Lecture Overview. Muscular System. Marieb s Human Anatomy and Physiology. Chapter 9 Muscles and Muscle Tissue Lecture 16

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1 Marieb s Human Anatomy and Physiology Marieb Hoehn Chapter 9 Muscles and Muscle Tissue Lecture 16 1 Lecture Overview Types, characteristics, functions of muscle Structure of skeletal muscle Mechanism of skeletal muscle fiber contraction Energetics of skeletal muscle contraction Skeletal muscle performance Types of skeletal muscle contractions Comparison of skeletal muscle with smooth muscle and cardiac muscle 2 Muscular System Review - Three Types of Muscle Tissues Skeletal Muscle usually attached to bones under conscious control (voluntary) striated multinucleated Smooth Muscle walls of most viscera, blood vessels, skin not under conscious control not striated Cardiac Muscle wall of heart not under conscious control striated branched 3 1

2 Functions of Muscle Provide stability and postural tone (skeletal) Fixed in place without movement Maintain posture in space Purposeful movement (skeletal) Perform tasks consciously, purposefully Regulate internal organ movement and volume (mostly involuntary - smooth) Guard entrances/exits (digestive/urinary skeletal and smooth) Generation of heat (thermogenesis - skeletal) 4 Characteristics of All Muscle Tissue Contractile Ability to shorten (if possible) with force; exerts tension CANNOT forcibly lengthen Extensible (able to be stretched) Elastic (returns to resting length) Excitable (can respond electrical impulses) Conductive (transmits electrical impulses) 5 Structure of a Skeletal Muscle Gross/Histological Level Figure from: Hole s Human A&P, 12 th edition, 2010 epimysium (around muscle) perimysium (around fascicles) endomysium (around fibers, or cells) 6 Alphabetical order of MUSCLE from largest to smallest: fascicle, fiber, fibril, and filament 2

3 Skeletal Muscle Fiber (Cellular level) Fully differentiated, specialized cell its structures are given special names sarcolemma (plasma membrane) sarcoplasm (cytoplasm) sarcoplasmic reticulum (ER) transverse tubule (T-tubule) triad cisternae of sarcoplasmic reticulum (2) transverse, or T-tubule myofibril (1-2 µm diam.) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Sarcoplasmic reticulum is like the ER of other cells; but it contains [Ca 2+ ] Transverse or T-tubules contain extracellular fluid ( [Na + ], [K + ]) 7 Structure of the Sarcomere (Histological Level) I band A band H zone Z line M line Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 (~ 2µm long) The sarcomere is the contractile unit of skeletal (and cardiac) muscle 8 Structure of the Sarcomere (Histological/Molecular Level) A in A band stands for Anisotropic (dark) I in I band stands for Isotropic (LIght) Zones of non-overlap: I band (thin filaments), and H zone (thick filaments) A sarcomere runs from Z line (disk) to Z line (disk) (From Z to shining Z!) Figure from: Saladin, Anatomy & Physiology, McGraw Hill,

4 Preview of Skeletal Muscle Contraction Major steps: T Tubule 1. Motor neuron firing Sarcoplasmic reticulum 2. Depolarization (excitation) of muscle cell 3. Release of Ca 2+ from sarcoplasmic reticulum 4. Shortening of sarcomeres 5. Shortening of muscle/cts and tension produced Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Physiology here we come!! 10 Grasping Physiological Concepts The steps in a physiological process give you the when, i.e. tell you when things happen and/or the order in which they happen. For each step in a process, you should MUST ask yourself the following questions - and be sure you get answers! How? (How does it happen?) Why? (Why it happens and/or why it s important?) What? (What happens?) See Figures 9.7 and 9.8 in your textbook for excellent overall summaries of the muscle contraction process 11 Sliding Filament Theory Figure from: Hole s Human A&P, 12 th edition, 2010 Theory used to explain these observations is called the sliding filament theory 13 4

5 Myofilaments (Molecular Level) Thick Filaments composed of myosin cross-bridges Thin Filaments composed of actin associated with troponin and tropomyosin 14 Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 The Sarcomere as a 3D Object 15 Mechanism of Sarcomere Contraction Figure from: Hole s Human A&P, 12 th edition, 2010 When you think myosin, think mover: 1. Bind 2. Move 3. Detach 4. Reset Ca 2+ troponin myosin actin 16 5

