Muscular System (Our Muscle)


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Learn about how our muscle functioning everyday. And check out the muscle roles!! Simple notes, Simple slides for the beginner person who's attracted to science.

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Muscular System (Our Muscle)

  1. 1. MUSCULAR SYSTEM OBJECTIVE: •Identify the basic behavioral properties of the musculotendinous unit •Structure of skeletal muscle •Change in muscle length with tension development •Factors affecting muscular force generation 1
  2. 2. BEHAVIORAL PROPERTIES OF THE MUSCULOTENDINOUS UNIT   Four behavioral properties of muscle tissue:  Extensibility  Elasticity  Irritability  The ability to develop tension These properties are common to all muscle, including the cardiac, smooth, & skeletal muscle of human beings. 2
  3. 3. Extensibility & Elasticity The properties of extensibility & elasticity are common to many biological tissues.  Extensibility – the ability to be stretched or to increase in length.  Elasticity – the ability to return to normal length after a stretch. Muscle’s elasticity returns it to normal resting length following a stretch & provides for the smooth transmission of tension from muscle to bone. 3
  4. 4. Two major components of the elastic behavior of muscle:  Parallel elastic component (PEC)  Passive elastic property of muscle derived from the muscle membranes.  Series elastic component (SEC)  Passive elastic property of muscle derived from the tendons.  Act as a spring to store elastic energy (EE) when a tensed muscle is stretched.  Contractile component  Muscle property enabling tension development by stimulated muscle fibers.  Membranes & tendons are respectively parallel to & in series (or in line) with the muscle fibers. 4
  5. 5. Parallel Elastic Component Contractile Component Series Elastic Component 5
  6. 6. The elasticity of human skeletal muscle is believed to be due primarily to the SEC.  When a tensed muscle is stretched, the SEC causes an elastic recoil effect  The stretch promotes subsequent forceful shortening of the muscle  This pattern of eccentric contraction followed immediately by concentric contraction is known as the stretch-shortening cycle. This phenomenon contributes to effective development of concentric muscular force in many sport activities. 6
  7. 7. The stretch-shortening cycle also promotes storage & use of elastic energy (EE) during running, particularly with the alternating eccentric & concentric tension present in the gastrocnemius. Both SEC & PEC have a viscous property that enable muscle to stretch & recoil in a timedependent fashion. When static stretch of a muscle group is maintained over time, the muscle progressively lengthens, increasing joint range of motion  After a group has been stretched, it does not recoil to resting length immediately, but shortens gradually over time  7
  8. 8. 8
  9. 9.  Extensibility  Elasticity  Irritability  The ability to develop tension 9
  10. 10. Irritability & the Ability to Develop Tension Irritability- The ability to respond to a stimulus. Stimuli affecting muscles are either:  Electrochemical – action potential from the attaching nerve.  Mechanical – an external blow to a portion of a muscle. Muscle stimulus Develop tension • The ability to develop tension is the one behavioral characteristic unique to muscle tissue. • Development of tension = contraction (eccentric or concentric) 10
  11. 11. STRUCTURAL ORGANIZATION OF SKELETAL MUSCLE Approximately 434 muscles in the human body (4045% of the body weight of most adult). About 75 muscle pairs are responsible for body movements & posture, with the remainder involved in activities such as eye control & swallowing. 11
  12. 12. Structure of Skeletal Muscle (muscle fiber) Epimysium Bone Epimysium Perimysium Endomysium Tendon (b) Perimysium Fascicle (a) Muscle fiber in middle of a fascicle Blood vessel Fascicle (wrapped by perimysium) Endomysium (between individual muscle fibers) Muscle fiber (single muscle cell) 12
  13. 13. Epimysium  The outermost layer that surround the entire muscle. Perimysium  Connective tissue surround individual bundles of muscle fibers (inward from the epimysium). Fascicle  Individual bundle of muscle fibers. Endomysium  Connective tissue surrounded for each muscle fiber within the fasciculus. 13
  14. 14. Sarcolemma ◦ The cell membrane surrounding the muscle fiber cell. Myofibrils ◦ Numerous threadlike structure that contain the contractile proteins (protein filaments)  Myosin – thick filaments composed of the protein.  Actin – thin filaments composed primarily of the protein. Sarcoplasmic reticulum ◦ The storage sites for calcium, which plays an important role in muscular contraction. Sarcomeres ◦ Myofibrils further subdivided into individual segments. 14
  15. 15. Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next (basic structural unit of muscle fiber). Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments. M line Bisect each sarcomere (middle) A band Contain thick, rough myosin filament, each of which is surrounded by thin, smooth actin filaments I band Contain only thin actin filaments Z lines (disc) Attachment of thin actin filaments H zones Center of A bands, contain only thick myosin 15
  16. 16. Part of a skeletal muscle fiber (cell) A band I band Z disc Myofibril I band H zone Z disc M line Sarcolemma Sarcolemma Triad: • T tubule • Terminal cisternae of the SR (2) Tubules of the SR Myofibrils Mitochondria 16 Figure 9.5
