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Monday, Jan. 23,
2006
03-55-485
Pathways through vestibular nuclei
• Cranial nerve VIII
--> vestibular nuclei
--> descending axons
Lateral vestibular tract
OR
Medial vestibular tract
Monday, Jan. 23,
2006
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Pathways through vestibular nuclei
• Also, pathways from upper motor
neurons to lower motor neurons that
control eye movements.
Monday, Jan. 23,
2006
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Reticular Formation
• Network of circuits
• Located at the brainstem core, from midbrain to
medulla.
• Descending motor control pathways to the spinal
cord
- terminate primarily in the medial parts of the gray
matter where they influence the local circuit neurons
that co-ordinate axial and proximal limb muscles.
Monday, Jan. 23,
2006
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Reticular formation: functions
•
•
•
•
•
cardiovascular & respiratory control.
sensory motor reflexes
org. of eye movements
regulate sleep and wakefullness
* temporal and spatial co-ordination of movement
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2006
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Posture
• In response to disturbances in body
position (env or self)
– -->Vestibular nuclei and reticular formation
– --> information to the spinal cord
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2006
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Vestibular nuclei
response from inner ear to change in balance
Inner ear
Vestibular nuclei
Direct projections to the spinal cord
Compensation in stability
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2006
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Adjustments to stabilize posture during ongoing
movements
• Motor centers in cortex or brain stem
reticular formation
Appropriate neurons are activated
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2006
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How do upper motor neurons of the
reticular formation maintain posture?
• Look at voluntary movements.
• Fig. 16.5. A subject uses his arm to pull
a handle in response to an auditory tone
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Feedforeward
• “predicts” body stability disturbance and
body can generate appropriate
stabilizing response
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2006
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Hear the auditory tone
activity in the biceps begins about 200
ms after the tone.
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2006
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This shows that posture control entails an
anticipation effect (feed forward).
• Effect of contracting the biceps will
move the body forward, and you need
the gastroc to be contracted to hold the
body weight.
Monday, Jan. 23,
2006
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Animal models (cats):
• Forepaw movement
feedforward postural adjustment to
other legs
Expt: electrical stimulation of motor
cortex forepaw lifted and postural
adjustment.
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2006
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Pharmacological blockade of the
reticular formation
electrical stimulation of motor cortex
forepaw lifted and NO postural
adjustment.
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2006
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Cortical upper motor neurons initiate both
forepaw movement and posture adustment.
• Direct
– Upper motor neurons from motor cortex project
directly to spinal cord
Indirect
 Upper motor neurons from the motor cortex
 project to brain stem areas (including reticular
formation)
 Activate neurons that project to the spinal cord
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2006
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Damage to direct corticospinal
pathway at medulla
 indirect projections from cortex to brainstem and
brainstem itself can sustain motor behaviour involving
proximal muscles.
 Direct projections for the motor cortex to the spinal cord
provide the speed and agility of movements, these
enable precision of finger movement.
 Eg. After motor cortex damage in humans, get partial
recovery of voluntary movements. These may be the
indirect projections through the brainstem centers.
Monday, Jan. 23,
2006
03-55-485