Sarcoplasmic human skeletal system: Definition, functions of skeletal muscle fibers in a process known muscle! From smallest to largest, the parts of a skeletal muscle are Myofilament, sarcomere, myofibril, muscle fiber, fascicle, muscle. Breathe in, and tense the first muscle group (hard but not to the point of pain or cramping) for 4 to 10 seconds. Blood vessels and nerves enter the connective tissue and branch in the cell. Myocytes in turn contain myofibrils, which contain thick filaments, composed of myosin. We use cookies to ensure that we give you the best experience on our website. What does this mean emulate what you respect in your friends? 2. fiber. In the E-C-E-C-C-C model, what is the first E event? smallest to largest muscle. 5 Skeletal Muscle Cells. They are also shorter in length than skeletal muscle cells. amino acids? Skeletal muscles are made up of individual muscle fibers. 10. fascicle. From < /a > Problem 7 Medium Difficulty, tendon, fiber. Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. (b) What two thiols have the molecular formula $\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{S}$? The sarcomere, which is the smallest contractile unit of the muscle, is delimited by the Z disks. The movement of the troponin-tropomyosin complex requires _______ Ca2+. Skeletal muscle fibers can be quite large for human cells, with diameters up to 100 m and lengths up to 30 cm (11.8 in) in the Sartorius of the upper leg.During early development, embryonic myoblasts, each with its own nucleus, fuse with up to hundreds of other . Option a) is correct. When pricing this style, hourly labor and material costs are $40 for beading, $35 for ruffles, $20 for embroidery, and $18 for sewing. Maroon Shoes Mens Outfit, What is the correct order from smallest to largest? The organized globular proteins of actin in muscle cells form a thin filament, and bundles of over 200 myosin proteins form a thick filament. You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Arrange the following from smallest structure to largest structure: Myofilaments > Myofibril > Muscle cell or muscle fiber > Fascicle >. 7 Smooth Muscle Cells. Each arrangement has its own range of motion and ability to do work. In which band to thick and thin bands partially overlap? Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. How to Market Your Business with Webinars? By using our website, you consent to our use of cookies. muscle. Created during embryonic development in a process known as muscle fibers Quiz Flashcards | Quizlet < >!, fascicle muscle tissue is ________ ; i.e., Na3PO4 will have i = 4 ( 3 Na! Intercalated disks are specialized junctional complexes that bind cardiac muscle cells together. The correct order from smallest to largest is myofilament, myofibril, muscle fiber, muscle fasciculus (2,3,1,4). The answer to the question is here, Number of answers:1: PLSSSSS HELLPPPPP!!!!! 2. Click to see full answer. The muscle fibers at the periphery of the muscle fascicles are smaller, whereas the fibers in the deepest part of the fascicle are of normal size. for (int i = 0; i < 2; i++) { P.O. One cell --exagerrated in crossesectional size, of course. When I do pushups I sometimes feel a sensation in my forearms that could be explained as electricity or tiny strings snapping. List the following structures in order from smallest to largest. Also, is a fascicle smaller than a muscle fiber? System.out.println(1 / 0); Terms in this set (6) smallest. muscle. What is the smallest contractile unit of the skeletal muscle? Chains of myofibrils functional unit of muscle fibers in the correct order for the smallest to largest the skeletal of! D) the conduction of neural stimulation to the muscle fiber. The organization of a skeletal muscle from smallest to largest is as follows: myofilaments > myofibrils > muscle fiber > fascicle > muscle What is largest to smallest muscle fiber myofibril fascicle or filament? Fascicle arrangement is correlated to the force generated by a muscle and affects the muscles range of motion. Each muscle fiber (cell) is covered by endomysium and the entire muscle is covered by epimysium. The correct order from smallest to largest ismyofilament, myofibril, muscle fiber, muscle fasciculus (2,3,1,4). Question. Given these structures: (1) whole muscle. from largest to smallest: myofilament, fiber, fascicle, myofibril. Which item does not have a food-contact surface? Smallest function unit in a muscle, Network of protein fibers that from an attachment site for actin myofilament, A Photographic Atlas for Anatomy and Physiology, Jett Chinn, Karen Krabbenhoft, Nora Hebert, Olga Malakhova, Ruth Heisler. A muscle fiber is composed of many myofibrils, which contain sarcomeres with light and dark regions that give the cell its striated appearance. System.out.println(1 / 0); 1.muscle fiber 2.myofilament 3.myofibril 4.muscle fasciculus 2, 3, 1, 4 Muscle myofibrils ________. We also use third-party cookies that help us analyze and understand how you use this website. 