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The Muscular System

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The Muscular System • Muscles are responsible for all types of

body movement • Three basic muscle types are found in the

body Functions of Muscles • Produce movement • Maintain posture • Stabilize joints • Generate heat

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Characteristics of Muscles

• Muscle cells are elongated (muscle cell = muscle fiber)

• Contraction of muscles is due to the movement of microfilaments

• All muscles share some terminology – Prefix myo refers to muscle – Prefix mys refers to muscle – Prefix sarco refers to flesh

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Characteristics of Smooth Muscle

-Found in walls of visceral organs

-No striations

-Involuntary, controlled by nervous and endocrine systems

-Very slow, contractions, often rhythmic

Characteristics of Cardiac Muscle

-Heart only

-Branching chains of striated cells

-Involuntary, nervous and endocrine controlled

-Slow, rhythmic contractions

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Skeletal Muscle Characteristics

• Most are attached by tendons to bones • Cells are multinucleate (largest is 1 foot

long) • Striated – have visible banding • Voluntary – subject to conscious control • Cells are surrounded and bundled by

connective tissue

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Head and Neck Muscles

Figure 6.15

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Trunk Muscles

Deep Trunk and Arm Muscles

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Muscles of the Pelvis, Hip, and Thigh Muscles of the Lower

Leg

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Superficial Muscles: Anterior

Figure 6.21

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Superficial Muscles: Posterior

Figure 6.22

Workbook Coloring Assignment • Pg. 58 – 1,2,3,4,7,9,15,16,17,18 • Pg. 59 – 8,9,10,11 • Pg. 60 – 1,2,3,5,8,18,23,28,29,30 • Pg. 62&63 – 1,2,3,5,6,7,12,13 • Pg. 64 – 1,2,3 • Pg. 70 – 2,3,6,10 • Pg.72 – 1,4,5,6,7,9 • Pg.74 – 3,4,6,20,21,22,23,24 • Pg. 76 – 1,3,4,5,6,8,13,14,15,16

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Muscles and Body Movements • Movement is attained due

to a muscle moving an attached bone

• Muscles are attached to at least two points

– Origin – attaches to the less movable bone

– Insertion- attachment to the more movable bone

• Results of increased muscle use: increase in strength and smoothness

Figure 6.12

Muscle Movement

• prime mover (agonist) – primarily responsible for movement

• synergists – assist prime mover • antagonist – resist prime mover’s action

and cause movement in the opposite direction

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Joint and Muscle Actions

• Animation of Action – https://www.wisc-online.com/learn/natural-

science/life-science/ap12004/movement-terminology

• Definition and Examples of Action – http://www.ivyroses.com/HumanBody/Skeletal

/Joints/Joint-Movements.php

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Joint and Muscle Actions

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• Flexion: A movement by which the angle of a joint is decreased

• Extension: A movement by which the angle of a joint is increased

• Adduction: Movement toward the central axis • Abduction: Movement away from the central axis • Medial rotation: Rotation toward the medial side of the body • Lateral rotation: Rotation towards the lateral side of the body • Elevation: movement in a superior directions • Depression: movement in an inferior direction • Protraction: movement of body part in anterior direction • Retraction: movement of body part in posterior direction • Circumduction: conical movement of a limb extending from

the joint at which the movement is controlled. 16

Special movement of Hands and Feet

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• Pronation: This movement occurs in the forearm whereby the palm is turned backwards

• Supination: This movement also occurs in the forearm whereby the palm is turned

• Dorsiflexion: flexion of the foot • Plantar flexion: extension of the foot • Eversion: tilt the foot away from the midline • Inversion: tilt the foot towards the midline

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Connective Tissue Wrappings of Skeletal Muscle • Fascia – on the

outside of the epimysium

• Epimysium – covers the entire skeletal muscle

• Perimysium – surrounds several (bundle) of muscle fibers

• Endomysium – covers each muscle fiber

Figure 6.1

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Skeletal Muscle Attachments

• Epimysium blends into a connective tissue attachment – Tendon – cord-like structure – Aponeuroses – sheet-like structure

• Sites of muscle attachment – Bones – Cartilages – Connective tissue coverings

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Microscopic Anatomy of Skeletal Muscle • Cells are multinucleate • Nuclei are just beneath the sarcolemma • Sarcolemma – plasma membrane of a muscle

cell • Sarcoplasmic reticulum – (Endoplasmic

reticulum) stores calcium that is needed for muscle contraction

Figure 6.3a

22 Figure 6.3b

Microscopic Anatomy of Skeletal Muscle

Myofibril - organelle that fills muscle cells, made of bundles of myofilaments

• I band = light band • A band = dark band

– These give it a striped appearance.

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Microscopic Anatomy of Skeletal Muscle • Sarcomere – from z disc to z disc

– Contractile unit of a muscle fiber, when lined up form a myofibril

– Bundles of myofibrils = muscle cell

Figure 6.3b

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Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere

– Thick filaments = myosin filaments

– Thin filaments = actin filaments

Figure 6.3c

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Microscopic Anatomy of Skeletal Muscle • Myosin filaments have

heads (extensions, or cross bridges)

• Myosin and actin overlap somewhat

• At rest, there is a bare zone that lacks actin filaments

• Sarcoplasmic reticulum (SR) – for storage of calcium

Figure 6.3d

Stimulus for Contraction

9-10

• acetylcholine (ACh) 1. nerve impulse causes

release of acetylcholine from synaptic vesicles

2. binds to acetylcholine receptors on motor end plate

3. generates a muscle impulse 4. muscle impulse eventually

reaches sarcoplasmic reticulum

Excitation Contraction Coupling

9-11

5. muscle impulses cause sarcoplasmic reticulum to release calcium ions into cytosol

6. calcium binds to troponin to change its shape

7. position of tropomyosin is altered

8. binding sites on actin exposed

9. actin and myosin cross bridge bind

Sliding Filament Theory

9-12

• When sarcromeres shorten, thick and thin filaments slide past one another • H zones and I bands get narrower • Z lines move closer together

Cross-bridge Cycling

9-13

• actin and myosin cross-bridge bind • myosin cross-bridge pulls actin

•ADP and phosphate released from myosin

• new ATP binds to myosin • linkage between actin and myosin cross-bridge break •ATP splits

•myosin cross-bridge goes back to original position

Relaxation

9-14

• acetylcholinesterase – breaks down acetylcholine • muscle impulse stops • calcium moves back into sarcoplasmic reticulum • myosin and actin binding prevented

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Contraction of a Skeletal Muscle

• Muscle fiber contraction is “all or none” • Within a skeletal muscle, not all fibers may

be stimulated during the same interval • Different combinations of muscle fiber

contractions may give differing responses • Graded response is a variable response

depending upon the number of contracting muscle fibers in a muscle.

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Muscle Response to Strong Stimuli

• Muscle force depends upon the number of fibers stimulated

• More fibers contracting results in greater muscle tension

• Muscles can continue to contract unless they run out of energy

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Energy for Muscle Contraction

• Initially, muscles used stored ATP for energy

– Bonds of ATP are broken to release energy – Only 4-6 seconds worth of ATP is stored by

muscles • After this initial time, other pathways must

be utilized to produce ATP

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Energy for Muscle Contraction

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Muscle Fatigue and Oxygen Debt • When a muscle is fatigued, it is unable to

contract • The common reason for muscle fatigue is

oxygen debt

Oxygen Debt

9-17

• oxygen not available • glycolysis continues • pyruvic acid converted to lactic acid • liver converts lactic acid to glucose

Oxygen debt – amount of oxygen needed by liver to convert lactic acid to glucose

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