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Chapter 6

Chapter 6. The Muscular System. Introduction. Muscular tissue enables the body and its parts to move Movement caused by ability of muscle cells (called fibers ) to shorten or contract

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Chapter 6

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  1. Chapter 6 The Muscular System

  2. Introduction • Muscular tissue enables the body and its parts to move • Movement caused by ability of muscle cells (called fibers) to shorten or contract • Muscle cells shorten by converting chemical energy ATP (obtained from food) into mechanical energy, which causes movement • Three types of muscle tissue exist in the body

  3. Muscle Tissue • Types of muscle tissue (F 6-1) • Skeletal muscle—also called striated or voluntary muscle • Is 40% to 50% of body weight (“red meat” attached to bones) • Microscope reveals crosswise stripes or striations • Contractions can be voluntarily controlled

  4. Muscle Tissue • Cardiac muscle—composes bulk of heart • Cardiac muscle cells branch frequently • Characterized by unique dark bands called intercalated disks- coordinate contraction • Interconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit

  5. Muscle Tissue • Smooth Muscle- Nonstriated muscle or involuntary muscle—also called smooth or visceral muscle • Lacks cross stripes or striation when seen under a microscope; appears smooth • Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters • Contractions not under voluntary control; movement caused by contractions is involuntary • Function—all muscle cells specialize in contraction (shortening)

  6. Structure of Skeletal Muscle • Structure • Each skeletal muscle is an organ composed mainly of skeletal muscle cells and connective tissue • Most skeletal muscles extend from one bone across a joint to another bone • Muscles have a fixed origin and a movable insertion attached by tendons

  7. Structure of Skeletal Muscle • Parts of a skeletal muscle (F 6-2) • Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs • Insertion—point of attachment to the bone that moves when a muscle contracts • Body—main part of the muscle

  8. Structure of Skeletal Muscle • Muscles attach to the bone by tendons—strong cords of fibrous connective tissue; some tendons enclosed in synovial-lined tubes and are lubricated by synovial fluid; tubes called tendon sheaths • Bursae—small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones

  9. Structure of Skeletal Muscle • Microscopic structure (6-3) • Contractile cells called fibers—grouped into bundles • Fibers contain thick myofilaments (containing the protein myosin) and thin myofilaments (composed of actin)

  10. Structure of Skeletal Muscle • Basic functional (contractile) unit called sarcomere; sarcomeres separated from each other by dark bands called Z lines • Sliding filament model explains mechanism of contraction • Thick and thin myofilaments slide past each other as a muscle contracts • Contraction requires calcium and energy-rich ATP molecules

  11. Functions of Skeletal Muscle • Movement • Muscles produce movement; as a muscle contracts, it pulls the insertion bone closer to the origin bone; movement occurs at the joint between the origin and the insertion

  12. Functions of Skeletal Muscle • Groups of muscles usually contract to produce a single movement • Prime mover—muscle whose contraction is mainly responsible for producing a given movement • Synergist—muscle whose contractions help the prime mover produce a given movement • Antagonist—muscle whose actions oppose the action of a prime mover in any given movement

  13. Functions of Skeletal Muscle • Posture • A specialized type of muscle contraction, called tonic contraction, enables us to maintain body position • In a tonic contraction, only a few of a muscle’s fibers shorten at one time • Tonic contractions produce no movement of body parts

  14. Functions of Skeletal Muscle • Tonic contractions maintain muscle tone called posture • Good posture reduces strain on muscles, tendons, ligaments, and bones • Poor posture causes fatigue and may lead to deformity

  15. Functions of Skeletal Muscle • Heat production • Survival depends on the body’s ability to maintain a constant body temperature • Fever—an elevated body temperature; often a sign of illness • Hypothermia—a reduced body temperature • Contraction of muscle fibers produces most of the heat required to maintain normal body temperature

  16. Fatigue • Reduced strength of muscle contraction • Caused by repeated muscle stimulation • Repeated muscular contraction depletes cellular ATP store and outstrips the ability of the blood supply to replenish oxygen and nutrients

  17. Fatigue • Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness • Oxygen debt—term used to describe the metabolic effort to burn excess lactic acid that may accumulate during prolonged periods of exercise; the body is attempting to return the cells’ energy and oxygen reserves to pre-exercise levels

  18. Role of Other Body Systems in Movement • Muscle functioning depends on the functioning of many other parts of the body • Respiratory, circulatory, nervous, muscular, and skeletal systems play essential roles in producing normal movements • Multiple sclerosis, brain hemorrhage, and spinal cord injury are examples of how pathologic conditions in other body organ systems can dramatically affect movement

  19. Motor Unit (F 6-4) • Stimulation of a muscle by a nerve impulse is required before a muscle can shorten and produce movement • A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction

