Skeletal Muscle Tissue Chapter 10

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 Skeletal muscle tissue Connective tissue

Fascia of Skeletal Muscle Epimysium Wraps muscle Perimysium Divides muscle into bundles (fasciculi) Endomysium Separates each muscle cell Human Anatomy, 3rd edition Prentice Hall, © 2001

Fascia of Skeletal Muscle FG09_01C.JPG Title: Structural Organization of Skeletal Muscle Notes: A skeletal muscle consists of bundles of muscle fibers (fascicles) enclosed within the epimysium. The fascicles are ensheathed by the perimysium, and within each fascicle the individual muscle fibers are surrounded by the endomysium. Keywords: skeletal muscles, fascicles, muscle fibers, epimysium, connective tissue, perimysium, endomysium, nuclei, mitochondria, myofibril, sarcoplasm, sarcolemma, tendon Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Tendons & Aponeuroses Epimysium Perimysium Endomysium Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Tendon Sheaths FG11_09D.JPG Title: Intrinsic Muscles, Tendons, and Ligaments of the Hand Notes: Anatomy of the right wrist and hand. (a)Posterior view. (b) Origins and insertions, posterior.(c)Origins, insertions;anterior. (d)Anterior view. (e)Plastic reconstruction, posterior. (f)Anterior view;muscle dissection. Keywords: wrist, hand, muscles, tendons, extensor indicis tendon, extensor pollicis longus, radial artery, extensor carpi radialis longus, extensor carpi radialis brevis, collateral ligament, extensor digiti minimi, extensor digitorum, dorsal interossei Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Nerve & Blood Supply Related to contraction Artery and 1 or 2 veins accompany each nerve Each muscle cell is in contact with capillaries Each muscle cell is in contact with a portion of a nerve cell Neuromuscular junction Human Anatomy, 3rd edition Prentice Hall, © 2001

Histology of Skeletal Muscle Tissue Muscle fibers = elongated cells Sarcolemma Sarcoplasm Sarcoplasmic reticulum T tubules Triad Muscle fibers consist of myofibrils Extend length of fiber Myofibrils consist of myofilaments Thin filaments Thick filaments Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Myofilaments Myofilaments do not extend entire length of fiber. Stacked in compartments = sarcomeres Partitioned by Z lines A band (dark) – contains thick filaments Includes H zone, zone of overlap I band (light) – thin filaments only H zone – thick filaments only Human Anatomy, 3rd edition Prentice Hall, © 2001

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

Contraction – Sliding Filament Theory Thin filaments slide inward toward the H zone Z lines are drawn toward the A band Sarcomere shortens Lengths of myofilaments do not change Cross bridges of thick filaments connect with actin Width of the H zone gets smaller Human Anatomy, 3rd edition Prentice Hall, © 2001

Neuromuscular Junction Contraction requires a stimulus An axon comes into close contact with a muscle membrane Motor end plate Acetylcholine transmits nerve impulse to the motor end plate Initiates contraction Axon terminal + motor end plate = neuromuscular junction Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Motor Unit Def. – motor neuron and all muscle cells it stimulates 1 motor neuron may innervate few or many muscle cells The number of muscle fibers/motor unit determines how precise a movement is. 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 Human Anatomy, 3rd edition Prentice Hall, © 2001

Physiology of Contraction – Stimulation of Muscle Nerve impulse reaches motor end plate 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 Cross bridges form 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

Physiology of Contraction FG09_12.JPG Title: The Events in Muscle Contraction Notes: Stepwise summary of the sequence of events in a muscle contraction from neural activation through contraction to rest. Keywords: muscle contraction, summary, motor end plate, synaptic terminal, T-tubule, action potential, receptor, sarcoplasmic reticulum, calcium, active site, cross-bridge, actin, myosin, acetylcholinesterase, relaxation Human Anatomy, 3rd edition Prentice Hall, © 2001

Fast, Slow, and Intermediate Muscles Duration of contraction varies with function Fast muscles (white) More extensive SR Lack myoglobin Fewer capillaries Slow muscles (red) Smaller fibers More capillaries Lots of myoglobin

Disorders Fibrosis Fibrositis Fibromyalgia Muscular dystrophy Myasthenia gravis

Classifications in 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

Arrangement of Fasciculi Parallel Convergent Pennate Unipennate Bipennate Multipennate Circular Arrangement is correlated with the power and range of movement of a muscle.

Arrangement of Fasciculi FG09_15.JPG Title: Skeletal Muscle Fiber Organization Notes: Four different arrangements of muscle fiber patterns are observed: (a) parallel, (b) convergent, (c) unipennate, (d) bipennate, (e) multipennate and (f) circular. Keywords: muscle fiber organization, fascicle, muscle, tendon, parallel muscle, convergent muscle, unipennate muscle, bipennate muscle, multipennate muscle, circular muscle Human Anatomy, 3rd edition Prentice Hall, © 2001

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

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