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Physiology Ch 12
questions for test 3 of chapter 12
| Question | Answer |
|---|---|
| 1. Name the two major functions of muscles | to generate motion and to generate force |
| 2. Name the three types of muscle tissue | Skeletal, cardiac, and smooth muscle tissues |
| 3. Which types are striated, and what causes this appearance | cardiac and skeletal muscles are striated, because they have alternating dark and light bands when seen under light microscopes |
| 4. Name three specific locations of smooth muscle | stomach, urinary bladder, and blood vessesls |
| 5. What controls the contraction of skeletal muscle | contract in response to a signal from a somatic motor neuron, their contraction is not influenced directly by hormones and they cannot initiate their own contraction. |
| how does the contraction of skeletal muscle differ from cardiac and smooth muscle? | skeletal muscle is voluntary; cardiac and smooth muscle contraction is involuntary, have multiple levels of control (primary extrinsic control—autonomic innervations), contract spontaneously (without signals), subject to modulation of the endocrine system |
| 6. What % of total body weight comes from skeletal muscle? | 40% |
| 7. Define tendons | attach skeletal muscles to bone, made of collagen |
| Define origin | the end of the muscle that is attached closest to the trunk or to the more stationary bone |
| Define insertion | the end of the muscle that is the more distal or more mobile attachment |
| Define flexor | Muscles that contract and cause the centers of the connected bones to be brought closer together, flexor muscles perform flexion |
| Define extensor | muscles that when contracted move the bones away from each other, extensor muscles perform extension |
| 8. What is a motor unit? | the basic unit of contraction, A collection of muscle cells that function together and the somatic motor neuron that innervates them. |
| How do motor unit sizes vary? | the number of muscle fibers in a motor unit varies (in muscles of the eyes, a motor unit contains 3 to 4 muscle fibers while muscles used for standing/walking, motor units contain hundreds or thousands of muscle fibers) |
| 9. How do some individual muscle cells develop into such large cells? | |
| 10. Define sarcolemma | the cell membrane of a muscle fiber |
| Define sarcoplasm | the cytoplasm of muscle fiber |
| Define myofibril | the main intracellular structures in striated muscles, highly organized bundles of contractile and elastic proteins that carry out the work of contraction |
| Define sarcoplasmic reticulum | a form of modified endoplasnmic reticulum that wraps around each myofibril like a piece of lace, longitudinal tubules that release Ca2+ ions |
| Define terminal cisternae | enlarged regions at the ends of the tubules that concentrate and sequester Ca2+ |
| Define transverse tubules (t-tubules) | adjacent to terminal cisternae, a continuation of the muscle fiber membrane, rapidly move action potentials from the cell surface into the interior of the fiber, increases response time of muscle fiber |
| Define triad | one t-tubule and its two flanking terminal cisternae |
| 11. How many myofibrils might be found in a skeletal muscle? | 250 myosin molecules join to create a thick filament |
| What determines how many myofibrils are found in a skeletal muscle? | |
| 12. Name the two contractile proteins of myofibrils | myosin and actin |
| In addition, name two regulatory proteins and two accessory proteins in myofibrils | tropomyosin and troponin (regulatory) titin and nebulin (accessory) |
| 13. Why do we have so many isoforms of myosin? | |
| 14. Describe the structure of the thick filament | arranged so that the myosin heads are clustered at each end of the filament, and the central region of the filament is a bundle of myosin tails |
| 15. What is G-actin vs. F-actin? | G-actin is a single actin molecule (globular protein), F-actin is a polymerized long chain/filamament of multiple G-actin molecules. 2 F-actin polymers twist to create the thin filaments of the myofibril |
| What are crossbridges, and what role do they play in muscle tension? | span the space between filaments and connect the parallel thick and thin filaments of myofibril, they form when myosin heads of thick filaments bind to actin in the thin filaments |
| 16. Define sarcomere | the contractile unit of a myofibril. |
| Draw a sarcomere, Label the I band, A band, M line, Z line, actin, myosin | |
| 17. Which proteins insure the proper alignment of six thin filaments with each thick filament? | titin and nebulin |
| 18. Describe the structure and role of titin | huge elastic molecule (returns stretched muscles to their resting length), the largest known protein (stabilize the position of the contractile filaments, composed of more than 25,000 amino acids), stretches from z disk to neighboring M line, 2 functions |
