Lecture 22:Locomotion

Locomotion is an activity leading to a change in the location of the body in external space. Examples: walking, running, hopping, swimming, flying, crawling, etc.

Important characteristics:

Velocity Stride length Relation between the support and swing phases Relative timing of the extremities (gait)

Locomotion: EMG PatternsDuring Human Walking

Locomotion in DifferentPreparations

Locomotion Inducedby Stimulation of MLR

Effects of Changingthe Stimulation Strength

The Locomotor Region and Strip

Experiments on Decerebrateand Spinal Animals

Electrical stimulation of certain brain (and spinal) areas can induce locomotion.

Gait changes with the strength of the stimulation.

Locomotion and gait changes can also be induced by treadmill motion and by intraspinal drugs (GABA).

Fictive locomotion can be seen.

The spinal cord is likely to contain one, two, or even four Central Pattern Generators (CPGs).

A CPG can be driven by descending and ascending signals.

It does not necessarily require either signal.

It can produce different gaits.

Graham Brown versus Sherrington:

Experiments on Decerebrateand Spinal Animals

Central Pattern Generator(CPG)

A CPG is a hypothetical structure in the central nervous system that can generate patterned (rhythmical) activity.

It can be driven by “higher” centers as well as by peripheral information.

Both sources of information can lead to gait changes.

Homunculus

A Simple Two-Half-Centers CPG

CPG

“Higher centers”

Afferents

-motoneurons

Central Pattern Generator

CPG in the Lamprey Has Been Mostly Deciphered

CPG in Humans:Starting Induced Locomotion

CPG in Humans: Aftereffectsof Spinal Stimulation

CPG in Humans: Different Effectsof Spinal Stimulation

INTERLIMBCOORDINATION

RHYTHMIC LEG MOVEMENTSWITH LOCOMOTOR SIGNS

TYPICAL ATYPICAL

CYCLESTRUCTURE

ASYMMETRIC CYCLES OF LEFT AND RIGHT LEGS

INCOMPLETE CYCLE

STEPPING

WALK-LIKE

RUN-LIKE UNILATERAL STEPS

IN-PHASE STEPS

DIFFERENT FREQUENCIES IN THE TWO LEGS

BILATERAL STEPS

UNUSUAL COORDINATION BETWEEN MOVEMENTS

IN PROXIMALAND DISTAL JOINTS ALTERNATING BETWEEN A FEW

STEP CYCLES OF ONE LEGAND THE OTHER LEG

CPG in Humans:Effects of Perturbations

Synergetic activity

Elements of synergy

Reaction to perturbation Hypothetic neuronal structures

1

Bipedal step-like movements

Left and right legs

Manual blocking of one leg motion increased the magnitude of movement of the other leg

CPGs for the left and right legs

Hip, knee and ankle joints of the leg

Manual blocking of one joint movement increased the magnitude of movements in other (non-blocked) joints of the same leg

CPGs for the joints of the leg

2

One leg step-like movements

Flexor and extensor half-centers of leg

Did not tested with perturbations. Flexor and extensor half- centers combining flexor and extensor generators of hip, knee and ankle joints

3 3

Rhythmic movements in pairs of joints

Pairs of homonymous or adjacent joints

Manual blocking of a joint leads to an increase in the magnitude of movement of the contralateral homonymous joint or to movements initiation in an adjacent joint

Generators of joint rhythmic activity

4 4

Single joint rhythmic flextion-extension

Muscles: flexors and extensors acting at a joint

Did not tested with perturbations. Var iability of the duration of the flexion and extension phases is higher than the variability of of the cycle duration.

Generators of rhythmic activity in flexors and extensors at a joint

CPGs in Humans:A Hypothetical Structure

Surface

StimStim

A B

Preprogrammed Reactionsin Locomotion

Corrective stumbling reaction:

Occurs during locomotion

Can be induced by a mechanical stimulus to the foot

Represents a complex pattern of EMG changes

Leads to a quick step over the obstacle

Preprogrammed Reactionsin Locomotion

Gait in Locomotion

Relative timing: a programmed feature versus an emergent property

Walking Trotting Galloping

Gaits in Quadrupeds

Relative Timing:Motor Programming

Relative Timing: Dynamic Systems

Relative Timing:Control + Coordination

Preparation for Stepping