Chapter 7 The Muscular System Mosby items and

INTRODUCTION • Muscular tissue enables the body and its parts to move • Three types of muscle tissue exist in body (see Chapter 3) • Movement caused by muscle cells (called fibers): shortening or contracting • Muscle movement occurs when chemical energy (obtained from food) is converted into mechanical energy Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 2

MUSCLE TISSUE • Types of muscle tissue (Figure 7 -1) • Skeletal muscle—also called striated or voluntary muscle • Microscope reveals crosswise stripes or striations • Contractions can be voluntarily controlled • Cardiac muscle—composes bulk of heart • Cardiac muscle fibers are branched • Has dark bands called intercalated disks • Cardiac muscle fiber interconnections allow heart to contract efficiently as a unit Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 3

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MUSCLE TISSUE (cont. ) • Types of muscle tissue (cont. ) • Nonstriated muscle, or involuntary muscle—also called smooth or visceral muscle • Lacks cross stripes or striations when seen under a microscope; appears smooth • Found in walls of hollow structures, such as digestive tract, blood vessels, etc. • Contractions not under voluntary control • Function—all muscle fibers specialize in contraction (shortening) Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 5

STRUCTURE OF SKELETAL MUSCLE • Muscle organs—mainly striated muscle fibers and connective tissue Connective tissue forms “wrappers” around each muscle fiber, around fascicles (groups) of muscle fibers, and around the entire muscle; fascia surrounds muscle organs and nearby structures Ø Most skeletal muscles extend from one bone across a joint to another bone Ø Regions of a skeletal muscle (Figure 7 -2) Ø • 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 6

STRUCTURE OF SKELETAL MUSCLE (cont. ) Ø Muscle organs (cont. ) • Muscles attach to bone by tendons— tendons strong cords or sheets of fibrous connective tissue that extend from the muscle organ; some tendons enclosed in synovial-lined tubes (tendon sheaths) and are lubricated by synovial fluid • Bursae— Bursae small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 7

STRUCTURE OF SKELETAL MUSCLE (cont. ) • Muscle organs (cont. ) • Microscopic structure and function (Figure 7 -3) • Contractile cells are called muscle fibers; connective tissue holds muscle fibers in parallel groupings • Fibers of the cytoskeleton form cylinders that contain thick myofilaments (containing myosin) and thin myofilaments (containing mainly actin) • 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 to contract • Contraction requires calcium and energy-rich ATP molecules (Figure 7 -4) Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 9

FUNCTIONS OF SKELETAL MUSCLE • Movement • Muscles produce movement by pulling on bones as a muscle contracts • The insertion bone is pulled closer to the origin bone • Movement occurs at the joint between the origin and the insertion • Groups of muscles usually contract to produce a single movement • • • Prime mover—mainly responsible for producing a given movement Synergist—helps the prime mover produce a given movement Antagonist—opposes the action of a prime mover in a given movement Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 12

FUNCTIONS OF SKELETAL MUSCLE (cont. ) • Posture • A continuous, low-strength muscle contraction called tonic contraction (muscle tone) enables us to maintain body position • • • Only a few of a muscle's fibers shorten at one time Produce no movement of body parts Maintain muscle tone called posture • Good posture favors best body functioning • Skeletal muscle tone maintains good posture by counteracting the pull of gravity Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 13

FUNCTIONS OF SKELETAL MUSCLE (cont. ) • 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 14

FUNCTIONS OF SKELETAL MUSCLE (cont. ) • Fatigue • Reduced strength of muscle contraction • Caused by repeated muscle stimulation without adequate periods of rest • Repeated muscular contraction depletes cellular ATP stores and outstrips the ability of the blood supply to replenish oxygen and nutrients • Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness • Oxygen debt—term used to describe the metabolic effort required to burn excess lactic acid that may accumulate during prolonged periods of exercise • Labored breathing after strenuous exercise is required to “pay the debt” • This increased metabolism helps restore energy and oxygen reserves to preexercise levels Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 15

