Human Anatomy and Physiology - Problem Drill 09: The Muscular System

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1 Human Anatomy and Physiology - Problem Drill 09: The Muscular System Question No. 1 of 10 The muscular system of the human body fulfills many different roles. Which of the following statements about the muscular system is correct? Question #01 A. There are 4 different types of muscle in the body. B. Skeletal muscles are the chief muscles found in internal organs. C. Cardiac muscle is in the heart and in the blood vessels in the periphery. D. Skeletal muscles support soft tissues such as the organs in the abdominal cavity. E. The entrance and exits of the digestive tract are regulated by the opening and closing of smooth muscle. There are three types of muscle in the body: skeletal, cardiac and smooth. Smooth muscles are the chief muscles found in internal organs. Cardiac muscle is found only in the heart, the blood vessels contain smooth muscle. D. Correct! Skeletal muscles of the abdominal wall do support the organs of the abdominal cavity. The entrance and exits of the digestive tract are regulated by the opening and closing of skeletal muscle. There are three types of muscles: (1) skeletal muscles, which are attached to bone and responsible for voluntary movement; (2) smooth muscles, which are the chief muscles found in internal organs and blood vessels, and perform involuntary movement; and (3) cardiac muscle, which is found only in the heart and is responsible for contraction of the heart and generation of blood pressure. Skeletal muscles produce the movements of the limbs and the entire body, through muscular contraction which delivers forces through tendons to move bones. Skeletal muscles also maintain body posture such as in a sitting or standing position. The position of the head on the neck, or the position of an arm or leg is also a result of skeletal muscle function. Skeletal muscles also support soft tissues, such as the organs in the abdominal cavity. These organs are supported in the cavity and protected by the skeletal muscle of the abdominal wall. The entrance and exits of the internal tracts such as the digestive tract, are regulated by the opening and closing of circular skeletal muscles. Additionally, because muscle contractions produce heat, skeletal muscles produce and help to maintain the internal body temperature.

2 Question No. 2 of 10 The entire skeletal muscle is surrounded by a special connective tissue. What is the name of that connective tissue covering: Question #02 A. Endomysium. B. Epimysium. C. Myoblast layer. D. perimysium. E. T tubules. The endomysium wraps around each individual muscle fiber. B. Correct! The epimysium is a dense, irregular connective tissue that covers the entire skeletal muscle and separates it from the surrounding tissues and organs. The epimysium covers the skeletal muscle, myoblasts differentiate into muscle cells. The perimysium groups the muscle into compartments that include the fascicles. The epimysium is the skeletal muscle covering; the T tubules are a network that extends into the sarcoplasm. Skeletal muscles are arranged in bundles of fibers, known as fascicles. The fascicle is wrapped in the perimysium. The perimysium is a connective tissue fiber that groups the muscle into compartments that contain the fascicles. Around the entire skeletal muscle is the epimysium, which is a dense, irregular connective tissue that separates the muscle from the surrounding tissue and organs. The endomysium is wrapped around each muscle fiber that supports connections to other fibers and provides support for the capillaries.

3 Question No. 3 of 10 Which of the following statements is correct about the portion of a muscle fiber, labeled in the image below? A Question #03 A. The T tubules are identified in the image. B. These proteins produce the energy required for muscle contraction. C. The letter A identifies a component of the muscle fiber that is approximately 1-2 µm in diameter and extends the length of the muscle cell. D. The Sarcoplasmic reticulum is identified in the image. E. This portion is not directly involved in the contraction of muscle. The letter A identifies the myofibrils; the T tubules are on top of the myofibrils. The myofibrils consume ATP to facilitate muscular contraction. C. Correct! The letter A does identify the myofibrils, which are approximately 1-2 µm in diameter and extend the length of the muscle cell. The letter A identifies the myofibrils; the Sarcoplasmic reticulum is where the calcium is sequestered between muscle contractions. This portion the myofibrils, is directly involved in muscular contraction as it contains the sarcomeres. Within the sarcoplasm of the muscle fiber are myofibrils. The myofibrils are approximately 1-2 µm in diameter and extend the length of the muscle cell. These myofibrils are made up of thick and thin filaments that are responsible for the contraction of the muscle fibers. The myofilaments consist of thick and thin filaments, known as actin and myosin. The bundles of myofilaments are organized into units, known as sarcomeres.

