The Nervous System and Basic Nerve Structures
The Motor Unit
Gradations in the Strength of Muscular Contractions
Posture and Locomotor Mechanisms
Central Nervous System: Levels of Control
Reciprocal Inhibition and Coactivation
At the conclusion of this chapter, the student should be able to:
Name and describe the functions of the basic structures of the nervous system.
Explain how gradations in strength of muscle contraction and precision of movements occur.
Name and define the receptors important in musculoskeletal movement.
Explain how the various receptors function, and describe the effect each has on musculoskeletal movement.
Describe reflex action, and enumerate and differentiate among the reflexes that affect musculoskeletal action.
Demonstrate a basic understanding of volitional movement by describing the nature of the participation of the anatomical structures and mechanisms involved.
Perform an analysis of the neuromuscular factors influencing the performance of a variety of motor skills.
The role of the bones, joints, and muscles in human movement were presented in the previous two chapters. The appropriate function of these systems requires an intact nervous system. Therefore, this chapter takes up the role of the nervous system in initiating, modifying, and coordinating muscular action.
Loofbourrow (1973) presented this topic so succinctly and vividly that his classic and still applicable introductory paragraph is quoted here in full as an introduction to this chapter:
The forces which move the supporting framework of the body are unleashed within skeletal muscles on receipt of signals by way of their motor nerves. In the absence of such signals, the muscles normally are relaxed. Movement is almost always the result of the combined action of a group of muscles which pull in somewhat different directions, so the control of movement involves a distribution of signals within the central nervous system (CNS) to appropriate motor nerves with precise timing and in appropriate number. In order for movements to be useful in making adjustments to external situations, it is necessary for the central nervous system to be appraised of these situations, which are continually changing. A means of providing this information promptly exists in a variety of receptors sensitive to changes in temperature, light, pressure, etc. These receptors are signal generators which dispatch signals (nerve impulses) to the CNS over afferent nerve fibers. The CNS receives these signals together with identical ones from within the muscles, joints, tendons, and other body structures and is led thereby to generate and distribute in fantastically orderly array myriads of signals to various muscles. This, despite the enormous complexity of the machinery involved, enables the individual to do one main thing at a time. This is integration. It is what Sir Charles Sherrington meant by “the integrative action of the nervous system.”