Chapter 9 Muscular System Three Types of Muscle Tissues Cardiac Muscle Skeletal Muscle Smooth Muscle 9-2

Structure of a Skeletal Muscle organ of the muscular system skeletal muscle tissue nervous tissue blood connective tissues fascia tendon 9-3

Structure of a Skeletal Muscle fascicles muscle fibers myofibrils thick and thin filaments 9-4

Skeletal Muscle Fiber sarcolemma sacroplasm triad myofibril sarcomere cisterna of sarcoplasmic reticulum transverse tubule myofibril sarcomere 9-5

Sarcomere I band A band H zone Z line M line 9-6

Myofilaments Muscle 3.mov Thin Filaments Thick Filaments associated with troponin and tropomyosin Thick Filaments Muscle 3.mov 9-7

Neuromuscular Junction site where axon and muscle fiber communicate motor end plate synaptic vesicles 9-8

Motor Unit 9-9

Stimulus for Contraction acetylcholine (ACh) binds to acetylcholine receptors on motor end plate Muscle 2.mov 9-10

Excitation Contraction Coupling position of tropomyosin is altered 9-11

Sliding Filament Theory When sarcromeres shorten, thick and thin filaments slide past one another 9-12

Cross-bridge Cycling Muscle 4.mov 0010.exe myosin cross-bridge pulls actin ADP and phosphate released from myosin linkage between actin and myosin cross-bridge break ATP splits Muscle 4.mov 0010.exe 9-13

Relaxation acetylcholinesterase – Muscle 4.mov 9-14

Energy Sources for Contraction 1) Creatine phosphate 2) Cellular respiration creatine phosphate – 9-15

Oxygen Debt Oxygen debt – oxygen not available glycolysis continues liver converts lactic acid to glucose 9-17

Muscle Fatigue commonly caused from decreased blood flow cramp – 9-18

Heat Production by-product of cellular respiration muscle cells are major source of body heat blood transports heat throughout body 9-19

Muscular Responses Threshold Stimulus Recording a Muscle Contraction twitch latent period period of contraction period of relaxation refractory period all-or-none response 9-20

Summation process by which individual twitches combine produces sustained contractions can lead to tetanic contractions 9-21

Recruitment of Motor Units whole muscle composed of many motor units as intensity of stimulation increases, recruitment of motor units continues until all motor units are activated 9-22

Sustained Contractions smaller motor units recruited first larger motor units recruited later muscle tone – 9-23

Types of Contractions isotonic – concentric – isometric – eccentric – 9-24

Fast and Slow Twitch Muscle Fibers Slow-twitch fibers (type I) most myoglobin good blood supply Fast-twitch fatigue-resistant fibers (type IIb) intermediate fibers Fast-twitch glycolytic fibers (type II) 9-25

Smooth Muscle Fibers Compared to skeletal muscle fibers single nucleus elongated with tapering ends myofilaments randomly organized lack transverse tubules sarcoplasmic reticula not well developed 9-26

Smooth Muscle Contraction Resembles skeletal muscle contraction interaction between actin and myosin both use calcium and ATP both depend on impulses Different from skeletal muscle contraction smooth muscle lacks troponin two neurotransmitters affect smooth muscle stretching can trigger smooth muscle contraction 9-28

Cardiac Muscle muscle fibers joined together by intercalated discs fibers branch network of fibers contracts as a unit self-exciting and rhythmic longer refractory period than skeletal muscle 9-29

Skeletal Muscle Actions origin – insertion – prime mover (agonist) – primarily responsible for movement synergists – assist prime mover antagonist – resist prime mover’s action and cause movement in the opposite direction 9-30

Major Skeletal Muscles 9-31

Major Skeletal Muscles 9-32

Life-Span Changes myoglobin, ATP, and creatine phosphate decline by age 80, half of muscle mass has atrophied adipose cells and connective tissues replace muscle tissue exercise helps to maintain muscle mass and function 9-65

Clinical Application Myasthenia Gravis autoimmune disorder receptors for acetylcholine on muscle cells are attacked weak and easily fatigued muscles result difficulty swallowing and chewing ventilator needed if respiratory muscles are affected treatments include drugs that boost acetylcholine removing thymus gland immunosuppressant drugs antibodies 9-66