Overview of Muscle Tissues - 난감형 ㅋ

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Types of Muscle Tissue (p. 244)
1. Skeletal muscle is attached to the skeleton, is striated, and can be controlled voluntarily.
2. Cardiac muscle forms the heart, is striated, and is controlled involuntarily.
3. Smooth muscle, located chiefly in the walls of hollow organs, is controlled involuntarily. Its fibers are not striated.
Functional Characteristics of Muscle Tissue (p. 244)
4. Special functional characteristics of muscle include excitability, contractility, extensibility, and elasticity.
Muscle Functions (pp. 244-245)
5. Muscles move internal and external body parts, maintain posture, stabilize joints, and generate heat.
Skeletal Muscle (pp. 245-272)
Gross Anatomy of a Skeletal Muscle (pp. 245-248)
1. Skeletal muscle fibers (cells) are protected and strengthened by connective tissue coverings. Deep to superficial, these are endomysium, perimysium, and epimysium.
2. Skeletal muscle attachments (origins/insertions) may be direct or indirect via tendons or aponeuroses. Indirect attachments withstand friction better.
Microscopic Anatomy of a Skeletal Muscle Fiber (pp. 248-252)
3. Skeletal muscle fibers are long, striated, and multinucleate.
4. Myofibrils are contractile elements that occupy most of the cell volume. Their banded appearance results from a regular alternation of dark (A) and light (I) bands. Myofibrils are chains of sarcomeres; each sarcomere contains thick (myosin) and thin (actin) myofilaments arranged in a regular array. The heads of myosin molecules form cross bridges that interact with the thin filaments.
5. The sarcoplasmic reticulum (SR) is a system of membranous tubules surrounding each myofibril. Its function is to release and then sequester calcium ions.
6. T tubules are invaginations of the sarcolemma that run between the terminal cisternae of the SR. They allow the electrical stimulus to be delivered quickly to deep cell regions.
Sliding Filament Model of Contraction (pp. 252-253)
7. According to the sliding filament theory, the thin filaments are pulled toward the sarcomere centers by cross bridge (myosin head) activity of the thick filaments.
Physiology of a Skeletal Muscle Fiber (pp. 253-259)
8. Regulation of skeletal muscle cell contraction involves (a) generation and transmission of an action potential along the sarcolemma and (b) excitation-contraction coupling.
9. An end plate potential is set up when acetylcholine released by a nerve ending binds to ACh receptors on the sarcolemma, causing changes in membrane permeability that allow ion flows that depolarize the membrane at the motor end plate. Once initiated, the action potential is self-propagating and unstoppable.
10. Current flows from the motor end plate depolarize the adjacent area of the sarcolemma, opening voltage-gated Na1 channels which allow Na1 influx. Then Na1 gates close and K1 voltage-gated channels open, repolarizing the membrane. These events generate the AP.
11. In excitation-contraction coupling, the action potential is propagated down the T tubules, causing calcium to be released from the SR into the cell interior.
12. Sliding of the filaments is triggered by a rise in intracellular calcium ion levels. Troponin binding of calcium moves tropomyosin away from myosin binding sites on actin, allowing cross bridge binding. Myosin ATPases split ATP, which energizes the working strokes and is necessary for cross bridge detachment. Cross bridge activity ends when calcium is pumped back into the SR.
Contraction of a Skeletal Muscle (pp. 259-264)
13. A motor unit is one motor neuron and all the muscle cells it innervates. The neuron’s axon has several branches, each of which forms a neuromuscular junction with one muscle cell.
14. A motor unit’s response to a single brief threshold stimulus is a twitch. A twitch has three phases: the latent period (preparatory events occurring), the period of contraction (the muscle tenses and may shorten), and the period of relaxation (muscle tension declines and the muscle resumes its resting length).
15. Graded responses of muscles to rapid stimuli are wave summation and unfused and fused tetanus. A graded response to increasingly strong stimuli is multiple motor unit summation.
