Chapter 9Muscular System

9-2

Three Types of Muscle Tissues

Skeletal Muscle• • •

Smooth Muscle• • •

Cardiac Muscle• • •

Structure of a Skeletal Muscle

9-3

Skeletal Muscle• organ of the muscular system• skeletal muscle tissue• nervous tissue• blood• connective tissues• fascia• tendon

Structure of a Skeletal Muscle

9-4

• • • •

• muscle• fascicles• muscle fibers• myofibrils• thick and thin filaments

Skeletal Muscle Fiber

9-5

• sarcolemma• sacroplasm• • • triad

• cisterna of sarcoplasmic reticulum• transverse tubule

• myofibril• • • sarcomere

Sarcomere

9-6

• I band• A band• H zone• Z line• M line

Myofilaments

9-7

Thick Filaments • •

Thin Filaments• • associated with troponin and tropomyosin

Muscle 3.mov

Neuromuscular Junction

9-8

• site where axon and muscle fiber communicate• • motor end plate• • synaptic vesicles•

Motor Unit

• •

9-9

Stimulus for Contraction

9-10

• acetylcholine (ACh)• • binds to acetylcholine receptors on motor end plate• •

Muscle 2.mov

Excitation Contraction Coupling

9-11

•

• • position of tropomyosin is altered•

•

Sliding Filament Theory

9-12

• When sarcromeres shorten, thick and thin filaments slide past one another• •

Cross-bridge Cycling

9-13

•

• myosin cross-bridge pulls actin

•ADP and phosphate released from myosin

•

• linkage between actin and myosin cross-bridge break

•ATP splits

• Muscle 4.mov0010.exe

Relaxation

9-14

• acetylcholinesterase –

• •

Muscle 4.mov

Energy Sources for Contraction

9-15

• creatine phosphate –

1) Creatine phosphate 2) Cellular respiration

Oxygen Debt

9-17

• oxygen not available• glycolysis continues•

• liver converts lactic acid to glucose

Oxygen debt –

Muscle Fatigue

9-18

• • commonly caused from

• decreased blood flow• •

• cramp –

Heat Production

9-19

• by-product of cellular respiration• muscle cells are major source of body heat• blood transports heat throughout body

Muscular Responses

9-20

Threshold Stimulus•

Recording a Muscle Contraction

• twitch• latent period• period of contraction• period of relaxation• refractory period• all-or-none response

Summation

9-21

• process by which individual twitches combine• produces sustained contractions• can lead to tetanic contractions

Recruitment of Motor Units

9-22

• recruitment -

• whole muscle composed of many motor units

• as intensity of stimulation increases, recruitment of motor units continues until all motor units are activated

Sustained Contractions

9-23

• smaller motor units recruited first• larger motor units recruited later• • muscle tone –

Types of Contractions

9-24

• isotonic – • concentric –

• eccentric – • isometric –

Fast and Slow Twitch Muscle Fibers

9-25

Slow-twitch fibers (type I)• • • • most myoglobin• good blood supply

Fast-twitch glycolytic fibers (type II)• • •

Fast-twitch fatigue-resistant fibers (type IIb)

• intermediate fibers• •

•

Smooth Muscle Fibers

9-26

Compared to skeletal muscle fibers• • single nucleus• elongated with tapering ends• myofilaments randomly organized• • lack transverse tubules• sarcoplasmic reticula not well developed

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

9-29

• • 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

Skeletal Muscle Actions

9-30

• 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

Major Skeletal Muscles

9-31

Major Skeletal Muscles

9-32

Life-Span Changes

9-65

• 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

Clinical Application

9-66

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