DPT 756- Posture

What 3 challenges must the postural system meet?

• Steady stance

• Anticipation

• Adaptation

What needs to occur in order to avoid destabilization of balance?

Precisely timed compensatory action is initiated first

What is integrated with postural control?

Voluntary control (capable of learning)

In order to maintain balance the nervous system must control what?

COM

Where is the human COM?

20mm anterior to S2

How does a forward flexed posture affect COM?

Pushes COM closer to the boundary of the BOS, inc risk of a fall.

A fall occurs when?

COM falls outside BOS

What two actions are required for upright stance?

• Maintaining support against gravity

• Maintaining balance

What things allow for a person to maintain support against gravity? (4)

• Passive bone on bone forces (eg, knees)

• Stretched ligaments (eg, hip)

• Tonic activation of antigravity muscles (eg, ankle, spine)

• Phasic muscle contraction (complex pattern of muscle activation)

What kind of responses counteract unexpected disturbances?

Adaptive or reactive response

Whats the latency of postural response?

80-120ms, which is shorter than voluntary reaction time

Adaptive/reactive responses rely on what?

Proprioception. If impaired may result in delayed or faulty postural response

Is the proprioceptive system capable of plasticity?

Yes and can be trained

What adaptive strategies help bring COM back over BOS?

Ankle strategy, Hip strategy, Stepping strategy

Why do people with good balance adopt ankle strategy?

Allows you to also use stepping strategy for correction

What strategy do you use with a narrow platform? Wider platform?

Narrow= Hip strategy

Wider= Ankle strategy

Anticipatory postural adjustments compensate for what?

voluntary movements (ex; shifting to the R when lifting L leg in air)

Anticipatory control relies on what? And precedes what?

Relies heavily on vision and precedes voluntary movement

What is postural orientation important for?

optimizing execution of tasks, interpreting sensations, and anticipating disturbances to balance

What can influence postural orientation? (3)

• Locked joints- minimizes forces supporting the body

• Unlocked require muscle tension for stabilization but allow for a quick response

• Task requirement- dual tasking, external perturbations, surfaces

What helps maintain equilibrium and orientation?

Sensory orientation, Which relies on sensory info from several modalities to be integrated

Proprioception is critical for what? Loss of these fibers cause what?

Maintaining balance.

Results in delayed postural responses and as a result COM moves faster and farther from initial position and takes longer to return.

What fibers mediate postural responses?

Largest and most rapidly conducting fibers (type 1 and A-alpha)

What 3 systems are apart of sensory orientation?

Vestibular, visual, proprioception

Are vestibular signals essential for normal timing of balance reactions?

No, but vestibular info does influence directional tuning of postural response

How does vestibular effect postural response deficits?

Angular motion- abnormal (opposite direction)

Linear motion-exaggerated postural

What occurs almost immediately after loss of vestib system?

In humans they become quite ataxic (especially pronounced with head turns where trunk motion cannot be distinguished from head motion).

How does vision play a role in sensory orientation?

• Reduces body sway and produces stabilizing clues

• Critical for anticipatory postural responses

• Powerful influence on postural orientation

What wont you be able to distinguish if you only relied on vision?

Self motion from object motion

What wont you be able to distinguish if you only relied on vestib?

• Head tilt from whole body tilt

• Head tilt from whole body acceleration

Is vision fast enough to affect postural response to a sudden balance disturbance?

No, it’s too slow

What wont you be able to distinguish if you only relied on proprioception?

Between body and surface motion

At what degree of tilt do the propricoeptive and vestibular systems predominate?

Proprioception- up to 2 degrees

Vestib- up to 4 degrees

What is balance body schema?

Dynamic system in which both spatial and temporal features are constantly being updated

What are the features of balance body schema? (3)

• Short term: experience to improve balance strategies

• Long term: as we age and our body changes in shape and size

• One way body schema adapts is by changing the weighting of each of the sensory modalities (vision, vestibular, and proprioception)

Influence of each sensory modality on balance and orientation changes according to what?

The task.

Ex1) firm, stable surface= proprioception info predominates

Ex2) moving or unstable surfaces= Visual and vestibular info predominates

Control of Posture is distributed in the nervous system to what structures?

• Reticular formation and Vestibulocerebellum

• Spinocerebellum

• Descending pathways (vestibulospinal and reticulospinal tracts)

Lesions to what tracts will result in profound ataxia?

Vestibulospinal and reticulospinal

What two structure are important for posture? And why?

• Spinocerebellum- magnitude of postural response adapts w/ experience or training

• Basal ganglia- important for quickly adjusting the postural set

What structure decides what muscles need to fire for a specific task?

Basal ganglia

Without basal ganglia you lack what aspect of posture?

The ability to establish postural set