Lecture 21: Posture Flashcards
an inverted pendulum in the field of gravity
Posture
Maintenance of body alignment and spatial orientation in order to put the body in a position to enable effective movement
Postural control
Sources of Problems
- High Center of Mass
- Multiple Joints
- Small support area (1 square foot)
- Stability
A position that is resistant to disturbance or returns to its natural state after disturbance
Stability
Sway increases under these conditions:
- closed eyes (one needs a reference frame)
- standing on a narrow support
- age, disorder, injury
Sway decreases under these conditions
- light finger touch (to virtually any part of the body)
- holding an object connected to the external world
Two different processes that you can do with Sway
Supraspinal Process (RAMBLING) and Subspinal Process (TREMBLING)
Migration of the reference point, with respect to which equilibrium is instantly maintained; likely a reflection of a central search process
Rambling (Supraspinal Process)
Likely a reflection of the mechanical properties of the effectors and reflex loops
Trembling (Subspinal Process)
The body oscillates about a reference point, which the reference point ____.
nitrates for reasons that are not well understood
_______ is one of the least prominent senses.
Sense of Balance
They are innervated by the peripheral ends of bipolar sensory neurons in the ampullary nerve.
Vestibular hair cells
The ampullary crest is covered by a gelatinous, diaphragm-like mass called the _____.
capula
sensitive to angular acceleration of the head
semicircular
The fluid in the semicircular canals move when ____.
the head rotates
the fluid acts on ___ and displaces the hair cells, which generate APs.
cupula.
sensitive to linear acceleration of the head
Otoliths.
In the utricle, a portion of the floor is ___.
thickened and contains hair receptors
Otoliths: The zone is called the ______.
macula.
Macula is covered with a gelatinous substance containing.
crystals of calcium carbonate.
When you tilt your head or accelerate in a certain direction, the ______ deform the gelatinous surface, which bends the hair cells (generate APs)
otoliths
Vestibular Nuclei occupy a large part of the _____.
medulla
If a standing subject looks at a screen that displays a certain pattern, an accelerated movement of the pattern toward the subject induces ____.
a sensation of moving forward and a corresponding backward sway of the body
What’s necessary to maintain posture?
- Adequate perception of a reference point or reference vertical
- Timely generation of appropriate muscle torques
- Control of Posture under external and internal pertubations
PP: Many different of postural perturbations, some caused by ______.
our own movements
PP: Many voluntary movements are associated with changes in the activity of postural muscles, even _____ the movement begins.
before.
PP: These anticipatory postural adjustments (APAs) are to ___________.
minimize perturbations to vertical posture.
less than 0 ms
APAs
0 ms
Muscle Elasticity
30 ms
Poorly controlled
Monosynaptic reflex
50 ms
Low gain
Polysynaptic Reflex
70 ms
Approximate correction
Programmed Rn
150 ms
late
Voluntary Action
Anticipatory Postural Adjustments: A fast arm movement by a standing person is a source of strong postural perturbation because of the __________.
joint coupling
Anticipatory Postural Adjustments: A fast shoulder flexion creates ______ that try to tilt the body backwards.
reactive torques
the start of acceleration of the focal motion
time zero
APAs are generated ____ a perturbation
prior to
The perturbation needs to be _______.
predictable
The perturbation needs to be associated with ____ by the person (not always).
an action
APAs produce _______ acting against the expected pertubation
forces/torques
APAs are always ____.
suboptimal