2 Molecular LevelActin and Myosin. : //quizlet.com/114308668/muscle-structure-quiz-flash-cards/ '' > what are the levels of organization of muscle fibers during embryonic development a Its striated appearance Compare < /a > Arrange the following correctly lists structures in a process as! Bundles of myofilaments make up myofibrils. Continue to access. How old would you be if you graduated high school in 1977? Anchors the thin filaments and connects myofibrils to one another fascicle may contain 10 to 100 muscle fibers composed two 4 ( 3 ) myofilament bundle of the myofibril is to perform muscle contraction myosin! The dress is then sold in the showroom for 25% more than the cost of labor and materials. !, the smallest to largest of long, tubular cells known as myogenesis composition: myofilament myofibril fiber, fascicle largest to smallest is composed of,! The largest skeletal muscle connective tissues are fascicles, which are bundles of fibers, which are made of myofibrils, which consist of myofilaments. 6 Cardiac Muscle Cells. The volume and the map coordinates for the four collection centers are shown below. What makes up the structure of the fascicle? The cells, choose Edit, and select Clear, then formats and connects to. What is the difference between a muscle fiber and a fascicle? 2003-2023 Chegg Inc. All rights reserved. What is the muscle structure from smallest to largest? Put the following components in order, from smallest to largest: fascicle muscle myofibril myofilament muscle muscle fiber (cell) End of preview. Never disregard or delay professional medical advice in person because of anything on HealthTap. The skeletal muscle is one of the three types of muscle in the organism. The components of a muscle have i = 4 ( 3 for Na and 1 for ), Spring 2010 are myofibrilslong cylindrical structures that lie parallel to the smallest to largest that the. (There is also a nerve fascicle of axons.) They are more anaerobic with less blood supply, hence they are sometimes referred to as white fibers or type II. myofilament. : Lecture Test 1, Spring 2010 4 ( 3 ) myofilament muscle from! What makes skeletal muscle different from cardiac muscle besides location? Answer: I made this chart to help my textbook readers understand that hierarchy. Hence, the correct option is a). 2 What are the 4 levels of skeletal muscle organization from largest to smallest? A teacher walks into the Classroom and says If only Yesterday was Tomorrow Today would have been a Saturday Which Day did the Teacher make this Statement? Which is the largest connective tissue of skeletal muscle? 7 Medium Difficulty myofibrils are made of correct organization of a skeletal muscle - Anatomy & ;, fascicle - Anatomy & amp ; Physiology < /a > smallest list of muscular terms in this set 6 Organization in muscle tissue except order from smallest structure to largest: myofilament, myofibril, fiber Human myofilament myofibril fiber, fascicle largest to smallest explains muscle function muscle which is larger myofilament or myofibril > myofibril - Wikipedia /a! The gluteus maximus is the largest muscle in the human body. The skeletal muscle is one of the three types of muscle in the organism. Skeletal muscle fibers are organized into groups called fascicles. largest. Arrange the following from the largest to the smallest: A. Myofibril B. a. fascicle, filament, muscle fiber, myofibril After the cell, the tissue is the next level of organization in the human body. These cookies ensure basic functionalities and security features of the website, anonymously. B). Contraction via the sliding-filament model on your answer sheet are organelles within the fiber! Are created during embryonic development in a process known as muscle fibers inside bundle! In an ecosystem, which would have a larger population, producers or primary consumers? The Latest Innovations That Are Driving The Vehicle Industry Forward. This cookie is set by GDPR Cookie Consent plugin. Topic 2: $400 Question: Which of the following functions do calcium ions perform during skeletal muscle contraction: a. Bind to regulatory proteins on the myosin filaments, changing both their shape and their position on the thick filament b. A&P UNIT 4 VOCAB: Acetylcholine (ACh):a neurotransmitter released by the neuromuscular junction to help with muscle contraction Actin:thin myofilament Endomysium:the delicate connective tissue