Chapter 12a Muscles

Mechanics of body movement Smooth muscle Cardiac muscle About this Chapter Skeletal muscle Mechanics of body movement Smooth muscle Cardiac muscle

Three Types of Muscle Nucleus Muscle fiber (cell) Striations (a) Skeletal muscle Figure 12-1a

Three Types of Muscle Striations Muscle fiber Intercalated disk Nucleus (b) Cardiac muscle Figure 12-1b

Three Types of Muscle Muscle fiber Nucleus (c) Smooth muscle Figure 12-1c

Usually attached to bones by tendons Origin: closest to the trunk Skeletal Muscle Usually attached to bones by tendons Origin: closest to the trunk Insertion: more distal Flexor: brings bones together Extensor: moves bones away Antagonistic muscle groups: flexor-extensor pairs

Antagonistic Muscle Groups Triceps muscle relaxes Biceps muscle contracts (flexor) (a) Flexion Figure 12-2a

Antagonistic Muscle Groups Triceps muscle contracts (extensor) Biceps muscle relaxes (b) Extension Figure 12-2b

Organization of Skeletal Muscle Tendon Nerve and blood vessels Connective tissue Muscle fascicle: bundle of fibers Connective tissue Nucleus Muscle fiber (a) Figure 12-3a (1 of 2)

Organization of Skeletal Muscle Figure 12-3a (2 of 2)

Ultrastructure of Muscle ANATOMY SUMMARY ULTRASTRUCTURE OF MUSCLE Mitochondria Sarcoplasmic reticulum Nucleus Thick filament Thin filament T-tubules Myofibril Sarcolemma (b) A band Sarcomere Z disk Z disk Myofibril (c) M line I band H zone Titin (d) Z disk Z disk M line Myosin crossbridges M line Thick filaments Thin filaments Titin (e) Myosin heads Troponin Nebulin Hinge region Myosin tail Tropomyosin G-actin molecule Myosin molecule (f) Actin chain Figure 12-3b-f

Ultrastructure of Muscle Mitochondria Sarcoplasmic reticulum Thick filament Thin filament Nucleus T-tubules Myofibril Sarcolemma (b) Figure 12-3b

Ultrastructure of Muscle Sarcomere A band Z disk Z disk Myofibril (c) M line I band H zone Figure 12-3c

Ultrastructure of Muscle Titin (d) Z disk Z disk M line Myosin crossbridges Figure 12-3d

Ultrastructure of Muscle M line Thick filaments (e) Myosin heads Hinge region Myosin tail Myosin molecule Figure 12-3e

Ultrastructure of Muscle Thin filaments Titin Troponin Nebulin Tropomyosin G-actin molecule Actin chain (f) Figure 12-3f

Ultrastructure of Muscle A band Sarcomere Z disk Z disk Myofibril (c) M line I band H zone Titin (d) Z disk Z disk M line Myosin crossbridges M line Thick filaments Thin filaments Titin (e) Troponin Nebulin Myosin heads Hinge region Myosin tail Tropomyosin G-actin molecule Myosin molecule Actin chain (f) Figure 12-3c-f

T-Tubules and the Sarcoplasmic Reticulum T-tubule brings action potentials into interior of muscle fiber. Thin filament Sarcolemma Thick filament Triad Sarcoplasmic reticulum stores Ca2+ Terminal cisterna Figure 12-4

The Two- and Three-Dimensional Organization of a Sarcomere A band I band H zone I band Thin filament Thick filament (a) Z disk M line Z disk (b) Z disk Z disk I band thin filaments only H zone thick filaments only M line thick filaments linked with accessory proteins Outer edge of A band thick and thin filaments overlap (c) Figure 12-5

Anatomy Review Animation PLAY Interactive Physiology® Animation: Muscular System: Anatomy Review: Skeletal Muscle Tissue

Muscle tension: force created by muscle Muscle Contraction Muscle tension: force created by muscle Load: weight that opposes contraction Contraction: creation of tension in muscle Relaxation: release of tension Steps leading up to muscle contraction: Events at the neuromuscular junction Excitation-contraction coupling Contraction-relaxation cycle

Summary of Muscle Contraction Figure 12-7

Events at the Neuromuscular Junction PLAY Events at the Neuromuscular Junction PLAY Interactive Physiology® Animation: Muscular System: Events at the Neuromuscular Junction

Changes in a Sarcomere During Contraction I band Myosin Z A band Z Actin Muscle relaxed Z line Z M Z A band Half of I band H zone Half of I band Sarcomere shortens with contraction Half of I band H M line Z line Z Z A band constant Muscle contracted I H I H zone and I band both shorten Figure 12-8

Sliding Filament Theory PLAY Interactive Physiology® Animation: Muscular System: Sliding Filament Theory

The Molecular Basis of Contraction Troponin G-Actin TN Myosin head Tropomyosin blocks binding site on actin ADP Pi (a) Relaxed state. Myosin head cocked. Figure 12-9a

