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732 > 706_Week 14 > Flashcards

706_Week 14 Flashcards

1
Q

Postural control -

A

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

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2
Q

In postural control, orientation =

A

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

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3
Q

In postural control, stability (postural equilibrium) =

A
  • ability to maintain one’s center of mass (COM) within the limits of the base of support (BOS)
  • commonly referred to as “balance”
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4
Q

Long Andy Tangent about posture, ask a friend

A

Long Andy Tangent about posture, ask a friend

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5
Q

In postural control, describe the contributing factors:

A
  • stability and orientation requirements vary with the task and the EN
  • orientation as primary goal (stability is sacrificed)
  • stability as primary goal
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6
Q

Is the body inherently stable?

A

No, the body is inherently unstable

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7
Q

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

A
  1. control position and motion of the body’s center of mass (COM)
  2. body’s rotation about the COM
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8
Q

Center of mass (COM) =

A

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

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9
Q

Center of gravity (COG) =

A

vertical projection of COM onto support surface

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10
Q

Base of support (BOS) =

A

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

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11
Q

Limits of stability (LOS) =

A

maximum range of COM can be moved without changing BOS

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12
Q

Center of pressure (COP)=

A

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

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13
Q

sheep =

sheepdog =

A 
sheep = COM
sheepdog = COP
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14
Q

Historically, where is postural control thought to arise from?

A

brainstem and spinal circuitry

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15
Q

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:

A

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

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16
Q

What does the systems framework for postural control include?

A

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

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17
Q

What are motor constraints of postural control?

A
  1. musculoskeletal (strength, ROM, alignment)

2. neuromuscular (postural tone, amplitude, timing)

18
Q

What are sensory constraints of postural control?

A

visual, vestibular and somatosensory

19
Q

What are cognitive constraints of postural control?

A

attention, adaptation, anticipation and confidence

20
Q

What 3 types of postural control do functional tasks require?

A
  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.
21
Q

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

A
  • in response to external disturbances to equilibrium

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

22
Q

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

A

pre-planned synergistic movements in anticipation of a voluntary movement

23
Q

faster =

A

more preplanning

24
Q

slower =

A

more time to plan, adjust/ react

25
Q

In a feedback task constraint loop the flow is:

A

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

26
Q

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

A

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

27
Q

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

A
  • 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)
28
Q

For motor systems in postural control, reactive balance control =

A
  • most knowledge generated from studies using controlled balance disruptions (perturbations)
  • AUTOMATIC POSTURAL RESPONSE
29
Q

Automatic postural response =

A

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)

30
Q

What are movement strategies?

A

movement patterns used to recover balance in sagittal plane

31
Q

Name 3 movement strategies:

A
  1. ankle strategy
  2. hip strategy
  3. stepping or suspensory strategy
32
Q

Movement strategies function along a continuum:

A
  • In slow movements, utilize primarily closed-loop control

- rapid movements greater open-loop control

33
Q

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

A
  1. biomechanical support
  2. task exposure
  3. sensory conditions
34
Q

What do RPA’s change with?

A

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

35
Q

In automatic postural response, postural strategy modulates according to:

A

• changing EN support
and
• repeated exposure to stimulus

(w/ exposure begin to show modulations)

36
Q

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

A
  • muscle latencies to visual cues –> 200ms
  • muscle latencies to somatosensory cues –> 80-100 ms

(e.g. UE force

37
Q

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

A

• 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)

38
Q

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

A

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)

39
Q

Anticipator postural control (APA) =

A
  • 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
40
Q

In anticipatory postural control, postural adjustments occur _________ action.

A

BEFORE

41
Q

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

A

voluntary movements only when needed

42
Q

What are the clinical applications of APA’s?

A

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)

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