Chapter at a Glance

Skeletal Muscles 326

Structure of Skeletal Muscles Motor Units 328

Mechanisms of Contraction 330

Sliding Filament Theory of Contraction 331

Cross Bridges 333 Regulation of Contraction 335

Role of Ca2+ in Muscle Contraction 336 Excitation-Contraction Coupling 336 Muscle Relaxation 338

Contractions of Skeletal Muscles 340

Twitch, Summation, and Tetanus

Treppe 340 Isotonic, Isometric, and Eccentric

Contractions 340 Series-Elastic Component 341 Length-Tension Relationship 341

Energy Requirements of Skeletal Muscles 342

Metabolism of Skeletal Muscles 342 Maximal Oxygen Uptake 343 Oxygen Debt 344 Phosphocreatine 344 Slow- and Fast-Twitch Fibers 344 Muscle Fatigue 346 Adaptations of Muscles to Exercise Training 346

Neural Control of Skeletal Muscles 347

Muscle Spindle Apparatus 348

Alpha and Gamma Motoneurons 349 Coactivation of Alpha and Gamma

Motoneurons 350 Skeletal Muscle Reflexes 350

The Monosynaptic Stretch Reflex 350 Golgi Tendon Organs 350 Reciprocal Innervation and the Crossed-Extensor Reflex 351 Upper Motor Neuron Control of Skeletal Muscles 352 Cerebellum 352 Basal Nuclei 352

Cardiac and Smooth Muscles 353

Cardiac Muscle 354 Smooth Muscle 355

Excitation-Contraction Coupling in Smooth

Muscles 355 Single-Unit and Multiunit Smooth

Muscles 357 Autonomic Innervation of Smooth Muscles 358

Interactions 359

Summary 360 Review Activities 362 Related Websites 363

Clinical Investigation

Maria, an energetic 40-year-old who plays softball and has been active in athletics most of her life, complains that she is experiencing fatigue and muscle pain and that her body just doesn't seem as limber as it should. Upon exercise testing, she is found to have a high maximal oxygen uptake. Her muscles, though not large, are well toned—perhaps excessively so. Laboratory tests reveal a normal blood level of creatine phosphokinase but an elevated blood Ca2+ concentration. She has hypertension, which is well controlled with a calcium channel-blocking drug.

What might be responsible for Maria's fatigue and muscle pain?

Chapter Twelve

Table 12.1

Skeletal Muscle Actions




Increases the angle at a joint


Decreases the angle at a joint


Moves limb away from the midline of the body


Moves limb toward the midline of the body


Moves insertion upward


Moves insertion downward


Rotates a bone along its axis


Constricts an opening

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  • melilot
    What might be responsible for fatigue and muscle pain?
    8 years ago

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