Section 03: The Muscular System

Transcription

1 Section 03: The Muscular System Chapter 18 Skeletal Muscle: Structure and Function Chapter 19 Neural Control of Human Movement Chapter 22 Muscular Strength: Training Muscles to Become Stronger (Part 2 Structural and Functional Adaptations to Resistance Training, pp ) HPHE 6710 Exercise Physiology II Dr. Cheatham Chapter 18 Skeletal Muscle: Structure and Function 1

2 Chapter Objectives Be able to identify the different overall structures/level of organization of muscle Identify the different components of a muscle fiber Understand the influence of muscle pennation on force production and velocity of contraction Understand the Sliding Filament Model Understand excitation contraction coupling Understand the different muscle fiber types and the influence on muscle performance Gross Structure of Skeletal Muscle Levels of Organization Connective tissue layers Endomysium Wraps each muscle fiber, separates from other fibers Perimysium Surrounds a bundle of fibers (up to 150) called a fasciculus Epimysium Surrounds all the bundles to form the entire muscle Tapers at both proximal and distal ends to form tendons (connect muscle to bone)» Origin: More stable bone» Insertion: Moving bone 2

3 Gross Structure of Skeletal Muscle Levels of Organization (cont d) Sarcolemma Thin elastic membrane that surrounds the muscle fiber Plasma membrane Bilayer lipid structure that conducts the electrochemical wave of depolarization over the surface of the muscle fiber Basement membrane Proteins and strands of collagen fibrils that fuse with the outer covering of the tendon Satellite Cells Between the plasma and basement membranes Cellular growth, recovery, hypertrophy Gross Structure of Skeletal Muscle 3

4 Gross Structure of Skeletal Muscle Levels of Organization (cont d) Sarcoplasmic Reticulum Extensive latticelike network of tubules and vesicles Provides structural integrity Stores, releases, and reabsorbs Ca 2+ Gross Structure of Skeletal Muscle 4

5 Gross Structure of Skeletal Muscle Chemical Composition 75% water 20% protein Myosin, actin, tropomyosin, troponin, myoglobin 5% salts, phosphates, ions, macronutrients Blood Supply Skeletal muscle has a rich vascular network 200 to 500 capillaries per mm 2 of muscle Flow is rhythmic Vessels compress during contraction phase Vessels open during relaxation phase Gross Structure of Skeletal Muscle 5

6 Skeletal Muscle Ultrastructure Myofibrils contain myofilaments. Actin (thin filament) Myosin (thick filament) Also of functional importance Troponin Tropomyosin In addition, there are several other structural proteins. Skeletal Muscle Ultrastructure 6

7 Skeletal Muscle Ultrastructure The Sarcomere Most basic, functional unit of a muscle fiber Runs from Z line to Z line Skeletal Muscle Ultrastructure 7

8 Skeletal Muscle Ultrastructure Sarcomere (cont d) A Band (Dark) Overlap of thick and thin filaments H Zone Lower density, lack of actin M Band Sarcomeres center I Band (Light) Lower density Skeletal Muscle Ultrastructure 8

9 Muscle Fiber Alignment Long axis of a muscle From origin to insertion Determines fiber arrangement Fusiform: Fibers run parallel to long axis Rapid muscle shortening Pennate: Fibers are at an oblique angle to long axis Bipennate, Multipennate Greater force production Fiber arrangement influences Force generating capacity Physiologic cross sections Muscle Fiber Alignment 9

10 Muscle Fiber Alignment Actin Myosin Orientation Actin filaments lie in a hexagonal pattern around myosin. Crossbridges spiral around the myosin where actin and myosin overlap. 10

11 Actin Myosin Orientation Tropomyosin Lies along actin in the groove formed by the double helix Inhibits actin myosin interaction Troponin Embedded at regular intervals along actin Interacts with Ca 2+ Moves tropomyosin, uncovering active actin sites Actin Myosin Orientation 11

12 Actin Myosin Orientation Intracellular Tubule Systems The T tubular system is distributed around the myofibrils such that each sarcomere has two triads. Each triad contains 2 vesicles 1 T tubule Actin Myosin Orientation 12

13 Chemical and Mechanical Events During Muscle Action and Relaxation Sliding Filament Model Contraction occurs as myosin and actin slide past one another. Myosin crossbridges cyclically attach, rotate, and detach from actin filaments. Energy is provided by ATP hydrolysis. Chemical and Mechanical Events During Muscle Action and Relaxation 13

14 Chemical and Mechanical Events During Muscle Action and Relaxation SarcomereLength Isometric Tension Chemical and Mechanical Events During Muscle Action and Relaxation Link Between Actin, Myosin, and ATP Myosin head bends around ATP molecule, becomes cocked Myosin interacts with actin. ATP is hydrolyzed. Energy release forces power stroke. 14

