Neuro Week 10: Functional Anatomy of the Cerebellum and Basal Ganglia

if you had a lesion on the left hemisphere of the lower thoracic cord of the spinal cord what motor deficits would you experience?

ipsilateral paralysis/paresis to the lower limbs

extrapyramidal systems

include other UMN tracts that do not run within the pyramids of the medulla

reticulospinal tract

reticular formation → through pyramids → spine

what kind of neurons are in the reticular formation

UMN

how do neurons terminate in the reticulospinal tract?

axons terminate bilaterally onto

LMNs in medial regions of ventral horn

function of the reticulospinal tract

initiates anticipatory, feedforward adjustments that stabilize posture during ongoing movements

what happens when we are about to pull on something strong standing up right? (think legs)

what are the correlations between SMA, Cerebellum, PMC, and Basal ganglia?

The basal ganglia works with motor cortex to initiate and terminate movements, while the cerebellum and SMA monitor ongoing activity to produce smooth movements

roles of the cerebellum

• Detects the difference or “motor error” between intended

and actual movements

• makes corrective adjustments via efferents to UMNs

• Important for balance and coordinated movements

• Functions ipsilaterally

cerebellar ataxia

• Jerky and imprecise trajectory

• Overshoots/undershoots target

• Requires frequent corrective movements

lobes of the cerebellum

• anterior lobe

• posterior lobe

• flocculonodular lobe (smallest)

what are the two fissures of the cerebellum

primary fissure (in between anterior and posterior lobe)

posterolateral fissure (in between flocculonodular and posterior)

what are the three functional divisions of the cerebellum?

1. Spinocerebellum – control of muscle tone and coordination (mostly vermis and anterior lobe)

2. Cerebrocerebellum – motor planning, learning and memory

3. Vestibulocerebellum – balance, postural adjustments, coordination of eye movements

where do cortical projection to the cerebellum come from?

relay neurons in the pons

what is the path of the cortical motor system?

cerebellar cortex → deep cerebellar nuclei → superior cerebellar peduncle → VL complex (thalamus) → PM and premotor cortex

what is the feedback circuit

cerebellum sends info back to itself to modulate its own activity

fastigial nucleus

is the major efferent output to the brainstem motor systems,

largely through connections to the superior colliculus and reticular

pathways and lesion of the cerebellar divisions

what happens to people with chronic alcohol abuse 

degeneration of the anterior portion of the spinocerebellum which is crucial for lower limb activity therefore they have a wide and staggering gait, but little impairment of upper limbs

spiny neurons

excitatory projection neurons

non-spiny neurons

inhibitory interneurons

2 layers (white matter isnt a layer) just outermost dark matter split into two layers

what layers can you see in a Nissl stain?

molecular and granule

what layer can you see with fluorescent yellow

purkinji

where do purkinje cells project to?

the molecular layer

where are purkinje cells found?

only the cerebellum

what are the two sources of convergent excitatory input to the purkinje cells?

1. Parallel fibers – axons from granule cells

- receives input from Mossy fibers

2. Climbing fibers – axons from inferior olive in the medulla (strong because its making the most contact on one dendrite (wrapping))

what inhibitory interneurons modulate the activity of Purkinje cells?

Basket cells – found in molecular layer; form an inhibitory “nest” of synapses with

Purkinje cell bodies

• Stellate cell – star-shaped, cell bodies in the molecular layer. Receives input from

parallel fibers and projects inhibitory input to Purkinje cells

• Golgi cells – cell bodies found in granule layer, but dendrites extend into molecular

layer. Also receive input from parallel fibers and provide feedback to granule cells

what is the purpose of having an indirect pathway for basic loopsof cerebellar processing 

error correction 

• if the amount of inhibition does not match the level of excitation, there is an error somewhere that needs to be fixed

which is more active at rest, purkinje cells or deep nuclear cells

purkinje

major input regions of the basal ganglia?

striatum - caudate nucleus and putamen

what are the principle neurons of the striatum

Medium Spiny Neurons

• make up 90% of cells of the striatum

• Large amount of spines on dendrites

• They are GABAergic (inhibitory)

types of Medium Spiny Neurons

• 2 distinct MSN phenotypes

  • D1-type MSNs (direct path)

    • facilitate movement

  • D2-type MSNs (indirect path)

    • suppress unwanted movement

dopamine role in basal ganglia

dopamine acts to reduce this inhibitory outputs

parkinson’s disease

• Hypokinesia and bradykinesia

• Tremor at rest

• Rigidity

• Postural instability

• Shuffling gait

• Cognitive deficits – decreased motivation and spontaneity,

depression, lack of affect

• effects substantia nigra

Huntington’s Disease

• Hyperkinesia: excessive movement

• Chorea

• Cognitive deficits – depression, personality changes (irritability, impulsiveness), deficits in memory and attention