| Describe the structure and role of nebulin | ineleastic giant protein that lies alongside thin filaments and attaches to the z disk, helps align the actin filaments of the sacromere |
| 19. In muscle physiology literature, the force created by the contracting muscle is called __ | muscle tension. |
| 20. Describe how contraction occurs during the sliding filament theory | overlapping actin and myosin filaments of fixed length slide past one another, moving the z disks of the sacromere closer together (shortens) in an energy-requiring process, |
| 21. Name the two binding sites on a myosin head | actin molecule binding site and ATP binding site |
| What is a power stroke? | when myosin crossbridges swivel and push the actin filaments toward the center of the sacromere |
| 22. Why is myosin referred to as a "motor protein"? | it is a protein with the ability to create movement |
| 23. What is the "rigor state" of skeletal muscle attributed to? | myosin heads are tightly bound to G-actin molecules, (No ATP?) |
| 24. What is crossbridge tilting? | the power stroke (because the myosin head and hinge region tilt from 90 degree angle to a 45 degree angle), which begins after ca2+ binds to troponin to uncover the rest of the myosin-binding site |
| What is the last step of crossbridge cycling prior to the extremely brief (normally) rigor state? | myosin releases ADP, the product of ATP hydrolysis |
| 25. Describe the state of the crossbridge during a time when skeletal muscle is relaxed | ATP hydrolysis provides energy for the myosin head to rotate and reattach to actin, which rotates it to the cocked position where it is ready to bind to actin |
| 26. Tropomyosin partially blocks the __. It can be moved by its regulation by __ so as to allow the power stroke to take place | myosin-binding sites / troponin |
| 27. Describe the troponin complex | troponin C binds reversibly to calcium, |
| Which part of the complex regulates contraction | Troponin C |
| how does the troponin complex exhibit control of contraction | calcium-troponin C complex pulls tropomyosin completely away from actin’s myosin binding sites, the on position enables the myosin heads to form strong, high force cross bridges and carry out their power strokes moving the actin filament |
| 28. How does muscle relax following contraction? | Ca2+ concentrations in the cytosol decrease, which unbinds from troponin, which allows tropomyosin to return to its off position, covering the actin’s myosin binding sites, sacremeres slide back to original positions |
| 29. What is excitation-contraction coupling | the process in which muscle action potentials initiate calcium signals that in turn activate a contraction-relaxation cycle |
| What are the four major events in E-C coupling? | 1. Ach is released from the somatic motor neuron, 2. Ach initiates an action potential in the muscle fiber, 3. muscle action potential triggers calcium release from the sarcoplasmic reticulum, 4. calcium combines with troponin and initiates contraction |
| Which neurotransmitter is responsible for initiating the action potential in muscle (in excitation-contraction coupling)? | Acetylcholine |
| 30. What is an end-plate potential? | (EEP) depolarization at the motor end plate due to acetylcholine |
| 31. The t-tubule membrane contains voltage-sensing receptors called __ that are mechanically linked to calcium ion release channels in the adjacent sarcoplasmic reticulum. These release channels are called __ or __. | L-type calcium channel (called dihydropyridine DHP receptor) / ryanodine receptors / RyR |
| 32. What is the magnitude of increase of calcium ion concentration from resting state to maximal contraction? | 100 fold (100x) |
| 33. Why is it so important to have phosphocreatine in skeletal muscle? | back up energy source with high energy phosphate bonds that are created from creatine and ATP when muscles are at rest, create ATP to power muscles |
| What enzyme catalyzes the reaction with PCR? | creatine kinase (CK) or creatine phosphokinase (CPK) |
| 34. When CPK is found in blood plasma, it is an indication of skeletal muscle or cardiac muscle damage. How can a clinician tell which tissue is damaged? | because the two muscle types contain different isozymes |
| 35. Which sources of energy are used during rest, light exercise, and heavy exercise? | rest and light exercise skeletal muscles butn fatty acids along with glucose, heavy exercise the muscles fibers rely on glucose |
| 36. Define fatigue | a reversible condition in which a muscle is no longer able to generate or sustain the expected power output |
