Compartmentalization of Muscles and Their Motor Nuclei: The Partitioning Hypothesis

Abstract

This review article is designed to expose physical therapists to an examination of muscle organization and the implications that this organization has for therapeutic applications. The partitioning hypothesis is based on the fact that an individual muscle is arranged in a more complex array than simply fibers attaching at aponeuroses, tendons, or bones with a single muscle nerve innervation. Neuromuscular compartments, which are distinct subvolumes of a muscle, each innervated by an individual muscle nerve branch and each containing motor unit territories with a unique array of physiological attributes, are described. In addition, the organization of individual muscles into these subunits is paralleled by the organization of their parent motoneurons within the spinal cord. These notions are detailed in a review of data derived from studies performed primarily in cat and rat models. Recent data derived from morphological and anatomical study of human muscles support the existence of similar neuromuscular partitions. These data are complemented by physiological studies, the results from which suggest that partitions may have functional or task-oriented roles; that is, different portions of one muscle may be called into play depending on the task demands of the situation. The importance of these observations for reconsidering how we provide clinical applications, such as neuromuscular stimulation or kinesiological monitoring, is discussed.

Evaluation of the neuromuscular compartments in the peroneus longus muscle through electrical stimulation and accelerometry

“…In addition, the motor point is the skin surface at which the maximal mechanical response is elicited with the minimum applied current. However, English et al 14 described a more complex organization of the studied region. They indicated that the nerve or primary motor branch continues its path inside the muscle, dividing into two or more secondary branches that reach the NMCs 14,31 .…”

“…The knowledge of the actions of muscle groups and of each muscle that constitutes them, as well as the contribution of each NMC to the final action of the muscle, is fundamental for the effective rehabilitation of patients afflicted by neurological and muscle dysfunctions that impede basic movements, such as walking, jumping, sitting, and standing, as well as more demanding activities, such as sports 14,15 . These movements require the constant activation of stabilizing muscles in static and dynamic positions at the joints of the lower limbs.…”

Tension Distribution of Single Motor Units in Multitendoned Muscles: Comparison of a Homologous Digit Muscle in Cats and Monkeys

“…Recently, however, muscles in various mammalian species have been shown to consist of multiple functional subdivisions (Burke, 1995;English et al, 1993;Windhorst et al, 1989). Within such a muscle, each subdivision consists of a region of muscle fibers innervated by a separate branch of the muscle nerve (English and Letbetter, 1982;English and Weeks, 1984;Balice-Gordon and Thompson, 1988;English, 1990;Segal et al, 1991;Drake et al, 1993;Serlin and Schieber, 1993;Sanders, et al, 1994;Vanden Noven et al, 1994).…”

Caracterización Morfológica del Músculo Bíceps Femoral del Perro

“…De acuerdo con English et al (1993), cada compartimiento contiene unidades motoras con un único ordenamiento de atributos fisiológicos. Por su acción sobre la articulación de la rodilla el músculo bíceps femoral constituye uno de los principales actores en la estabilidad estática y dinámica del miembro pelviano del canino.…”

“…Los músculos esqueléticos de los mamíferos están compuestos por subvolúmenes denominados compartimientos neuromusculares, en los cuales pueden variar el diseño arquitectónico macroscópico y las características de las fibras. Kernell (1998), define al compartimiento neuromuscular como subvolúmenes inervados exclusivamente por una rama primaria del nervio, con una población fibrilar y arquitectura características.De acuerdo con English et al (1993), cada compartimiento contiene unidades motoras con un único ordenamiento de atributos fisiológicos. Por su acción sobre la articulación de la rodilla el músculo bíceps femoral constituye uno de los principales actores en la estabilidad estática y dinámica del miembro pelviano del canino.…”