The Molecular Basis of Contraction 1 Cytosolic Ca2+ 1 Ca2+ levels increase in cytosol. 3 Tropomyosin shifts, exposing binding site on actin 2 2 Ca2+ binds to troponin (TN). TN 3 Troponin-Ca2+ complex pulls tropomyosin away from actin’s myosin-binding site. 5 Actin moves ADP Power stroke 4 Pi 4 Myosin binds to actin and completes power stroke. 5 Actin filament moves. (b) Initiation of contraction Figure 12-9b

The Molecular Basis of Contraction G-actin molecule Myosin binding sites Myosin filament 1 ATP binds to myosin. Myosin releases actin. Tight binding in the rigor state ATP ADP 2 Myosin hydrolyses ATP. Myosin head rotates and binds to actin. 4 Myosin releases ADP. Contraction- relaxation Actin filament moves toward M line. Sliding filament ADP Ca2+ signal Pi Pi 3 Power stroke Relaxed state with myosin heads cocked Figure 12-10

The Molecular Basis of Contraction G-actin molecule Myosin binding sites Myosin filament Tight binding in the rigor state Figure 12-10, step 0

The Molecular Basis of Contraction G-actin molecule Myosin binding sites Myosin filament 1 ATP binds to myosin. Myosin releases actin. T ight binding in the rigor state ATP Figure 12-10, steps 0–1

The Molecular Basis of Contraction 1 ATP binds to myosin. Myosin releases actin. 2 Myosin hydrolyses ATP. Myosin head rotates and binds to actin. ADP ATP Pi Relaxed state with myosin heads cocked Figure 12-10, steps 1–2

The Molecular Basis of Contraction 2 Myosin hydrolyses ATP. Myosin head rotates and binds to actin. 3 Power stroke Actin filament moves toward M line. Ca2+ signal ADP Pi Pi Relaxed state with myosin heads cocked Figure 12-10, steps 2–3

The Molecular Basis of Contraction 3 Power stroke 4 Myosin releases ADP. Actin filament moves toward M line. ADP Pi Figure 12-10, steps 3–4

Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Muscle fiber 1 Somatic motor neuron releases ACh at neuromuscular junction. ACh 2 2 Net entry of Na+ through ACh receptor-channel initiates a muscle action potential Na+ Motor end plate RyR T-tubule Ca2+ Sarcoplasmic reticulum DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Figure 12-11a

Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Muscle fiber 1 Somatic motor neuron releases ACh at neuromuscular junction. ACh Motor end plate RyR T-tubule Ca2+ Sarcoplasmic reticulum DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Figure 12-11a, step 1

Excitation-Contraction Coupling Axon terminal of somatic motor neuron 1 Muscle fiber 1 Somatic motor neuron releases ACh at neuromuscular junction. ACh 2 2 Net entry of Na+ through ACh receptor-channel initiates a muscle action potential Na+ Motor end plate RyR T-tubule Ca2+ Sarcoplasmic reticulum DHP Z disk Troponin Actin Tropomyosin M line Myosin head Myosin thick filament (a) Initiation of muscle action potential KEY DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Figure 12-11a, steps 1–2

Excitation-Contraction Coupling 3 Action potential in t-tubule alters conformation of DHP receptor. 4 DHP receptor opens RyR Ca2+ release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm. 4 3 5 Ca2+ binds to troponin, allowing actin-myosin binding. 7 Ca2+ released 5 6 Myosin heads execute power stroke. 6 Myosin thick filament 7 Actin filament slides toward center of sarcomere. Distance actin moves KEY (b) Excitation-contraction coupling DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Figure 12-11b

Electrical and Mechanical Events in Muscle Contraction A twitch is a single contraction-relaxation cycle Muscle fiber +30 Action potential from CNS Neuron membrane potential in mV -70 Motor end plate Recording electrodes Time Axon terminal +30 Muscle fiber membrane potential in mV Muscle action potential -70 2 msec Time Latent period Contraction phase Relaxation phase Development of tension during one muscle twitch Tension 10–100 msec Time Figure 12-12

Phosphocreatine Creatine phosphate Glycolysis Krebs cycle Figure 12-13

Locations and Possible Causes of Muscle Fatigue Figure 12-14

Causes of Muscle Fatigue During Exercise Extended submaximal exercise Depletion of glycogen stores Short-duration maximal exertion Increased levels of inorganic phosphate May slow Pi release from myosin Decrease calcium release Maximal exercise Potassium (K+) leaves muscle fiber, leading to increased concentration that is believed to decrease Ca2+

Skeletal Muscle Metabolism During Fatiguing Submaximal Exercise Question 12-1

Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers Figure 12-15

Fast-Twitch Glycolytic and Slow-Twitch Oxidative Muscle Fibers Table 12-2

Length-Tension Relationships in Contracting Skeletal Muscle Figure 12-16