Human Biology

Sylvia S. Mader Michael Windelspecht Chapter 12 Muscular System Lecture Outline Part 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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12.2 Skeletal Muscle Fiber Contraction What role does ATP play in muscle contraction and rigor mortis?

• ATP is needed to attach and detach the myosin heads from actin.

• After death, muscle cells continue to produce ATP through ______________ and muscle cells can continue to contract.

• When ATP runs out, some myosin heads are still attached and cannot detach, causing rigor mortis.

• Rigor mortis and body ___________ may be used to estimate time of death.

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12.3 Whole Muscle Contraction

Terms to describe whole muscle contraction

• _________ – a nerve fiber and all of the muscle fibers it stimulates • ____________ – a single contraction lasting a fraction of a second • ____________ – an increase in muscle contraction until the maximal sustained contraction is reached

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12.3 Whole Muscle Contraction

Terms to describe whole muscle contraction

• _________ – maximal sustained contraction • ___________ – a continuous, partial contraction of alternate muscle fibers causing the muscle to look firm

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12.3 Whole Muscle Contraction Physiology of skeletal muscle contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

contraction period relaxation period latent period Stimulus Time a.

tetanus summation fatigue Stimuli Time b.

Figure 12.9

The three phases of a single muscle twitch and how summation and tetanus increase the force of contraction.

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12.3 Whole Muscle Contraction

Where are the fuel sources for muscle contraction?

• Stored in the muscle – Glycogen – Fat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

60 50 muscle triglycerides plasma fatty acids blood glucose muscle glycogen 40 30

• In the blood – Glucose – Fatty acids

20 10 0 0 1 2 Exercise time (hr) 3 4 Figure 12.10

The sources of energy for muscle contraction.

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12.3 Whole Muscle Contraction •

What are the sources of ATP for muscle contraction?

Limited amounts of ATP are stored in muscle fibers.

• Creatine phosphate pathway (CP) builds up when a muscle is resting – ________ way to acquire ATP but only sustains a cell for _______; • Fermentation – fast-acting but results in _______ build up • Cellular respiration (aerobic) – not an immediate source of ATP but the best _________ source

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12.3 Whole Muscle Contraction Acquiring ATP for muscle contraction

Anaerobic

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Anaerobic Aerobic creatine phosphate glycogen glycogen or fatty acids O 2 fermentation creatine + ATP lactate + ATP CO 2 + H 2 O + ATP b.

c.

a.

Figure 12.11

The three pathways by which muscle cells produce the ATP energy needed for contraction.

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12.3 Whole Muscle Contraction

Muscle fibers come in 2 forms

Fast-twitch fibers • Rely on CP and fermentation (anaerobic) • Adapted for strength • Light in color • Few mitochondria • Little or no myoglobin • Fewer blood vessels than slow-twitch

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12.3 Whole Muscle Contraction

Muscle fibers come in 2 forms

Slow-twitch fibers • Rely on aerobic respiration • Adapted for endurance • Dark in color • Many mitochondria • Myoglobin • Many blood vessels

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