1. Anatomy and Physiology, Seventh Edition
Rod R. Seeley Idaho State University
Trent D. Stephens Idaho State University
Philip Tate Phoenix College
Chapter 09
Lecture Outline*
*See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Muscular System: Histology and Physiology
Chapter 9
Muscular System: Histology and Physiology

3. Muscular System Functions
Body movement
Maintenance of posture
Respiration
Production of body heat
Communication
Constriction of organs and vessels
Heart beat

4. Properties of Muscle
Contractility: ability of a muscle to shorten with force
Excitability: capacity of muscle to respond to a stimulus
Extensibility: muscle can be stretched to its normal resting length and beyond to a limited degree
Elasticity: ability of muscle to recoil to original resting length after stretched

5. Muscle Tissue Types Skeletal Smooth Cardiac
Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
Voluntary
Smooth
Walls of hollow organs, blood vessels, eye, glands, skin
Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow
In some locations, autorhythmic
Controlled involuntarily by endocrine and autonomic nervous systems
Cardiac
Heart: major source of movement of blood
Autorhythmic

7. Skeletal Muscle Structure
Composed of muscle cells (fibers), connective tissue, blood vessels, nerves
Fibers are long, cylindrical, multinucleated
Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm- 4 cm in length
Develop from myoblasts; numbers remain constant
Striated appearance due to light and dark banding

8. Connective Tissue Layers Fascia: connective tissue sheet
External lamina. Delicate, reticular fibers. Surrounds sarcolemma
Endomysium. Loose C.T. with reticular fibers.
Perimysium. Denser C.T. surrounding a group of muscle fibers. Each group called a fasciculus
Epimysium. C.T. that surrounds a whole muscle (many fascicles)
Fascia: connective tissue sheet
Forms layer under the skin
Holds muscles together and separates them into functional groups.
Allows free movements of muscles.
Carries nerves (motor neurons, sensory neurons), blood vessels, and lymphatics.
Continuous with connective tissue of tendons and periosteum.
Connective Tissue

9. Nerve and Blood Vessel Supply
Motor neurons: stimulate muscle fibers to contract. Nerve cells with cell bodies in brain or spinal cord; axons extend to skeletal muscle fibers through nerves
Axons branch so that each muscle fiber is innervated
Capillary beds surround muscle fibers

10. Muscle Fiber Anatomy Nuclei just inside sarcolemma
Cell packed with myofibrils within cytoplasm (sarcoplasm)
Threadlike
Composed of protein threads called myofilaments: thin (actin) and thick (myosin)
Sarcomeres: highly ordered repeating units of myofilaments

11. Parts of a Muscle

12. Structure of Actin and Myosin

13. Actin (Thin) Myofilaments
Two strands of fibrous (F) actin form a double helix extending the length of the myofilament; attached at either end at sarcomere.
Composed of G actin monomers each of which has an active site
Actin site can bind myosin during muscle contraction.
Tropomyosin: an elongated protein winds along the groove of the F actin double helix.
Troponin is composed of three subunits: one that binds to actin, a second that binds to tropomyosin, and a third that binds to calcium ions. Spaced between the ends of the tropomyosin molecules in the groove between the F actin strands.
The tropomyosin/troponin complex regulates the interaction between active sites on G actin and myosin.
Actin (Thin) Myofilaments

14. Myosin (Thick) Myofilament
Many elongated myosin molecules shaped like golf clubs.
Molecule consists of two heavy myosin molecules wound together to form a rod portion lying parallel to the myosin myofilament and two heads that extend laterally.
Myosin heads
Can bind to active sites on the actin molecules to form cross-bridges.
Attached to the rod portion by a hinge region that can bend and straighten during contraction.
Have ATPase activity: activity that breaks down adenosine triphosphate (ATP), releasing energy. Part of the energy is used to bend the hinge region of the myosin molecule during contraction

15. Sarcomeres: Z Disk to Z Disk
Z disk: filamentous network of protein. Serves as attachment for actin myofilaments
Striated appearance
I bands: from Z disks to ends of thick filaments
A bands: length of thick filaments
H zone: region in A band where actin and myosin do not overlap
M line: middle of H zone; delicate filaments holding myosin in place
In muscle fibers, A and I bands of parallel myofibrils are aligned.
Titin filaments: elastic chains of amino acids; make muscles extensible and elastic
Sarcomeres: Z Disk to Z Disk

16. Sliding Filament Model
Actin myofilaments sliding over myosin to shorten sarcomeres
Actin and myosin do not change length
Shortening sarcomeres responsible for skeletal muscle contraction
During relaxation, sarcomeres lengthen because of some external force, like contraction of antagonistic muscles
Insert Animation: Sliding Filaments.exe

