Differences in Structure & Function of Skeletal, Cardiac, and Smooth Muscle - Prof. Carol , Study notes of Physiology

Download Differences in Structure & Function of Skeletal, Cardiac, and Smooth Muscle - Prof. Carol and more Study notes Physiology in PDF only on Docsity! Chapter 10 Chapter Objectives INTRODUCTION 1. Describe the primary function of muscle. The transformation of chemical energy into mechanical energy to generate force, perform work, and produce movement. Muscles also stabilize body position, regulate organ volume, generate heat, and propel fluids and matter through various body systems. 2. Define myology. The study of muscles. OVERVIEW OF MUSCLE TISSUE Types of Muscle Tissue 3. Describe the major structural and functional differences among the three types of muscle tissue. Skeletal Muscle: Striated; voluntary; move bones in the skeleton Cardiac Muscle: only contained in the heart; striated; involuntary; autorhythmicity (built-in rhythm in the heart because of a pacemaker that initiates each contraction); regulated by neurons that are part of the autonomic (involuntary) division of the nervous system and by hormones released by endocrine glands. Smooth Muscle: located in the walls of hollow structures (e.g. blood vessels, airways, and most organs in the abdominopelvic cavity, also found in skin and attached to hair follicles); nonstriated; usually involuntary and sometimes is autorhythmic (e.g. muscles propelling food through gastrointestinal tract); regulated by neurons that are part of the autonomic (involuntary) division of the nervous system and by hormones released by endocrine glands. Functions of Muscle Tissue 4. Describe the four key functions of muscle. 1) Producing body movements- rely on integrated functioning of skeletal muscles, bones, and joints. 2) Stabilizing body positions- skeletal muscle contractions stabilize joints and help maintain body positions. 3) Storing and moving substances within the body- storage is accomplished by sustained contractions of ring-like bands of smooth muscles called sphincters (prevent outflow of the contents of a hollow organ). *Smooth muscle sphincters close off the outlets of the stomach and bladder to store their contents. Contraction and relaxation of smooth muscle in the walls of blood vessels help adjust vessel diameter and regulates the rate of blood flow. Smooth muscle also moves substances through the gastrointestinal tract, push gametes through reproductive systems, and propel urine through the urinary system. *Cardiac muscle contractions pump blood through the heart. *Skeletal muscle contractions promote the flow of lymph and aid the return of blood to the heart. Nerve and Blood Supply 9. Describe the route and purpose of motor neurons and blood vessels that service each muscle cell. Somatic motor neurons- each one has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers. The axon of the somatic motor neuron typically branches many times, each branch extending to a different skeletal muscle fiber. Capillaries- are microscopic blood vessels; each muscle fiber is in close contact with one or more capillaries. The blood capillaries bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism. Microscopic Anatomy of a Skeletal Muscle Fiber 10. Explain the role of myoblasts and satellite cells in muscle development. Myoblasts- skeletal muscle fibers arise from myoblasts during embryonic development. Once fusion has occurred the muscle fiber loses its ability to undergo cell division. Thus, the number of skeletal muscle fibers you have is set before you are born, and most of these cells last a lifetime Satellite cells- a few myoblast cells do persist in skeletal muscle as satellite cells. These cells retain the capacity to fuse with one another or with damaged muscle fibers to regenerate functional muscle fibers. Skeletal muscle can only regenerate to a limited extent. 11. Discuss the connection between the sarcolemma and the Transverse tubules. Sarcolemma- plasma membrane of a muscle cell Transverse (T) tubules- thousands of tiny invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber *Muscle action potentials travel along the sarcolemma and through the t- tubules, quickly spreading throughout the muscle fiber. This arrangement ensures that an action potential excites the whole muscle fiber in the same instant. 12. Describe the makeup of sarcoplasm. Cytoplasm of the muscle fiber. Includes a substantial amount of glycogen that can be used for the synthesis of ATP. It also contains a red-colored protein called myoglobin (binds oxygen molecules that diffuse into muscle fibers from interstitial fluid). Myoglobin releases oxygen when it is needed by the mitochondria for ATP production. 