brain’s intention with the body’s performance and sends out messages to initiate the appropriate measures </li></ul><ul><li>In this way, it helps to promote smooth voluntary movements that are precise and economical in terms of muscular effort </li></ul>
  54. 55. The Cerebellum <ul><li>Cerebellar injury results in the loss of muscle tone and clumsy, unsure movements, and sometimes even impaired thoughts about movements </li></ul>
  55. 56. Clinical Considerations <ul><li>Signs of Dysfunction </li></ul><ul><ul><li>Impaired Muscle Synergy </li></ul></ul><ul><ul><li>Reduced Muscle Tone </li></ul></ul><ul><ul><li>Evident in Skilled Tasks </li></ul></ul><ul><ul><li>Nystagmus </li></ul></ul><ul><ul><li>Ataxia : incoordination of movement </li></ul></ul><ul><li>- decomposition of movement </li></ul><ul><li>- dysmetria, past-pointing </li></ul><ul><li>- dysdiadochokinesia </li></ul><ul><li>- gait ataxia, truncal ataxia </li></ul><ul><ul><ul><li>Slow Movement (Bradykinesia) </li></ul></ul></ul><ul><ul><ul><li>Mild Muscular Weakness (Asthenia) </li></ul></ul></ul><ul><ul><ul><li>Asynergia </li></ul></ul></ul><ul><ul><ul><li>Speech difficulties (Ataxic Dysarthria) </li></ul></ul></ul><ul><ul><ul><ul><li>affects respiration, phonation, resonance and articulation, but most pronounced in articulation and prosody. </li></ul></ul></ul></ul>
  56. 57. Clinical Considerations 2 <ul><li>Dysdiadochokinesia </li></ul><ul><ul><li>Clumsiness in Alternating Movements </li></ul></ul><ul><ul><li>Tapping, Speech Sound </li></ul></ul><ul><li>Dysarthria </li></ul><ul><ul><li>Ataxic Dysarthria </li></ul></ul><ul><ul><li>Scanning Speech </li></ul></ul><ul><ul><li>Slurred and Disjointed Speech </li></ul></ul><ul><li>Dysmetria </li></ul><ul><ul><li>Error in Judgment of Range and Distance of Target </li></ul></ul><ul><ul><li>Undershooting or Overshooting </li></ul></ul>
  57. 58. Clinical Considerations 3 <ul><li>Intentional Tremor </li></ul><ul><ul><li>Accessory Movement During Volitional Task </li></ul></ul><ul><ul><li>vs. Parkinson’s Disease Where Tremor Lessens During Volitional Movement </li></ul></ul><ul><li>Hypotonia </li></ul><ul><ul><li>Reduced Resistance to Passive Stretch </li></ul></ul><ul><li>Rebounding </li></ul><ul><ul><li>Inability to Predict Movement </li></ul></ul><ul><ul><li>Cannot Hold Back Movement </li></ul></ul><ul><li>Disequilibrium </li></ul><ul><ul><li>Unsteady Gait, Body Wavering </li></ul></ul>
  58. 59. Cerebellar Pathologies <ul><li>Cerebrovascular Accident (CVA) </li></ul><ul><ul><li>Thrombotic, embolic or hemorrhagic </li></ul></ul><ul><ul><li>Vertebrobasilar Artery </li></ul></ul><ul><li>Toxicity </li></ul><ul><ul><li>Chronic Alcoholism </li></ul></ul><ul><li>Progressive Cerebellar Degeneration </li></ul><ul><ul><li>Friedrich's Ataxia: Autosomal Recessive Heredity Degenerative Condition </li></ul></ul><ul><ul><li>Combined Sensory and Motor Dysfunctions </li></ul></ul>
  59. 60. Posture Gait – Ataxia Tremor
  60. 61. Cerebellar Ataxia Ataxic gait and position: Left cerebellar tumor a. Sways to the right in standing position b. Steady on the right leg c. Unsteady on the left leg d. ataxic gait a b c d
  61. 62. Cerebellar tumors on vermis - Truncal Ataxia - Frequent Falling The child in this picture: - would not try to stand unsupported - would not let go of the bed rail if she was stood on the floor. Cerebellar Medulloblastoma