Flashcards in 706_Week 14 Deck (42)
Postural control -
controlling the body's position in space with dual purpose of: orientation and stability (postural equilibrium)
In postural control, orientation =
the ability to maintain an appropriate relationship between body segments and between the body and EN
In postural control, stability (postural equilibrium) =
• ability to maintain one's center of mass (COM) within the limits of the base of support (BOS)
• commonly referred to as "balance"
Long Andy Tangent about posture, ask a friend
Long Andy Tangent about posture, ask a friend
In postural control, describe the contributing factors:
• stability and orientation requirements vary with the task and the EN
• orientation as primary goal (stability is sacrificed)
• stability as primary goal
Is the body inherently stable?
No, the body is inherently unstable
What are the primary goals of the nervous system in postural control?
1. control position and motion of the body's center of mass (COM)
2. body's rotation about the COM
Center of mass (COM) =
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
Center of gravity (COG) =
vertical projection of COM onto support surface
Base of support (BOS) =
area of the body that is in contact with the support surface
Limits of stability (LOS) =
maximum range of COM can be moved without changing BOS
Center of pressure (COP)=
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
sheep = COM
sheepdog = COP
Historically, where is postural control thought to arise from?
brainstem and spinal circuitry
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:
complex motor skill derived form interaction of multiple sensorimotor processes and systems.
What does the systems framework for postural control include?
Individual (motor, sensory, cognitive), postural task (steady state proactive, reactive), and EN (support surface sensory context cognitive load)
What are motor constraints of postural control?
1. musculoskeletal (strength, ROM, alignment)
2. neuromuscular (postural tone, amplitude, timing)
What are sensory constraints of postural control?
visual, vestibular and somatosensory
What are cognitive constraints of postural control?
attention, adaptation, anticipation and confidence
What 3 types of postural control do functional tasks require?
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.
In postural control, feedback control (closed-loop) is used in response to what?
• in response to external disturbances to equilibrium
• during gait and in response to disruptions of gait (trip/slip_
In postural control, feed-forward control (open-loop) is used in response for what?
pre-planned synergistic movements in anticipation of a voluntary movement
more time to plan, adjust/ react
In a feedback task constraint loop the flow is:
central command --> limb movement --> postural disturbance --> (feedback for unexpected postural disturbance ----->) postural adjustment
In a feed-forward task constraint loop the flow is:
central command --> (feed-forward for expected postural disturbance ----->) postural adjustment
For motor systems in postural control, steady state ("static") balance =
• 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)
For motor systems in postural control, reactive balance control =
• most knowledge generated from studies using controlled balance disruptions (perturbations)
• AUTOMATIC POSTURAL RESPONSE
Automatic postural response =
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)