Muscular System Chapter 8

Introduction Muscles are responsible for movement –Contraction & relaxation Muscles make up 40 – 50 % of a human’s total body weight

Characteristics of Muscle Tissue Excitability –Can receive & respond to stimuli Contractility –Can shorten & thicken Extensibility –Can be stretched Elasticity –Can return to its original shape

Functions of Muscle Tissue Motion Maintenance of posture Heat production

Kinds of Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth Muscle

The Muscular System Muscle tissue = all contractile tissue Muscular system = –Skeletal muscle tissue –Connective tissue

Human Anatomy, 3rd edition Prentice Hall, © 2001 Skeletal Muscle Tissue Fascia –Sheet or band of fibrous connective tissue around muscles and other organs Fascia of skeletal muscle –Surrounds muscle –Subdivides muscle

Human Anatomy, 3rd edition Prentice Hall, © 2001 Structural Organization of Skeletal Muscle

Human Anatomy, 3rd edition Prentice Hall, © 2001 Tendons Cord of connective tissue that attaches a muscle to the periosteum of a bone Extensions of fascia

Human Anatomy, 3rd edition Prentice Hall, © 2001 Nerve & Blood Supply Each skeletal muscle is well-supplied with nerves and blood vessels –Related to contraction Contraction requirements –Stimulation by impulse from a nerve cell –Energy –Waste products eliminated

Human Anatomy, 3rd edition Prentice Hall, © 2001 Skeletal Muscle Fiber Muscle fibers = elongated cells –Sarcolemma –Sarcoplasm –Sarcoplasmic reticulum –T tubules Muscle fibers consist of myofibrils Extend length of fiber

Human Anatomy, 3rd edition Prentice Hall, © 2001 Histology of Skeletal Muscle Tissue Myofibrils consist of myofilaments - proteins that cause contraction –Thick filaments –Thin filaments

Human Anatomy, 3rd edition Prentice Hall, © 2001 Myofilaments Myofilaments do not extend entire length of fiber. Stacked in compartments = sarcomeres

Human Anatomy, 3rd edition Prentice Hall, © 2001 Thick and Thin Filaments Thin filaments –Composed mostly of actin –Contain tropomyosin and troponin –Double-stranded coil Thick filaments –Composed mostly of myosin –Rod-shaped (tail) with head Cross bridges

Human Anatomy, 3rd edition Prentice Hall, © 2001 Contraction – Sliding Filament Theory Thin filaments slide inward Sarcomere shortens Lengths of myofilaments do not change Sliding of myofilaments and shortening of sarcomeres causes the shortening of muscle fibers

Human Anatomy, 3rd edition Prentice Hall, © 2001 Neuromuscular Junction Contraction requires a stimulus from a neuron An axon comes into close contact with a muscle membrane = neuromuscular junction Small vesicles in end of axon release acetylcholine (Ach) Acetylcholine transmits nerve impulse to the muscle fiber –Initiates contraction

Human Anatomy, 3rd edition Prentice Hall, © 2001 Physiology of Contraction – Relaxed Muscle Sarcoplasm is low in calcium ATP is bound to myosin cross bridges Tropomyosin- troponin complex is attached to actin

Physiology of Contraction – Muscle is Stimulated –Nerve impulse reaches neuromuscular junction –Neuron releases ACh –Electrical charge travels along sarcolemma –Electrical charge travels down T tubules –Electrical charge travels to S.R. –S.R. releases calcium into sarcoplasm

Physiology of Contraction – Activation of Myosin Calcium binds to troponin –Frees receptor sites of actin for myosin cross bridge Cross bridges attach to actin Calcium acts as an enzyme –Breaks down ATP to ADP + P Myosin cross bridges move Sarcomere shortens Muscle shortens

Physiology of Contraction – Relaxation of Muscle Nerve impulse ends ACh is broken down by acetylcholinesterase Calcium is actively transported back into S.R. ADP + P = ATP –Binds to cross bridges Myosin cross bridges separate from actin Binding sites on actin are covered Thin myofilaments slip back to resting position Sarcomeres return to resting length Muscle fiber returns to resting length

Human Anatomy, 3rd edition Prentice Hall, © 2001 Physiology of Contraction

Disorders Fibrosis Fibrositis Fibromyalgia Muscular dystrophy Myasthenia gravis

Abnormal Contractions –Spasm –Cramp –Convulsion –Fibrillation –Tic

Anatomy of the Muscular System

How Skeletal Muscles Produce Movement Exert force on tendons Attached to articulating bones forming a joint When muscle contracts, one bone moves toward the other Attachments –Origin = attachment to stationary bone –Insertion = attachment to moveable bone –Belly = fleshy portion of muscle between tendons

Group Actions Agonist or prime mover –Causes desired action Antagonist –Effect is opposite to agonist Synergist –Assists agonist

Naming of Skeletal Muscles Direction of muscle fibers Location Size Number of origins Shape Origin & insertion Action

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Anterior Trunk and Shoulder –Sternocleidomastoid –Pectoralis major –Rectus abdominus –External oblique –Deltoid

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Posterior Trunk and Shoulder Trapezius Latissimus Dorsi Deltoid

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Arm –Deltoid –Biceps brachii –Brachioradialis –Triceps brachii

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Forearm –Flexors - anterior side –Extensors – posterior side

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Anterior Thigh –Gracilis –Adductor longus –Sartorius –Quadriceps Rectus femoris Vastus lateralis Vastus medialis

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Posterior Thigh –Gluteus maximus –Hamstrings Biceps femoris Semitendinosis Semimembranosis

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Anterior and Lateral Leg –Tibialis anterior –Peroneus longus –Extensor digitorum longus

Human Anatomy, 3rd edition Prentice Hall, © 2001 Muscles of the Posterior Leg –Gastrocnemius –Soleus –Achilles tendon (nonmuscular)