17. Sarcomere Shortening

18. Physiology of Skeletal Muscle
Nervous system controls muscle contractions through action potentials
Resting membrane potentials
Membrane voltage difference across membranes (polarized)
Inside cell more negative due to accumulation of large protein molecules. More K+ on inside than outside. K+ leaks out but not completely because negative proteins hold some back.
Outside cell more positive and more Na+ on outside than inside. Na/K pump maintains this situation.
Must exist for action potential to occur
Insert Fig. 9.7; insert Animation Sodium-Potassium Exchange Pump.exe

19. Ion Channels Types Each is specific for one type of ion
Ligand-gated. Ligands are molecules that bind to receptors. Receptor: protein or glycoprotein with a receptor site
Example: neurotransmitters
Gate is closed until neurotransmitter attaches to receptor molecule. When Ach attaches to receptor on muscle cell, Na gate opens. Na moves into cell due to concentration gradient
Voltage-gated
Open and close in response to small voltage changes across plasma membrane
Each is specific for one type of ion

20. Action Potentials Phases
Depolarization: Inside of plasma membrane becomes less negative. If change reaches threshold, depolarization occurs
Repolarization: return of resting membrane potential. Note that during repolarization, the membrane potential drops lower than its original resting potential, then rebounds. This is because Na plus K together are higher, but then Na/K pump restores the resting potential
All-or-none principle: like camera flash system
Propagate: Spread from one location to another. Action potential does not move along the membrane: new action potential at each successive location.
Frequency: number of action potential produced per unit of time

21. Gated Ion Channels and the Action Potential

22. Action Potential Propagation

23. Neuromuscular Junction
Synapse: axon terminal resting in an invagination of the sarcolemma
Neuromuscular junction (NMJ):
Presynaptic terminal: axon terminal with synaptic vesicles
Synaptic cleft: space
Postsynaptic membrane or motor end-plate

24. Function of Neuromuscular Junction
Synaptic vesicles
Neurotransmitter: substance released from a presynaptic membrane that diffuses across the synaptic cleft and stimulates (or inhibits) the production of an action potential in the postsynaptic membrane. Acetylcholine
Acetylcholinesterase: A degrading enzyme in synaptic cleft. Prevents accumulation of ACh
Insert Fig WITHOUT PROCESS; Insert Animation Neuromuscular Junction.exe

26. Excitation-Contraction Coupling
Mechanism where an action potential causes muscle fiber contraction
Involves
Sarcolemma
Transverse (T) tubules: invaginations of sarcolemma
Terminal cisternae
Sarcoplasmic reticulum: smooth ER
Triad: T tubule, two adjacent terminal cisternae
Ca2+
Troponin

27. Action Potentials and Muscle Contraction
Insert Process Figure 9.14 with verbiage; Insert Animation Action Potentials and Muscle Contraction.exe

28. Cross-Bridge Movement
Insert Process Figure 9.15 with verbiage; Insert Animation Breakdown of ATP and Cross Bridge Movement During Muscle Cont.exe

29. Relaxation
Ca2+ moves back into sarcoplasmic reticulum by active transport. Requires energy
Ca2+ moves away from troponin-tropomyosin complex
Complex re-establishes its position and blocks binding sites.

30. Muscle Twitch
Muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers
Phases
Lag or latent
Contraction
Relaxation

32. Stimulus Strength and Muscle Contraction
All-or-none law for muscle fibers
Contraction of equal force in response to each action potential
Sub-threshold stimulus: no action potential; no contraction
Threshold stimulus: action potential; contraction
Stronger than threshold; action potential; contraction equal to that with threshold stimulus
Motor units: a single motor neuron and all muscle fibers innervated by it

33. Contraction of the Whole Muscle
Strength of contraction is graded: ranges from weak to strong depending on stimulus strength
Multiple motor unit summation: strength of contraction depends upon recruitment of motor units. A muscle has many motor units
Submaximal stimuli
Maximal stimulus
Supramaximal stimuli

34. Multiple-Wave Summation
As the frequency of action potentials increase, the frequency of contraction increases
Incomplete tetanus: muscle fibers partially relax between contraction
Complete tetanus: no relaxation between contractions
Multiple-wave summation: muscle tension increases as contraction frequencies increase

35. Treppe Graded response Occurs in muscle rested for prolonged period
Each subsequent contraction is stronger than previous until all equal after few stimuli
Possibly explanation: more and more Ca2+ remains in sarcoplasm and is not all taken up into the sarcoplasmic reticulum

36. Types of Muscle Contractions
Isometric: no change in length but tension increases
Postural muscles of body
Isotonic: change in length but tension constant
Concentric: overcomes opposing resistance and muscle shortens
Eccentric: tension maintained but muscle lengthens
Muscle tone: constant tension by muscles for long periods of time

