Subcortical Control

• What does the telecephalon form into?

  Cortex

  Basal ganglia
• Whar does the diencephalon form into?

  Thalamus

  Hypothalamus

  Retina
• Where does the basal ganglia receive its inputs from?

  From cortex (almost the entire cortex) -> to striatum

  From dopaminergic nuclei (substantia nigra) -> to striatum
• What is Huntington's chorea?

  Autosomal dominant inherited condition

  Presents in middle ear

  Loss of striatal & cortical tissue (ventricles expand, due to loss of grey & white matter and CSF pressure) -> disproportionate loss of indirect pathway circuits -> hyperkinesia
• What is the function of Huntington protein?

  Involved in vesicle transport along axons
• Fill in the blanks

  A) Fornix

  B) Midbrain Tegmentem

  C) Basilar pons

  D) Pontine tegmentum

  E) Medulla

  F) Tonsil of cerebellum

  G) Tectum

  
• Fill in the blanks

  A) Thalamus

  B) Superior colliculus

  C) Inferior colliculus

  D) Cerebral aqueduct

  E) Fourth ventricle

  F) Medulla

  G) Basilar pons

  H) Oculomotor nerve

  I) Mammilary body

  J) Optice nerve

  K) Optic chiasm

  L) Hyth

  
• Describe the direct basal ganglia pathway.

  FUNCTION: Reinforces cortical activity

  Cortex sends excitatory impulse to striatum -> striatum sends inhibitory impulses to globus pallidus interna -> less inhibitory signals sent from GPI to thalamus -> more excitatory impulses from thalamus to cortex 
• Describe the indirect basal ganglia pathway. (w/o subthalamic nucleus)

  Cortex sends excitatory impulses to the striatum -> striatum sends inhibitory impulses to the globus pallidus externa -> GPE in inhibited from sending its inhibitory impulses to GPI -> so GPI sends more inhibitory signals to the thalamus -> thalamus is inhibited, so doesn’t send excitatory signals to the cortex 
• Describe the indirect basal ganglia pathway. (w/ subthalamic nucleus).

  Cortex sends excitatory impulses to the striatum -> striatum sends inhibitory impulses to the globus pallidus externa -> GPE is inhibited from sending inhibitory impulses to subthalamic nucleus -> subthalamic nucleus sends excitatory impulses to globus pallidus interna -> GPI sends inhibitory impulses to thalamus -> thalamus is inhibited, so doesn’t send excitatory signals to the cortex 
• What is the function of the 3 basal ganglia pathways?


  Direct -> reinforce cortical activity

  Indirect -> inhibits cortical activity of neighbouring areas of cortex

  Hyperdirect -> thought to prevent unwanted movement in advance
• Describe the hyperdirect basal ganglia pathway.

  Cortex sends excitatory impulses to the subthalamic nucleus -> subthalamic nucleus sends excitatory signals to globus pallidus interna -> GPI sends inhibitory impulses to thalamus -> thalamus is inhibited, so doesn’t send excitatory signals to the cortex 
• A given area of cortex will reinforce its own activity through direct pathway AND inhibits the surrounding cortical area activity through indirect pathway 

  E.g. in bicep contraction 

  Bicep area of MI = direct pathway (to reinforce activity) 

  Tricep area of MI = indirect pathway (to inhibit activity) 

  ^^ this is a simplistic example of basal ganglia pathways 

  Not only in M1, it is seen in emotions, vision etc. 

  NOT JUST MOTOR
• Pathophys of Huntington's

  Mutations of Huntington gene -> CAG repeat sequence (encodes glutamine) -> misfolded protein (more than 40 CAG repeats) -> protein aggregation & neuronal death (striatum) -> loss of indirect circuits -> shift in direct vs indirect balance towards direct pathway -> hyperkinesia (loss of inhibition)

  NOTE: not only the striatum dies, but usually the first to go
• The receptor determines the activity of the synpase, NOT the neurotransmitter.
• NOTE: The basal ganglia is not only involved with M1. All areas of the cortex rpject to the basal ganglia (to either dorsal or ventral striatum).
• Give 4 basal ganglia loops.