13. Describe the myofibrils and the membranous sacs that encircle them. Myofibrils- contractile organelles of the skeletal muscle. They extend the entire length of the muscle fiber. Their prominent striations make the entire skeletal muscle fiber appear striated. Sarcoplasmic Reticulum- the membranous sacs that encircles each myofibril. Similar to Smooth ER in nonmuscular cells. Stores calcium ions. The release of these ions triggers muscle contraction. 14. Explain what is meant by muscle atropy and hypertrophy. Atrophy- wasting away of muscles because of a progressive loss of myofibrils. Common in bedridden individuals. Hypertrophy- increase in the diameter of muscle fibers due to increased production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles. It is caused by forceful muscular activity. 15. Explain how the arrangement of the thick and thin myofilaments forms the observed sarcomere structural patterns of the myofibril. The myofilaments inside of a myofibril do not extend the length of a muscle fiber. Instead, they are arranged in compartments called sarcomeres, which are the basic functional units of a myofibril. Z Discs- separate one sarcomere from the next; which means that a sarcomere extends from one Z disc to the next 16. Explain how the molecular components of thick and thin filaments fit together to form their respective interactive units. The thick and thin filaments overlap one another to a greater or lesser extent, depending on whether the muscle is contracted, relaxed, or stretched. The pattern of the overlap creates the striations that can be seen both in single myofibrils and in whole muscle fibers. A Band- darker middle part of sarcomere, extends the entire length of thick filament. I Band- lighter, less dense area that contains the rest of the thin filaments, but no thick filaments. A Z disc passes through the center of each I band. H Zone- in the center of each A band; contains thick, but no thin filaments 1) ATP Hydrolysis- reorients and energizes the myosin head. Products= ADP and a phosphate group (still attached to myosin head at the end of this phase) 2) Attachment of Myosin to Actin to Form Crossbridges- the myosin head attaches to the actin and releases the phosphate group. Crossbridges are formed when the myosin head attaches to actin during contraction. 3) Power Stroke- the site on the crossbridge where ADP is still located opens. Then, the crossbridge rotates and releases the ADP. The crossbridge generates force as it rotates toward the center of the sarcomere, sliding the thin filament past the thick toward the M Line. 4) Detachment of Myosin from Actin- crossbridge remains firmly attached to actin until it binds another molecule of ATP. As ATP binds to the ATP binding site on the myosin head, the myosin head detaches from actin. 22. Illustrate the structural relationships of the Sarcoplasmic Reticulum, Transverse tubules, and sarcomere and how they generally function as part of the excitation-coupling mechanism. Relate the role of calcium. When the muscle action potential propagates along the sarcolemma and into the t tubules, it causes calcium release channels in the SR membrane to open Ca flows out of SR into cytosolconcentration in cytosol risesreleased Ca ions combine with troponin, causing it to change shape moves tropomyosin away from the myosin binding sites on actin binding sites are free crossbridges formed contraction cycle begins 23. Describe the condition called rigor mortis and its cause. 24. Illustrate the relationship of sarcomere length (myofilament overlap) and discuss the amount of tension that results from changes in length. As the sarcomeres of a muscle fiber are stretched to a longer length, the zone of overlap shortens, and fewer myosin heads can make contact with thin filaments. Tension the fiber can produce decreases. As sarcomere lengths become shorter than the optimum, the tension that can develop again decreases because thick filaments crumble as they are compressed by Z discs and fewer myosin heads make contact with the thin filaments. When a skeletal muscle fiber is stretched 170% of its optimal length, there is no overlap between the thick and thin filaments. No myosin heads can bind, the muscle fiber cannot contract, and the tension is zero The Neuromuscular Junction 25. Show the general features of the neuromuscular junction that allows signals coming from the brain to be conveyed across the gap between the neuron motor cell and the sarcolemma of the muscle cell. Somatic Motor Neuron- has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibers. A muscle fiber contracts in response to one or more action potentials propagating along its sarcolemma and through its system of t tubules. Neuromuscular Junction- where muscle action potentials arise; the synapse between a somatic motor neuron and skeletal muscle fiber Synapse- a region where communication occurs between 2 neurons, or between a neuron and target cell—in this