1. Monday, Jan. 23, 2006

2. Pathways through vestibular nuclei
Cranial nerve VIII
--> vestibular nuclei
--> descending axons
Lateral vestibular tract OR
Medial vestibular tract
Monday, Jan. 23, 2006

3. Pathways through vestibular nuclei
Also, pathways from upper motor neurons to lower motor neurons that control eye movements.
Monday, Jan. 23, 2006

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.
Extends from the rostral midbrain to caudal medulla.
Function: cardiovascular & respiratory control.
- sensory motor reflexes
- org. of eye movements
- regulate sleep and wakefullness
- * temporal and spatial co-ordination of movement
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

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
Monday, Jan. 23, 2006

6. Posture In response to disturbances in body position (env or self)
-->Vestibular nuclei and reticular formation
--> information to the spinal cord
Vestibular nuclei and reticular formation
information to the spinal cord
Posture in response to environmental including self induced disturbances of body position and stability.
Monday, Jan. 23, 2006

7. Vestibular nuclei response from inner ear to change in balance
Direct projections to the spinal cord
Compensation in stability
Vestibular nuclei
response from inner ear to change in balance
Inner ear
Direct projections to the spinal cord
Compensation in stability
Monday, Jan. 23, 2006

8. Adjustments to stabilize posture during ongoing movements
Motor centers in cortex or brain stem
reticular formation
Appropriate neurons are activated
Motor centers in cortex or brain stem
reticular formation
Neurons to initiate adjustments to stabilize posture during ongoing movements
Monday, Jan. 23, 2006

9. How do upper motor neurons of the reticular formation maintain posture?
Look at voluntary movements.
Fig A subject uses his arm to pull a handle in response to an auditory tone
How do upper motor neurons of the reticular formation maintain posture? .
Monday, Jan. 23, 2006

10. Feedforeward
“predicts” body stability disturbance and body can generate appropriate stabilizing response
Feed foreward
Hear the Auditory tone
activity in the biceps begins about 200 ms after the tone.
Contraction of biceps is accompanied by a significant increase in the activity of a proximal leg muscle, the gastrocnemius. The contraction of the gastoc begins well before the biceps contracts.
Monday, Jan. 23, 2006

11. Hear the auditory tone
activity in the biceps begins about 200 ms after the tone.
Monday, Jan. 23, 2006

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.
The feed forward “predicts” the resulting disturbance in body stability and generates an appropriate stabilizing response.
Animal models (cats)
Monday, Jan. 23, 2006

13. Animal models (cats): Forepaw movement
feedforward postural adjustment to other legs
Expt: electrical stimulation of motor cortex forepaw lifted and postural adjustment.
Pharmacological blockade of the reticular formation
--> electrical stimulation of motor cortex
forepaw lifted and NO postural adjustment.
How can this happen?
Monday, Jan. 23, 2006

14. Pharmacological blockade of the reticular formation
electrical stimulation of motor cortex
forepaw lifted and NO postural adjustment.
Monday, Jan. 23, 2006

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
Monday, Jan. 23, 2006

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.
Monday, Jan. 23, 2006