37. Muscle Length and Tension
Active tension: force applied to an object to be lifted when a muscle contracts
Stretched muscle- not enough cross-bridging
Crumpled muscle- myofilaments crumpled, cross-bridges can't contract
Passive tension: tension applied to load when a muscle is stretched but not stimulated
Total tension: active plus passive

38. Fatigue
Decreased capacity to work and reduced efficiency of performance
Types
Psychological: depends on emotional state of individual
Muscular: results from ATP depletion
Synaptic: occurs in NMJ due to lack of acetylcholine

39. Physiological Contracture and Rigor Mortis
Physiological contracture: state of fatigue where due to lack of ATP neither contraction nor relaxation can occur
Rigor mortis: development of rigid muscles several hours after death. Ca2+ leaks into sarcoplasm and attaches to myosin heads and crossbridges form. Rigor ends as tissues start to deteriorate.

40. Energy Sources
ATP provides immediate energy for muscle contractions. Produced from three sources
Creatine phosphate
During resting conditions stores energy to synthesize ATP
Anaerobic respiration
Occurs in absence of oxygen and results in breakdown of glucose to yield ATP and lactic acid
Aerobic respiration
Requires oxygen and breaks down glucose to produce ATP, carbon dioxide and water
More efficient than anaerobic
Oxygen debt: oxygen taken in by the body, above that required for resting metabolism after exercise. ATP produced from anaerobic sources contributes

41. Slow and Fast Fibers Slow-twitch or high-oxidative
Contract more slowly, smaller in diameter, better blood supply, more mitochondria, more fatigue-resistant than fast-twitch, large amount of myoglobin.
Postural muscles, more in lower than upper limbs. Dark meat of chicken.
Fast-twitch or low-oxidative
Respond rapidly to nervous stimulation, contain myosin that can break down ATP more rapidly than that in Type I, less blood supply, fewer and smaller mitochondria than slow-twitch
Lower limbs in sprinter, upper limbs of most people. White meat in chicken.
Distribution of fast-twitch and slow-twitch
Most muscles have both but varies for each muscle
Effects of exercise: change in size of muscle fibers
Hypertrophy: increase in muscle size
Increase in myofibrils
Increase in nuclei due to fusion of satellite cells
Increase in strength due to better coordination of muscles, increase in production of metabolic enzymes, better circulation, less restriction by fat
Atrophy: decrease in muscle size
Reverse except in severe situations where cells die

43. Heat production Exercise: metabolic rate and heat production increase.
Post-exercise: metabolic rate stays high due to oxygen debt.
Excess heat lost because of vasodilation and sweating
Shivering: uncoordinated contraction of muscle fibers resulting in shaking and heat production

44. Not striated, fibers smaller than those in skeletal muscle
Spindle-shaped; single, central nucleus
More actin than myosin
Caveolae: indentations in sarcolemma; may act like T tubules
Dense bodies instead of Z disks as in skeletal muscle; have noncontractile intermediate filaments
Ca2+ required to initiate contractions; binds to calmodulin which regulates myosin kinase. Cross-bridging occurs
Relaxation: caused by enzyme myosin phosphatase
Smooth Muscle

46. Types of Smooth Muscle
Visceral or unitary: cells in sheets; function as a unit
Numerous gap junctions; waves of contraction
Often autorhythmic
Multiunit: cells or groups of cells act as independent units
Sheets (blood vessels); bundles (arrector pili and iris); single cells (capsule of spleen)

47. Electrical Properties of Smooth Muscle
Slow waves of depolarization and repolarization transferred from cell to cell
Depolarization caused by spontaneous diffusion of Na+ and Ca2+ into cell
Does not follow all-or-none law
May have pacemaker cells
Contraction regulated by nervous system and by hormones

48. Functional Properties of Smooth Muscle
Some visceral muscle exhibits autorhythmic contractions
Tends to contract in response to sudden stretch but not to slow increase in length
Exhibits relatively constant tension: smooth muscle tone
Amplitude of contraction remains constant although muscle length varies

49. Smooth Muscle Regulation
Innervated by autonomic nervous system
Neurotransmitters are acetylcholine and norepinephrine
Hormones important as epinephrine and oxytocin
Receptors present on plasma membrane which neurotransmitters or hormones bind determines response

50. Cardiac Muscle Found only in heart Striated
Each cell usually has one nucleus
Has intercalated disks and gap junctions
Autorhythmic cells
Action potentials of longer duration and longer refractory period
Ca2+ regulates contraction

51. Effects of Aging on Skeletal Muscle
Reduced muscle mass
Increased time for muscle to contract in response to nervous stimuli
Reduced stamina
Increased recovery time
Loss of muscle fibers
Decreased density of capillaries in muscle