PHTH 734 PC Exam
distal, proximal
ankle (_____ to _____)
forward, posterior, gastroc, hamstrings, paraspinals
ankle: backward directed platform - _____ sway - _____ muscles respond - 3 muscles
backward, anterior, tib anterior, quadriceps, abdominals
ankle: forward directed platform - _____ sway - ____ muscles respond - 3 muscles
base of support
area of body in contact with the surface
somatosensory
body in relation to its segments and the surface
vesibulospinal reflex
stabilization of the body when encountering a destabilizing force
vestibulo-ocular reflex
stabilization of the eyes/vision with head motion (gaze stabilization)
vestibulocolic reflex
stabilization of the head on a moving body
angular motion
"no" motion
tilt
"yes" motion
cerebral cortex
- adaptable postural control - visual contribution
spinal cord
- anti-gravity support with tonic extensor activity - somatosensory contributions - ground reaction force orientation
muscle recruitment order reversal
- appears there is an inability to recruit and to regulate firing frequency of motor neurons in people with spastic hypertonia - results in terms of function -- large lateral shifts -- less torque generated on impaired side - in sitting: normal recruitment pattern is distal to proximal beginning with muscles closes to support surface
basal ganglia
- controls ability to make quick changes in muscle patterns - background muscle tone
cerebellum
- controls adaptations to changes in task or environment
visual reference
- orientation of head and trunk in space in relation to vision - stable environment offer visual vertical and horizontal references useful for postural control - visual substitution for vestibular if possible -- but, if peripheral visual cues move slowly or are not aligned with gravity - destabilization may occur
otolith system
- position of head in relation to gravity - horizontal and vertical accelerations (riding in a car or elevator)
postural control modification difficulties
- postural adaptation problems - match between scaling and degree of instability - force outputs must match amplitude of instability - possible origins of adaptation problems : limited ability to increase agonist muscle recruitment (strength) - difficulty scaling/modulating amplitude of postural responses in response to changing balance perturbation levels - hypermetric postural responses in an individual with an anterior lobe cerebellar lesion
ankle strategy
- restores COM to a position of stability - generally used when perturbations are small and surface is solid
hip strategy
- restores COM to a position of stability through movement of the hip joint - restores equilibrium in response to a larger, faster perturbations or more compliant surface
brainstem
- vestibular - with cerebellum, controls postural tone
coactivation
activation of muscles on both sides of joints results in joint stiffening, resulting in ineffective and inefficient means of recovering balance
linear motion
change of speed when driving in a car
visual
critical to feedforward and feedback control in changing environment
delayed recruitment of proximal synergistic muscles
delayed activation of proximal synergists is often seen in children with down syndrome and in individuals post s/p TBI
somatosensory
dominant sense for upright postural control
limits of stability
farthest distance in any direction a person can leean without need to change the BOS with step, reach, or fall
opposite
head moves ____ to hip/ankle
proximal, distal
hip (_____ to ______)
forward, anterior, abs, quads
hip: backward directed platform: - ____ sway - _____ muscles respond - 2 muscles
backward, posterior, paraspinals, hamstrings
hip: forward directed platform: - ____ sway - ____ muscles respond - 2 muscles
peripheral (ambient) vision
largely subconscious info - motion of self-relevant to the environment -- motion of the head while body is moving -- postural sway
central set
modifications that are task/environment dependent
central (foveal) motion
mostly conscious info - environmental orientation - reference for verticality - perception of object motion - identification of hazards and opportunities
semicircular canals
movement of the head
somatosensory
on its own, ______ system cannot distinguish surface tilt from body tilt
visual
on its own, the ____ system cannot discriminate between movement of the body and movement of the environment
vestibular
on its own, the ____ system cannot tell if head movement in space is the results of neck, trunk, or hip motion
top-down
orientation of head and trunk in space in relation to gravitational forces - most important when balancing on unstable surfaces -- vertical and horizontal visual references are inadequate -- deciphers when body is moving on the surface is moving - head maintains a gravity neutral upright posture even with surface oscillation
bottom-up
orientation of the head in reference to the surface through cutaneous, proprioceptive, pressure, and stretch receptors or muscles and joints - head stays in reference to the surface
utricle
oriented horizontally when person is upright; sense horizontal linear acceleration
saccule
oriented vertically when person is upright; sense vertical linear acceleration
center of mass
point that is at center of the total body mass
delayed activation
problems with sequencing, timing, and amplitude of postural muscle activity in paretic limbs -- onset latencies are longer - delays in activation of distal muscles - may be compensatory action of proximal muscles on nonparetic side for those with hemiplegia
roll
rotation around x axis (lateral tilt; head to shoulder)
pitch
rotation around y axis (fore tilt, "yes" motion)
yaw
rotation around z axis ("no" motion)
semicircular canals
sense angular velocity
otolith organs
sense linear acceleration and gravity
anticipatory postural adjustments
similar to APR's but occur before postural disturbance - relies upon prediction which depends upon experience in interaction with the environment
somatosensory
triggers automatic postural responses
vestibular
uniquely important: differentiates self-motion from movement in environment
center of gravity
vertical projection of COM - an imaginary point in space, calculated biomechanically from forces and moments, where the sum total of all forces equal zero - located level S2 in adults who are standing quietly - constantly changing when the body is in motion
surge
x-axis; anterior-posterior
sway
y-axis; lateral
heave
z-axis; occipito-caudal