1. Copyright © 2010 Pearson Education, Inc. UNIT 3 Chapters 9 and 10 Muscle and Nerves

2. Copyright © 2010 Pearson Education, Inc. Table 9.3 Three Types of Muscle Tissue

3. Copyright © 2010 Pearson Education, Inc. Muscle Functions 1.Movement of bones or fluids (e.g., blood) 2.Maintaining posture and body position 3.Stabilizing joints 4.Heat generation (especially skeletal muscle)

4. Copyright © 2010 Pearson Education, Inc. Special Characteristics of Muscle Tissue Excitability (responsiveness or irritability): ability to receive and respond to stimuli Contractility: ability to shorten when stimulated Extensibility: ability to be stretched Elasticity: ability to recoil to resting length

5. Copyright © 2010 Pearson Education, Inc. Figure 9.1 Bone Perimysium Endomysium (between individual muscle fibers) Muscle fiber (Muscle cell) Fascicle (wrapped by perimysium) Epimysium Tendon Epimysium Muscle fiber in middle of a fascicle Perimysium Endomysium Fascicle (b) Layers of the muscle**

6. Copyright © 2010 Pearson Education, Inc. Table 9.1

7. Copyright © 2010 Pearson Education, Inc. Nucleus Light I bandDark A band Sarcolemma Mitochondrion Myofibril Densely packed, rodlike elements ~80% of cell volume Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands Muscle Fiber/ Cell Myofibril

8. Copyright © 2010 Pearson Education, Inc. Figure 9.2c, d I band A band Sarcomere H zone Thin (actin) filament Thick (myosin) filament Z disc M line (c) myofibril Z disc M line Sarcomere Thin (actin) filament Thick (myosin) filament (d) sarcomere Smallest contractile unit (functional unit) of a muscle fiber The region of a myofibril between two Z discs Composed of thick (Myosin) and thin (Actin) myofilaments Thick filaments: run the entire length of an A band Thin filaments: run the length of the I band and partway into the A band Z disc: anchors the thin filaments and connects myofibrils to one another H zone: lighter midregion where filaments do not overlap M line: line of protein myomesin that holds adjacent thick filaments together Sarcomere**

9. Copyright © 2010 Pearson Education, Inc. Figure 9.3 Flexible hinge region Tail Tropomyosin TroponinActin Myosin head ATP- binding site Heads Active sites for myosin attachment Actin subunits Actin-binding sites Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. A thin filament consists of two strands of actin subunits twisted into a helix plus two types of regulatory proteins (troponin and tropomyosin). Thin filament Thick filament Longitudinal section of filaments within one sarcomere of a myofibril Portion of a thick filament Portion of a thin filament Myosin molecule Actin subunits

10. Copyright © 2010 Pearson Education, Inc. Figure 9.5 Myofibril Myofibrils Triad: Tubules of the SR Sarcolemma Mitochondria I band A band H zoneZ disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisternae of the SR (2) M line Sarcoplasmic Reticulum (SR) Network of smooth endoplasmic reticulum membrane surrounding each myofibril Functions in the regulation of intracellular Ca 2+ levels T Tubules Continuous with the sarcolemma Penetrate the cell’s interior at each A band–I band junction Associate with the paired terminal cisternae to form triads that encircle each sarcomere

11. Copyright © 2010 Pearson Education, Inc. Figure 9.6 Fully relaxed sarcomere of a muscle fiber ZZ II H A Z Z I IA Fully contracted sarcomere of a muscle fiber Sliding Filament Model of Contraction In the relaxed state, thin and thick filaments overlap only slightly During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line As H zones shorten and disappear, sarcomeres shorten, muscle cells shorten, and the whole muscle shortens

12. Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 1 Axon terminal of motor neuron Muscle fiber Triad One sarcomere Synaptic cleft Setting the stage Sarcolemma Action potential is generated Terminal cisterna of SR ACh Ca 2+ Motor Neuron ↓ Synapse ↓ Muscle Cell

13. Copyright © 2010 Pearson Education, Inc. Figure 9.8 Nucleus Action potential (AP) Myelinated axon of motor neuron Axon terminal of neuromuscular junction Sarcolemma of the muscle fiber Ca 2+ Axon terminal of motor neuron Synaptic vesicle containing ACh Mitochondrion Synaptic cleft Junctional folds of sarcolemma Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber Postsynaptic membrane ion channel opens; ions pass. Na + K+K+ Ach – Na + K+K+ Degraded ACh Acetyl- cholinesterase Postsynaptic membrane ion channel closed; ions cannot pass. 1 Action potential arrives at axon terminal of motor neuron. 2 Voltage-gated Ca 2+ channels open and Ca 2+ enters the axon terminal. 3 Ca 2+ entry causes some synaptic vesicles to release their contents (acetylcholine) by exocytosis. 4 Acetylcholine, a neurotransmitter, diffuses across the synaptic cleft and binds to receptors in the sarcolemma. 5 ACh binding opens ion channels that allow simultaneous passage of Na + into the muscle fiber and K + out of the muscle fiber. 6 ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase.

