Anatomy Physiology Lecture 7 Chapter 10 Muscle Tissue

Anatomy & Physiology Lecture 7: Chapter 10 Muscle Tissue Pages: 283 -325 Lecturer: Dr. Barjis Room: P 313 /P 307 Phone: (718)2605285 E-Mail: ibarjis@citytech. cuny. edu Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings Frederic H. Martini Fundamentals of

Learning Objectives • Describe the organization of muscle and the unique characteristics of skeletal muscle cells. • Identify the structural components of the sarcomere. • Summarize the events at the neuromuscular junction. • Explain the key concepts involved in skeletal muscle contraction and tension production.

Learning Objectives • Describe how muscle fibers obtain energy for contraction. • Distinguish between aerobic and anaerobic contraction, muscle fiber types, and muscle performance. • Identify the differences between skeletal, cardiac and smooth muscle.

Skeletal muscle tissue and the Muscular System Three types of muscle • Skeletal – attached to bone • Cardiac – found in the heart • Smooth – lines hollow organs

Skeletal muscle functions • Produce skeletal movement • Maintain posture and body position • Support soft tissues • Guard entrances and exits • Maintain body temperature

Anatomy of Skeletal Muscle Organization of connective tissues • Epimysium surrounds muscle • Perimysium sheathes bundles of muscle fibers • Epimysium and perimysium contain blood vessels and nerves • Endomysium covers individual muscle fibers • Tendons or aponeuroses attach muscle to bone or muscle Animation: See tutorial

The Organization of Skeletal Muscles

Skeletal muscle fibers • Sarcolemma (cell membrane) • Sarcoplasm (muscle cell cytoplasm) • Sarcoplasmic reticulum (modified ER) • T-tubules and myofibrils aid in contraction • Sarcomeres – regular arrangement of myofibrils

The Structure of a Skeletal Muscle Fiber

Sarcomere Structure, Part I

Myofibrils • Thick and thin filaments • Organized regularly

Sarcomere Structure, Part II

Levels of Functional Organization in Skeletal Muscle Fiber

Thin filaments • F-actin • Nebulin • Tropomyosin • Covers active sites on G-actin • Troponin • Binds to G-actin and holds tropomyosin in place

Thick filaments • Bundles of myosin fibers around titan core • Myosin molecules have elongate tail, globular head • Heads form cross-bridges during contraction • Interactions between G-actin and myosin prevented by tropomyosin during rest

Thick and Thin Filaments

Sliding filament theory • Explains the relationship between thick and thin filaments as contraction proceeds • Cyclic process beginning with calcium release from SR • Calcium binds to troponin • Trponin moves, moving tropomyosin and exposing actin active site • Myosin head forms cross bridge and bends toward H zone • ATP allows release of cross bridge

Changes in the appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber

The Contraction of Skeletal Muscle Tension • Created when muscles contract • Series of steps that begin with excitation at the neuromuscular junction • Calcium release • Thick/thin filament interaction • Muscle fiber contraction • Tension

An Overview of the Process of Skeletal Muscle

Control of skeletal muscle activity occurs at the neuromuscular junction • Action potential arrives at synaptic terminal • ACh released into synaptic cleft • ACh binds to receptors on post-synaptic neuron • Action potential in sarcolemma

Skeletal Muscle Innervation

Skeletal Muscle Innervation Animation: See tutorial

Excitation/contraction coupling • Action potential along T-tubule causes release of calcium from cisternae of SR • Initiates contraction cycle • Attachment • Pivot • Detachment • Return

The Contraction Cycle

The Contraction Cycle

The Contraction Cycle

The Contraction Cycle

Relaxation • Acetylcholinesterase breaks down ACh • Limits the duration of contraction Animation: See tutorial

Tension Production Tension production by muscle fibers • All or none principle • Amount of tension depends on number of cross bridges formed • Skeletal muscle contracts most forcefully over a narrow ranges of resting lengths

The Effect of Sarcomere Length on Tension

• Twitch • Cycle of contraction, relaxation produced by a single stimulus • Treppe • Repeated stimulation after relaxation phase has been completed

Summation • Repeated stimulation before relaxation phase has been completed • Wave summation = one twitch is added to another • Incomplete tetanus = muscle never relaxes completely • Complete tetanus = relaxation phase is eleminated