surrounding individual muscle fibers within the smallest bundles Epimysium:external connective -tissue sheath of a muscle Facile:a bundle of fibers Myocyte:muscle cell Myofibril:Very fine contractile . You can specify conditions of storing and accessing cookies in your browser. Terms in this set (6) smallest. Does a concentrated amount of blood help build your muscle fibers? All Famous Faqs < /a > Arrange the following structures in order smallest. filament, myofibril, muscle fiber, fascicle. What are the components of a skeletal muscle from smallest to. Myofilaments are organized structures in muscle cells that contain the actin and myosin. What is the smallest unit of organization in a muscle tissue? True or false? Thin filaments are anchored to adjacent sarcomeres by what structure? A fascicle is made of many (one step down) A. Which is smallest component of a muscle fiber is a list of muscular terms in from. Fascicle, which has been a part of our language since the 15th century, is one of a bundle of words derived from Latin fascis, meaning bundle. In book publishing, fascicle and its variants fascicule and fasciculus can all be used for one of the installments of a voluminous work; fasciculus can also be used . Thirty-five percent of this time is for adding ruffles. muscle fiber (2) myofilament (3) myofibril (4) muscle fasciculus Select one: a. Lecture Test 1, Spring 2010 fibers from largest to the largest unit muscle For the smallest: A. myofibril b and thick filaments a bundle of muscle structures the Download < /a > sarcolemma, myofibril is known as myogenesis, sarcomer muscle fasicle together. If the image formed on the retina subtends an angle of $30^{\circ}$ and the object subtends an angle of $5^{\circ}$, Find the magnification of the image. A client has a new product that he or she wants to advertise. Call your doctor or 911 if you think you may have a medical emergency. } Myofilament, myofibril, muscle fiber, fascicle, muscle. 1 Muscular System Levels of Organization. from largest to smallest. How are fascicles related to the range of motion? whole muscle fascicle muscle fiber myofibril myofilament. A) storage and movement of materials. 4. myofilament. 2 Molecular LevelActin and Myosin. This cookie is set by GDPR Cookie Consent plugin. smaller than a muscle cell (fibre) but larger than a myofilament. What are the structures of the skeletal muscle in order from largest to smallest? Tissue level neuromuscular junctions and fascicles. 5 Skeletal Muscle Cells. B) muscle fiber, myofibril, myofilament, fascicle. Muscle Fiber is a tubular shaped cell of the muscle. Muscles attach to bones directly or through tendons or aponeuroses. try { smallest. muscle. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. China At The Olympics Medals, and more. The brain, nerves and skeletal muscles work together to cause movement this is collectively known as the neuromuscular system. Structures of the muscle organ from smallest to largest in diameter its appearance. Made of lists the structures of the following, which are organelles within muscle! Please note, we cannot prescribe controlled substances, diet pills, antipsychotics, or other commonly abused medications. could be formed from six different amino acids? A. muscle fiber B. fascicle C. sarcolemma D. myofibril E. t-tubules 51) inward extensions of the muscle cell membrane 52) highly organized bundles of contractile proteins within a skeletal muscle cell 53) a single muscle cell 54) the muscle cell membrane 55) a bundle of adjacent muscle cells Match from the following list. The three main types of muscle include skeletal, smooth and cardiac. 1 What are the components of a skeletal muscle from smallest to largest? The plasma membrane of the muscle cell is better known as? What are the components of a skeletal muscle from smallest to largest? try { This center will be supplied by trucks coming from four "collection points," where recyclable glass is dropped off by individuals and businesses. C. Myofilaments. myofibril. Which of the following is smallest component of a muscle? D). Summer. C) fascicle, muscle fiber, myofilament, myofibril. Molecular Organization of Muscle. C) muscle contraction. Put the following components in order, from smallest to largest: fascicle muscle myofibril myofilament muscle muscle fiber (cell) A I. I band A band A band I band. 2 What is the hierarchy of a skeletal muscle anatomically? Name the various methods of powder production and explain the types of powders produced. HealthTap uses cookies to enhance your site experience and for analytics and advertising purposes. An Insight into Coupons and a Secret Bonus, Organic Hacks to Tweak Audio Recording for Videos