Locomotion Flashcards
minimal gait speed for walking is:
1.2 mi/hr
How does load influence locomotion?
WB enhances extensor activity in stance
Locomotion does not require:
sensation
Locomotion neurology is:
basic neural fxn
distributed in several areas of CNS
hierarchically organized
plastic
Describe the hierarchal organization of locomotion:
prefrontal (goal) motor cortex BG, Cb, brainstem SC - CPG PNS and muscle
Describe CPG’s distribution throughout the cord:
in ventral and intermediate horns at every SC level
In animal studies with SC transection, stereotyped limb mvmnts are induced by:
cutaneous stimulation
limb mvmnt
pharmacological agents
–> NOT dependent on afferent input but sensor input IS important
CPG fictive locomotion is:
stimulation of motor neuron pool in a rhythmical pattern consistent with locomotion
CPG fictive locomotion can be done by:
stimulation of higher centers
pharmacological agents
CPG half center model is based on
reciprocal inhibition pools of motor neurons on both sides of the SC
flexors and extensors alternate - reverberate
CPG half center model depends on:
tonic input from higher center
CPG’s are involved in _____ and _____ coordination.
both intra and inter-limb
CPG output can be modified (adaptation). Can react to:
- sensory inputs
- change in higher center input
ex: with obstacle on treadmill, if limb is in swing will enhance flexor activity. cutaneous input can enhance EMG activity. Higher centers may change gait velocity, or stepping pattern, etc.
In humans compares to animals, CPGs may be more dependent on:
supraspinal initiation (ie: require higher centers) (we don't have the same level of evidence as we do for animals)
What requirements do we have for fxnal walking?
- Equilibrium during propulsion (vestibular and Cb)
- basic reciprocal mvmnts (MLR, R-S, vest-sp, Cb, CPG, BG)
- adaptation to task goals and restraints (Cb, Cx)
What regions hold the keys for fxnal walking?
brainstem and SC
What is the MLR?
mesencephalic locomotor region
mesencephalic = midbrain
The MLR influences locomotion through:
activation of other brainstem areas
What tracts are involved in MLR locomotor fxn?
reticulospinal
vestibulspinal
Describe the fxn of the two reticulospinal tracts:
pontine: excite extensors (inhibit flexors)
medullary: excite flexors (inhibit extensors)
ACTIVITY DURING GAIT CYCLE OSCILLATES B/W THE TWO
R-S output is modified by several inputs:
CPG
vision
vestibular
–> WALKING IS MORE ADAPTIVE TO ENVIRONMENTAL CONTEXT
Vestibulospinal tracts fxn:
excites extensors during stance (against gravity)
The MLR functions to control locomotion by:
activating and controlling activity of CPGs
maintaining equilibrium during locomotion
adapting limb mvmnts to external conditions
coordinating locomotionw ith other motor acts
The sensory motor cortex is especially active in:
complex, novel tasks
Cb contribution to locomotion:
timing of sequential activation fine tuning (receives copy of output from CPGs
BG contribution to locomotion:
initiation
termination
timing
What tracts are essential to locomotion?
tracts in anterior cord
reticulospinal: flexors/extensors
vestibulospinal: extensor drive
* ventral sparing in SCI incr. chance of walking post SCI
What about C-S involvement in locomotion?
responsible for fractionated mvmnt –> not as important for walking
Describe the role of sensory afferents in locomotion:
NOT essential except for adaptation (sensory input essential for modifying CPG’s in response to environmental demands)
Which sensory afferents contribute?
cutaneous receptors
joint receptors
muscle spindle (esp. Ia)
GTO (Ib)
Describe how low threshold cutaneous input facilitate CPG’s:
extensors in stance and flexors in swing
Describe how Ia fibers are involved in reciprocal inhibition:
Ia fibers presynaptically inhibited by Ia collaterals from opposing muscle groups
Fxn: decrease resistive reflexes that would impede locomotion
Describe how phase transitions are important in locomotion:
Hip extension: critical in transition from stance to swing (hip flexor muscle spindles activate ipsi flex and contra ext)S
Triceps Surae: stretch in late stance also facilitates transition from stance to swing
Stretch reflexes are phasic ally modulating during walking. This means that sensitivity to stretch depends on:
what part of the gait cycle
What is the role of GTO in locomotion?
can have bimodal response during some activities like ambulation - facilitate extensor during stance and inhibit during swing
(role in motor control much more complex than originally thought)
Afferents from muscle spindle and GTO also affect higher centered via _____ tract and provide info from periphery that modifies _____ tract output.
spino-Cb
reticulo-spinal
In summary, sensory input shapes the final motor output by:
modifying composition of active CPG circuits and their synaptic connections
allowing for adaptation
What biomechanics factors influence locomotion?
gait speed
environment
load (WB inc. extensor activity in stance)
What is the minimal gait speed for arm swing?
1.2 mi/hr
Describe CPG coordination:
more than one CPG may be activated
separate for UE and LE
multiple for LE and/or trunk
In asymmetrical lesions (like brown sequard hemilesion), recovery mechanisms include:
significant reorganization of spared pathways
no ipsilateral regeneration, but ingrowth of contralateral collaterals
What are the training and outcome considerations re: locomotion status?
peripheral sparing
use dependent plasticity
normalizing input
maximizing output
Anterior or Poster SC more important to preserve to maximize locomotion?
anterior SC
Training can improve locomotion and result in fxnal walking without:
any change in MMT
Peripheral sparing includes preservation of which tracts?
vetibulo-spinal
reticulospinal
(both for CPGs)
Which motor tract is not essential for locomotion?
lateral cortico-spinal
With complete SCI, what is the purpose of locomotion training?
CV, pulmonary, etc
How does AD use influence locomotion?
ideally the AD normalizes walking so CPGs are effective: want to maintain reciprocal arm swing, etc
What human locomotion patterns are unique from animal studies?
bipedal (greater control for upright posture)
more dependent of supra spinal input
CPG organized differently
What applications can help normalize afferent input for locomotion?
normal gait kinematics (feedback to reticulo-spinal centers and CPGs)
maintain tonic locomotor drive
Walking speed for goal of BWS training:
1m/sec
Walking speed for functional walking:
0.8m/sec
How does walking speed influence locomotion?
Faster speed means more input to locomotor centers
What are the considerations for program development and progression:
load postural control speed endurance IND adaptation
What is better, treadmill or over ground?
over ground for fxnal walking
over ground requires more postural adjustments, more PF, more adaptation demands, and different GFRs than treadmill
Emphasize ____ phase components in order to active CPGs.
stance phase
loading (IC)
