Locomotion

Goal of movement

Transporting body while maintaining

• equilibrium during propulsive movement

• Basic reciprocal movement synergy

  • Adaptation to behavioral goals and external constraints

Reciprocal movement

rhythmical lower extremity muscle activation

Task and environmental adaptation

goal-directed movement in spatial contexts

Somatosensation is critical for

activation of swing/stance muscle activity

Somatosensation contributes to

appropriate step timing and amplitude

somatosensation is used for

obstacle navigation

Vision is used to

survey support surface, environmental obstacles, and body orientation

when walking, vision is in… rather than saccades

traveling fixation

Traveling fixation

looking down, but a few feet ahead

Vestibular system

monitors and detects deviation of head position and modulates descending reticulospinal activity

If the vestibular system detects deviation,

it will attempt to fix it from a whole body perspective

Sensory afferents are

necessary for effective function

Spinal effectors

circuit that produces locomotion

Hip flexor stretch generates

swing phase

sensory afferents

receive, interpret, and process sensory information, and is used to generate motor output

Body load achieves

goal of stance

spinal effectors are needed for

stepping adjustments with unexpected obstacles

CPG

Central pattern generators (Rhythmics)

Distinct CPGs control

forward and backward ambulation for each leg

Each CPG can be modulated by

sensory input and descending supra spinal inputs

spinal effectors have subgroups for

R/L and phases of gait (FLX/EXT) patterns

Locomotor spinal effectors theorized to be in

lumbosacral spinal cord

alpha motor neuron pool activation results in

muscle synergy activity

recruitment of spinal effectors is

task dependent and specifies the timing of the firing of each individual muscle

Evidence of specific spinal effectors

Burts of activity noted within the gait cycle

Human evidence for spinal effector control of locomotion

rhythmic stepping patterns in infants and locomotor capability in individuals with SCI

animal studies indicate that supraspinal commands

aren’t necessary for basic movement production

spinal circuits are modified by

descending signals

spinal pattern generators do not require

sensory input, but are regulated by limb proprioceptors

In complete SCI, EMG activity can be recovered

but it is non functional

Midbrain locomotor region has

context dependent permission to CPGs to activate

MLR determines

level of activity in the spinal pattern generators, initiates walking pattern, controls gait speed, and exerts an indirect influence on the spinal pattern generators

MLR synapses on

medullary reticular formation neurons

MLR reaches CPGs via

RST

MLR needs permission from

Basal ganglia (to decrease baseline inhibition)

Basal ganglia

selects appropriate motor behaviors, initiates and terminates motion, links automatic movement sequences with volitional act, tunes automatic in context of volitional gait, exerts inhibition of MLR at rest

Activation of MLR occurs through

finely tuned output nuclei inhibition

When SNPr inhibits, the

MLR can go

Medial Cerebellum locomotor control

postural control mechanisms and interlimb coordination

intermediate Cerebellum locomotor control

Regulation of gait via somatosensory inputs, contributes to specific limb placement

lateral Cerebellum locomotor control

adjusts gait under novel conditions with visual guidance

Cerebellum does not talk with

CPGs

Cerebellum influences CPGs via

tracts (has no direct LMN connections)

cerebellum is involved in regulation of

all stepping movements

cerebellum influences

rubrospinal, reticulospinal, and vestibulospinal activity

Externally guided cortical locomotor control

visuomotor transformation

guided cortical locomotor control function

precision walking (obstacles, targets, routes)

Internally guided cortical locomotor control

sensorimotor transformation

guided cortical locomotor control function

utilization of mechanical events relative to self for postural set, changing gait patterns, etc.

PPC

posterior parietal cortex/parietal association area

PPC does

planning locomotion based on estimate of position relative to environmental object

Motor cortex contributes

modulation of synergistic motor neuron pools

Locomotor stability has greater demands… than…

medial to lateral, anterior to posterior

locomotor control requires

dynamic control of center of mass

postural correction is

instability specific (where in the gait cycle you are)

feedforward mechanisms

anticipatory postural demands

feedback mechanisms

ongoing balance and postural control (lets you know if things are going well or if you need to adjust)

ongoing balance and postural control happens via

postural set correction, visual orientation, and righting responses