16. Isotonic contractions occur when the muscle shortens (concentric contraction) or lengthens (eccentric contraction) as the load is moved. Isometric contractions occur when muscle tension produces neither shortening nor lengthening.
Muscle Metabolism (pp. 264-267)
17. The energy source for muscle contraction is ATP, obtained from a coupled reaction of creatine phosphate with ADP and from aerobic and anaerobic metabolism of glucose.
18. When ATP is produced by nonaerobic pathways, lactic acid accumulates and an oxygen debt occurs. To return the muscles to their resting state, ATP must be produced aerobically and used to regenerate creatine phosphate and glycogen reserves and to oxidize accumulated lactic acid.
19. Only about 40% of energy released during ATP hydrolysis powers contractile activity. The rest is liberated as heat.
Force of Muscle Contraction (pp. 268-269)
20. The force of muscle contraction is affected by the number and size of contracting muscle cells (the more and the larger the cells, the greater the force), the frequency of stimulation, and the degree of muscle stretch.
21. In twitch contractions, the external tension exerted on the load is always less than the internal tension. When a muscle is tetanized, the external tension equals the internal tension.
22. When the thick and thin filaments are slightly overlapping, the muscle can generate maximum force. With excessive increase or decrease in muscle length, force declines.
Velocity and Duration of Contraction (pp. 269-271)
23. Factors determining the velocity and duration of muscle contraction include the load (the greater the load, the slower the contraction) and muscle fiber types.
24. There are three types of muscle fibers: (1) fast glycolytic (fatigable) fibers, (2) slow oxidative (fatigue-resistant) fibers, and (3) intermediate fast oxidative (fatigue-resistant) fibers. Most muscles contain a mixture of fiber types.
Effect of Exercise on Muscles (pp. 271-272)
25. Regular aerobic exercise results in increased efficiency, endurance, strength, and resistance to fatigue of skeletal muscles.
26. Resistance exercises cause skeletal muscle hypertrophy and large gains in skeletal muscle strength.
27. Immobilization of muscles leads to muscle weakness and severe atrophy.
28. Improper training and excessive exercise result in overuse injuries, which may be disabling.
Smooth Muscle (pp. 272-278)
Microscopic Structure of Smooth Muscle Fibers (pp. 272-274)
1. Smooth muscle fibers are spindle shaped and uninucleate; they display no striations.
2. Smooth muscle cells are most often arranged in sheets. They lack elaborate connective tissue coverings.
3. The SR is poorly developed; T tubules are absent. Actin and myosin filaments are present, but sarcomeres are not. Intermediate filaments and dense bodies form an intracellular network that harnesses the pull generated during cross bridge activity and transfers it to the extracellular matrix.
Contraction of Smooth Muscle (pp. 274-276)
4. Smooth muscle fibers may be electrically coupled by gap junctions, the pace of contraction may be set by pacemaker cells.
5. Smooth muscle contraction is energized by ATP and is activated by a calcium pulse. However, calcium binds to calmodulin rather than to troponin.
6. Smooth muscle contracts for extended periods at low energy cost and without fatigue.
7. Neurotransmitters of the autonomic nervous system may inhibit or stimulate smooth muscle fibers. Smooth muscle contraction may also be initiated by pacemaker cells, hormones, or other local chemical factors that influence intracellular calcium levels, and by mechanical stretch.
8. Special features of smooth muscle contraction include the stress-relaxation response, the ability to generate large amounts of force when extensively stretched, and hyperplasia under certain conditions.
Types of Smooth Muscle (pp. 276-278)
9. Single-unit smooth muscle has electrically coupled fibers that contract synchronously and often spontaneously.
10. Multiunit smooth muscle has independent, well-innervated fibers that lack gap junctions and pacemaker cells. Stimulation is via autonomic nerves (or hormones). Multiunit muscle contractions are rarely synchronous.

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