  20. Motor Unit (…Cont’d) • A neurotransmitter junction is the specialized point of contact between a nerve ending and the muscle fiber it innervates • A motor unit is the combination of a motor neuron with the muscle cell or cells it innervates

  21. Muscle Stimulus • A muscle will contract only if an applied stimulus reaches a certain level of intensity • A threshold stimulus is the minimal level of stimulation required to cause a muscle fiber to contract • Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called all or none • (Cont’d…)

  22. Muscle Stimulus (…Cont’d) • Different muscle fibers in a muscle are controlled by different motor units having different threshold-stimulus levels • Although individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does not • Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force

  23. Types of Skeletal Muscle Contraction p.117 • Twitch and tetanic contractions • Twitch contractions are laboratory phenomena and do not play a significant role in normal muscular activity; they are a single contraction of muscle fibers caused by a single threshold stimulus • Tetanic contractions are sustained and steady muscular contractions caused by a series of stimuli bombarding a muscle in rapid succession ex. muscle spasms, cramps, & some seizures

  24. Types of Skeletal Muscle Contraction • Isotonic contractions • Contraction of a muscle that produces movement at a joint • During isotonic contractions, the muscle changes length, causing the insertion end of the muscle to move relative to the point of origin • Most types of body movements such as walking and running are caused by isotonic contractions

  25. Types of Skeletal Muscle Contraction • Isometric contractions (F 6-5) • Isometric contractions are muscle contractions that do not produce movement; the muscle as a whole does not shorten • Although no movement occurs during isometric contractions, tension within the muscle increases

  26. Effects of Exercise on Skeletal Muscles • Exercise, if regular and properly practiced, improves muscle tone and posture, results in more efficient heart and lung functioning, and reduces fatigue

  27. Effects of Exercise on Skeletal Muscles • Effects of Exercise on Skeletal Muscles • Muscles undergo changes related to the amount of work they normally do • Prolonged inactivity causes disuse atrophy • Regular exercise increases muscle size, called hypertrophy (cont’d)

  28. Effects of Exercise on Skeletal Muscles • Strength training is exercise involving contractions of muscles against heavy resistance • Strength training increases the numbers of myofilaments in each muscle fiber, and as a result, the total mass of the muscle increases • Strength training does not increase the number of muscle fibers

  29. Effects of Exercise on Skeletal Muscles • Endurance training is exercise that increases a muscle’s ability to sustain moderate exercise over long periods; it is sometimes called aerobic training • Endurance training allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow • Endurance training does not usually result in muscle hypertrophy

  30. Skeletal Muscle Groups • Muscles of the head and neck (F 6-7) • Facial muscles • Orbicularis oculi • Orbicularis oris • Zygomaticus

  31. Skeletal Muscle Groups • Muscles of mastication • Masseter • Temporal • Sternocleidomastoid—flexes head • Trapezius—elevates shoulders and extends head

  32. Skeletal Muscle Groups • Muscles that move the upper extremities • Pectoralis major—flexes upper arm • Latissimus dorsi—extends upper arm • Deltoid—abducts upper arm • Biceps brachii—flexes forearm • Triceps brachii—extends forearm

  33. Skeletal Muscle Groups • Muscles of the trunk • (F 6-8) • Abdominal muscles • Rectus abdominis • External oblique • Internal oblique • Transversus abdominis • Respiratory muscles • Intercostal muscles • Diaphragm

  34. Skeletal Muscle Groups • Muscles that move the lower extremities • Iliopsoas—flexes thigh • Gluteus maximus—extends thigh • Adductor muscles—adduct thighs • Hamstring muscles—flex lower leg • Semimembranosus • Semitendinosus • Biceps femoris

  35. Skeletal Muscle Groups • Muscles that move the lower extremities • Quadriceps femoris group—extend lower leg • Rectus femoris • Vastus muscles • Tibialis anterior—dorsiflexes foot • Gastrocnemius—plantar flexes foot • Peroneus group—flex foot

  36. Types of Movements Produced by Skeletal Muscle Contractions (F 6-9,10) • Flexion—movement that decreases the angle between two bones at their joint: bending • Extension—movement that increases the angle between two bones at their joint: straightening

  37. Types of Movements Produced by Skeletal Muscle Contractions (F 6-11) (…Cont’d) • Abduction—movement of a part away from the midline of the body • Adduction—movement of a part toward the midline of the body • Rotation—movement around a longitudinal axis • (Cont’d…)

  38. Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) • Supination and pronation—hand positions that result from rotation of the forearm; supination results in a hand position with the palm turned to the anterior position; pronation occurs when the palm faces posteriorly • (Cont’d…)

  39. Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) • Dorsiflexion and plantar flexion—foot movements; dorsiflexion results in elevation of the dorsum or top of the foot; during plantar flexion, the bottom of the foot is directed downward

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