Muscular System Functions

Transcription

1 BMI 04 Skeletal Muscle & Force Generator J F Grosset BMI J F GROSSET 1 Muscular System Functions Body movement (Locomotion) Maintenance of posture Respiration Diaphragm and intercostal contractions Communication (Verbal and Facial) Constriction of organs and vessels Peristalsis of intestinal tract Vasoconstriction of b.v. and other structures (pupils) Heart beat Production of body heat (Thermogenesis) BMI J F GROSSET 2

2 Muscle Properties Excitability: capacity of muscle to respond to a stimulus Contractility: ability of a muscle to shorten and generate pulling force Extensibility: muscle can be stretched back to its original length Elasticity: ability of muscle to recoil to original resting length after stretched BMI J F GROSSET 3 Types of Muscle Skeletal Attached to bones Makes up 40% of body weight Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement Voluntary in action; controlled by somatic motor neurons Smooth In the walls of hollow organs, blood vessels, eye, glands, uterus, 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 Controlled involuntarily by endocrine and autonomic nervous systems BMI J F GROSSET 4

3 Different type of Muscle Tissues BMI J F GROSSET 5 Antagonistic Muscle Action Muscles are either contracted or relaxed When contracted the muscle exerts a pulling force, causing it to shorten Since muscles can only pull (not push), they work in pairs called antagonistic muscles The muscle that bends the joint is called the flexor muscle The muscle that straightens the joint is called the extensor muscle BMI J F GROSSET 6

4 Elbow Joint The best known example of antagonistic muscles are the brachial bicep & triceps muscles Elbow joint flexed Flexor muscles contracted Extensor muscles relaxed Elbow joint extended Extensor muscles contracted Flexor muscles relaxed Section through arm biceps triceps Flexor muscles Humerus Bone Extensor muscles BMI J F GROSSET 7 Skeletal Muscle Structure Composed of muscle cells (fibers), connective tissue, blood vessels, nerves Fibers are long, cylindrical, and 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 Nuclei are peripherally located BMI J F GROSSET 8

5 Parts of a Muscle BMI J F GROSSET 9 Sarcoplasmic Reticulum (SR) BMI J F GROSSET 10

6 Sarcomeres: Z Disk to Z Disk Sarcomere repeating functional units of a myofibril About 10,000 sarcomeres per myofibril, end to end Each is about 2 µm long Differences in size, density, and distribution of thick and thin filaments gives the muscle fiber a banded or striated appearance. A bands: a dark band; full length of thick (myosin) filament M line protein to which myosins attach H zone thick but NO thin filaments I bands: a light band; from Z disks to ends of thick filaments Thin but NO thick filaments Extends from A band of one sarcomere to A band of the next sarcomere Z disk: filamentous network of protein. Serves as attachment for actin myofilaments Titin filaments: elastic chains of amino acids; keep thick and thin filaments in proper alignment BMI J F GROSSET 11 BMI J F GROSSET 12

7 Structure of Actin and Myosin BMI J F GROSSET 13 Myosin (Thick) Myofilament Many elongated myosin molecules shaped like golf clubs. Single filament contains roughly 300 myosin molecules 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 1. Can bind to active sites on the actin molecules to form cross bridges. (Actin binding site) 2. Attached to the rod portion by a hinge region that can bend and straighten during contraction. 3. 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 BMI J F GROSSET 14

8 Thin Filament: composed of 3 major proteins 1. F (fibrous) actin 2. Tropomyosin 3. Troponin 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 a myosin binding site (see yellow dot) 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: Tn A : binds to actin Tn T :binds to tropomyosin, Tn C :binds to calcium ions. Actin (Thin) Myofilaments BMI J F GROSSET 15 Now, putting it all together to perform the function of muscle: Contraction BMI J F GROSSET 16

9 Sliding filament model Sarcomere Relaxed Sarcomere Partially Contracted Sarcomere Completely Contracted BMI J F GROSSET 17 Sliding filament model BMI J F GROSSET 18

10 Sliding filament model BMI J F GROSSET 19 Muscle Architecture Fusiform vs pennate muscle Lm = Lf Lm Lf BMI J F GROSSET 20

11 shortening Three potential actions during muscle contraction Biceps muscle shortens during contraction (Isotonic: shortening against fixed load, speed dependent on M ATPase activity and load) isometric lengthening Biceps muscle lengthens during contraction Most likely to cause muscle injury BMI J F GROSSET 21 Muscle Architecture Rest vs contraction BMI J F GROSSET 22 Narici et al (1996)

12 Neuromuscular Junction BMI J F GROSSET 23 BMI J F GROSSET 24

13 Motor Unit All muscle cells are controlled by one nerve cell BMI J F GROSSET 25 Motor Units in a Skeletal Muscle BMI J F GROSSET 26

14 Muscle Fibers Classification Classification Basis Contractile Properties slow fast Metabolic Properties oxidative glycolytic Color Properties red white Staining Properties enzymes ph BMI J F GROSSET 27 Contractile Properties BMI J F GROSSET 28

15 Contractile Properties BMI J F GROSSET 29 Motor Unit Recruitment BMI J F GROSSET 30

16 BMI J F GROSSET 31 Shortening velocity distribution under zero force (Bottinelli et al., 1991) BMI J F GROSSET 32

17 Contraction Speed BMI J F GROSSET 33 Fiber Types Characteristics BMI J F GROSSET 34

18 Distribution of Fiber Types (Tirrell et al, 2012) BMI J F GROSSET 35 Distribution of Fiber Types (Tirrell et al, 2012) BMI J F GROSSET 36

