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PART 2 Support and Movement

Heat Production

1. Heat is a by-product of chemical reactions in muscles.2. Shivering produces heat to maintain body temperature.

4. Relaxation results when myosin phosphatase removes a phosphategroup from the myosin molecule.

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9.7 Energy Sources for MuscleContraction (p. 296)

Energy for muscle contraction comes from ATP.

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If phosphate is removed while the cross-bridges are attached,relaxation occurs very slowly, and this is referred to as the latchstate.If phosphate is removed while the cross-bridges are not attached,relaxation occurs rapidly.

Aerobic and Anaerobic Respiration

1. The ATP synthesized by aerobic respiration produces energy formuscle contractions under resting conditions or during exercises suchas long-distance running. Although ATP is produced more efficiently,it is produced more slowly.2. The ATP synthesized by anaerobic respiration provides energy fora short time during intense exercise. Anaerobic respiration producesATP less efficiently but more rapidly than aerobic respiration. Lactatelevels increase because of anaerobic respiration.

Types of Smooth Muscle

1. Visceral smooth muscle fibers contract slowly, have gap junctions(and thus function as a single unit), and can be autorhythmic.2. Multiunit smooth muscle fibers contract rapidly in response to stimu-lation by neurons and function independently.

Electrical Properties of Smooth Muscle

1. Spontaneous contractions result from Na + and Ca 2 leakage into cells; + Na + and Ca 2 movement into the cell is involved in depolarization.2. The autonomic nervous system, hormones, and chemicals producedlocally can inhibit or stimulate action potentials (and thus contrac-tions). Hormones can also stimulate or inhibit contractions withoutaffecting membrane potentials.

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Creatine Phosphate

ATP synthesized when ADP reacts with creatine phosphate provides energyfor a short time during intense exercise.

Recycling of ADP

Two ADP are converted to one ATP and one AMP during intense exercise.

Functional Properties of Smooth Muscle

1. Smooth muscle can contract autorhythmically in response to stretchor when stimulated by the autonomic nervous system or hormones.2. Smooth muscle maintains a steady tension for long periods.3. The force of smooth muscle contraction remains nearly constant,despite changes in muscle length.4. Smooth muscle does not develop an oxygen deficit.

Muscle Fatigue

1. Fatigue, the decreased ability to do work, can be caused by the cen-tral nervous system, depletion of ATP in muscles, or depletion ofacetylcholine in the neuromuscular junction.2. Physiological contracture (the inability of muscles to contract orrelax) and rigor mortis (stiff muscles after death) result from inad-equate amounts of ATP.

Regulation of Smooth Muscle

1. Smooth muscle is innervated by the autonomic nervous system andis involuntary.2. Hormones are important in regulating smooth muscle. Certain hor- + mones can increase the Ca 2 permeability of some smooth musclemembranes and therefore cause contraction without a change in theresting membrane potential.

Muscle Soreness

Soreness is caused by inflammation in the muscle.

Oxygen Deficit and Recovery OxygenConsumption

After anaerobic respiration, aerobic respiration is higher than normal, as theimbalances of homeostasis that occurred during exercise become rectified.

9.9 Cardiac Muscle (p. 306)

Cardiac muscle fibers are striated, have a single nucleus, are connected byintercalated disks (and thus function as a single unit), and are capableof autorhythmicity.

9.8 Smooth Muscle (p. 300)

1. Smooth muscle cells are spindle-shaped with a single nucleus. Theyhave actin myofilaments and myosin myofilaments but are not striated.2. The sarcoplasmic reticulum is poorly developed, and caveolae mayfunction as a T tubule system.3. Calcium ions enter the cell to initiate contraction; calmodulin binds + to Ca 2 and activates an enzyme that transfers a phosphate groupfrom ATP to myosin. When phosphate groups are attached to myosin,cross-bridges form.

9.10 Effects of Aging on Skeletal Muscle(p. 307)

Aging skeletal muscle is associated with reduced muscle mass, increasedtime that muscle takes to contract in response to nervous stimuli, lessprecise muscle control, and a longer recovery period.

1. Which of these is true of skeletal muscle?a. spindle-shaped cellsb. under involuntary controlc. many peripherally located nuclei per muscle fiberd. forms the walls of hollow internal organse. may be autorhythmic

2. Which of these is not a major property of muscle?a. contractility d. extensibilityb. elasticity e. secretabilityc. excitability