| Name a few of the potential causes of fatigue during exercise | excitation-contraction failure in the muscle fiber, low pH from acid production during ATP hydrolysis, neural causes such as communication failure at neuromuscular junction or CNS command neurons, ion imbalance |
| What is central fatigue? | fatigue that arises in the central nervous system |
| 37. Although each muscle fiber has the potential to express proteins in such a fashion as to be completely different from one another, generally muscle fibers can be classified into three broad groups. Name the three groups | slow-twitch fibers (ST or Type I), fast-twitch oxidative-glycolytic fibers (FOG or Type IIA), fast-twitch glycolytic fibers (FG or Type IIB) |
| 38. Be familiar with the speed, metabolic and fatigue-related differences of Type I | develop tension 2-3x slower than type II, contractions last 10x as long, used constantly for maintaining posture, standing, or walking, have more mitochondria, more blood vessels |
| Be familiar with the speed, metabolic and fatigue-related differences of Type IIA | develop tension 2-3x faster than type I (split ATP more rapidly and can complete multiple contractile cycles faster) pump Ca2+ more rapidly but last only 7.5 msec, used for fine movements, rely on oxidative phosphorylation for ATP, more mitochondria |
| Be familiar with the speed, metabolic and fatigue-related differences of Type IIB | develop tension 2-3x faster than type I (split ATP more rapidly and can complete multiple contractile cycles faster), rely on anaerobic glycolysis to produce ATP, fatigue the easiest |
| 39. How is tension of a muscle related to length of the sarcomeres within the muscle fibers? | because each sarcomere contracts with optimum force if it is at optimum length, tension a muscle fiber can generate is directly proportional to the number of crossbridges formed between the thick and thin filaments |
| 40. How do we control the level of contraction of an individual muscle fiber? | with the frequency of action potentials |
| What is unfused tetanus? | incomplete tetanus, stimulation rate of the muscle fiber is not at a maximum value, and consequently the fiber relaxes slightly between stimuli |
| What is fused tetanus? | complete tetanus, the stimulation rate is fast enough that the muscle fiber does not have time to relax, reaching maximum tension and staying there, |
| 41. How do the muscle fibers of one motor unit become so similar to one another? | during embryological development each somatic motor neuron secretes a growth factor that directs the differentiation of all muscle fibers in its motor unit so that they develop into the same muscle fiber type |
| 42. How do we recruit a greater number of motor units to be active during a whole muscle contraction? | recruitment, using stronger stimuli to activate motor neurons with larger thresholds |
| Which motor units are recruited first during a whole muscle contraction? | those with the lowest thresholds |
| 43. What is the purpose of asynchronous recruitment of motor units? | a way for the nervous system to avoid fatigue in sustained contractions, by modulating the firing rates of the motor neurons so that different motor units take turns maintaining muscle tension, alternating acticve motor units allows motor units to rest |
| 44. Define isotonic contraction | contractions that creates force and move loads, such as lifting weights, |
| Define concentric contraction | shortening contractions of the muscles |
| Define eccentric contraction | lengthening contractions of the muscles, lead to delayed muscle soreness and cellular damage |
| Define isometric contraction | contractions that create force without moving a load |
| Define series elastic elements | elastic fibers in the muscle that stretch during isometric contraction |
| 45. Describe the role of the position of insertion in a 3rd class lever system with regard to a person's ability to exert external force and external speed | this type of lever-fulcrum system is that it maximizes speed and mobility, small movements closer to fulcrum become large movements nearer the load |
| 46. Name the three most common sites of muscle disorders | signals from the nervous system, miscommunication at the neuromuscular junction, or defects in the muscle |
| 47. What is the most common cause of muscular atrophy? | prolonged inactivity |
| 48. How does smooth muscle differ from striated muscle in terms of speed and resistance to fatigue? | smooth muscle twitch contractions occur much more slowly, use less energy to generate a given amount of force, low oxygen consumption rate, maintain force for long periods w/o fatiguing, generates maximum tension at 25-30% of active crossbridges |
| How do smooth muscle traits help with muscle tone? | because it can sustain contractions for extended periods without fatiguing, the tone is maintained, despite continued load, and maintains tension. |
