Motor control for physical therapy ppt.pptx

moto control

1. Motor control translating research into clinical practice Normal postural control Part 3 Prof. Dr. Khaled Ayad By: Mahmoud A. Elbayom y

2. Adapting motor strategies Adaptation is a term reflects the ability to modify behavior in response to new task demands. Normal subject can shift relatively quickly from one postural movement strategy to another to maintain stability in response to new task demands .

3. With repeated perturbations, movement strategies change (within 5-15 trials) while experiencing AP platform displacement. During transition from one strategy to the next , subjects used complex movement strategies that were combination of the pure strategies ( Horak & nashner , 1986) . Several studies in normal adults found reduced sway with repeated exposure to platform movements . subject refine their response characteristics to optimize response efficiency.

4. Neural subsystems controlling postural orientation and stability Spinal Cord Spinal cats can activate extensor muscles to support body but their postural stability is poor Postural stability is NOT organized at the spinal cord level Brainstem Regulation of postural tone Integration of sensory information for postural and balance. Contribute to anticipatory postural control for voluntary movements Brain stem reticular formation (RF) is important in generating anticipatory postural adjustments ( APAs ) which are absent once RF is inactivated with pharmacological agents.

5. Neural subsystems controlling postural orientation and stability Basal ganglia-cortical loop controls postural set, i.e. the ability to modify the postural muscle activation patterns to changes in the task or environmental conditions. Cerebellar-cortical loop controls the adaptation of postural muscle activation amplitudes, i.e. scaling, in response to changes in task and environmental conditions

6. Perceptual systems in postural control

7. Senses contributing to postural control The central nervous system( CNS )processes information from sensory receptors throughout the body to determine the body’s position in space Vision (especially peripheral vision) Somatosensory ( proprioception, cutaneous, joint receptors) Vestibular system Each sense provides a different frame of reference for postural control, i.e. “map”

8. Visual inputs : are an important source of information for postural control but they are not absolutely necessary as normal subject can control quiet stance with closed eyes or in dark room. The visual system has difficulty distinguishing between object motion referred to as “exocentric motion” and self motion , referred to as “egocentric motion”. The somatosensory inputs : provide the CNS with position and motion information about the body with reference to supporting surface . in addition somatosensory inputs throughout the body report information about the relationship of body segments to one another .

9. Vestibular input : is powerful source of information for postural control. The vestibular system provides the CNS with information about the position and movement of the head with respect to gravity and inertial forces “ gravito -inertial frame of reference for postural control”. CNS cannot provide information whether it is just head bending forward or the whole body is leaning forward by using vestibular inputs alone.

10. Central integration: combining and adapting senses for postural control

11. Sensory strategies during quiet stance Visual contribution ↑ in sway in normal subject with eye closed The ratio of body sway with eye open and closed has been referred to as “Romberg quotient” With room oscillation normal adult begin to sway showing important role of visual inputs on postural control. ↑ sway in young children and old adults with room oscillation (may be due to reduced somatosensory inputs from the feet and ankles.

12. Somatosensory Contributions Lightly touching a stable surface reduces sway significantly. The somatosensory inputs from the touch, rather than the contact force through touching a surface ( Jeka , 1994; Lackner , 1999 ).The somatosensory inputs from all parts of the body plays an important role in maintenance of postural control and body orientation in quiet stance. Somatosensory inputs appear to dominate postural control in response to transient or fast surface perturbations . When all three senses are present ,they each contribute to postural control during quiet stance .

13. Sensory strategies during perturbed stance In moving room. Young children (1-year olds) compensate for this illusory loss of balance with motor responses to restore vertical position these motor responses causing infants to fall in the direction of room movement . Vision may be a dominant input in compensating for transient perturbations in infants first learning to stand. In older children and adult visions doesn’t appear to play an important role in compensating for transient perturbations as they show less sway responses to theses illusory movement

14. Sensory strategies during perturbed stance CNS relies on somatosensory inputs for controlling body sway caused by rapid displacements of the supporting surface The vestibular inputs paly minor role in postural control when supporting surface is displaced horizontally while they are important for stabilization of balance with platform rotations.

15. Adapting the organization of sensory inputs to changes in the context There are two hypotheses describing the process by which the CNS organizes sensory information for postural control. Intermodal theory of sensory organization All three senses contribute equally to postural orientation at all times. Information critical for postural orientation is gained through the interaction of the different sensory systems. The organization of sensory information for postural orientation is based on lawful relationships between patterns of sensory stimulation and properties of environment. and these relationships are called “invariants”. In this model there is never sensory conflict ,there is no relative weighting of sensory information.

16. Sensory Weighting Hypothesis Postural control system is able to reweight sensory inputs in order to optimize stability in altered sensory environments. The “gain” of a sensory input will depend on its accuracy as a reference for body motion In this model the CNS has to resolve sensory conflicts ( situation in which there is disagreement among sensory inputs) by changing the relative weight of a sensory input to postural control.

17. Testing Adaptation of Postural to Changing Sensory Conditions: Sensory Organization Test (SOT)

18. SOT Normal Results Adults and children over age 7 easily maintain balance on all conditions Least sway on conditions 1, 2, & 3 where the support service is providing accurate sensory information Greatest sway on conditions 5 & 6 because only one set of sensory inputs (vestibular) are accurate and available Visual cues are more important when the balance task becomes more challenging (Sensory Weighting Hypothesis)

19. Adapting senses when learning a new task (Lee and lishman , 1975) found increased reliance on visual inputs when adult were just learning a task. As task become more automatic , there appeared to be a decrease in the relative importance of visual input and increase reliance on somatosensory input.

20. Anticipatory Postural control

21. Anticipatory Postural Adjustments (APAs) The APAs consist of preprogrammed activation of the muscles, according to task parameters and are important to minimize the effects of planned postural perturbations. Postural muscles are activated prior to the prime movers that produce movement in the preparatory phase to compensate the destabilizing effect of the movement . In compensatory phase Postural muscles are again activated after prime movers for further stability of the body.

22. Anticipatory Postural Adjustments (APAs) In A, Gastrocnemius (postural muscle) was activated prior to biceps. In B, subject was support at the shoulders so the arm movement did not disturb posture. Thus, APAs were not needed.

23. Anticipatory Postural Adjustments (APAs) In Cordo and Nashner’s study (1982), A & B had different “Central Set”, which refers to a state of the nervous system that influenced or determined by the context of a task. Practicing the task cause reduction in postural response magnitude and in the amplitude of antagonist muscle responses .

24. Clinical application of research on anticipatory postural control APAs increase with ↑ movement magnitudes and speed. APAs more frequently present with faster movements and heavier loads Practice can affect the timing of APAs, e.g. dancers activate APAs much earlier in a leg-lifting task than untrained individuals APAs are reduced when a support is given  patients will never improve balance if they practice balance tasks while holding on to // bars!

25. Cognitive systems in postural control Normal posture control occurs automatically , few attentional resources were needed when controlling balance Attention : is information processing capacity of an individual. This capacity is limited for any individual and that performing any task requires a portion of this capacity.

26. Cognitive systems in postural control -Dual-task paradigms If two tasks are performed together and require more than the total capacity . The performance on either or both task will deteriorate. Different postural and secondary tasks affect postural control differently Older or balance-impaired individuals increase postural sway with ↑ difficulty of secondary cognitive tasks

27. Cognitive systems in postural control As the difficulty for maintaining stability ↑ , there is ↑ in attention resources required by the postural control system seated postural control The maintenance of postural control in the seated position has not been studied in depth . Concepts important for stance postural control will be shown to be equally for postural control in sitting