Control of Movement

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Control of Movement
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Patterns of Connections Made by Local Circuit
Neurons in the Intermediate Zone of the Spinal
Cord Gray Matter
Long distance interneurons project bilaterally,
innervate multiple segments. Used for posture
control.
Short distance interneurons project over a few
segments, remain ipsilateral. Used for distal
muscle groups.
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Descending Projections from the Brainstem to the
Spinal Cord
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Feed forward processing

• Able to predict changes in posture, and generate
  an appropriate stabilizing response.
• Some muscles fire in anticipation of a need for
  postural adjustment.
• For example, the gastrocnemius muscle needs to
  adjust for the anticipation of contracting the
  biceps that would naturally pull the body forward
  stabilizing response
• Reticular formation and Reticulospinal tract
  important for this.
• Lesion or pharmacologically block it in a cat and
  compensatory muscle changes do not occur.
• Stimulate motor cortex in the right place can
  induce paw lifting, also induces other limbs
  muscles to fire. Inhibit reticulospinal tract,
  paw still moves but other legs do not.

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Anticipatory Maintenance of Body Posture
EMG elecromyography. Measure muscle APs
Gastrocnemius stimulation happens before
biceps cut reticulospinal tract Biceps will fire
but not Gastrocnemius
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Feedforward and Feedback Mechanisms of Postural
Control

• PN17050.JPG

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Direct and indirect projections form motor cortex

• Motor cortex makes two types of projections.
• A direct pathway to the ventral lateral spinal
  cord
• An indirect pathway to the reticular formation
  (which subsequently goes to medial spinal cord).
• For example a direct pathway will move the hand
  and the indirect pathway will posture the body.
• Cutting the direct pathway, leaving the indirect
  pathways intact will not affect ability to walk,
  run, etc, but will prevent the distal parts of
  limbs from being used.

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Pathways from the Motor Cortex to the Spinal Cord
Direct pathway lateral corticospinal
and rubrospinal tracts, distal fine motor
movements. Pyramidal System
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Pathways from the Motor Cortex to the Spinal Cord
Indirect pathway postural adjustments. Ventral
corticospinal tract, cortico-reticulospinal
tract. Extrapyramidal System
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Motor cortex

• in the frontal lobe
• several interconnected areas
• Primary motor cortex in the precentral gyrus.
• Gets input from basal ganglia, cerebellum and
  other cortical areas.
• Has 6 layers, layer V is the output layer
  (pyramidal cells or Betz cells).
• Primary pathway- the pyramidal system.

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Architecture of motor cortex is different than
the sensory cortex.
Betz cells
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The corticospinal tract.
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Motor fields

• Stimulation of a neuron in primary motor cortex
  activates several muscles, and inhibits other
  muscles.
• Multiple neurons can activate the same muscle.
• The motor field of a cortical motor neuron has
  to do with organized movements rather than
  specific muscle groups.

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Directional Tuning of an Upper Motor Neuron in
the Primary Motor Cortex
Monkey trained to move joystick in response to
light
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Directional Tuning of an Upper Motor Neuron in
the Primary Motor Cortex
movement starts at 0. Yellow activity of
neuron is increased. Purple activity is
decreased. Neurons have preferred direction
Activity of a single neuron in motor
cortex anticipates future movement.
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Directional Tuning of an Upper Motor Neuron in
the Primary Motor Cortex
Individual neurons tuned too broadly to
accurately predict movement direction.
Populations of neurons can calculate a direction.
Summed population responses give the actual
direction of movement.
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Premotor cortex

• Rostral to primary motor cortex
• Extensive reciprocal connections with primary
  motor cortex
• Also projects directly to spinal cord (30 of
  axons in the pyramidal tract).

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Supplementary premotor cortex

• mediates selection of movements
• specified by internal rather than external cues.
• Cells fire when just thinking about an event.

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Lateral Premotor Cortex-

• Neurons fire earlier than primary motor cortex.
  Important in conditional motor tasks that pair a
  movement with a visual cue.
• Neurons fire before initiation of the task. Used
  for intentions.
• Lesions in monkey prevent vision-conditioned
  tasks, although vision is ok and the task could
  be performed in other ways.

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Motor cortex areas
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The Primary Motor Cortex and Premotor Area in the
Human Cerebral Cortex
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Photograph of sagittal section through brain stem
and cerebellum
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Cerebellar cortex
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Cerebellar circuits