| 49. What about smooth muscle is more difficult to study than striated muscle? | has more variety, anatomy makes functional studies difficult, contractions controlled by hormones and paracrines as well as neurotransmitters, variable electrical properties, contraction/relaxation is influenced by multiple pathways |
| How are contraction/relaxation of smooth muscle influenced? | neurotransmitters, hormones, and paracrinces acting on a smooth muscle fiber inhibit contractions as well as stimulate it, requiring the smooth muscle fiber to act as an integrating center to produce the correct effect when contradictory info is received |
| What electrical properties of smooth muscle differ from skeletal muscle? | smooth muscles exhibit a variety of electrical behaviors including, hyperpolarizing and depolarizing, depolarize w/o action potentials, contractions occur after AP, subthreshold graded potential or w/o any change in membrane potential |
| What can controls smooth muscle contraction | acetylcholine, norepinephrine, and a variey of other neurotransmitters, hormones, and paracrines |
| How does smooth muscle have more variety? | six major groups of smooth muscle, that have different functions in the body and their physiology reflects their specialized functions |
| What are the six major groups of smooth muscle | vascular (blood vessel walls), gastrointestinal (walls of digestive tract and associated organs, gallbladder), urinary (walls of bladder and ureters), respiratory (aiway passages), reproductive (uterus and others), and ocular (eye) |
| What about smooth muscle anatomy makes functional studies difficult? | contractile fibers are arranged in oblique bundles rather than in parallel sarcomeres, contractions pull the cell membrane in many directions at once, layers of muscle may run in several directions, making it hard to measure tension in both layers at once |
| 50. What is the shape and size of a smooth muscle cell? | ssmall, spindle-shaped cells with a single nucleus, |
| Where are the nuclei of smooth muscle cells? | at the center of the actin myosin lattice arrangement |
| 51. Smooth muscle has more __ filaments (proportionally) than skeletal muscle, and because it has no troponin, __ are responsible for controlling contraction and relaxation | Actin, tropomyosin |
| 52. The SR of smooth muscle is __ linked to the cell membrane rather than __ linked as occurs in skeletal muscle | myosin linked, troponin and troponmyosin linked |
| 53. How does visceral smooth muscle exhibit its action as a single unit? | all the fibers are electrically connected to one another, and an action potential in one cell spreads rapidly through gap junctions to make the entire sheet of tissue contract |
| 54. Multi-unit smooth muscle only occurs in a few places in the human body. Which tissue in humans can switch from multi-unit to single-unit? | the uterus during labor and delivery (other locations are the iris and ciliary body of the eye, the male reproductive tract) |
| 55. Name a few advantages of smooth muscle over skeletal muscle with regard to matching its specific functions? | smooth muscle can be stretched while maintaining enough overlap and create optimal tension, has finer contractions |
| 56. What is calmodulin? | a binding protein for Ca2+ found in the cytosol |
| What is the role of MLCK and MLCP in contraction of smooth muscle? | MLCK enhances myosin ATPase activity by phosphorylating light protein chains near the myosin head (aids contraction), |
| What is the role of caldesmon? | |
| 57. What are slow wave potentials vs. pacemaker potentials in smooth muscle? | slow wave potentials are cyclic depolarization and repolarization of the membrane potential, pacemaker potentials are regular rhythms of contractions that always reach threshold and fire an AP |
| 58. What is calcium-induced calcium release? | when graded potentials open a few Ca2+ channels, allowing small amounts of calcium into the cell, depolarizing the cell even more, causing more VG calcium channels to open |
| What types of stimuli might initiate the calcium channels at the cell membrane to open? | signal ligands such as norepinephrince, Ach, other neurotransmitters, hormones and paracrines, depolarization, or stretch |
| Are calcium channels opened only by action potentials? | no, graded potentials can open the channels, and pharmacomechanical coupling causes smooth muscle contraction which occur without a significant change in membrane potential |
| 59. Although smooth muscles can release calcium in response to stretch, the calcium channels exhibit __ and calcium channels begin to close in a time-dependent fashion | myogenic contraction... or adaption |
Created by:
alechsu