706_Week 14

Question 1

Postural control -

Answer 1

controlling the body’s position in space with dual purpose of: orientation and stability (postural equilibrium)

Question 2

In postural control, orientation =

Answer 2

the ability to maintain an appropriate relationship between body segments and between the body and EN

Question 3

In postural control, stability (postural equilibrium) =

Answer 3

• ability to maintain one’s center of mass (COM) within the limits of the base of support (BOS)
• commonly referred to as “balance”

Question 4

Long Andy Tangent about posture, ask a friend

Answer 4

Long Andy Tangent about posture, ask a friend

Question 5

In postural control, describe the contributing factors:

Answer 5

• stability and orientation requirements vary with the task and the EN
• orientation as primary goal (stability is sacrificed)
• stability as primary goal

Question 6

Is the body inherently stable?

Answer 6

No, the body is inherently unstable

Question 7

What are the primary goals of the nervous system in postural control?

Answer 7

1. control position and motion of the body’s center of mass (COM)
2. body’s rotation about the COM

Question 8

Center of mass (COM) =

Answer 8

point that represents the average position of the body’s total mass.
• in humans, located in abdomen approximately 20mm anterior to S2 is erect stance (anatomical position), instantaneous location depends on body position (may move outside of body with hip/trunk flexion)
• force of gravity acts on all body segments, net effect on body acts through center of mass

Question 9

Center of gravity (COG) =

Answer 9

vertical projection of COM onto support surface

Question 10

Base of support (BOS) =

Answer 10

area of the body that is in contact with the support surface

Question 11

Limits of stability (LOS) =

Answer 11

maximum range of COM can be moved without changing BOS

Question 12

Center of pressure (COP)=

Answer 12

center of distribution of total force applied to support surface.
•for body to be in static equilibrium, COP and COM must align over BOS
• action of trunk and limb mm create torque to restore COM to desired position

Question 13

sheep =

sheepdog =

Answer 13

sheep = COM
sheepdog = COP

Question 14

Historically, where is postural control thought to arise from?

Answer 14

brainstem and spinal circuitry

Question 15

Historically, motor control of posture, assumed that postural control consisted of a set of reflexes that triggered equilibrium responses based on visual/ vestibular/ somatosensory triggers. Now viewed as:

Answer 15

complex motor skill derived form interaction of multiple sensorimotor processes and systems.

Question 16

What does the systems framework for postural control include?

Answer 16

Individual (motor, sensory, cognitive), postural task (steady state proactive, reactive), and EN (support surface sensory context cognitive load)

Question 17

What are motor constraints of postural control?

Answer 17

1. musculoskeletal (strength, ROM, alignment)

2. neuromuscular (postural tone, amplitude, timing)

Question 18

What are sensory constraints of postural control?

Answer 18

visual, vestibular and somatosensory

Question 19

What are cognitive constraints of postural control?

Answer 19

attention, adaptation, anticipation and confidence

Question 20

What 3 types of postural control do functional tasks require?

Answer 20

1. steady state - control COM relative to BOS in predictable, non-changing conditions
2. reactive - recover a stable position after an unexpected perturbation
3. proactive - activation of mm in advance of potentially destabilizing voluntary movements to avoid instability.

Question 21

In postural control, feedback control (closed-loop) is used in response to what?

Answer 21

• in response to external disturbances to equilibrium

* during gait and in response to disruptions of gait (trip/slip_

Question 22

In postural control, feed-forward control (open-loop) is used in response for what?

Answer 22

pre-planned synergistic movements in anticipation of a voluntary movement

Question 23

faster =

Answer 23

more preplanning

Question 24

slower =

Answer 24

more time to plan, adjust/ react

Question 25

In a feedback task constraint loop the flow is:

Answer 25

central command --> limb movement --> postural disturbance --> (feedback for unexpected postural disturbance ----->) postural adjustment

Question 26

In a feed-forward task constraint loop the flow is:

Answer 26

central command --> (feed-forward for expected postural disturbance ----->) postural adjustment

Question 27

For motor systems in postural control, steady state ("static") balance =

Answer 27

* musculoskeletal alignment * muscle tone (intrinsic stiffness, background muscle tone - exists normally due to neural contributions (e.g. stretch reflex) * postural tone - activation of antigravity mm (cutaneous, vestibular inputs) * movement strategies (motor)

Question 28

For motor systems in postural control, reactive balance control =

Answer 28

* most knowledge generated from studies using controlled balance disruptions (perturbations) *  AUTOMATIC POSTURAL RESPONSE

Question 29

Automatic postural response =

Answer 29

synergistic activation of a group of muscles in a characteristic sequence to maintain equilibrium • latencies of muscle response 80-120 ms (some as long as 160-200 ms) • reactive postural adjustment (RPA)

Question 30

What are movement strategies?

Answer 30

movement patterns used to recover balance in sagittal plane

Question 31

Name 3 movement strategies:

Answer 31

1. ankle strategy 2. hip strategy 3. stepping or suspensory strategy

Question 32

Movement strategies function along a continuum:

Answer 32

- In slow movements, utilize primarily closed-loop control | - rapid movements greater open-loop control

Question 33

For automatic postural responses, RPA's adapt to changes in the requirement for support. Set of muscles activated depends on what 3 factors?

Answer 33

1. biomechanical support 2. task exposure 3. sensory conditions

Question 34

What do RPA's change with?

Answer 34

biomechanical conditions • with translation of wide surface, sequential activation of GAS/HS/PSP (ankle strategy) • with narrow beam, primary activation of proximal mm. ie quad/ abdom (hip strategy) • ROM/ strength impairment will shift demand to other muscles /joints

Question 35

In automatic postural response, postural strategy modulates according to:

Answer 35

• changing EN support and • repeated exposure to stimulus (w/ exposure begin to show modulations)

Question 36

In automatic postural responses, what do RPA's modulate according to sensor conditions. Availability of sensory inputs such that:

Answer 36

* muscle latencies to visual cues --> 200ms * muscle latencies to somatosensory cues --> 80-100 ms (e.g. UE force

Question 37

In the sensory weighting hypothesis (RPA's modulate according to sensory conditions):

Answer 37

• each sense provides unique contribution • the "gain", or relative weight given to the sensory input by the brain, varies according to the accuracy as a reference point (-if touch becomes less reliable _ peripheral neuropathy_ visual inputs are weighted more heavily) (nashner: sensory organization in balance)

Question 38

In automatic postural responses, RPA's adjust according to situational predictability or LEARnING. An example of this is:

Answer 38

Central set: • defined as a state of the nervous system influenced by the context of a task • organized of postural responses depends on expectations of stability and / or perturbations (in expected perturbations, postural responses are highly organized in a feed-forward control model, i.e. selected in advance / standing on a bus example) • with experience, increased spatial organization/ decreased EMG amplitude (functional application: ACL injury)

Question 39

Anticipator postural control (APA) =

Answer 39

* synergistic postural responses executed IN ADVANCE of primary body movement * nervous system has advance knowledge * relate this to potential influence of motor programs involved in postural control

Question 40

In anticipatory postural control, postural adjustments occur _________ action.

Answer 40

BEFORE

Question 41

In anticipatory postural control it has been found that postural adjustments accompany what?

Answer 41

voluntary movements only when needed

Question 42

What are the clinical applications of APA's?

Answer 42

Behavioral context and speed of focal movement affect APA's • with fast movements, APA's are earlier and more reliable • greater movement resistance increases likelihood of APA's • external support reduces APA's • degree of practice (more research is needed in conditions of pathology)