ROLE OF OTHER BODY SYSTEMS IN MOVEMENT • Muscle functioning depends on the functioning of many other parts of the body • Most muscles cause movements by pulling on bones across moveable joints • 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 pathological conditions in other body organ systems can dramatically affect movement Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 16

MOTOR UNIT • 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 • Neuromuscular junction (NMJ)—point of contact between a nerve ending and the muscle fiber • Motor unit—combination of a motor neuron with the muscle fibers it controls (Figure 7 -6) Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 17

MUSCLE STIMULUS • A muscle will contract only if an applied stimulus reaches a certain level of intensity • Threshold stimulus—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 • 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 19

TYPES OF SKELETAL MUSCLE CONTRACTION • Twitch and tetanic contractions • Twitch contractions are laboratory phenomena and not normal muscle activity; they are a single contraction of muscle fibers caused by a single threshold stimulus • Tetanic contractions are sustained muscular contractions caused by stimuli hitting a muscle in rapid succession Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 20

TYPES OF SKELETAL MUSCLE CONTRACTION (cont. ) • Isotonic contractions • Contractions that produce movement at a joint because the muscle changes length • Concentric contractions—the muscle shortens at the insertion end of the muscle to move toward the point of origin • Eccentric contractions—the muscle lengthens under tension, thus moving the insertion away from the origin • Most types of body movements (walking, running, etc. ) are produced by isotonic contractions Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 21

TYPES OF SKELETAL MUSCLE CONTRACTION (cont. ) • Isometric contractions • Contractions that do not produce movement; the muscle as a whole does not shorten • Although no movement occurs, tension within the muscle increases Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 22

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 • Muscles change in relation to the amount of work they normally do • Prolonged inactivity causes disuse atrophy • Regular exercise increases muscle size, called hypertrophy Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 23

EFFECTS OF EXERCISE ON SKELETAL MUSCLES (cont. ) • Strength training is exercise involving contraction of muscles against heavy resistance • Strength training increases the number 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 24

EFFECTS OF EXERCISE ON SKELETAL MUSCLES (cont. ) • Endurance training is exercise that increases a muscle’s ability to sustain moderate exercise over a long period; 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 25

MOVEMENTS PRODUCED BY SKELETAL MUSCLE CONTRACTIONS (Figures 7 -7 through 7 -9) • • Flexion—decreases an angle Extension—increases an angle Abduction—away from the midline Adduction—toward the midline Rotation—around an axis Circumduction—move distal end of a part in a circle Supination and pronation—hand positions that result from twisting the forearm • Dorsiflexion and plantar flexion—foot movements (upward and downward ankle movement) • Inversion and eversion—foot movements (sideways) Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 26

SKELETAL MUSCLE GROUPS (Table 7 -1) • Muscles of the head and neck (Figures 7 -10 and 7 -11) • Facial muscles • • • Orbicularis oculi Orbicularis oris Zygomaticus • Muscles of mastication • Masseter • Temporal • • Sternocleidomastoid—flexes head Trapezius—elevates shoulders and extends head Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 30

SKELETAL MUSCLE GROUPS (cont. ) • 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 Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 34

SKELETAL MUSCLE GROUPS (cont. ) • Muscles of the trunk (Figure 7 -12) • Abdominal muscles • • Rectus abdominis External oblique Internal oblique Transversus abdominis • Respiratory muscles • Intercostal muscles • Diaphragm Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 35

SKELETAL MUSCLE GROUPS (cont. ) • Muscles that move the lower extremities • • Iliopsoas—flexes thigh Gluteus maximus—extends thigh Adductor muscles—adduct thighs Hamstring muscles—flex lower leg • Semimembranous • Semitendinosus • Biceps femoris • Quadriceps femoris group—extend lower leg • Rectus femoris • Vastus muscles • Tibialis anterior—dorsiflexes foot • Gastrocnemius—plantar flexes foot • Peroneus group—flex foot Mosby items and derived items © 2012 by Mosby, Inc. , an affiliate of Elsevier Inc. Slide 37