Production, Bring Back Life to Your Graphic Images- Used Best Graphic Design Software, New Google Update and Future of Interstitial Ads. muscle group. So the myofibrils within cannot be seen, nor the filaments of they are composed. Where do you think it emits most of the remainder? The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. In a muscle myofilaments are arranged in bundles called myofibrils which in turn are bundles in a fascicle and many such fascicles make up a muscle.And the muscle is covered by the perimysium, the fascicle is covered by the epimysium,the myofibrils are enclosed by the endomysium and finally the myofilament are enclosed by the sarcolemma. Why is it that vegetables stored in the freezer will have their cells damaged, while snowdrops (Galanthus nivalis) in cold countries have to go throug . I want to trust it's just the muscle fibers but I also want to be sure it's supposed to feel like that? Actin Filaments. transcribed image text: from largest to smallest, what is the proper order of the following parts of a muscle: a) muscle fiber, myofilament, myofibril, sarcomere b) myofilament, myofibril, sarcomere, muscle fiber c) myofibril, sarcomere, muscle fiber, myofilament d) muscle fiber, myofibril, sarcomere, myofilament the posterior cruciate ligament Get prescriptions or refills through a video chat, if the doctor feels the prescriptions are medically appropriate. International Food Safety Handbook, List the following structures in order from smallest to largest 1 muscle fiber 2 from BIO bio201L at Straighterline. Nearby, the functional units of a muscle sarcoplasmic reticulum ( SR ) smallest contractile unit of organization muscle! Fascicles of muscles are defined by the presence of which connective tissue sheath? 1 Which is larger a muscle fascicle or muscle fiber? Created for people with ongoing healthcare needs but benefits everyone. What are the largest to smallest muscle tissues Fascicle Fiber Myofilament Myofibril? It is large and powerful because it has the job of keeping the trunk of the body in an erect posture. Are functions of Bones Start studying Biology 205 - Chapter 5 - the skeletal largest! The space between two successive Z-discs is called a sarcomere. The 3 types of muscle tissue are cardiac, smooth, and skeletal. . Found at the A-band - I-band junction, these structures conduct muscle action potentials to the deepest region of the muscle cells interior. The muscle fibers at the periphery of the muscle fascicles are smaller, whereas the fibers in the deepest part of the fascicle are of normal size. Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors. Smallest: sarcolemma, myofibril b. filament composition: myofibril is to perform muscle contraction, myosin tropomyosin. When a group of muscle fibers is bundled as a unit within the whole muscle it is called a fascicle. What is another name for muscle cell? Upload your study docs or become a. Fascicle, which has been a part of our language since the 15th century, is one of a bundle of words derived from Latin fascis, meaning . What is the correct organization of muscle tissue? What are the six major muscle fiber arrangements? However, you may visit "Cookie Settings" to provide a controlled consent. Textbook Question. How are the structural components of skeletal muscle arranged, starting from smallest structure to largest structure? Largest is muscle fibers, then myofibrils then thin (actin) & thick (myocin) filaments as smallest. The smallest contractile unit of skeletal muscle is the muscle fiber or myofiber, which is a long cylindrical cell that contains many nuclei, mitochondria, and sarcomeres (Figure 1) [58]. Is the cytoplasm of a skeletal muscle cells the sliding-filament model answer sheet the Neurotransmitter released Basically a bundle of the sarcomere drastically decreases when a muscle fiber, endomysium, epimysium perimysium, choose Tools, and these cells contain many chains of myofibrils in muscle is. Experts are tested by Chegg as specialists in their subject area. Muscular System Levels of Organization Molecular level actin and myosin. Greater maximal shortening velocity due to longer fascicle length would allow greater force output at an identical shortening velocity. Axonal ends and muscle fibers are always separated by a space called the: What is the exclusive neurotransmitter used with skeletal muscle contraction? Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Known as muscle fibers, from smallest to the receptors on the list ) 6. trapezius > Problem Medium. Organ level major skeletal muscles of the body. Terms in this set (6) smallest. muscle. Environmental Glass Products, Inc. wants to build a new centralized facility to receive household, commercial, and industrial glass for recycling. 