case, between a somatic motor neuron and a muscle fiber. Synaptic Cleft- separates the 2 interacting cells. Because the cells do not physically touch, the action potential cannot jump from one cell to another. Instead, the first cell communicates with the other by releasing a neurotransmitter. Axon terminal- divides into a cluster of synaptic end bulbs. Synaptic Vesicles- hundreds of membrane enclosed sacs that are suspended in the cytosol within each synaptic end. Acetylcholine- thousands of molecules inside the synaptic vesicle; release at the NMJ. Motor End Plate- region of the sarcolemma opposite of the synaptic end bulbs; muscle fiber part of NMJ Acetylcholine Receptors- integral transmembrane protein that are inside each motor end plate that bind specifically to ACh; abundant in junctional folds (deep grooves in the motor end plate that provide a large surface area for ACh; ligand- gated ion channels *** A neuromuscular junction includes all the synaptic end bulbs on one side of the synaptic cleft, plus the motor end plate of the muscle fiber on the other side. 26. Describe the steps and components in the mechanism that cause a motor neuron action potential to result in a muscle cell action potential. A huge amount of ATP is needed to power the contraction cycle, to pump calcium into the sarcoplasmic reticulum, and for other metabolic reactions involved in muscle contraction. Muscle fibers have 3 ways to produce ATP: 1) From creatine phosphate 2) anaerobic cellular respiration 3) aerobic cellular respiration 30. Describe the use of creatine phosphate in muscles to produce ATP. Excess ATP is used to synthesize creatine phosphate. Creatine phosphate is an energy-rich molecule found only in muscle fibers. The enzyme creatine kinase (CK) catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine phosphate and ADP. Creatine phosphate is 3-6 times more plentiful than ATP in sarcoplasm of a relaxed muscle fiber. When contraction begins and the ADP level starts to rise CK catalyzes the transfer of a high energy phosphate group from creatine phosphate back to ADP. This direct phosphorylation reaction quickly regenerates new ATP molecules. Together, creatine phosphate and ATP provide enough energy for muscles to contract maximally for about 15 secs. 31 Discuss the pros and cons of creatine supplementation. 32. Describe the chemical fate of pyruvic acid coming out of the anaerobic glycolysis pathway and its dependence on the rate of oxygen supply and energy demand. Glycolysis quickly breaks down each glucose molecule into 2 molecules of pyruvic acid. These reactions use 2 molecules of ATP but produce 4, for a net gain of 2 molecules of ATP. Ordinarily, the pyruvic acid formed by glycolysis in the cytosol enters mitochondria, where it undergoes a series of oxygen-requiring reactions called aerobic cellular respiration that produce a large amt of ATP. Together, conversion of creatine phosphate and glycolysis can provide plenty of ATP (enough for 400-meter race). 33. Describe the chemical fate of lactic acid when exercise has ceased and oxygen is being delivered as fast as it is needed (aerobic metabolism) If not enough oxygen is available, anaerobic reactions (a series of oxygen- requiring reactions that produce ATP in the mitochondria. If sufficient oxygen is present, pyruvic acid enters the mitochondria, where it is completely oxidized in reactions that generate ATP, carbon dioxide, water, and heat. ***Slower than glycolysis, but produces more ATP (about 100 molecules)) convert most of the pyruvic acid to lactic acid in cytosol. About 80% of lactic acid produced diffuses out of skeletal muscle fibers into the blood. Liver cells can convert it back to glucose and reduce acidity of blood and provide 30-40 secs of maximal muscle activity. 34. Discuss the relative durations of time that each form of ATP production provides for sustained activity. I ALREADY DID!!!!!!!!!!! Muscle Fatigue 35. Discuss the major known factors that cause muscle fatigue. Central fatigue- caused by changes in central nervous system (brain and spinal cord). Inadequate release of calcium ions from SR, resulting in decline of calcium concentration in sarcoplasm Depletion of creatine phosphate’ however, ATP levels in fatigued muscle are not much different than levels in resting muscle. Insufficient oxygen Depletion of glycogen and other nutrients Buildup of lactic acid and ADP Failure of action potentials in motor neuron to release enough acetylcholine Oxygen Consumption after Exercise 36. Define recovery oxygen uptake (oxygen debt) and discuss the purpose of the elevated use of oxygen after exercise. Refers to added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise. The extra oxygen is used to pay back/restore metabolic conditions to resting level in 3 ways: (1) convert lactic acid back into glycogen stores