Figure 10.17

Figure 10.17 The Arrangement of Motor Units in a Skeletal Muscle

• Internal tension generated inside contracting muscle fibers

• External tension generated in extracellular fibers

Tension production by skeletal muscles

Figure 10.16 Internal and External Tension

Figure 10.16

• Motor units– All the muscle fibers innervated by one neuron– Precise control of movement determined by number

and size of motor unit

• Muscle tone– Stabilizes bones and joints

Figure 10.17

Figure 10.17 The Arrangement of Motor Units in a Skeletal Muscle

• Isometric– Tension rises, length of muscle remains constant

• Isotonic• Tension rises, length of muscle changes

• Resistance and speed of contraction inversely related

• Return to resting lengths due to elastic components, contraction of opposing muscle groups, gravity

Contractions

Figure 10.18 Isotonic and Isometric Contractions

Figure 10.18

Figure 10.19

Figure 10.19 Resistance and Speed of Contraction

• Creatine phosphate (CP) releases stored energy to convert ADP to ATP– CP made creatine with excess ATPs

– Returns energy to ATP via enzyme creatine phosphokinase (CPK); excess in blood with muscle damage

• Aerobic metabolism (req. O2) provides most ATP needed for contraction

• Glycolysis in cytoplasm; oxidative phosphorylation in mitochondria

• At peak activity, anaerobic glycolysis needed to generate ATP

• Fermentation- lactate from pyruvate; temporarily maintains glycolysis without O2; far less ATP produced

Muscle Contraction requires large amounts of E

Figure 10.20 Muscle Metabolism

Figure 10.20

Figure 10.20 Muscle Metabolism

Figure 10.20

• Energy production and use patterns mirror muscle activity

• Fatigued muscle no longer contracts– Build up of lactic acid– Exhaustion of energy resources

• lack of ATP, CP, pH drop (lactate)

Energy use and level of muscular activity