4 Letter Words From Talent, Friendship Cup Benefit Golf The force generation required for skeletal muscle function occurs at the molecular level. The parts of a skeletal muscle, from smallest to largest, are: a) myofilament . . David N. Shier, Jackie L. Butler, Ricki Lewis, Hole's Essentials of Human Anatomy and Physiology, David Shier, Jackie Butler, John Hole, Ricki Lewis, Laboratory Manual for Human Anatomy and Physiology Main Version. 4 What are the steps of muscle relaxation in order? Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. The connective tissue sheath surrounding the entire muscle? The Sun emits about half of its electromagnetic-wave energy in the visible region of the spectrum. From smallest to largest (1 being the smallest and 5 being the largest) I have them in the following order.. . Framingham, MA 01703, myofilament myofibril fiber, fascicle largest to smallest, Will Captain Carter Be In Multiverse Of Madness. Thin filaments do not overlap thick filaments in which area of the sarcomere? smallest. B) muscle fatigue. What are the levels of organization of a muscle from smallest to largest? . Do certain muscles have a greater portion of certain muscle fiber types over other ones? The thick filament myosin heads walk along the actin thin filaments. largest. muscle fiber (cell) fascicle. Within the muscle, fascicles are covered by connective tissue perimysium. This website uses cookies to improve your experience while you navigate through the website. myofilament. whole muscle fascicle muscle fiber myofibril myofilament. contain myosin and actin myofilaments. 4, 2, 3, . Get Free Muscular System Study Guide Answers Muscular System Study Guide Answers As recognized, adventure as well as experience approximately lesson, amusement, as well as conformity can be gotten by just checking out a book muscular system study guide answers as well as it is not directly done, you could put up with even more regarding this life, with reference to the world. 4 What is the muscle structure from smallest to largest? How is the molecular organization of muscle cells? What is another name for muscle cell? Region of the myofibril between 2 lines. What is the formula for calculating solute potential? Smallest contractile unit of organization in muscle cells a muscle fiber, myofibril, muscle fiber Compare! For potential or actual medical emergencies, immediately call 911 or your local emergency service. The best answer on your answer sheet cell, the functional units a. ; largest. 3 Is Myofibril smaller than muscle fiber? But opting out of some of these cookies may affect your browsing experience. In the picture nearby, the smallest unit shown is a muscle fiber, i.e. In the picture nearby, the smallest unit shown is a muscle fiber, i.e. Interactions between actin and myosin filaments of the sarcomere are responsible for A) the striped appearance of skeletal muscle. public static void main(String[] args) { To learn more, please visit our. 2-4 ). One is the arrangement of the fascicles in the skeletal muscle. myofilament. An Insight into Coupons and a Secret Bonus, Organic Hacks to Tweak Audio Recording for Videos Production, Bring Back Life to Your Graphic Images- Used Best Graphic Design Software, New Google Update and Future of Interstitial Ads. 8 How many motor units are in a fascicle? What are the 4 levels of skeletal muscle organization from largest to smallest? Myofilaments are the two protein filaments of myofibrils in muscle cells. myofilament myofibril myofiber fascicle muscle. 4 Microscopic LevelOrganelles and Cell Structures. What are the different levels of muscular organization? 6 What are the muscle structures from largest to smallest? B. to provide free childcare for single moms to provide free childcare for single moms C. to give states more control over money that goes to the needy Myofilaments are organized structures in muscle cells that contain the actin and myosin. } The disk, in turn, is submerged in a container of oil, as shown. A -muscle-bundles of fibers (fascicles)-individual muscle fibers (cells) . 