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Lecture 17

PSL300H1 Lecture Notes - Lecture 17: Rubrospinal Tract, Reticular Formation, Vestibulospinal Tract


Department
Physiology
Course Code
PSL300H1
Professor
Michelle French
Lecture
17

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PSY300H1F L17; Oct. 21, 2011
Cortical Motor Areas
Higher Motor Centers
…..moving beyond postural support
•ex. Using limbs for things besides support
Red nucleus – 1st for distal limb movement programming
• Rubro(red)spinal cells activate localized synergies,
especially in distal limbs and face preferentially, (other
parts of body too)
•use distal limbs & face
• ex. gripping & twisting movements of hands
• contrast to reticulospinal & vestibulospinal tracts that
organize widespread postural and locomotory synergies
– activate huge sets of muscles; red nuc focuses on
discrete muscles (like motor cortex)
Section of midbrain; s.
colliculus on top
Aqueduct of silvius,
just half shown
Red nuc deep down in
midbrain, large in
humans, often
overlooked when talk
about motor system –
overtaken by motor
cortex but still there,
organizes more gross
movements
Rubrospinal tract
descends, crosses
almost immediately,
to lateral funiculus in
white matter, project
to interneurons or
directly to
motorneurons
innervating distal
muscles
Synergy
• Definition: grp of muscles contracting together for a
specific purpose
• ex. writing, holding a cup, playing instrument – involve
dif combos of muscles
• synergies organized by reticulospinal tract are very
widespread (typically cover half of body) for generating
support postures
• rubrospinal (and corticospinal) synergies are highly
localized
Motor Cortex
• more space available so motor area took over here,
able to program more synergies; programs more recent
uses of distant limbs; ex. Vocal apparatus for language
• Precentral gyrus – front of central sulcus, extends to
bottom of central sulcus
• somatotopic organization – order or muscles
recpresented w feet medially, head laterally, so
representation upside-down like in S1
• layer 5 (output layer) pyramidal cells – large; project to
motor nuclei & interneurons in brainstem & spinal cord
(corticobulbar(cortex to brainstem & motor nuc)/spinal
tract) – long trajectory/axons, so need support so pyr
cells large
• direct corticospinal synapses on motoneurons mostly
to distal limb and speech motor nuclei – at least ¾ of
connections on interneurons in spinal tract, so most
connections not directly on motorneurons
Central sulcus dividing
frontal from parietal
Motor cortex area 4 on
anterior bank of central
sulcus, down wall
Bulge in motor cortex –
knob – interesting
feature in most ppl, note
where finger muscles
represented
Speech at bottom
Biggest representations
of speech & finger, most
synergies, highest
receptor density
Feet on medial walls btwn hemispheres; upside-down
representation of body
Knob, speech muscles at lateral side above lateral
fissure
Layer 5 pyr cells give rise to descending tract thru
bottom of midbrain and white matter underneath red
nuc, extends along bottom of medulla most axons
cross over at lateral white matter down spinal cord
Rubrospinal tract at same location, axons in
corticospinal grp, terminating in intermediate zone or
directly on motor nuc
Some axons don’t cross – variable in ppl but never
>15% of entire tract, in some ppl nothing – probably
depends on motor bhvrs the indiv trains
Multiple Representation
• every muscle has own motor nuc in spinal cord or
brainstem
• Single motor nuclei (muscles) represented in columns
at many loci in motor cortex that project to the motor
nuc
• each muscle column is in a different ‘neighborhood’,
i.e. different adjacent columns
• each cortical locus represents a different synergy;
muscles which participate in most synergies have
biggest representation – so whole synergy can be
activated together efficiently
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