4 Question No. 4 of 10 A 55-year-old man is diagnosed with a disease in which a mutated gene results in the absence of the A band and all of its contents from the sarcomeres in his skeletal muscles. Based on this information, which of the following statements is correct? Question #04 A. This disease would lead to the absence of the attachment point for the thick filaments. B. The Z line would be absent as a consequence of this disease. C. The attachment point for the thin filaments would be absent in this disease. D. The disease would result in the absence of the component of the sarcomere that normally moves inward during the contraction of the sarcomere. E. This patient s disease, would lead to the absence of the actin binding sites. A. A. Correct! The A band contains the M line, which is the attachment point for the thick filaments. The Z line is located within the I band of the sarcomere. The attachment point for the thin filaments is the Z disc, which is located in the I band. The Z lines move closer together during contraction of the sarcomere. Myosin binds to actin to form the cross-bridge prior to contraction. A sarcomere is made up of thick and thin filaments; these produce the banding patterns, known as striations. This arrangement can be seen in the image above, which depicts the overlap that occurs during muscular contraction. The thin filaments are made of actin and the thick filaments are made of myosin. The A band is the darkest of the bands and it encompasses the thick filament. Within the A band is the lighter region, known as the H zone. Within the H zone, there is a dark line known as the M line, which is the attachment site for the thick filaments. The other band is called the I band. This is the region occupied by the thin filaments. Within the I band is the Z disc, which is the attachment site for thin filaments. A sarcomere is from Z line to Z line. In the relaxed state, the actin binding sites are completely blocked by troponin, and the associated tropomyosin. When calcium is released into the fiber, it binds to troponin. This makes the actin-binding sites available. Next, myosin binds to actin and forms a cross-bridge. Binding triggers a hinge-like movement by myosin, pulling the thin filament inward.

5 Question No. 5 of 10 An individual undergoes a muscle biopsy during a work-up for a generalized muscle weakness. The biopsy revealed a deficiency in the medium (fast-twitch oxidative) fibers. Based on this information which of the following is correct? Question #05 A. The patient has a deficiency in the muscle fibers with the largest diameter. B. The medium fibers have a short contraction duration. C. The fibers that are affected in this patient, fatigue easily. D. Only A is correct. E. Both A and C are correct. The fibers that are affected in this patient are medium diameter in size. B. Correct! The medium fibers do have a short contraction duration. The medium fibers that are affected in this patient, are fatigue-resistant. Answer choice A is incorrect. Both answer choice A and C are incorrect.

6 Question No. 6 of 10 The skeletal muscles of the body have different patterns of arrangement of their fascicles. Which of the following is correct about muscle fiber arrangement is correct? Question #06 A. The muscle that open and closes the eyelids is an example of a muscle with a circular pattern. B. The deltoid muscle would be an example of a parallel muscle pattern. C. There are six different patterns of muscle fiber arrangement. D. The arrangement of the muscle fiber plays no role in the function of the muscle. E. The biceps brachii is an example of a muscle with a convergent pattern of its fibers. A. Correct! Muscles with a circular pattern of fibers, open and close orifices and openings in tracts of the body such as the digestive tract. The deltoid muscle is an example of a convergent pattern, which is a muscle with a broad origin that converges to a narrow insertion. There are four different patterns of muscle fiber arrangement in the body. The arrangement of the muscle fibers directly affects the function of the muscle. For example, a circular pattern is perfectly suited for closing the opening of an orifice. The biceps brachii is an example of a muscle with a parallel pattern of muscle fibers. Muscle fibers are arranged into bundles, called fascicles. The pattern of fascicles affects muscle strength and motion. Skeletal muscle fibers are arranged in 4 distinct patterns: (A) Parallel, (B) Circular, (C) Convergent and (D) Pennate. In a parallel muscle, the fascicles are parallel with the longitudinal axis of the muscle, such as the biceps brachii muscle. This pattern represents the majority of the muscles in the body. If the muscle is attached to cord-like tendons, the central body is called the belly or gaster. The body of a parallel muscle, such as the biceps brachii, increases as the muscle is flexed. This is the muscle bulge visible as one flexes their biceps. In circular muscles, the fascicles are arranged in a circular pattern and enclose an orifice. An example is the orbicularis oculi muscle that surrounds the eye socket. As the circular muscle contracts, the opening or orifice it surrounds decreases. These muscles function at the entrances and exits of internal tracts, such as the digestive and urinary tracts. A convergent muscle contains the fascicles in a broad origin that converges to a narrow insertion. An example includes the deltoid muscle of the shoulder. In general, convergent muscles may pull a tendon, a tendinous sheet or a slender band of collagen fibers. In a pennate muscle, the fascicles are short in relation to the entire length of the muscle, and the tendons extend almost the entire length of the muscle. An example is the extensor digitorum longus muscle of the shin area.