14. Copyright © 2010 Pearson Education, Inc. Figure 9.9 Na + Open Na + Channel Closed K + Channel Action potential + + ++ + + + + ++ + + Axon terminal Synaptic cleft ACh Sarcoplasm of muscle fiber ecc movie K+K+ 2 Generation and propagation of the action potential (AP) 3 Repolarization 1 Local depolarization: generation of the end plate potential on the sarcolemma K+K+ K+K+ Na + K+K+ W a v e o f d e p o l a r i z a t i o n Closed Na + Channel Open K + Channel

15. Copyright © 2010 Pearson Education, Inc. Figure 9.10 Na + channels close, K + channels open K + channels close Repolarization due to K + exit Threshold Na + channels open Depolarization due to Na+ entry Events at Muscle Cell Membrane movie gap

16. Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 4 Steps in E-C Coupling: Terminal cisterna of SR Voltage-sensitive tubule protein T tubule Ca 2+ release channel Ca 2+ Sarcolemma Action potential is propagated along the sarcolemma and down the T tubules. Calcium ions are released. 1 2 Pap movie

17. Copyright © 2010 Pearson Education, Inc. Figure 9.11, step 7 TroponinTropomyosin blocking active sites Myosin Actin Active sites exposed and ready for myosin binding Ca 2+ Myosin cross bridge Calcium binds to troponin and removes the blocking action of tropomyosin. Contraction begins The aftermath 3 4 At low intracellular Ca 2+ concentration: Tropomyosin blocks the active sites on actin Myosin heads cannot attach to actin Muscle fiber relaxes At higher intracellular Ca 2+ concentrations: Ca 2+ binds to troponin Troponin changes shape and moves tropomyosin away from active sites Events of the cross bridge cycle occur When nervous stimulation ceases, Ca 2+ is pumped back into the SR and contraction ends Cbc movie

18. Copyright © 2010 Pearson Education, Inc. Figure 9.13a Spinal cord Motor neuron cell body Muscle Nerve Motor unit 1 Motor unit 2 Muscle fibers Motor neuron axon Axon terminals at neuromuscular junctions Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies Small motor units in muscles that control fine movements (fingers, eyes) Large motor units in large weight-bearing muscles (thighs, hips) Muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle Motor units in a muscle usually contract asynchronously; helps prevent fatigue

19. Copyright © 2010 Pearson Education, Inc. Graded Muscle Responses Variations in the degree of muscle contraction Responses are graded by: 1.Changing the frequency of stimulation 2.Changing the strength of the stimulus

20. Copyright © 2010 Pearson Education, Inc. Muscle Metabolism: Energy for Contraction ATP is the only source used directly for contractile activities Available stores of ATP are depleted in 4–6 seconds ATP is regenerated by: 1.Direct phosphorylation of ADP by creatine phosphate (CP) 2.Anaerobic pathway (glycolysis) 3.Aerobic respiration

21. Copyright © 2010 Pearson Education, Inc. Figure 9.19b Energy source: glucose Glycolysis and lactic acid formation (b) Anaerobic pathway Oxygen use: None Products: 2 ATP per glucose, lactic acid Duration of energy provision: 60 seconds, or slightly more Glucose (from glycogen breakdown or delivered from blood) Glycolysis in cytosol Pyruvic acid Released to blood net gain 2 Lactic acid O2O2 O2O2 ATP At 70% of maximum contractile activity: Bulging muscles compress blood vessels Oxygen delivery is impaired Pyruvic acid is converted into lactic acid Lactic acid: Diffuses into the bloodstream Used as fuel by the liver, kidneys, and heart Converted back into pyruvic acid by the liver

22. Copyright © 2010 Pearson Education, Inc. Figure 9.19c Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism (c) Aerobic pathway Aerobic cellular respiration Oxygen use: Required Products: 32 ATP per glucose, CO 2, H 2 O Duration of energy provision: Hours Glucose (from glycogen breakdown or delivered from blood) 32 O2O2 O2O2 H2OH2O CO 2 Pyruvic acid Fatty acids Amino acids Aerobic respiration in mitochondria Aerobic respiration in mitochondria ATP net gain per glucose Produces 95% of ATP during rest and light to moderate exercise Fuels: stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids

23. Copyright © 2010 Pearson Education, Inc. Figure 9.21 Large number of muscle fibers activated Contractile force High frequency of stimulation Large muscle fibers Muscle and sarcomere stretched to slightly over 100% of resting length

24. Copyright © 2010 Pearson Education, Inc. Effects of Exercise Aerobic (endurance) exercise leads to increased: Results in greater endurance, strength, and resistance to fatigue Resistance exercise (typically anaerobic) results in: Muscle hypertrophy (due to increase in fiber size) The Overload Principle Forcing a muscle to work hard promotes increased muscle strength and endurance Muscles adapt to increased demands Muscles must be overloaded to produce further gains