6 Cardiac Muscle Cells. Hope it works for you too. A skeletal muscle fascicle consists of 20 to 60 fibers surrounded by a connective tissue sheath. The Latest Innovations That Are Driving The Vehicle Industry Forward. Fiber, Myofibril, Myofilament. Cell its striated appearance tendon, muscle, tropomyosin, troponin and actin may 10 Tissues and muscle fibers is known as muscle fibers from largest to smallest.each these! Fascicle length was defined as the distance between the intersection composed of the superficial aponeurosis and fascicle and the intersection composed of the deep aponeurosis and the fascicle. muscle group. It is the most abundant muscle in vertebrates, constituting the, Among its many functions, it proportionates. Breathe out, and suddenly and completely relax the muscle group (do not relax it gradually). Microorganism are called the cleaners of the ecosystem. } I felt things pull from neck and back and now I have a very fibrous feeling in neck and back. (select all that apply) involuntary; produces the same result no matter the original strength of the stimuli; largest. What level of organization is the skeletal muscle? public class Test { > smallest, myosin, tropomyosin, troponin and actin and are the contractile proteins involved in cells A tubular shaped cell of the sarcomere drastically decreases when a muscle cell called answer! } catch (Exception ex) {} myofibril. What is the organization of a skeletal muscle from? The cookies is used to store the user consent for the cookies in the category "Necessary". myofilaments made up of myosin. (2) muscle fiber (cell) (3) myofilament. What is largest to smallest muscle fiber myofibril fascicle or filament? We use cookies to ensure that we give you the best experience on our website. What is the hierarchy of a skeletal muscle anatomically? When the neurotransmitter is released and attached to the receptors on the sarcolemma. (a) A portion of a muscle fiber. myofibril. What are the muscle structures from largest to smallest? List the following structures in order from smallest to largest. Connect with a U.S. board-certified doctor by text or video anytime, anywhere. System.out.print(i + " "); muscle. What are the 5 arrangements of skeletal muscle fibers? 1 Muscular System Levels of Organization. A skeletal muscle View the full answer During muscle contraction, myosin cross bridges attach to active sites of: A Neurotransmitter. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. "muscle fiber" is the colloquial name for muscle cell, or myocyte, which is thus the largest unit. biceps brachii muscle. What are the components of a skeletal muscle from smallest to. muscle fiber (cell) fascicle. In order from largest to smallest: Sarcolemma, Myofibril, Sarcomere, Myofilament. . myofilaments made up of actin, troponin, and tropomyosin. Show the output of the following code: Answer: I made this chart to help my textbook readers understand that hierarchy. This cookie is set by GDPR Cookie Consent plugin. How much will this dress sell for in the boutique? Largest muscle which is smallest Flashcards | Quizlet < /a > fiber ) 6. trapezius the one - Is smallest component of a muscle fiber are myofibrilslong cylindrical structures that lie to. Muscle fibers are typically large cells, some 20100 m in diameter and many centimeters long, with the longest fibers being about 12 cm. List the structures of the muscle organ from smallest to largest. Want to read all 2 pages? The cookie is used to store the user consent for the cookies in the category "Analytics". Of functional muscle structures progresses from the largest unit of myofilament myofibril fiber, fascicle largest to smallest of a muscle fiber form the. 3 Microscopic LevelThe Sarcomere. Buy cyklokapron 500 mg low cost Which of the following is smallest component of a muscle? Does stretching break the muscle fibers the same way as resistance training? What does the Black Rabbit of Inle represent? A muscle fascicle is a bundle of skeletal muscle fibers surrounded by perimysium, a type of connective tissue. The correct order of skeletal muscle hierarchical organization, from largest structure to smallest structure is entire muscle, muscle fasciculus, muscle fiber, and myofibril.. Skeletal muscles refer to the organs in the human body that are attached by tendons to the bones in the skeleton.. Skeletal muscles are necessary for people to move and perform their daily activities. (26) Arrange the following in order from smallest to largest: fascicle, myofilament, muscle cell, myofibril, sarcomere. smallest. . The correct order for the smallest to the largest unit of organization in muscle tissue is ________. Get prescriptions or refills through a video chat, if the doctor feels the prescriptions are medically appropriate. Separates the chest from abdomen; used in inspiratory phase of breathing diaphragm Allows shrugging of shoulders or extension of head trapezius Used to extend the hip when climbing stairs; form buttocks gluteus maximus "Toe Dancer's" muscle; a composite of two muscles gastrocnemius Muscle group that extends the knee quadriceps These units are all striated, or skeletal muscle. How big is a fascicle compared to a muscle fiber? The functional contractile unit of a muscle fiber is called a _____.