in liver (2) resynthesize creatine phosphate and ATP in muscle fibers (3) replace oxygen removed from myoglobin CONTROL OF MUSCLE TENSION 37. Since each muscle fiber can only contract fully when stimulated, list the events that allow the muscle as a whole to produce varying levels of tension. Unfused (incomplete) tetanus- when skeletal muscle fiber is stimulated at a higher rate of 80-100 times per second, it does not relax at all. Infused (complete) tetanus- a sustained contraction in which individual twitches cannot be detected. Wave summation and both kind of tetanus occur when additional calcium is released by SR by subsequent stimuli while the levels of calcium in sarcoplasm are still elevated by the stimulus. Because of the buildup of the calcium level, the peak tension generated during fused tetanus is 5-10 times larger than the peak tension produced in a single twitch. Smooth, sustained voluntary muscle contractions are achieved mainly by out-of-synch unfused tetanus in diff motor units. The stretch of elastic components (tendons and connective tissues) affects wave summation. During wave summation, elastic components are not given much time to spring back b/t contractions and remain extended. The elastic comp don’t require much stretching before the next contraction. The combination of the extension of the elastic comp and partially contracted state of the filaments enables the force of another contraction to be greater than the one before it. 41. Indicate the means by which complete and incomplete tetanus are elicited and the resulting force of the fiber. ANSWER ABOVE, STUPID!!!!! Motor Unit Recruitment 42. Discuss the effects, on contraction force, of increasing the number of active motor units. Motor Unit Recruitment- process in which the number of active motor units increases While some motor units contract, others relax. This pattern of motor unit activity delays muscle fatigue and allows contraction of a whole muscle to be sustained for long periods. The weakest motor units are recruited first, with progressively stronger motor units added if the task requires more force. 43. Describe the benefits of and differences between aerobic and strength training. Muscle Tone 44. Define muscle tone and note how it normally works in body posture maintenance. Muscle Tone- a small amount of tension in the muscles due to weak, involuntary contractions of its motor units; Muscle tone is established by neurons in brain and spinal cord that excites the muscle’s motor neurons; To sustain muscle tone, small groups of motor units are alternatively active and inactive in a constantly shifting pattern. Muscle tone keeps skeletal muscles firm, but it does not result in a force strong enough to produce movement. 45. Define hypotonia and hypertonia and describe the symptoms. Isotonic and Isometric Contractions 46. Compare and contrast isotonic and isometric contractions. Isotonic Contractions- the tension developed by the muscle remains almost constant while the muscle changes its length. Used for body movements and for moving objects. Cocentric Isotonic- if tension generated is enough to overcome the resistance of the object to be moved, the muscle shortens and pulls on another structure (such as a tendon) to produce movement and to reduce the angle at a joint. Eccentric Isotonic- when the length of a muscle increases during a contraction. The tension exerted by the myosin crossbridge resists movement of an object and slows the lengthening process. Repeated eccentric isotonic contractions produce more muscle damage and more muscle soreness. Isometric Contraction- the tension generated IS NOT enough to exceed the object to be moved, and the muscle does not change length. Important for maintain posture and for supporting objects in a fixed position. Although these contractions do not result in body movement, energy is still expended. TYPES OF SKELETAL MUSCLE FIBERS 47. Describe the structural and functional characteristics that allow skeletal muscle to be classified into three main types. Composition: Myoglobin- high amt and appear dark (red muscle fibers); contain more mitochondria and are supplied by more blood capillaries. EXERCISE AND SKELETAL MUSCLE TISSUE 52 Discuss the role of genetics in the relative ratio of fast-twitch and slow-twitch fibers in each muscle and how this ratio may account for individual differences in physical performance. The relative ratio of FG (short and intense workouts) and SO (endurance) fibers in each muscle is genetically determined and helps account for individual differences in physical performance. 