 |  Biology, 6/e Author Dr. George B. Johnson,
Washington University
Author Dr. Peter H. Raven,
Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer,
Carleton College
Contributor Dr. Jonathan Losos,
Washington University
Locomotion
Answers to Review Questions|
Chapter 50 (p. 1016)
1. The main matrix components of bone are calcium salts in the form of hydroxyapatite, which makes bones hard, and collagen, which confers resiliency to the bone. Since the calcium salts are embedded in a collagen matrix, even if a shock is hard enough to break the calcium, the collagen fibers absorb the shock.
2. Vertebrate joints include the immovable joints (such as the sutures in the skull), the slightly moveable joints (such as the joints between the vertebrae in the spine), and the freely moveable joints (such as the hip or shoulder joints).
3. The origin of a muscle is where it attaches to the stable, or nonmoving bone. The insertion is in the bone that does the moving when the muscle contracts.
4. Thick filaments are composed of myosin. Thin filaments are composed of actin.
5. The resting myosin head attaches to the actin filament at the angle between the S-1 and S-2 units, which is 90o. A power stroke reduces the angle between S-1 and S-2, resulting in the advancement of myosin filament relative to the actin filament. The globular head detaches from the actin filament and the head returns to the previous 90o angle configuration and starts the cycle again. ATP is used at the power stroke step, when the angle between S-1 and S-2 is reduced.
6. Contraction is initiated by a nerve impulse. The chemical released is acetylcholine. It depolarizes the muscle membrane, which opens calcium channels in it. When Ca++ is present in the sarcoplasm, cross-bridges between the actin and myosin can form, and contraction is initiated.
7. The somatic motor neuron releases ACh at its synapse with the muscle fiber. ACh acts on the muscle fiber membrane, causing it to produce its own electrochemical impulse.
8. The normal contraction of a muscle in response to a single electrical stimulus is called a twitch. The smooth, sustained contraction of a muscle as a result of continued stimulation and shortening the relaxation time between stimuli is called tetanus.
9. Since all of the cells in a myocardium are stimulated to contract as a unit, the heart is incapable of summated contraction or tetanus.
10. In smooth muscle, thick and thin filaments are not organized into sarcomeres. Calcium is required for smooth muscle contraction, but it comes from extracellular fluid rather than from a sarcoplasmic reticulum, which is absent in smooth muscle cells. Smooth muscle has the ability to contract even when it is greatly distended, which would not be possible because of tearing in skeletal muscles.
11. All animal locomotion involves contraction of filaments, such as muscle fibers, to push some body part against its environment, whether it be air, water, or land. As the animal pushes against its environment, the animal is moved along in the opposite direction in obedience to Newton’s third law of motion.
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2002 McGraw-Hill Higher Education