PHYS: Voluntary Control of Movement

Question 1

What are the principal descending motor pathways in the spinal cord?

Answer 1

• Direct pathway (from cortex to spinal cord)
  
  • Corticospinal tract - cortex to spine, most descneding motor information goes through here
  • Rubrospinal tract - supplementary, influences mainly lateral MNs innervating distal limb muscles
• Indirect pathways (via brainstem to spinal cord)
  
  • Reticulospinal tract - surverys everything, not specifically going somewhere
  • Vestibulospinal tract - balance
  • Tectospinal tract - superior (visual) & inferior (hearing) colliculi

Question 2

What is the pathway of the corticospinal tract (aka pyramidal tract?)

Answer 2

(Primary motor cortex, SMA, somatosesnrosy cortex) -> Internal capsule -> pyramids of medulla

• Lateral corticospinal tract - 75-80% decussate at medulla (contralateral)
  
  • Innervate distal limb muscles
• Ventral corticospinal tract - 20-25% ipsilateral projection to spinal cord
  
  • Innervate axial and proximal limb muscles

Question 3

What is the pathway of the rubrospinal tract?

Answer 3

Origin: red nucleus (mesencephalon/midbrain)

Functions in closs association with CS tract.

Red nucleus > decussates lower brain stem > descends lateral columns

Innverates mostly interneurones

Question 4

What are the 3 ventromedial (indirect) tracts again?

Answer 4

• Reticulospinal tract
  
  • pontine: enhances antigravity reflexes
  • medullary: relaxes antigravity muscles from reflext control
• Vestibulospinal
  
  • Balance/equilibrium
• Tectospinal
  
  • Visual adjustments

Question 5

Explain the reticulospinal tract

Answer 5

From reticular formation of brainstem -> thalamus and spinal cord

• Medial reticulospinal tract (pons) - excites axial and extensor muscles
• Lateral reticulospinal tract (medulla) - inhibits excenstor muscles and excites flexors

Antagonistic function to control anti-gravity muscles

Question 6

Explain the vestibulospinal tract

Answer 6

Align head and body to gravity.

Vestibular system (vestibule) -> vestibular nuclei -> VST -> spinal cord -> postural muscles

Connects with cerebellum and reticular formation

Question 7

Explain the tecotospinal tract

Answer 7

Adjust eye position during head movement, orients the head and neck during eye movements

Tract:

Visual input -> superior colliculus -> tectospinal tract -> cervical spinal cord -> neck/head muscles

Question 8

What is the role of the cerebllum in movement control?

Answer 8

• Compares actual movement (from sensory feedback) with intended movement (cortical output)
• Important in timing/coordination (eg activation pattern of agonist and antagonist muscle groups)

Cerebellar input:

• From brain
  
  • continuous from cortical motor control
  • continuous from vestibule, audio and visual inputs
  • basal ganglia and spinal cord
• From periphery
  
  • spindles/Golgi tendon organs
  • spinal cord anterior horns - tells CB which signals have arrived at motor regins

Cerebellar outputs:

• vestibular nuclei –> vst (axial muscles - balance)
• medial + lateral descending tracts –> distal limb muscles
• thalamus -> motor and pre-motor cortex

Question 9

What are the 2 functions of basal ganglia in movement, and what are their pathways?

Answer 9

• Putamen circuit:
  
  • Controls complex patterns of motor activity (with CS system)
• Caudate circuit:
  
  • Controls cognitive sequences of motor patterns (thought –> movement)
  • Can modulate how we enact things, but can’t change/control primary motor cortex directly