25. Copyright © 2010 Pearson Education, Inc. Table 9.2 Muscle Fiber Type: Speed and Metabolism

26. Copyright © 2010 Pearson Education, Inc. Figure 9.26 Small intestine Mucosa Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section) Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers) Found in walls of most hollow organs (except heart) Usually in two layers (longitudinal and circular) SMOOTH MUSCLE

27. Copyright © 2010 Pearson Education, Inc. Peristalsis Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs Longitudinal layer contracts; organ dilates and shortens Circular layer contracts; organ constricts and elongates

28. Copyright © 2010 Pearson Education, Inc. Microscopic Structure: Smooth Muscle Spindle-shaped fibers: thin and short compared with skeletal muscle fibers Connective tissue: endomysium only SR: less developed than in skeletal muscle Pouchlike infoldings (caveolae) of sarcolemma sequester Ca 2+ No sarcomeres, myofibrils, or T tubules

29. Copyright © 2010 Pearson Education, Inc. Table 9.3

30. Copyright © 2010 Pearson Education, Inc. Table 9.3

31. Copyright © 2010 Pearson Education, Inc. Table 9.3

32. Copyright © 2010 Pearson Education, Inc. Figure 9.27 Smooth muscle cell Varicosities release their neurotransmitters into a wide synaptic cleft (a diffuse junction). Synaptic vesicles Mitochondrion Autonomic nerve fibers innervate most smooth muscle fibers. Varicosities Innervation of Smooth Muscle Autonomic nerve fibers innervate smooth muscle at diffuse junctions Varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters

33. Copyright © 2010 Pearson Education, Inc. Figure 9.28a Myofilaments in Smooth Muscle Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2) Thick filaments have heads along their entire length No troponin complex; protein calmodulin binds Ca 2+ Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner Dense bodies: proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals

34. Copyright © 2010 Pearson Education, Inc. Contraction of Smooth Muscle Slow, synchronized contractions Cells are electrically coupled by gap junctions Some cells are self-excitatory (depolarize without external stimuli); act as pacemakers for sheets of muscle Rate and intensity of contraction may be modified by neural and chemical stimuli Sliding filament mechanism Final trigger is  intracellular Ca 2+ Ca 2+ is obtained from the SR and extracellular space Ca 2+ binds to and activates calmodulin Activated calmodulin activates myosin (light chain) kinase Activated kinase phosphorylates and activates myosin Cross bridges interact with actin

35. Copyright © 2010 Pearson Education, Inc. Figure 9.29, step 1 Calcium ions (Ca 2+ ) enter the cytosol from the ECF via voltage- dependent or voltage- independent Ca 2+ channels, or from the scant SR. Extracellular fluid (ECF) Ca 2+ Plasma membrane Sarcoplasmic reticulum Cytoplasm 1

36. Copyright © 2010 Pearson Education, Inc. Figure 9.29, step 2 Ca 2+ Inactive calmodulinActivated calmodulin Ca 2+ binds to and activates calmodulin. 2

37. Copyright © 2010 Pearson Education, Inc. Figure 9.29, step 3 Inactive kinaseActivated kinase Activated calmodulin activates the myosin light chain kinase enzymes. 3

38. Copyright © 2010 Pearson Education, Inc. Figure 9.29, step 4 ATP PiPi PiPi ADP Inactive myosin molecule Activated (phosphorylated) myosin molecule The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases. 4

39. Copyright © 2010 Pearson Education, Inc. Figure 9.29, step 5 Activated myosin forms cross bridges with actin of the thin filaments and shortening begins. Thin filament Thick filament 5

40. Copyright © 2010 Pearson Education, Inc. Regulation of Contraction Neural regulation: Neurotransmitter binding   [Ca 2+ ] in sarcoplasm Response depends on neurotransmitter released and type of receptor molecules Hormones and local chemicals: May bind to G protein– linked receptors May either enhance or inhibit Ca 2+ entry

41. Copyright © 2010 Pearson Education, Inc. Special Features of Smooth Muscle Contraction Stress-relaxation response: Responds to stretch only briefly, then adapts to new length Retains ability to contract on demand Enables organs such as the stomach and bladder to temporarily store contents Length and tension changes: Can contract when between half and twice its resting length Hyperplasia: Smooth muscle cells can divide and increase their numbers Example: estrogen effects on uterus at puberty and during pregnancy

42. Copyright © 2010 Pearson Education, Inc. Types of Smooth Muscle Single-unit (visceral) smooth muscle: Sheets contract rhythmically as a unit (gap junctions) Often exhibit spontaneous action potentials Arranged in opposing sheets and exhibit stress- relaxation response Multiunit smooth muscle: Located in large airways, large arteries, arrector pili muscles, and iris of eye Gap junctions are rare Arranged in motor units Graded contractions occur in response to neural stimuli

43. Copyright © 2010 Pearson Education, Inc. Muscular Dystrophy Group of inherited muscle- destroying diseases Muscles enlarge due to fat and connective tissue deposits Muscle fibers atrophy Duchenne muscular dystrophy (DMD): Most common and severe type Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin Victims become clumsy and fall frequently; usually die of respiratory failure in their 20s No cure, but viral gene therapy or infusion of stem cells with correct dystrophin genes show promise