The Twitch and the Development of Tension

Effects of Repeated Stimulations

Tension production by skeletal muscles • Internal tension generated inside contracting muscle fibers • External tension generated in extracellular fibers

Internal and External Tension

• Motor units • All the muscle fibers innervated by one neuron • Precise control of movement determined by number and size of motor unit • Muscle tone • Stabilizes bones and joints

The Arrangement of Motor Units in a Skeletal Muscle

Tension production by skeletal muscles • Internal tension generated inside contracting muscle fibers • External tension generated in extracellular fibers

Internal and External Tension

• Motor units • All the muscle fibers innervated by one neuron • Precise control of movement determined by number and size of motor unit • Muscle tone • Stabilizes bones and joints

The Arrangement of Motor Units in a Skeletal Muscle

Contractions • Isometric • Tension rises, length of muscle remains constant • Isotonic • Tension rises, length of muscle changes • Resistance and speed of contraction inversely related • Return to resting lengths due to elastic components, contraction of opposing muscle groups, gravity Animation: See tutorial

Isotonic and Isometric Contractions Figure 10. 18

Resistance and Speed of Contraction Animation: See tutorial

Energy Use and Muscle Contraction requires large amounts of energy • Creatine phosphate releases stored energy to convert ADP to ATP • Aerobic metabolism provides most ATP needed for contraction • At peak activity, anaerobic glycolysis needed to generate ATP

Muscle Metabolism

Muscle Metabolism

Energy use and level of muscular activity • Energy production and use patterns mirror muscle activity • Fatigued muscle no longer contracts • Build up of lactic acid • Exhaustion of energy resources

Recovery period • Begins immediately after activity ends • Oxygen debt (excess post-exercise oxygen consumption) • Amount of oxygen required during resting period to restore muscle to normal conditions

Muscle Performance Types of skeletal muscle fibers • Fast fibers • Slow fibers • Intermediate fibers

Fast versus Slow Fibers

Fast fibers • Large in diameter • Contain densely packed myofibrils • Large glycogen reserves • Relatively few mitochondria • Produce rapid, powerful contractions of short duration

Slow fibers • Half the diameter of fast fibers • Take three times as long to contract after stimulation • Abundant mitochondria • Extensive capillary supply • High concentrations of myoglobin • Can contract for long periods of time

Intermediate fibers • Similar to fast fibers • Greater resistance to fatigue

Muscle performance and the distribution of muscle fibers • Pale muscles dominated by fast fibers are called white muscles • Dark muscles dominated by slow fibers and myoglobin are called red muscles • Training can lead to hypertrophy of stimulated muscle

Physical conditioning • Anaerobic endurance • Time over which muscular contractions are sustained by glycolysis and ATP/CP reserves • Aerobic endurance • Time over which muscle can continue to contract while supported by mitochondrial activities Animation: See tutorial

Cardiac Muscle Tissue Structural characteristics of cardiac muscle • Located only in heart • Cardiac muscle cells are small • One centrally located nucleus • Short broad T-tubules • Dependent on aerobic metabolism • Intercalated discs where membranes contact one another

Cardiac Muscle Tissue

Functional characteristics of cardiac muscle tissue • Automaticity • Contractions last longer than skeletal muscle • Do not exhibit wave summation • No tetanic contractions possible

Smooth Muscle Tissue Structural characteristics of smooth muscle • Nonstriated • Lack sarcomeres • Thin filaments anchored to dense bodies • Involuntary

Smooth Muscle Tissue

Functional characteristics of smooth muscle • Contract when calcium ions interact with calmodulin • Activates myosin light chain kinase • Functions over a wide range of lengths • Plasticity • Multi-unit smooth muscle cells are innervated by more than one motor neuron • Visceral smooth muscle cells are not always innervated by motor neurons • Neurons that innervate smooth muscle are not under voluntary control

You should now be familiar with: • The organization of muscle and the unique characteristics of skeletal muscle cells. • The structural components of the sarcomere. • The events at the neuromuscular junction. • The key concepts involved in skeletal muscle contraction and tension production. • How muscle fibers obtain energy for contraction. • Aerobic and anaerobic contraction, muscle fiber types, and muscle performance. • The differences between skeletal, cardiac and smooth muscle