Chapter 3: The Musculoskeletal System: The Musculature

Outline

• Skeletal Muscle Structure

  Properties of Muscular Tissue

  The Muscle Fiber

  Slow- and Fast-Twitch Fibers

  Muscular Attachment

  Structural Classification of Muscles on the Basis of Fiber Arrangement

  Effect of Muscle Structure on Force and Range of Motion

• Skeletal Muscle Function

  Line of Pull

  Types of Contraction

  Influence of Gravity

  Length-Tension Relationship

  Force-Velocity Relationship

  Stretch-Shortening Cycle

• Coordination of the Muscular System

  Roles of Muscles

  Cocontraction

  Action of Biarticular Muscles

  Types of Bodily Movements

• Methods of Studying the Actions of Muscles

  Conjecture and Reasoning

  Dissection

  Inspection and Palpation

  Models

  Muscle Stimulation

  Electromyography (EMG)

  Imaging

• Muscular Analysis

• Laboratory Experiences

Objectives

At the conclusion of this chapter, the student should be able to:

1. Describe the structure and properties of the whole muscle, fast- and slow-twitch muscle fiber, and the myofibril.

2. Explain how the relationship of the muscle's line of pull to the joint axis affects the movement produced by the muscle.

3. Describe the relationship between the skeletal muscle's fiber arrangement and its function.

4. Define the roles a muscle may play (agonist, antagonist, and synergist), and explain the cooperative action of muscles in controlling joint actions by naming and explaining the muscle roles in a specified movement.

5. Define the types of muscular contraction (concentric, eccentric, and static), and name and demonstrate each type of action.

6. Demonstrate an understanding of the influence of gravity and other external forces on muscular action by correctly analyzing several movement patterns in which these forces influence the muscular action.

7. Describe the various methods of studying muscle action, citing the advantages and disadvantages of each method.

8. State the force-velocity and length-tension relationships of muscular contraction, and explain the significance of these relationships in static and dynamic movements.

9. Identify the muscle groups active in a variety of motor skills.

Body parts are moved by external or internal forces. The internal force responsible for the movement and positioning of the bony segments of the body is the action of skeletal muscles. These muscles are able to serve this function because they can contract, they are attached to the bones, and they cross a joint. In addition, they are constructed of bundles of striated muscle fibers, which differ in both structure and function from the highly specialized cardiac muscle and from the smooth muscle of blood vessels, digestive organs, and urogenital organs.

Skeletal Muscle Structure

Properties of Muscular Tissue

The properties of striated muscle tissue are extensibility, elasticity, and contractility. The first two enable a muscle to be stretched like an elastic band and, when the stretching force is discontinued, to return again to its normal resting length. Tendons, which are simply continuations of the muscle's connective tissue, also possess these properties. Contractility, the ability to shorten and produce tension at its ends, is a unique property possessed by muscle tissue only. The average muscle fiber can shorten to ...