15 Chemical and Mechanical Events During Muscle Action and Relaxation Chemical and Mechanical Events During Muscle Action and Relaxation 15

16 Chemical and Mechanical Events During Muscle Action and Relaxation Chemical and Mechanical Events During Muscle Action and Relaxation Excitation Contraction Coupling 16

17 Muscle Fiber Types Fast Twitch Fibers (Type II) High capacity to transmit AP High myosin ATPase activity Rapid Ca 2+ release and uptake by SR High rate of crossbridge turnover Capable of high force generation Rely on anaerobic metabolism Slow Twitch Fibers (Type I) Low myosin ATPase activity Slower Ca 2+ release and uptake by SR Low glycolytic capacity Large and numerous of mitochondria Muscle Fiber Types Fast Twitch Subdivisions IIa fibers Fast shortening speed Moderately well developed capacity for both anaerobic and aerobic energy production IIb fibers Most rapid shortening velocity Rely on anaerobic energy production 17

18 Muscle Fiber Types Muscle Fiber Types 18

19 Muscle Fiber Types Muscle Fiber Types 19

20 Muscle Fiber Types Muscle Fiber Types 20

21 Chapter 19 Neural Control of Human Movement Chapter Objectives Review the CNS and peripheral nervous system Understand motor unit anatomy Review the action potential Understand the concept of excitationcontraction coupling Understand the activities of the motor unit as they relate to force production Be familiar with the characteristics of different muscle fiber types Understand proprioception 21

22 Neuromotor System Organization Human nervous system has two major parts: Central Nervous System Peripheral Nervous System Neuromotor System Organization CNS The Brain Six main areas: Medulla oblongata Pons Midbrain Cerebellum Diencephalon Telencephalon 22

23 Neuromotor System Organization CNS The Brain (cont d) Cerebellum Receives motor output signals from the central command in the cortex Obtains sensory input from peripheral receptors in muscles, tendons, joints, skin and from auditory, visual, and vestibular end organs Serves as the major comparing, evaluating, and integrating center for postural adjustments, locomotion, maintenance of equilibrium, perceptions of speed of body movement Neuromotor System Organization CNS The Brain (cont d) Diencephalon Thalamus Hypothalamus Regulates metabolic rate and body temperature Influences activity of the ANS Regulates and maintains the body s internal milieu 23

24 Neuromotor System Organization CNS The Brain (cont d) Telencephalon Contains two hemispheres of cerebral cortex 4 lobes Frontal Parietal Temporal Occipital Neuromotor System Organization CNS The Brain (cont d) Brainstem Medulla oblongata Serves as bridge between the two hemispheres of the cerebellum Pons Midbrain 24

25 Neuromotor System Organization CNS The Spinal Cord 45 cm long, 1 cm diameter Encased by 33 vertebrae Provides for two way flow of communication between brain and periphery via nerve tracts and sensory receptors Spinal cord contains three types of neurons Motor neurons Efferent fibers run to the skeletal muscle fibers Sensory neurons Afferent fibers that enter the spinal cord from the periphery Interneurons Neuromotor System Organization 25

26 Neuromotor System Organization Peripheral Nervous System 31 pairs of spinal nerves 12 pairs of cranial nerves Two types of efferent neurons Somatic neurons: innervate skeletal muscle Autonomic neurons: activate smooth muscle, cardiac muscle, sweat and salivary glands, and some endocrine glands Sympathetic and Parasympathetic Nervous Systems Neuromotor System Organization 26

27 Neuromotor System Organization Neuromotor System Organization The Reflex Arc 27

28 Nerve Supply to Muscle One nerve innervates at least one of the body s approximately 250 million muscle fibers Individuals possess approximately 420,000 motor neurons The number of muscle fibers per motor neuron generally relates to a muscles movement pattern Thinking question: Which neurons would only innervate a few muscle fibers? Which neurons would innervate several hundred muscle fibers? Nerve Supply to Muscle Motor Unit Anatomy Motor Unit: The functional unit of movement Motor neuron and innervated muscle fibers Motor Neuron Pool: The collection of alpha motor neurons that innervate a single muscle 28

29 Nerve Supply to Muscle Motor Unit Anatomy (cont d) The Anterior Motor Neuron Nerve Supply to Muscle Motor Unit Anatomy (cont d) The Anterior Motor Neuron Neuromuscular Junction 29