  Body movement loop

  Oculomotor loop -> eye movement

  Prefrontal loop

  Limbic loop

  Principles of a feedback system are the same throughout all loops (direct & indirect pathways).
• Fill in the blanks

  A) Vermis

  B) Spinocerebellum

  C) Cerebrocerebellum

  D) Vestibulocerebellum

  E) Nodulus

  F) Flocculus

  
• Fill in the blanks

  A) Thalamus

  B) Internal capsule

  C) Caudate nucleus

  D) Putamen

  E) Midbrain

  F) Vermis

  G) Cerebellar peduncles

  H) Superior

  I) Middle

  J) Inferior

  K) Cerebellar hemisphere

  L) Deep cerebellar nuclei

  
• Fill in the blanks

  A) Vermis

  B) Superior cerebellar peduncle

  C) Inferior cerebellar peduncle

  D) Middle cerebellar peduncle

  E) Flocculus

  F) Nodulus

  G) Cerebellar hemisphere

  
• Fill in the blanks

  A) Fourth ventricle

  B) Superior cerebellar peduncle

  C) Middle cerebellar peduncle

  D) Inferior cerebellar peduncle

  E) Flocculus

  F) Nodulus

  G) Cerebellar cortex

  H) Folia

  
• What are the functional subdivisions of the cerebellum?

  Vestibulocerebellum

  Cerebrocerebellum

  Spinocerebellum
• What are the cerebellar peduncles?

  Axon tracts that link the cerebellum & rest of the brain
• What are the lower inputs to the cerebellum?

  From spinal cord & brainstem

  Vestibular system

  Precerebellar sysem (e.g. external cuneate & Clarke's nucleus)
• What are the higher inputs to the cerebellum?

  Inputs from cortex

  EITHER via midbrain nucleus/inferior olive OR via Pontine nucleus (more important in humans)
• What is the Pontine nucleus?

  Mulitple nuclei in the pons

  Recieve projections/information from the cortex & project into cerebellum
• Conscious vestibular circuitry.

  Projects to vestibular nuclei in brainstem -> project to multiple nuclei in thalamus -> projects to distributed network of cortical areas involved in conscious vestibular sensation (e.g. S1 & vestibulocortical areas in lobes) -> contribute to sense of self in space 
• Unconscious vestibular circuitry

  Vestibular neurons project directly to the cerebellum or from lateral vestibular nucleus (more common) -> unconscious sensation -> computed in cerebellum (specifically the vestibulocerebellum – posterior region) -> brainstem (vestibular nuclei & superior colliculus) -> aids in vestibular reflexes
• What are the inferior cerebellar projections?

  To brainstem & spinal cord

  • superior colliculus -> vestibulo-ocular reflex (vestibulocerebellum)
  • reticular formation -> rections to things & subconscious modulation of reflexes (spinocerebellum)
  • vestibular nuclei -> helps vestibular reflexes (vestibulocerebellum)
• What are the superior cerebellar projections?

  To thalamus (ventral lateral nucleus) then projects to cortex
• Spinocerebellum - higher cerebellar projections

  Feedback to M1 

  Projections from deep cerebellar nuclei to red nucleus & thalamus -> projections from thalamus to M1 
• Cerebrocellubellum - higher cerebellar projections

  Projections from deep cerebellar nuclei to red nucleus & thalamus -> projections from thalamus to frontal cortex -> projections to more frontal areas (premotor (movement planning), prefrontal (thinking planning, decision making, emotional regulation etc)) 
• Majority of the cerebellum is cerebrocellum -> involved with frontal & prefrontal cortices.
• Cerebellum contains around 80% of the neurons in the brain.
• What can cerebellar disease lead to?

  Cerebellar disease (e.g. tumours, strokes, genetic syndromes)

  Defects in motor function, thought, or in emotional regulation