Cerebellum Flashcards
What are the 3 lobes of the cerebellum?
- Anterior lobe
- Posterior lobe
- Flocculonodular lobe (underside) - “vestibulocerebellum”
What are the 3 bands of the cerebellum?
- Vermis - input mainly from SC
- Intermediate Zone - input mainly from SC
- Lateral Zone - input mainly from cortex
What is the basic cerebellar circuit? 4 deep nuclei
- INPUT —> Purkinje (direct or via interneuron) —> inhibit deep cerebrally nucleus neurons via GABA —> “meaningful pauses” —> OUTPUT
- 4 deep cerebellar nuclei
- “Don’t Eat Greasy Foods”
- Dentate nucleus (most lateral) - input from lateral zone - planning movement
- Emboliform nucleus - input from intermediate zone - distal body movement
- Globose nucleus - input from intermediate zone - distal body movement
- **Emboliform + globose = interpositus
- Fastigial nucleus (most medial) - input from vermis - proximal body movement
- ***Flocculonodular lobe does not project to deep nucleus but projects to vestibular nuclei
- “Don’t Eat Greasy Foods”
2 Types of Cerebellum Afferents
- Mossy Fibers - come from all other sources and terminate on granule cells in innermost layer
- Climbing Fibers - come only form inferior olive; terminate on Purkinje (ea Purkinje gets input from only ONE climbing fiber)
- Synaptic transmission from climbing fiber —> Purkinje —> Ca++ action potential (“complex spike”) which leads to long-term changes in excitability (“teaching signal”)
3 Peduncles
- Superior - major output pathway (thalamus —> cortex)
- All output from here must cross to contralateral side b/c going to cortex SO the input (ventral spinocerebellar tract) also crosses with it on its way into cerebellum- Middle - only gets input from pontine gray; no output
- Inferior - a lot of sensory input; dorsal spinocerebellar tract
Dysmetria v. DDK v. Dyssynergia
- Dysmetria - lack of coordination overshoot (hypermetria) or undershoot (hypometria)
- Greater latency and lower velocity in affected limb
- Dysdiadochokinesia (DDK)- trouble w/ rapid alternating movements (test via pronation/supination)
Dyssynergia - movement decomposition; segmented movements instead of one smooth
Intention Tremor
broad, low frequency tremor that inc as you get to end of task
Why does cerebellar damage cause hyporeflexia and hyptonia?
Dec activity of gamma motoneurons SO … less activation of alpha motoneurons
Causes of Bilateral Cerebellar Ataxia
- Bilateral/Widespread
- ACUTE
- Acute alcohol intoxication
- Other drugs and toxins
- Wernicke’s encephalopathy - Vit B1 deficiency; treat w/ thiamine
- SUB-ACUTE
- Paraneoplastic Syndrome - secondary to cancer; may be first sign; manifests as inflammation or secretory factors
- CHRONIC
- Alcoholic degeneration
- Idiopathic degeneration
- Hereditary Degeneration
- Hypothyroidism (treatable - thyroid replacement)
- Progressive MS
- ACUTE
Causes of Unilateral or Asymmetric Ataxia
- ACUTE
- Infarct
- Hemorrhage
- Acute MS
- Encephalitis (infection)
- Abscess
- SUB-ACUTE
- Primary or secondary neoplasm
- CHRONIC
- Low grade tumor
Sensory Ataxia
- Sensory Ataxia (accompanied by problems w/ proprioception)
- Peripheral Nervous System
- Inflammatory/auntoimmune
- Paraneoplastic
- B6 toxicity - SC/Dorsal Column Disease
- B12 deficiency (pernicious anemia - degeneration of myelin of SC; tx is B12 sup)
- Hereditary ataxias
- Tabes dorsalis (neurosyphilis)
How to localize cerebellar dysfunction
Flocculonodular Lobe - Loss of balance; truncal ataxia; cannot adjust to changes in vestibulo-ccular reflex (important when getting new glasses)
Fastigial nucleus or Vermis -Truncal ataxia
Intermediate zone or Interpositus -Appendicular ataxia (lack of coordination of distal limbs)
Cerebrocerebellum (lateral zone or dentate nucleus)-
Dysmetria, DDK, intention tremor, Dyssynergia, hypotonia, hyporeflexia
