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Neuronal Control of Functional Movement

Introduction

In the 18th century, the investigation of movement was based on the premise that upright stance and gait, and also differentiation of hand movements, represented a basic requirement for human cultural development (Herder 1785). This necessitates that the nervous system must function to automatically balance the body’s Centre of mass over the feet during all motor activities. In other words, every movement must begin and end with a postural adjustment.

Basic requirements

The relative significance of reflexes on central rhythms and programming in locomotion has been addressed. Hoffmann (1922) described the monosynaptic pathway as the simplest spinal feedback system and emphasized that in humans, the so-called ‘Eigenreflexapparat’ is responsible for the adaptation of muscle innervation to unexpected stress. Förster (1927) suggested that slow stretch reflexes and ‘adaptation reflexes’ were an essential contribution to motor coordination.

Central programming

A ‘motor programme’ has been variously defined in the literature as ‘communications in the CNS that are based on past experience and that can generate postural adjustments and movements’ (Brooks 1979) or as ‘a set of muscle commands that are structured before a movement sequence begins and that allows the entire sequence to be carried out uninfluenced by peripheral feedback’ (Keele 1968). However, in human gait, neither definition is totally accurate. With respect to the first definition, programmes are not based solely upon experience but are also innate.

Steplike movements are present at birth, spontaneously initiated or triggered by peripheral stimuli. A central origin of these movements is implied, as the EMG bursts precede the actual mechanical events (Forssberg 1986). Infant stepping also occurs in anencephalic children (Forssberg 1986), which suggests that a spinal mechanism coordinates the movement. More generally, central programming in the context of gait generates a complex and widespread pattern of muscle activation triggered by external or internal events.

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