6 Mechanism of Sarcomere Contraction 4. Reset Figure from: Hole s Human A&P, 12 th edition, Bind 3. Detach 2. Move Cycle repeats about 5 times/sec Each power stroke shortens sarcomere by about 1% So, each second the sarcomere shortens by about 5% See Textbook Figure 9.12 (Focus Cross Bridge Cycle) What would happen if ATP was not present? 17 site where axon and muscle fiber communicate motor neuron motor end plate synaptic cleft synaptic vesicles neurotransmitters Neuromuscular Junction The neurotransmitter for initiating skeletal muscle contraction is acetylcholine (ACh) Ca2+ Ca 2+ Ca2+ Ca 2+ Ca 2+ Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 SR 18 Stimulus for Contraction: Depolarization nerve impulse causes release of acetylcholine (ACh) from synaptic vesicles ACh binds to acetylcholine receptors on motor end plate generates a muscle impulse muscle impulse eventually reaches sarcoplasmic reticulum (via T tubules) and Ca 2+ is released acetylcholine is destroyed by the enzyme acetylcholinesterase (AChE) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Linking of nerve stimulation with muscle contraction is called excitation-contraction coupling (See Fig 9.11 in textbook) 19 6

7 Summary of Skeletal Muscle Contraction Figure from: Martini, Anatomy & Physiology, Prentice Hall, Contraction Cycle begins - Bind (Ca, myosin) - Move - Detach - Reset Contraction Relaxation See Textbook Figure 9.12 (Focus Cross Bridge Cycle) 20 Modes of ATP Synthesis During Exercise Muscle stores enough ATP for about 4-6 seconds worth of contraction, but is the only energy source used directly by muscle. So, how is energy provided for prolonged contraction? Continual shift from one energy source to another rather than an abrupt change 21 Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 Energy Sources for Contraction (Creatine-P) Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 myoglobin stores extra oxygen so it can rapidly supply muscle when needed 22 7

8 Oxygen Debt (Excess Post Exercise O 2 Consumption EPOC) EPOC - amount of extra oxygen needed by liver to convert lactic acid to glucose, resynthesize creatine-p, make new glycogen, and replace O 2 removed from myoglobin. when oxygen is not available glycolysis continues pyruvic acid converted to lactic acid (WHY?) liver converts lactic acid to glucose Figure from: Hole s Human A&P, 12 th edition, 2010 (The Cori Cycle) 23 Muscle Fatigue Inability to maintain force of contraction although muscle is receiving stimulus to contract Commonly caused by decreased blood flow ion imbalances accumulation of lactic acid relative (not total) decrease in ATP availability decrease in stored ACh Cramp sustained, involuntary contraction 24 Length-Tension Relationship Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 Maximum tension in striated muscle can only be generated when there is optimal (80-100%) overlap between myosin and actin filaments 25 8

9 Muscular Responses Threshold Stimulus minimal strength required to cause contraction in an isolated muscle fiber Record of a Muscle Contraction = myogram latent period period of contraction period of relaxation refractory period all-or-none response Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 An individual muscle fiber (cell) is either on or off and produces maximum tension at that resting length for a given frequency of stimulation 26 Treppe, Wave Summation, and Tetanus Treppe, Wave Summation, and Tetanus all involve increases in tension generated in a muscle fiber after more frequent re-stimulation The difference among them is WHEN the muscle fiber receives the second, and subsequent, stimulations: Treppe stimulation immediately AFTER a muscle cell has relaxed completely. Wave Summation Stimulation BEFORE a muscle fiber is relaxed completely Incomplete (unfused) tetanus partial relaxation between stimuli Complete (fused) tetanus NO relaxation between stimuli 27 Treppe, Wave Summation, and Tetanus Treppe (10-20/sec) Wave (Temporal) Summation Little/no relaxation period Incomplete Tetanus (20-30/sec) Complete Tetanus (>50/sec) Tetany is a sustained contraction of skeletal muscle Figure from: Martini, Anatomy & Physiology, Prentice Hall,

