Skeletal Muscle Review Sheet A&P 1 Name ______________________________________ 1. Name the 5 structures that the skeletal muscle are composed of from largest to smallest Muscle – fascicle – muscle fiber – myofibril – filaments 2. Identify the 3 layers of connective tissue found within muscles and tell what cover and what type of CT they are composed of. Epimysium – dense irregular connective tissue Perimysium – fibrous connective tissue Endomysium – reticular connective tissue 3. Describe the structure of a fascicle. A fascicle is surrounded by a layer of connective tissue called the perimysium. All of the fascicles of a muscle are held together by the epimysium. Inside the fascicle are thousands of muscle fibers, each separated from the others by the connective tissue of the endomysium. 4. Describe the role of each thin-filament protein and each thick-filament protein in muscle contraction.
Roles of muscle filament proteins: G actin – globular molecules with active sites for myosin head binding during contraction. F actin – 300-400 G actins twisted together into a strand. Nebulin – protein core supporting the an F actin strand. Tropomyosin – regulatory protein that blocks or exposes active sites on G actins. Troponin – bind tropomyosin to G actin and reacts with calcium ions causing tropomyosin to move and expose active sites for contraction. Myosin – golf-club shaped proteins of thick filaments. The heads bind to active sites on G actin then pull the thin filament toward the middle of the sarcomere. Titin – molecule attaching the ends of thick filaments to the Z line.
5. Describe the structure of a sarcomere. A sarcomere consists of thin and thick filaments arranged so they can slide over each other. The boundary of the sarcomere are the Z lines. Thin filaments extend from the Z lines and overlap with thick filaments in the middle of the sarcomere. The I band is on each side of the Z line where only thin filaments occur. The A band is the length of the thick filaments and is divided into three parts; the zone of overlap is on each end where thin and thick filaments occur, the H band is in the middle and has only thick filaments, and the M line is the center of the A band. 6. Write the name of the sarcomere structure defined below. A structure may be used more than once, and a definition may apply to more than one structure. a. length does not change when sarcomere shortens A-band b. area that is the length of thick filaments A-band c. length decreases when sarcomere shortens H-zone, I-band
d. e. f. g. h.
this area only contains thin filaments I-band this area only contains thick filaments H-zone this area contains overlapping thick and thin filaments A-band the area from Z disc to Z disc sarcomere this area disappears in a fully contracted muscle H-zone
7. Describe the structures and events of the neuromuscular junction. A motor neuron and all the skeletal muscle fibers it innervates are a motor unit. Within the muscle, the axon of a motor neuron divides into many branches or axon terminals, each which forms a neuromuscular junction with a skeletal muscle fiber. At the neuromuscular junction, each axon terminal divides into synaptic end bulbs. Within the synaptic end bulbs are synaptic vesicles filled acetylcholine. When a nerve impulse reaches the synaptic end bulb, acetylcholine is released and diffuses across the synaptic cleft. Acetylcholine molecules bind to receptors in the motor end plate, the region of the sarcolemma directly across from the synaptic end bulb. If enough acetylcholine binds, an action potential is generated, stimulating the skeletal muscle to contract. 8. What are the neurotransmitters found in the synaptic end bulbs of an axon terminal? acetylcholine 9. How does a motor neuron stimulate a muscle fiber to contract? When an action potential reaches the synaptic knob, the knob’s membrane becomes more permeable to extracellular calcium ions. Calcium diffuses into the knob and triggers the synaptic vesicles to release acetylcholine into the synaptic cleft. ACh binds to receptors on the sarcolemma and stimulates the muscle fiber to contract by sending an action potential through the T-tubules of the sarcolemma. 10. Why do muscles become very stiff (contracted) when rigor mortis occurs? ATP synthesis stops shortly after breathing stops and the cross-bridge detatchment becomes impossible. Actin and myosin become irreversibly cross-linked, producing the stiffness of rigor mortis, which then disappears as muscle proteins break down several hours after death. 11. Which type of muscle would fatigue faster, one that has many blood vessels, or one that has fewer blood vessels? A muscle with fewer blood vessels would fatigue faster. Muscles with more blood vessels would be able to make more ATP by aerobic respiration because of the increased amount of oxygen they receive. Anaerobic respiration produces lactic acid as a by product and produces less ATP than aerobic respiration, both causing a muscle to fatigue faster. 12. Distinguish between isometric and isotonic contractions. During an isometric contraction, the muscle stays the same length while the tension changes. Since the muscle’s length is relatively constant during the contraction, no movement of the body occurs. An isotonic contraction causes movement because the muscle shortens while tension is constant.
13. Which muscle groups work as synergists to extend the vertebral column? The longissimus and spinalis muscle groups work together to extend the head and vertebral column. 14. The anterior abdominal wall lacks bone. This being true, on what structure do the abdominal muscles insert? The muscles of the abdominal wall attach to strong fibrous connective tissues. The linea alba is midsagittal sheet of tissue dividing the rectus abdominis. The external, internal, and transverse abdominal muscles insert on the linea alba. 15. Which muscle group is the antagonist to the muscles of the hamstrings? The quadriceps femoris muscle group is antagonistic to the hamstrings. The vastus muscles and the rectus femoris extend the leg. The rectus femoris also flexes the thigh. 16. Why would a dislocated shoulder also potentially result in injury to the rotator cuff? The glenoid fossa of the scapula is a shallow depression that is surrounded by muscles of the rotator cuff to hold the humerus in position. A dislocated shoulder may include injury to the rotator cuff muscles and an unstable humerus at the ball and socket joint of the shoulder. 17. Identify the muscles of the head that you use when you whistle. orbicularis oris and buccinator 18. Identify the major thigh and leg muscles you use when you kick a ball. quadriceps femoris and tibialis anterior 19. Identify the forearm muscles you use when you turn a key in a lock. Supinator, biceps brachii, and pronotar teres 20. Identify the major arm muscles you use when you lift a glass to drink from it. biceps brachii, deltoid (anterior portion), brachioradialis and brachialis 21. Identify the neck muscles you use when you look both ways to cross a street. sternocleidomastoid 22. Identify the abdominal muscles you use when you do the “twist”. external and internal obliques 23. Identify the muscles used to bend the trunk when you touch your toes. Rectus abdominis
Matching ___I___ 1. sarcomere ___L__ 2. epimysium ___J___ 3. perimysium __H___ 4. endomysium __E___ 5. myofibril ___A__ 6. striations ___K__ 7. sarcolemma ___G__ 8. transverse tubule __B ___ 9. sarcoplasmic reticulum __C__ _10. actin ___F__ 11. myosin ___D__ 12. fascicle A. B. C. D. E. F. G. H. I. J. K. L. banding pattern in muscle tissue storage site for calcium ions protein of thin filaments group of muscle fibers cylinder composed of filaments protein of thick filaments carries action potentials deep into fiber connective tissue covering fiber repeating organization of filaments connective tissue covering fascicles cell membrane of muscle fiber connective tissue covering muscle
__E___ 1. glossal __B___ 2. cleido __H___ 3. scapularis __C___ 4. abductor __A___ 5. oris __K___ 6. brevis __F___ 7. adductor __G___ 8. oculi __D___ 9. vastus __L___10. rectus __I___11. tensor __J___12. capitis
A. mouth B. clavicle C. moves away D. great E. tongue F. moves toward G. eye H. scapula I. tenses J. head K. short L. straight