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 03-55-485

Pathways through vestibular nuclei Also, pathways from upper motor neurons to lower motor neurons that control eye movements. Monday, Jan. 23, 2006 03-55-485

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 03-55-485

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 03-55-485

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 03-55-485

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 03-55-485

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 03-55-485

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 How do upper motor neurons of the reticular formation maintain posture? . Monday, Jan. 23, 2006 03-55-485

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 03-55-485

Hear the auditory tone activity in the biceps begins about 200 ms after the tone. Monday, Jan. 23, 2006 03-55-485

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 03-55-485

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 03-55-485

Pharmacological blockade of the reticular formation electrical stimulation of motor cortex forepaw lifted and NO postural adjustment. Monday, Jan. 23, 2006 03-55-485

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 03-55-485

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