53 Examine how various types of exercise can induce changes in the fibers in skeletal muscle. Endurance exercises result in cardiovascular and respiratory changes that cause skeletal muscles to receive better supplies of oxygen and nutrients but do not increase muscle mass. Increase in size is due to thick and thin filaments 54 Describe the consequences of taking anabolic steroids. Liver cancer, kidney disease, risk of heart disease, stunted growth, mood swings, acne, irritability and agression CARDIAC MUSCLE TISSUE 55. Compare and contrast differences in cardiac and skeletal muscle cell structure and physiology. Have same arrangement of actin and myosin and the same bands, zones, and Z discs. However, cardiac muscle fibers have intercalated discs- irregular transverse thickenings of sarcolemma that connect the ends of cardiac muscle fibers to one another. Contain desmosomes which holds the fibers together Contain gap junctions which allow muscle action potentials to spread from one cardiac fiber to another. Lacks epimysium Cardiac muscle tissue remains contracted 10-15 times longer than skeletal muscle tissue. Cardiac- calcium enters sarcoplasm from SR and interstitial fluid. The channels stay open a long time and cause the contraction to last longer than a skeletal muscle twitch. Cardiac muscle contracts when stimulated by its own autorhythmic muscle fibers, unlike skeletal muscle’s need for acetylcholine More mitochondria in cardiac Cardiac muscle fibers also use lactic acid produced by skeletal muscle fibers to produce ATP 56 Discuss the cardiac cellular components that sustain the continuous aerobic metabolism and uninterrupted, protracted autorhythmicity. Contracts and relaxes about 75 times a minute SMOOTH MUSCLE TISSUE 57. Indicate the differences between single-unit and multiunit smooth muscle in terms of their function and organs of the body where each predominates. Single unit (visceral) smooth muscle- found in tubular arrangements that form parts of walls of small arteries and veins and hollow organs; autorhythmic; fibers connect by gap junctions, forming a network through which action potentials can spread. When an autorhythmic signal stimulates one fiber, the muscle action potential is transmitted to neighboring fibers, which then contract as a single unit. Multiunit Smooth Muscle Tissue- consists of individual fibers, each w/ its own motor neuron terminals and w/ few gap junctions; stimulation of one fiber causes contraction of that one fiber only, unlike visceral smooth muscle; found in walls of large arteries, airway to lungs, arrector pili muscles, muscles of the iris, and ciliary body in lens of the eye. Microscopic Anatomy of Smooth Muscle 58 Compare skeletal and smooth muscle cells with respect to organelles, cytoskeleton, and contractile filaments. Smooth Muscle Fibers- thickest in the middle and it tapers at each end; each fiber has a single, oval centrally located nucleus; contains thick and thin filaments, not arranged in orderly sarcomeres; contain intermediate filaments; no striations; lack t tubules and have small amt of SR for storage of calcium; thin filaments attach to dense bodies (similar to Z discs); during contraction the sliding filament mechanism involving thick and thin filaments generates tension that is transmitted to intermediate filamentspull on dense bodies attached to sarcolemma causing a system. These columns of mesoderm undergo segmentation into a series of cube- shaped structures called somites. Cardiac muscle develops from mesodermal cells that migrate to and envelop the developing heart. Smooth muscle develops from mesodermal cells that migrate to and envelop the developing gastrointestinal tract and viscera. Somites- 1st pair appears on 20th day of embryonic development. 42-44 pairs by end of 5th week. Number of somites can be correlated to apprx age of embryo. Differentiate in 3 regions: Myotome-forms skeletal muscles of head, neck, and limbs Dermatome- forms connective tissues, including dermis Sclerotome- gives rise to vertebrae AGING AND MUSCULAR TISSUE 64. Describe the sources of muscle mass loss and alteration of fiber composition with progressive age. Slow progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue due to decreased levels of physical activity. Decrease in maximal strength, slower muscle reflexes, loss of flexibility. Relative number of SO fibers appears to increase. DISORDERS: HOMEOSTATIC IMBALANCES 65. Discuss the origin, symptoms, characteristics, and treatment of myasthenia gravis, muscular dystrophy, and abnormal contractions of skeletal muscle. MEDICAL TERMINOLOGY 66. Define the medical terminology associated with muscle tissue. Muscle strain- tearing of muscle b/c forceful impact Myalgia- pain assoc w/ muscles Myoma- tumor of muscle tissue Myomalacia- pathological softening of muscle tissue Myositis- inflammation of muscle fibers Myotonia- increased muscular excitability Volkmann’s contracture- permanent shortening of muscle due to replacement of destroyed muscle fibers by fibrous connective tissue. Typically occurs in forearm flexor muscles