19 Distribution of Fiber Types Animal (Tirrell et al, 2012) BMI J F GROSSET 37 Distribution of Fiber Types Great variation between individuals Vastus lateralis of elite distance runners had 79% ST, untrained had 58% Available evidence indicates that the distribution of slow and fast twitch fibers is genetically determined and not altered by training BMI J F GROSSET 38

20 Relationship between mechanical response and muscle activation Electrical stimulation Force sensor Parameters: Electrmechanical delay (EMD) Peak twitch (Pt) Contraction time (CT) Half relaxation time (HRT) Rate of torque development(dpt/dt) BMI J F GROSSET 39 3 Phases of a muscle Twitch 1. Latent period before contraction: the action potential moves through sarcolemma causing Ca 2+ release 2. Contraction phase: calcium ions bind tension builds to peak 3. Relaxation phase: Ca 2+ levels fall active sites are covered tension falls to resting levels BMI J F GROSSET 40

21 Muscle twitch and fiber type BMI J F GROSSET 41 BMI J F GROSSET 42

22 BMI J F GROSSET 43 Single twitch Incomplete Tetanus Complete Tetanus If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction BMI J F GROSSET 44

23 Three element Hill muscle model Modèle de Hill (1938) modifié par Shorten (1987) CC: Actin myosin cross bridges SEC: Actin myosin cross bridges + tendinous structures PEC: titin, connective tissues (fascia, epimysium, perimysium and endomysium) BMI J F GROSSET 45 Contractile Component Tension Length relationship under isometric condition st st st Lo L1 L2 P2 Force = 0 Po P1 An isolated muscle under tetanic contraction maximal isometric force for each muscle lenght Force-muscle lenght relationship BMI J F GROSSET 46

24 Contractile Component Force-muscle length relationship for isolated muscle Total tension Force (%) Active tension Passive tension Muscle lenght BMI J F GROSSET 47 Contractile Component Tension and Sarcomere Length BMI J F GROSSET 48

25 Contractile Component Force- muscle length relationship for different muscles with the same myotypology Gastrocnemius medialis Semi membranosus Tension Lenght Lenght Pennated muscle Short muscle fibers. Important conjonctive tissu Thin muscle with parallel fibers Influence on: Stretching capacity Passive tension Twitch force Tetanic force BMI J F GROSSET 49 Contractile Component Force- muscle length relationship and myotypology Soleus (slow) Flexor hallucis longus (fast) A = Tetanic forces B = Twitch forces C = Passive forces Influence on: Stretching capacity Passive tension Twitch force Tetanic force BMI J F GROSSET 50

26 Contractile Component Torque- angle Relationship Elbow BMI J F GROSSET 51 Contractile Component Torque- angle Relationship BMI J F GROSSET 52

27 Contractile Component Force shortening velocity relationship Po P P = 0 Lo Slope = shortening velocity An isolated muscle under tetanic contraction imposed shortening maximal isometric force for each muscle length constant velocity (isokinetic contraction) Force-shortening velocity relationship BMI J F GROSSET 53 Contractile Component Force shortening velocity relationship P/Po Hill s equation: ( P + a ) ( V + b ) = b ( Po + a ) Hyperbolic shape V = b ( Po - P) / ( P + a ) Vmax = shortening velocity under zero load Vmax 0 Velocity Vmax = b Po / a a = constant in force b = constant in velocity BMI J F GROSSET 54

28 Contractile Component Shortening velocity & fiber type BMI J F GROSSET 55 Contractile Component Force shortening velocity relationship & Fiber type BMI J F GROSSET 56

29 Contractile Component Maximal shortening velocity (Vmax) & temperature BMI J F GROSSET 57 Contractile Component Force shortening velocity relationship & temperature BMI J F GROSSET 58

30 Contractile Component Influence of muscle architecture PCSA Fascicule length L = Max tension L Max tension = Vmax = Max tension Vmax Max tension = BMI J F GROSSET 59 Lieber et Friden (2000) Contractile Component Plasticity Cross innervation BMI J F GROSSET 60

31 Contractile Component Plasticity Plyometric training BMI J F GROSSET 61 Contractile Component Plasticity Plyometric traning Soleus muscle before training (Rat) Soleus muscle after plyometric training (Rat) BMI J F GROSSET 62

32 Contractile Component Plasticity Hyper activity BMI J F GROSSET 63 Contractile Component Plasticity Fiber length & running perf Abe et al (2000) Kumagai et al (2000) BMI J F GROSSET 64

33 Serie Elastic Component Quick Release Controlled Release BMI J F GROSSET 65 Serie Elastic Component Tension extension relationship Mechanical parameters: - stiffness (ΔP/ΔL) - compliance (ΔL/ΔP) - maximal extension - potential elastic energy BMI J F GROSSET 66

34 Serie Elastic Component Tension extension relationship & Fiber types BMI J F GROSSET 67 Serie Elastic Component Tension extension relationship & activity BMI J F GROSSET 68

35 Parallel Elastic Component BMI J F GROSSET 69 Parallel Elastic Component Passive stress strain relationship Stress N.m -2 Strain (%) Mechanical parameters: stiffness index maximal stress maximal strain BMI J F GROSSET 70

36 Parallel Elastic Component Fiber type BMI J F GROSSET 71 Parallel Elastic Component Plasticity BMI J F GROSSET 72

37 Parallel Elastic Component Ageing BMI J F GROSSET 73