HUMAN LOCOMOTION

Irfan

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HUMAN LOCOMOTION

“RESTORING GAIT-GETTING PEOPLE UP AND RUNNING-IS ONE OF THE CORE ELEMENTS OF PHYSIOTHERAPY.”

PROFESSOR R. TALLIS

FRONTLINE NOV 2001

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LOCOMOTION

DEFINED BY THE OXFORD ENGLISH DICTIONARY AS;

“The act, fact, ability, or power of moving.

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LOCOMOTION IN HUMANS

• Locomotion is a complex task in humans which has evolved through the maturation of many differing but harmoniously interlinked systems of control within the CNS.

• Although locomotion is a voluntary action once initiated it does not require conscious direction under normal circumstances for that individual.

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LOCOMOTION

CAN BE SEPARATED INTO TWO COMPONENTS

GAIT manner of walking or running study of supraspinal controls.

WALKING automatic pattern or action. study of Central Pattern Generators.

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LOCOMOTION

• Walking is a basic requirement of daily life as well as one of the most complex.

• The goal of walking is to move forward.

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Gait

• movements that produces locomotion• including, for humans:

– walking, – running, – swimming,– cycling, etc

• characteristics: – energy-economical, particularly walking– flexibility to cope with different speeds, terrains etc.– sophisticated control mechanisms (bipedal gait inherently

unstable)

ESSENTIAL REQUIREMENTS

• Progressive Requirement - Basic locomotory patterns that move the body in the required direction.

• Stability Requirement – The ability to maintain the body up against gravity.

• Adaptive Requirement – The ability to adapt locomotion to the demands of the environment.

PROGRESSIVE REQUIREMENT

• A) Pattern Generation• B) Timing• C) Coordination• D) Initiation• E) Motivation• F) Purpose• G) Altering Locomotion

Pattern generation

• Spinal CordThe spinal cord is necessary but not sufficient for the expression of even the most rudementary of stepping behaviour (Bronstein, Brandt and Woollacott 1996)

• Central Pattern generatorsNeuronal networks in the spinal cord capable of producing rhythmical movements such as walking. (Mackay-Lyons 2002) Produce stereotyped locomotor patternsEach limb has its own pattern generator ( Leonard 1998)

• Descending tractsProvide modulation to the spinal circuitry during locomotion

Descending Tracts - which system?

• Tops up excitation to the extensor motor neurons during stance phase?

• Tops up excitation to the flexor motor neurone pool during swing phase?

• Is excitatory during stance and swing phase and generally enhances postural tone?

• Is involved in more complex walking.

Timing

• Somatosensory System– input comes from afferent receptors in muscles tendons skin.– Gives us information on orientation of body parts, movement of body parts,

muscle tension, orientation of support surfaces and body with reference to support surface.

• Visual Systemvisual clues help in alignment, step frequency and even step length. Gives us

movement relative to environment.

• CerebellumTiming cannot be considered without considering the cerebellum

Co-ordination

Cerebellum• receives a huge amount of information during locomotion.

• If information is unexpected the olive is able to modify walking via the reticulospinal, vestibulospinal and rubrospinal tracts.

• The cerebellum does not initiate walking but is more involved in the modulation of CPGs where necessary.

• In order to learn to cope with a variety of of complex environments there is a need to be exposed to different situations to enable the cerebellum to develop strategies.

• It is also thought that the cerebellum can alter step cycle according to visual information received.

• The overall function of the cerebellum is improved inter and inter limb co-ordination

Initiation

Basal ganglia

• Thought to be involved in initiation and termination of activity• processing of sensory stimuli• attaching emotional and situational significance to sensory input

Reticulospinal system

• Involved in increasing the sensitivity of the CPGs via the release of glutamate. Therefore has a role in initiation

Motivation

• Limbic System

Involved in core emotions / motivations (eg fight or flight reactions)

Purpose

Cortex• Known functions include :

– cognitive aspects of motor control– visuomotor co-ordination– motor planning

• Cortical neurons– often fire before the onset of movement– typically fire phasically during locomotion– increase intensity of activity during swing phase.

Altering locomotion

Cortex

• During normal level path unobstructed locomotion the cortical level involvement is minimal: when the animal is required to go over barriers in the travel path or is constrained to place its paws on a specific location (such as rungs of a ladder) the intensity (but not the phase) of the activity in the corticospinal tract increases dramatically (Bronstein et al 2003)

Altering locomotion

Central pattern generators• It is thought highly likely that there are separate networks for each limb

and that these can be segmentalised and recombined for different types of locomotion under differing modulatory and presynaptic controls (Beheshti 1997)

• Extensive “sculpting “ of CPG networks by using different combinations of basic cellular and synaptic processes creates a variety of alternative functional circuits, each with the capacity to generate a distinct motor pattern within a family of function-related behaviours (MacKay-Lyons 2002)

STABILITY REQUIREMENT

• A) Modulation of Postural tone

• B) Alignment

A) Modulation of postural tone

Midpontine neuronal structures– caudal tegmental field (ventral and dorsal)– stimulation of VTF --> increase level of extensor muscle tone– stimulation of DTF --> reduces extensor muscle tone

Cerebellum– provides regulation of postural control appropriate to the phase of

walking

A) Modulation of postural tone

Reticulospinal system

– postural tone is created and sustained during locomotion by a balance of the inhibitory effects on stretch reflexes (lateral reticulospinal ) and the facilitatory effects on the extensor tone ( medial reticulospinal )

– Receives input from many sources and fires in all phases of locomotion.

B) Alignment

spinal cord

vestibular system

visual system

joint receptors

muscle spindles

golgi tendon organs

cutaneous

ADAPTIVE REQUIRMENT

• A) Reactive Balance Strategies

• B) Proactive Balance Strategies

Reactive balance Strategies

• Ongoing modification

• The three sensory systems contribute to reactive balance strategies during walking.

• Cerebellum plays a crucial role in reactive balance strategies

Proactive Balance Strategies• Primarily mediated by the visual system which is used to identify potential

obstacles in the environment and then predict the destabilising effect of performing simultaneous tasks (Shumway-Cook, Woollacott 2002)

• Avoidance Strategy– change foot placement, increase ground clearance, change direction or stop)

• Accommodation Strategy– Locomotion is adapted over a longer time.(e.g. reduced step length when

walking on ice) (Shumway-Cook, Woollacott 2002)

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Note:

•Alternating periods of double and single support

•About 70:30 split between single and double support in normal walking