10 Motor Unit single motor neuron plus all muscle fibers controlled by that motor neuron Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, Recruitment of Motor Units recruitment - increase in the number of motor units activated to perform a task whole muscle composed of many motor units as intensity of stimulation increases, recruitment of motor units continues, from smallest to largest, until all motor units are activated 30 Sustained Contractions smaller motor units recruited first larger motor units recruited later produces smooth movements muscle tone continuous state of partial contraction 31 10

11 Types of Contractions isotonic muscle contracts and changes length concentric shortening contraction eccentric lengthening contraction isometric muscle contracts but does not change length Figure from: Hole s Human A&P, 12 th edition, Alternate name Types of Skeletal Muscle Fibers Slow Oxidative (SO) (REDSOX) Slow-Twitch Type I Fast Oxidative- Glycolytic (FOG) Fast-Twitch Type II-A Fast Glycolytic (FG) Fast-Twitch Type II-B Myoglobin (color) +++ (red) ++ (pink-red) + (white) Metabolism Strength Oxidative (aerobic) Small diameter, least powerful Oxidative and Glycolytic Intermediate diameter/strength Glycolytic (anaerobic) Greatest diameter, most powerful Fatigue resistance High Moderate Low Capillary blood supply Dense Intermediate Sparse All fibers in any given motor unit are of the same type 33 Types of Skeletal Muscle Fibers All fibers in any given motor unit are of the same type 34 11

12 Smooth Muscle Fibers Compared to skeletal muscle fibers shorter single nucleus elongated with tapering ends myofilaments organized differently no sarcomeres, so no striations lack transverse tubules sarcoplasmic reticula not well developed exhibit stress-relaxation response (adapt to new stretch state and relax) Figure from: Martini, Anatomy & Physiology, Prentice Hall, Types of Smooth Muscle Single-unit (unitary) smooth muscle visceral smooth muscle sheets of muscle fibers that function as a group, i.e., a single unit fibers held together by gap junctions exhibit rhythmicity exhibit peristalsis walls of most hollow organs, blood vessels, respiratory/urinary/ reproductive tracts Multiunit Smooth Muscle fibers function separately, i.e., as multiple independent units muscles of eye, piloerector muscles, walls of large blood vessels 36 Smooth Muscle Contraction Resembles skeletal muscle contraction interaction between actin and myosin both use calcium and ATP both depend on impulses Different from skeletal muscle contraction smooth muscle lacks troponin smooth muscle depends on calmodulin two neurotransmitters affect smooth muscle acetylcholine and norepinephrine hormones affect smooth muscle have gap junctions stretching can trigger smooth muscle contraction (but briefly, then relaxation again occurs) smooth muscle slower to contract and relax smooth muscle more resistant to fatigue smooth muscle can undergo hyperplasia, e.g., uterus 37 12

13 Cardiac Muscle only in the heart muscle fibers joined together by intercalated discs fibers branch network of fibers contracts as a unit (gap junctions) self-exciting and rhythmic longer refractory period than skeletal muscle (slower contract.) cannot be tetanized fatigue resistant has sarcomeres Figure from: Martini, Anatomy & Physiology, Prentice Hall, Review Three types of muscle tissue Skeletal Cardiac Smooth Muscle tissue is Contractile Extensible Elastic Conductive Excitable 39 Review Functions of muscle tissue Provide stability and postural tone Purposeful movement Regulate internal organ movement and volume Guard entrances/exits Generation of heat Muscle fiber anatomy Actin filaments, tropomyosin, troponin Myosin filaments Sarcomere Bands and zones 40 13

14 Review Muscle contraction Sliding filament theory Contraction cycle (Bind, Move, Detach, Release) Role of ATP, creatine Metabolic requirements of skeletal muscle Stimulation at neuromuscular junction Muscular responses Threshold stimulus Twitch latent period, refractory period All or none response Treppe, Wave summation, and tetanus 41 Review Muscular responses Recruitment Muscle tone Types of muscle contractions Isometric Isotonic Concentric Eccentric Fast and slow twitch muscle fibers Slow Oxidative (Type I) (think: REDSOX) Fast Oxidative-glycolytic (Type II-A) Fast Glycolytic (Type II-B) 42 14