Cerebellum

Question 0

Peduncles

Answer 0

Connectivity

Superior (aka brachium conjunctivum)
- superior -> decussates in caudal midbrain-> deep to corpora quadremina (colliculi) -> red nucleus -> VA/VL (thalamus)
- output -> midbrain
Middle (aka brachium pontis)
- input from pons (indirect cortex)
Inferior (aka restiform body) - just posterior to inf olive (associated with CN 7 and 8)
- input + output from medulla and spinal cord
- ex input vestibular nerve and nucleus

Question 1

Overview of cerebellum

Answer 1

Function - modulate upper motor neurons
- adjusting for conditions, learning new skills
- other types of learning, emotions
Ipsilateral! (sometimes bilateral)

Anatomy - enclosed by hemispheres, fourth ventricle

Question 2

Structure of cerebellum

Answer 2

Hemisphere - connected by vermis (midline)
- white matter -> arbor vitae (tree-like)
- grey matter = folia
Lobes - anterior, posterior, floculonodular
- divided by primary and posterolateral fissures
- tonsil = lobule of posterior lobe, just superior to foramen magnum (herniation!)

Question 3

Vestibulocerebellum

Answer 3

Floculonodular - aka archicerebellum (ancient)

Input: ipsilateral inf peduncles -> mossy fibers -> granular
- vestibular apparatus (direct) - christae, maculae
- vestibular nucleus (brainstem)
Output: inf peduncles (no synapse in deep nuclei)
- ipsilateral vestibular nucleus
-> vestibulospinal -> posture, muscle tone
-> vestibulo-ocular reflex (bilateral via nuclei, MLF)

Question 4

Spinocerebellum

Answer 4

Functional division aka paleocerebellum
Vermis + intermediate zone
(= most of anterior, medial posterior lobes)
Input: ipsilateral proprioception -> inf peduncle
- dorsal spinocerebellar = leg, cuneocerebellar = arm
- also receive auditory, visual
-> somatotopy (vermis axial, intermediate limbs)

Output:

• Vermis -> ipsilateral fastigial nuc -> inf peduncle ->b/l brainstem
  
  • vestibular nucleus -> vestibulospinal -> axial
  • reticular formation -> reticulospinal -> axial
  • some to thalamus -> cortex -> ventral corticospinal (-> axial), corticobulbar (-> face, tongue)
• intermediate zone -> ipsilateral interposed -> sup peduncle -> decussate -> contralateral
  
  • red nucleus -> rubrospinal -decussates> ipsilateral limbs
  • VL -> cortex -> lateral corticospinal -decussates> ipsilateral limbs

Question 5

Cerebrocerebellum

Answer 5

aka pontocerebellum, neocerebellum
-> initiation, planning, learning of skilled movements

Lateral hemispheres
Input from broad cortex (sensory, motor, association)
-> corticopontine tract (ipsi) -> synapse -> “transverse pontine fibers” -> decussate -> middle peduncle -> contralateral cerebellum
Output -> dentate -> sup peduncle -> decussate in midbrain
- dentothalamic fibers -> VL -> contralateral motor, premotor (powerful) -> movement on ipsilateral
- dentorubral -> contralateral parvocellular red nucleus (NOT rubrospinal) -> inferior olive -decussate in medulla> climbing fibers -> all areas of cerebellum
(= feedback loop for error detection, triangle of Molleret)

Question 6

Deep cerebellar nuclei

Answer 6

Within deep white matter
Fastigial (medial) - input from vermis
Interposed (= globose, emboliform) - input from intermediate zone
Dentate - input from lateral hemispheres

Fx - receive input from cortex, process cerebellar output

Question 7

Cerebellar cortex

Answer 7

Three layers, all cells are GABA except granular

Molecular - few cells (basket, stellate), branches of Purkinje dendrites
Purkinje - single layer of large cells
- input - granular parallel fibers
- climbing fibers - direct from inferior olive (highly specific, excitatory)
- axons -> white matter -> deep or vestibular nuclei
Granular - huge number of small granular cells (some Golgi)
- input - spinal and pontine -> mossy fibers (excitatory)
- output - axons -> molecular layer -> extend laterally (parallel fibers) -> excite Purkinje (convergence 300K:1)

Circuitry - input from climbing (olive), mossy (all others)

• directly excites deep nuclei
• climbing -> Purkinje (powerful), mossy -> granular -> Purkinje
• Purkinje inhibits deep nuclei -> integrates response “inhibitory sculpting”

Question 8

Learning in cerebellum

Answer 8

Plasticity of parallel fibers -> Purkinje synapse

Short term plasticity - 30 min - +/- of receptor synthesis, traffic

Climbing fibers - motor error
- aspartate -> strong AP response, intracellular Ca
Parallel fibers -
- glutamate -> AMPA, metabotropic
-> metabotropic -> DAG, IP3 -(if Ca from climbing)> active PKC
-> phosphorylates (inactivates) AMPA -> short term
-> internalization of AMPA -> long term

ex vestibulo-ocular reflex after “minifying” glasses - few hours to correct