SENSORIMOTOR VISUAL SYSTEM

Sensorimotor Visual System

Sensorimotor Visual System

The sensorimotor system, a subcomponent of the comprehensive motor control system of the body, is extremely complex. The term sensorimotor system was adopted by the participants of the 1997 Foundation of Sports Medicine Education and Research workshop to describe the sensory, motor, and central integration and processing components involved in maintaining joint homeostasis during bodily movements (functional joint stability). The components giving rise to functional joint stability must be flexible and adaptable because the required levels vary among both persons and tasks. The process of maintaining functional joint stability is accomplished through a complementary relationship between static and dynamic components. Ligaments, joint capsule, cartilage, friction, and the bony geometry within the articulation comprise the static (passive) components. Dynamic contributions arise from feedforward and feedback neuromotor control over the skeletal muscles crossing the joint. Underlying the effectiveness of the dynamic restraints are the biomechanical and physical characteristics of the joint. These characteristics include range of motion and muscle strength and endurance.

Figure 1

The sensorimotor system incorporates all the afferent, efferent, and central integration and processing components involved in maintaining functional joint stability. Although visual and vestibular input contributes, the peripheral mechanoreceptors are (more ...) From these descriptions of static and dynamic stability components, it becomes apparent that the terms are not synonymous. Integrity of static stabilizers is measured through clinical joint stress testing (ligamentous laxity testing) and arthrometry, giving rise to the frequently used term clinical stability. Because of the complexity of the control over the dynamic restraints, measuring dynamic stability is more challenging. Currently, as described in a companion paper, we are only able to quantitatively measure certain characteristics of the dynamic stability mechanism.

Attempts to localise specific brain regions responsible for motor function accelerated in the later part of the 19th centuries with the work of Sherrington, Ferrier and others (Porter and Lemon 1993). Evidence accumulated that removal of cortex in the precentral region produced movement abnormalities, and that stimulation of the same cortex could elicit muscle responses in dogs (Fritsch and Hitzitg 1870) and monkeys. Working on chimpanzees, gorillas and orang-utans, Sherrington and colleagues mapped out motor responses elicited by stimulating points along the precentral gyrus (Leyton and Sherrington 1917; Grunbaum and Sherrington 1908).

Around the same time Brodmann was performing histological studies to map out cortical cytoarchitecture (Figure 1.3). Suggestions were made that anatomical divisions would correspond to functional divisions. The first clear link was made between histology and physiology when Campbell, who had been performing similar work to Brodmann, performed histological analysis of tissue from some of the animals that had been studied electrophysiologically.

In their experiments on non-human primates, Sherrington and colleagues demonstrated that stimulation of different points along the precentral gyrus evoked movements of different body parts. A similar somatotopic organisation of excitable cortex was later found in human subjects by Penfield and colleagues who stimulated pre- and postcentral sites during surgery for removal of tumours or epileptic foci (Figure 1.4). They found that the majority of effective sites were in the ...