Sample Lecture Outline

1. Types of muscles
   1. Smooth
   2. Cardiac
   3. Skeletal
2. Functional anatomy of skeletal muscle (Visit the University of California at San Diego Muscle Physiology and Design page.)
   1. Connective tissue coverings
      1. Epimysium
      2. Perimysium
      3. Endomysium
         

         Key Point: The connective tissue coverings of muscle are continuous with tendons that, in turn, attach muscle to bone.

   2. Muscle fiber structure
      1. Sarcolemma
      2. Sarcoplasm
      3. Transverse tubules
      4. Sarcoplasmic reticulum
      5. Myofibrils
         1. Striations
         2. Sarcomere
         3. Myosin and actin filaments
            

            Key Point: The actin filament is actually a complex structure composed of three different protein molecules: actin, tropomyosin, and troponin.

3. Muscle fiber contraction
   1. Initiation of the contractile process
      1. Motor unit (motor unit and muscle fiber)
      2. Neuromuscular junction
      3. Motor impulse
      4. Action potential generation
      5. Calcium release by the sarcoplasmic reticulum
   2. Sliding filament theory
      

      Key Point: The striated appearance of a skeletal muscle fiber results from partial overlapping of actin and myosin filaments. When contraction (i.e., fiber shortening) takes place, the appearance of changes is not due to shortening of the myofilaments but is due to the actin and myosin sliding past each other, which increases the degree of overlap between them.

   3. End of muscle contraction
4. Muscle fiber types
   1. Type I (slow-twitch) muscle fibers
   2. Type II (fast-twitch) muscle fibers
      

      Key Point: Muscle fibers are classified as type I or type II based on differences in their speeds of shortening and strength, which a relative predominance of either “fast” or “slow” myosin ATPase (adenosine triphosphatase) primarily determines.

   3. Characteristics of fiber types
      1. Oxidative capacity
      2. Glycolytic capacity
      3. Contractile speed
      4. Fatigue resistance
      5. Motor unit strength
   4. Type I and type II motor units
   5. Fiber type distribution
   6. Fiber type determination
      1. Primarily a genetic determination
      2. Possible effects of training and detraining
5. Muscle fiber recruitment
   1. All-or-none response
      1. Individual fibers
      2. Motor units (Visit the University of Utah, Spencer S. Eccles Health Sciences Library and the Kansas University Medical Center JayDoc HistoWeb.)
   2. Factors that influence motor-unit recruitment patterns
      1. Motor neuron size
      2. Required force generation (exercise intensity)
      3. Fatigue
6. Characteristics of whole-muscle function (Visit the Loyola University Medical Education Network Master Muscle List.)
   1. Functional classification of individual muscles
      1. Agonists
      2. Antagonists
      3. Synergists
         

         Key Point: Depending on the specific movement being considered, a given muscle can function as an agonist, an antagonist, or a synergist. For example, the triceps brachii is the agonist (or prime mover) for elbow extension, an antagonist for elbow flexion, and a synergist for arm adduction.

   2. Types of muscle action
      1. Dynamic (Visit Muscles in Action.)
         1. Concentric
         2. Eccentric
      2. Static (isometric)
7. Factors that influence force generation by a muscle
   1. Number of motor units activated
   2. Type of motor units activated (type I or type II)
   3. Muscle size
   4. Initial muscle length
   5. Joint angle (Visit the University of California Muscle Physiology page.)
   6. Speed of muscle action (shortening or lengthening)

Sample Student Assignments

1. Answer the following questions and bring the information to class for discussion:
• Describe the sequence of events in muscle contraction. What is the importance of calcium in this sequence?
• Discuss the relationship between distribution of muscle fiber type and performance. How might exercise training modify or change a person’s fiber-type distribution?
• How does the velocity (speed) of skeletal muscle contraction affect its force and power development?
• Explain the differences between concentric, eccentric, and isometric contractions in terms of actin–myosin interaction, muscle shortening or lengthening, and relative force production.
2. List, then diagram (from largest to smallest) the components of a skeletal muscle.