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