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Pathways through Vestibular Nuclei and Reticular Formation: Postural Control and Motor Coordination

This article explores the pathways from cranial nerve VIII to vestibular nuclei, as well as pathways from upper motor neurons to lower motor neurons that control eye movements. It also discusses the functions of the reticular formation, including cardiovascular and respiratory control, sensory motor reflexes, regulation of eye movements, and temporal and spatial coordination of movement. Additionally, it covers the adjustments made to stabilize posture during ongoing movements and how upper motor neurons of the reticular formation maintain posture. Animal models and pharmacological blockade experiments are also discussed, along with the effects of damage to direct corticospinal pathways.

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Pathways through Vestibular Nuclei and Reticular Formation: Postural Control and Motor Coordination

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  1. 03-55-485

  2. Pathways through vestibular nuclei • Cranial nerve VIII --> vestibular nuclei --> descending axons Lateral vestibular tract OR Medial vestibular tract 03-55-485

  3. Pathways through vestibular nuclei • Also, pathways from upper motor neurons to lower motor neurons that control eye movements. 03-55-485

  4. 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. 03-55-485

  5. Reticular formation: functions • cardiovascular & respiratory control. • sensory motor reflexes • org. of eye movements • regulate sleep and wakefullness • * temporal and spatial co-ordination of movement 03-55-485

  6. Posture • In response to disturbances in body position (env or self) • -->Vestibular nuclei and reticular formation • --> information to the spinal cord 03-55-485

  7. Vestibular nuclei • response from inner ear to change in balance • Inner ear • Vestibular nuclei • Direct projections to the spinal cord • Compensation in stability 03-55-485

  8. Adjustments to stabilize posture during ongoing movements • Motor centers in cortex or brain stem • reticular formation • Appropriate neurons are activated 03-55-485

  9. 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 03-55-485

  10. Feedforeward • “predicts” body stability disturbance and body can generate appropriate stabilizing response 03-55-485

  11. Hear the auditory tone • activity in the biceps begins about 200 ms after the tone. 03-55-485

  12. 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. 03-55-485

  13. Animal models (cats): • Forepaw movement • feedforward postural adjustment to other legs Expt: electrical stimulation of motor cortex forepaw lifted and postural adjustment. 03-55-485

  14. Pharmacological blockade of the reticular formation • electrical stimulation of motor cortex • forepaw lifted and NO postural adjustment. 03-55-485

  15. 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 03-55-485

  16. 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. 03-55-485

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