Cerebellum

• Cerebellum


  Structure containing 80% of the brain's neurons despite being only 10% of total brain mass
• Cerebellum


  Galen, Fluorens, Purkinye, and Cajal all recognized its importance to motor systems
• Cerebellum


  Plays a role in integrating sensory information to produce coordinated movements, refining motor-related outputs to learn motor tasks, and processing cognitive and execultive funtions.
• Nonmotor functions of the ecrebellum have recently gotten attention for the first time:

  • deep stimulation = behavioral reactions (autonomic + complex)
  • Associative learning occurs there
  • Purkinje cell loss = tied to autism
  • CCAS impairs a bunch of higher order functions
• Cerebellar abnormalities like purkinje cell loss may be involved with autism
• Cerebellar cognitive affective disorder (CCAS) is characterized by issues with executive functioning, new finding on non-motor cerebellar functions
• Cerebellum anatomy:

  • external layer of gray matter (cerebellar cortex)
  • internal core of white matter
  • 3 pairs of deep nuclei
  • fastigial nucleus
  • interposed nucleus
  • dentate neucleus
  • Connected to dorsal brain stem with 3 stalks of tissue:
  • inferior cerebellar peduncle
  • middle cerebellar peduncle
  • superior cerebellar peduncle
• Lobules


  Parallel folds on the surface of the cerebellum
• Primary + posterolateral fissures divide the cerebellum into 3 lobes: anterior and posterior on the dorsal end by the Primary and flocculondular lobe is separated on the ventral side
• Vermis


  Midline region separating the hemispheres of the cerebellum, named after the Latin for "worm"
• Vestibulocerebellum 


  Composed of the flocculonodular lobe, most evolutionarily conserved, integrates visual and vestibular inputs, 2 regions: lateral and medial
• Medial vestibulocerebellum controls trunk, head, posture + limb extensor molecules which means balance. Lateral vestibulocerebellum = eye movements and coordinates head+eyes
• Spinocerebellum


  Vermis + intermediate regions of the hemispheres, receives somatosensory + proprioceptive inputs from the spinal chord and is important for locomotion and extremity movement
• The cerebellum is mostly somatotopic : regions of neurons control regions of the body
• Dorsal spinocerebellar tract carries joint + muscle info to the cerebellum = sensory feedback for voluntary + involuntary. Ventral spinocerebellar tract is only active during voluntary movements. Sends copy of spinal motor neuron activity so it knows about the commands formed at the spinal level
• Cerebrocerebellum


  Lateral regions of the cerebellum, most evolutionarily recent + bigger in humans and apes. Communicate with the cerebral cortex to motor and premotor cortices and help with planning and executing movements. Also targets nonmotor targets like prefrontal + posterior partietal cortices, which help with cognitive functions like memory, pain, addiction, and language
• Dysarthria


  Speech disorder which comes from difficulty articulating language
• Ataxia


  Condition characterized by poor coordination of voluntary movements, atypical eye movements, change of gait, and poor balance which also go with dysarthia. Alcohol intoxication is a good approximation of this
• Cerebellar cortex has 3 distinct layers of neurons

  • deepest: granular layer
  • middle: purkinje cell layer
  • external: molecular layer
• Granular layer


  Deepest layer + input layer of CC. Made up mostly of granule neurons, which are small, excitatory and densely packed. Has some sparsely populated inhibitory (Lugaro, Golgi, chendelier) and excitatory (unipolar brush cells) interneurons. Mossy fibers terminate here
• Mossy fibers


  One of two major afferent cell types in the cerebellum. Form synaptic complexes with Golgi and granule cells, which are called cerebellar glomeruli
• Purkinje cell layer


  Middle cell layer (and output layer) made up of one layer of titular cells that have giant cell bodies and dendrites which extend to the surface of the cerebellum. Their axons are responsible for output to the white matter or vestibular nuclei in the brain stem, where they release GABA
• Molecular layer


  External layer of the cerebellar cortex which includes the purkinje cell dendrites and parallel fibres, which are the granule cells' axons which ascend from the granular layer and bifurcate mediolaterally to be parallel with the long axis of the lobules. In this layer there are also stellate and basket cells, which provide feed-forward inhibition to purkinje cells