Brainstem + Cerebellum

Brainstem + Cerebellum

1. Descending spinal tracts

   • Lateral pathways
     • voluntary movement distal musculature
       • (fine motor)
     • Corticospinal
       • Cortex
         • Cerebral peduncle
           • medullary pyramid
             • Spinal cord
       • May branch and connect....
         • Red nucleus
         • RF
           • Pontine
           • Medullary
           • spinal cord
     • Rubrospinal
       • Red nucleus
         • Medulla
           • Spinal cord
     • Direct cortical control
     • Lesions
       • finger/joint indep movement
         • recover via spared pathway
   • Ventromedial pathways
     • Brain stem control
       • balance and posture
     • Vestibulospinal
       • vestibular nuc
         • spinal cord
       • bilateral head movement
       • Posture/balance
         • SC can maintain antgravity but NOT balance
     • tectospinal
       • superior colliculus
         • spinal cord
       • visual
         • orient head
     • Pontine and medullary reticular
       • balance, posture, trunk
       • initiate/halt ongoing
       • speed
     • lesions
       • postural abnormality
       • difficulty sitting/walking

2. Function

   • Balance
   • vestibular
     • synchronize eye and body equilibrium when stand and walk
   • timing
     • especially across multiple joints
   • control ongoing
     • error correction
       • intended vs. outcome

3. Gross anatomy

   • Deep cerebellar nuclei
     • relay cerebellar cortical output to brain stem
       • Fastigial nuclei
         • relay vermis
       • interposed nucleus
         • relay paravermis
       • dentate nucleus
         • relay hemispheres
       • innervated by
         • purkinje (inhib)
         • climbing and mossy (excite)
   • Vermis
     • contributes to ventromedial pathways
   • Cerebellar
     • lateral pathways

4. Cellular

   • Molecular layer
     • Stellate
     • Basket
       • innervated by parallel fibers
         • inhibitory synapse on purkinje dendrites
         • inhibitory synapse on purkinje axon hillock
   • Purkinje
     • Purkinje
       • only output of cerebellar cortex
       • GABAergic
       • Activated by
         • Climbing fibers
           • inferior olivary
           • event detection
             • Each purkinje 1
             • each many purkinje
             • collateral w/ deep cerebellar nuclei
         • Mossy fibers
           • brainstem/ spinal cord
             • (indirect)
               • rosette
                 • (activate granule which activates purkinje
   • Granular
     • Golgi
       • receive from parallel and mossy
         • inhibit granule cells
           • negative feedback
     • Granule

5. Circuits

   • learns and stores motor programs
     • smooth movement and limit need conscious control
       • often prior/learned programs
   • corticopontocerebellar proj
     • motor loop through lateral cerebellum
       • Cortex
         • Pontine nuclei
           • Cerebellum
             • purkinje
               • dentate nucleus
                 • superior cerebellar peduncle
                   • contralateral
                     • VLc (thalamus
                     • red nucleus
           • mossy fibers
             • contralateral
         • axons from layer V
           • sensorimotor

6. Motor learning

   • Marr-Albus theory
     • parallel fiber
       • active at same time as climbing fiber
         • onto purkinje
           • LTD

7. Dysfunction

   • Hypotonia
     • Decrease tonic muscle tone
     • diminished resistance to movement
   • Dysarthria
     • speech articulation
   • Dysdiadochokineasia
     • inability to perform rapid alternating movements
   • Dysmetria
     • error range or force of movement
     • hypometria
       • undershooting
     • hypermetria
       • overshooting
   • Intention tremor
     • tremor during movement
   • spinocerebellum
     • Truncal ataxia
       • drunken sailor gait
     • vermis + midline
   • vestibulocerebellum
     • postural instability
       • loss of equilibrium
     • nystagmus
       • involuntary, rhythmic eye movement

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