NROC64H3 Lecture Notes - Lecture 8: Globus Pallidus, Pliers, Spinal Cord

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17 Mar 2012
NROC64H3S Sensory and Motor Systems
SAQ What is the inverse model?
- The brain influences activity of the SC Voluntary movements
- Hierarchy of controls:
1. Highest Level: Strategy
2. Middle Level: Tactics
3. Lowest Level: Execution
- Sensorimotor System: Sensory information used by motor system
Descending Spinal Tract
- Axons descend along 2 major pathways:
1. Lateral Pathway (distal muscles, esp. flexors): Voluntary movements under cortical control
Components: Corticospinal tract = pyramidal tract,
rubrospinal tract
Effects of Lateral Pathway Lesions: Experimental lesions make
impaired fractionate movements of arms and hands
2. Ventromedial Pathway: Posture and locomotion (proximal
and axial muscles) under brain stem control
Vestibulospinal Tracts - vestibular nuclei in medulla, head
(stabilize eyes), legs (posture),
Tectospinal tract SC, head for gaze movements
Pontine and medullar Reticulospinal tract: Antigravity
Central vs. Peripheral lesions: Alpha motor neurons (paresis,
paralysis, atrophy) Lack of muscle coordination etc
Central Lesions: Spinal shock phase (hypotonia, hemiplegia),
hypertonia, hyperrfelxia, Babinski
Opposite of the lesions babinski: sole and babies and stretching out
The PLannign of Movement by the Cerebral Cortex
- Cerebral Cortex
Motor Cortex: Area 4 and 6 of frontal lobe
Area 6 = “Higher Motor Area” (Penfield)
Lateral region: Premotor Area/PMA
Medial region: Supplementary motor area (SMA)
Motor maps of PMA and SMA have similar functions but different
groups of muscles innervated
Different functions
Depending on the situation the inverse model relies on
external/internal cases
Mushiake et al: External/internal guidance for button presses
Contributions of Posterior Parietal and Prefrontal Cortex
Represent highest level of motor control: Decisions about actions and outcomes
Area 5: Input form 3,1,2
Area 7: Input from higher-order visual cortical areas (i.e. MT) Major entry point for MOTION NOT the
site for lesions causing neglect
Anterior Frontal Lobes: Abstract though, decision making and anticipating consequences for action
Area 6: Actions converting into signals on how actions will be performed
Neuronal Correlates of Motor Planning
Evarts: Record activity in motor areas of awake behaving animals
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Demonstrated importance of Area 6 in planning movement
“Ready” = Parietal and frontal lobe
“Set” = Supplementary and premotor areas
“Go” – Area 6
Computational Principles of Motor Control
- The cortex specifies high-level motor commands
Stimulation in M1 elicits complex movements
- Cortical areas are hierarchically organized (I.E. SMA and M1)
Bizzi et al.: Pointing in deafferented monkey no somatosensation). Am is mechanically displaced w/ onset of
pointing arm. After release, arm first moves back towards resting position JUST THINK ABOUT IT + MEMORY,
Depending on the complexity of the task, different areas will be lighted
Roland: PET during finger movements
Gerloff et al: TMS on M1: Jerking fingerers; SMA: “lost track” in sequence tis a brain fart
- Motor control is redundant
i.e. smiles
i.e. neurological patient: impaired
speaking; preserved singing
- Population vector represent the
collective activity of many neurons in
Input Organization fo M1
Betz cells: Pyramidal cells in
Cortical Layer 5
2 sources of input: Cortical
areas and Thalamus
Collective activity of neurons in
M1 encode force and direction
of movement
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