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NS19 - Posture + Gait (ii) (successful gait control (4 control mechanisms.…
NS19 - Posture + Gait (ii)
Normal gait cycle
stance
62%
start = heel contact
end = toe of same foot leaves ground
shock absorption, stability
hip extension, ankle dorsiflexion, lat shift of pelvis
body moves over foot like an inverted pendulum
swing
38%
start = toe leaves ground
end = just before heel contact of same foot
foot clearance NB
knee flexion (passive), hip flexion, rotation of pelvis
pre-positioning for stance again
knee extend, anke dorsiflexes
(passive) no muscles needed due to momentum
successful gait control
command from CNS -> transits signal to PNS
tension via muscle contractions
forces generated @ joints - > movement of segments
ground reaction force
sensory feedback: real time info
4 control mechanisms...
1) spinal cord
2) decerebrate preparation: cerebellum + brainstem
weight support, active propulsion, coordination
stimulus required to mesencephalic locomotor region in brainstem
cerebellum essential for correcting CPGs
3) decorticate preparation: basal ganglia
allows for walking on uneven surfaces
ext stimulus not required
vision need to navigation + seeing surfaces
goal directed
4) intact system: cortex
called the spinal cat
Central Pattern Generators (CPGs)
= neuronal circuits activated in rhythmic motor patterns
can be induced in incomplete spinal cord lesions using mechanical stimulation (e.g. treadmill)
can be induced in complete spinal cord lesions using electrical stimulation
CV + mental health benefits, could mean walking again one day
Abnormal postures
decerebrate posture
lesion BELOW red nucleus
arms + legs held straight out, toes pointed, head + neck arched backwards
EXTENSION, flexors blocked
decorticate posture
lesion ABOVE red nucleus
arms + wrists + fingers adducted + flexed, legs extend + int rotated, toes pointed
UL FLEXION
Abnormal gaits
can have atypical presentations due to compensation by patient
classifications poorly standardised - often classified by conditions
high-stepping gait: problem with proprioception
spastic gait
dragging stiff leg due to muscle spasticity
how to assess
watch them walking into room (assistance symmetry, smooth, controlled, speed, energy efficiency)
full neurological exam
how to treat
reverse/control pathology via drugs/surgery
rehab = physiotherapy
spontaneous recovery
augmented recovery
compensatory strategies