30 Action Potential Review Action Potential Review 30

31 Action Potential Review Nerve Supply to Muscle Motor Unit Anatomy (cont d) The Anterior Motor Neuron Excitation Facilitation» Temporal summation» Spatial Summation Inhibition 31

32 Nerve Supply to Muscle Nerve Supply to Muscle 32

33 Motor Unit Functional Characteristics Twitch Characteristics Motor Unit Functional Characteristics Twitch Characteristics (cont d) 33

34 Motor Unit Functional Characteristics Tension Characteristics All or none principle Gradation of force Motor unit recruitment To increase force, more motor units are recruited Motor units are recruited from smaller axons to larger axons (size principle) Discharge frequency Motor Unit Functional Characteristics Tension Characteristics (cont d) Neuromuscular Fatigue Fatigue is the decline in muscle tension or force capacity with repeated stimulation Voluntary muscle contractions are the result of a chain of events/systems: CNS» Alterations in neurotransmitters, ammonia, cytokins (central fatigue) Peripheral Nervous System» Fatigue?? Neuromuscular Junction» Fatigue?? Muscle Fiber» Glycogen depletion, PO 2, H +, reduced enzyme activity, etc. (p. 409) 34

35 Receptors in Muscles, Joints, and Tendons: The Proprioceptors Muscle Spindles Provide sensory feedback about changes in muscle fiber length and tension Receptors in Muscles, Joints, and Tendons: The Proprioceptors Muscle Spindles (cont d) Stretch Reflex Spindle responding to stretch Afferent nerve fiber Efferent spinal cord motor neuron 35

36 Receptors in Muscles, Joints, and Tendons: The Proprioceptors Golgi Tendon Organs Located at musculotendonous junction Detect difference in tension generated by active muscle Respond to tension generated by Muscle contraction Passive stretch Protect muscle from excessive load Receptors in Muscles, Joints, and Tendons: The Proprioceptors 36

37 Receptors in Muscles, Joints, and Tendons: The Proprioceptors Pacinian Corpuscles Small ellipsoidal bodies Located near Golgi tendon organs Embedded in a single unmyelinated nerve fiber Detect changes in movement or pressure Chapter 22 Muscular Strength: Training Muscles to Become Stronger (Part 2 Structural and Functional Adaptations to Resistance Training, pp ) 37

38 Section Objectives Understand the mechanisms relating to muscle hypertrophy Understand the mechanisms relating to muscle fiber type alteration Introduction 38

39 Factors That Modify the Expression of Human Strength Psychologic Neural Factors Factors That Modify the Expression of Human Strength 39

40 Factors That Modify the Expression of Human Strength Journal of Applied Physiology, Factors That Modify the Expression of Human Strength 40

41 Factors That Modify the Expression of Human Strength Factors That Modify the Expression of Human Strength Psychologic Neural Factors (cont d) 41

42 Factors That Modify the Expression of Human Strength Muscular Factors Factors That Modify the Expression of Human Strength Muscular Factors Muscle Hypertrophy The primary stimulus for muscle hypertrophy is an increase in muscular tension/force Mechanical stress triggers signaling proteins to activate genes that activate translation of mrna and stimulate protein synthesis What, though, signals this response to occur Will cover in a few slides (Muscle Cell Remodeling) 42

43 Factors That Modify the Expression of Human Strength Factors That Modify the Expression of Human Strength Significant Metabolic Adaptations Occur Fiber type alteration I IIA IIX IIB 43

44 Factors That Modify the Expression of Human Strength Factors That Modify the Expression of Human Strength Muscle Cell Remodeling: Current Thinking Muscle is a dynamic tissue in that it can change It is well established that muscle hypertrophy can occur and most likely fiber types can change as well What changes actually occur?: Fiber Type Most likely changes in the myosin ATPase isoform expression Increase in muscle size Hypertrophy: the addition of more muscle proteins to existing muscle fibers Hyperplasia: new muscle fibers 44

45 Factors That Modify the Expression of Human Strength Muscle Cell Remodeling: Current Thinking These changes to muscle have one thing in common: There is a change in gene expression or mrna which will lead to an increase (or decrease) in protein synthesis The underlying question: What signals cause gene expression to be turned on or turned off for a specific protein The answer to this question is not entirely clear Factors That Modify the Expression of Human Strength Fiber Type Changes Again, the change really is a change in the isoform of myosin ATPase Intracellular calcium may play a role Hypertrophy Autocrine signals (IFG 1, Prostaglandins) Acute immune response (IL 6) Growth factors Early response genes Regulation of myostatin Activation of satellite cells 45

46 Factors That Modify the Expression of Human Strength Factors That Modify the Expression of Human Strength 46

47 Factors That Modify the Expression of Human Strength 47