7 Question No. 7 of 10 Which of the following statements about a muscle contraction is correct? Question #07 A. The force of the stimulation, not the stimulation pulse rate determines the total number of fibers that contract within a skeletal muscle. B. A muscle twitch is the complete contraction of the muscle in a calcium independent manner. C. Summation occurs when there is no rest between action potentials. D. A muscle twitch is an instant response; there is not latent period prior to the contraction of the muscle. E. The stimulation rate does not affect muscle contraction. The total amount of fibers that contract within a skeletal muscle depend on the stimulation pulse rate it receives. A muscle twitch is calcium dependent and at the end of it the calcium is pumped back into the Sarcoplasmic reticulum. C. Correct! Summation does occur when there is no rest between action potentials. There is a latent period prior to the onset of the contraction phase of a twitch. The stimulation rate does affect muscle contraction, if the rate is to infrequent the muscle will twitch and relax. The total amount of fibers that contract within a skeletal muscle depend on the stimulation pulse rate it receives. In order to recruit the entire muscle into contraction, a sufficient number and intensity of stimuli is required. If a single stimulus activates the muscle, it will twitch and relax. This occurs because Ca2+ is rapidly pumped back into the sarcoplasmic reticulum. Repetitive stimulation is necessary to activate the muscle into a complete contraction (tetanus) and to generate the necessary force to complete the task. Summation occurs when there is no rest between action potentials.

8 Question No. 8 of 10 Which of the following statements about muscle fatigue is correct? Question #08 A. Fatigue is a condition in which the muscle is no longer able to generate or sustain power. B. Fatigue is a condition in which the muscle can only generate an average amount of power. C. The intensity of the activity the muscle is used for does not impact muscle fatigue. D. This fitness level of the individual, but not the ATP source used by the muscle, has an effect on muscle fatigue. E. None of the answers is correct. A. Correct! Fatigue is a condition in which the muscle is no longer able to generate or sustain power. Fatigue is a condition in which the muscle is no longer able to generate or sustain power. The intensity of the activity the muscle is used for does contributes to muscle fatigue. Both the fitness level of the individual and the ATP source used by the muscle, effect muscle fatigue. Answer A is correct. Fatigue is a condition in which muscle is no longer able to generate or sustain power. It is influenced by the intensity and duration of an activity, type of ATP source, composition of muscle, and the fitness of an individual. Central fatigue includes the subjective feeling of tiredness and a desire to cease activity. In other words, the will to continue exercising is lost!

9 Question No. 9 of 10 Muscles require energy to perform work. Which of the following statements about the energy sources for muscle contraction is correct? Question #09 A. The energy used for muscular contraction must be produced in an aerobic environment. B. Phosphocreatine is produced in muscles at rest. C. Phosphocreatine is combined with ATP to form ADP. D. The ATP stores in muscle fibers can provide enough energy for the muscles to contract for approximately 8 minutes. E. None of the answers are correct. Muscle fibers shift to anaerobic glycolysis when O 2 is low. B. Correct! Phosphocreatine is produced in muscles at rest. When a muscle is at rest, it takes ATP from creatine and uses it to make phosphocreatine. The amount of ATP within the muscle fiber is only sufficient for about eight twitches. Answer b is correct. Muscles require energy constantly. The amount of ATP within the muscle fiber is only sufficient for about eight twitches. Muscles contain phosphocreatine which is a molecule that has high energy phosphate bonds created from creatine and ATP when the muscles are at rest. Muscle also contains an enzyme called creatine kinase. This enzyme transfers the phosphate group. Muscle fibers shift to anaerobic glycolysis when O 2 is low. When a muscle is at rest, it takes ATP from creatine and uses it to make phosphocreatine. When the muscle is at work, it uses the phosphocreatine and ADP to make ATP with the help of creatine kinase.

10 Question No. 10 of 10 Skeletal muscles are capable of both isotonic and isometric contractions. Which of the following statements about these types of contractions is correct? Question #10 A. An isotonic contraction does not result in the movement of the load. B. A concentric action is a lengthening contraction. C. Eccentric action is a lengthening contraction. D. An isometric contraction creates force and movement. E. An isotonic contraction is characterized by a dynamic tension, while the muscle s length remains the same. An isotonic contraction is any contraction that creates force and moves a load. A concentric action is a shortening contraction. C. Correct! Eccentric action, is a lengthening contraction (exerts a force while lengthening). Isometric contractions create force without movement. An isotonic contraction is any contraction that creates force and moves a load. It is characterized by a steady tension, while the muscle s length changes. An isotonic contraction is any contraction that creates force and moves a load. It is characterized by a steady tension, while the muscle s length changes. There are two types of isotonic contractions: Concentric action is a shortening contraction; the external force on the muscle is less than the force the muscle is generating. Eccentric action A lengthening contraction (exerts a force while lengthening); the absolute tension achieved can be very high relative to the muscle s maximum tension capacity. For example, you can set down a heavier object than you can lift. Isometric contractions create force without movement. An example would be picking up a weight and holding it stationary in front of you. This is due to elastic fibers in the connective tissue, attached to the muscle.