  17. 17. Motor Units Composed of a single motor neuron & all fibers innervated by it. Typically, there is only 1 end plate per fiber. A single mammalian motor unit may contain from less than 100 to nearly 2000 fibers, depending on the type of movements the muscle executes.   Movements that are precisely controlled (eyes, fingers) produced by motor units with small numbers of fibers Gross, forceful movements (gastrocnemius) result of the activity of large motor units 17
  18. 18. Spinal cord Motor Motor unit 1 unit 2 Axon terminals at neuromuscular junctions Nerve Motor neuron cell body Motor Muscle Motor end plate neuron axon Muscle fibers Axons of motor neurons extend from the spinal cord to the muscle. There each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle. 18 Figure 9.13a
  19. 19. Fiber Types Slow twitch fiber (ST) ◦ A fiber that reaches peak tension relatively slowly. Fast twitch fiber (FT) ◦ A fiber that reaches peak tension relatively quickly. ◦ Fast-twitch Oxidative Glycolytic ◦ Fast-twitch Glycolytic 19
  20. 20. SKELETAL MUSCLE FIBER CHARACTERISTICS CHARACTERISTIC TYPE 1 SLOWTWITCH OXIDATIVE (SO) TYPE IIA FAST-TWITCH OXIDATIVE GLYCOLYTIC (FOG) TYPE IIB FASTTWITCH GLYCOLYTIC (FG) Contraction speed Slow Fast Fast Fatigue rate Slow Intermediate fast Diameter Small Intermediate Large ATPase concentration Low High High Mitochondrial concentration High High Low Glycolytic enzyme concentration Low Intermediate High 20
  21. 21. FT ST Twitch tension Time 21
  22. 22. Fiber Architecture Two categories of muscle fiber arrangement ◦ Parallel fiber arrangement  Pattern of fibers within a muscle in which the fibers are roughly parallel to the longitudinal axis of the muscle.  E.g. sartorius, rectus abdominis, biceps brachii. 22
  23. 23. Pennate fiber arrangement  Pattern of fibers within a muscle with short fibers attaching to one or more tendons (lie at an angle).  E.g. tibialis posterior, rectus femoris, deltoids 23
  24. 24. SKELETAL MUSCLE FUNCTION When an activated muscle develops tension, the amount of tension present is constant throughout the length of the muscle, & at the sites of the musculotendinous attachments to bone. The tensile force (stretching force) developed by the muscle pulls on the attached bones & create torque at the joints crossed by the muscle. 24
  25. 25. Torque (Tm ) produced by a muscle at the joint center of rotation is the product of muscle force ( Fm ) & muscle moment arm ( d⊥ ). 25
  26. 26. The torque exerted by the biceps brachii (Fb) must counteract the torques created by the force developed in the triceps brachii (Ft), the weight of the forearm & hand (wtf), & the weight of the shot held in the hand (wts). 26
  27. 27. Recruitment of motor units The CNS exerts an elaborate system of control that enables: ◦ Matching of the speed & magnitude of muscle contraction to the requirements of the movement so that:  Smooth, delicate, & precise movements can be executed. Slow twitch (ST) motor units generally have low thresholds & are relatively easy to activate. Fast twitch (FT) motor units are supplied by nerves more difficult to activate. 27
  28. 28. Change in Muscle Length with Tension Development When muscular tension produces a torque larger than the resistive torque at a joint, the muscle shortens, causing a change in the angle at the joint. Type of contraction; ◦ Concentric ◦ Eccentric ◦ Isometric 28
  29. 29. Concentric    Eccentric Isometric Contraction involving shortening of muscle Resulting joint movement is in the same direction as the net torque generated by the muscle. A single muscle fiber is capable of shortening to approximately one-half of its normal resting length. 29
  30. 30. Concentric      Eccentric Isometric When opposing joint torque exceeds that produced by tension in a muscle, the muscle lengthens. When a muscle lengthens as it is being stimulated to develop tension. The direction of joint motion is opposite that of the net muscle torque. The eccentric tension acts as a braking mechanism to control movement speed. E.g. without the presence of eccentric tension in muscles, the forearms, hand, & weight would drop uncontrolled because of the force of gravity. 30
  31. 31. Concentric   Eccentric Isometric Muscular tension is developed but no change in muscle length. Opposing torque at the joint crossed by the muscle is equal to the torque produced by the muscle (with zero net torque present), ◦ Muscle length remains unchanged & no movement occurs at the joint. 31
  32. 32. SKELETAL MUSCLE FUNCTION Recruitment of motor units  Change in muscle length with tension development  Roles assumed by muscles  32
  33. 33. Roles Assumed by Muscles  Agonist  Antagonist  Stabilizers  Neutralizer 33
  34. 34. Agonist    Prime mover. When a muscle contracts & causes movement of a body segment at a joint. E.g. ◦ During the elbow flexion phase of a forearm curl, the brachialis & the biceps brachii act as the primary agonist, with the brachioradialis, extensor carpi radialis longus, & pronator teres serving as assistant agonist. 34
  35. 35. Antagonist     Muscle with actions opposite those of the agonist act. Opposers by developing eccentric tension at the same time that the agonists are causing movement. Agonists & antagonists are typically positioned on opposite sides of a joint. E.g. ◦ During elbow flexion when the brachialis & the biceps brachii are primary agonists, the triceps could act as antagonists by developing resistive tension. 35
  36. 36. Stabilizers   Stabilizing a portion of the body against a particular force. ◦ The force may be internal, from tension in other muscles, or external, such as the weight of an object being lifted. E.g. ◦ The rhomboids act as stabilizers by developing tension to stabilize the scapulae against the pull of the tow rope during water skiing, or on tugof-war event. 36
  37. 37. Neutralizer    Neutralizers muscle prevent unwanted accessory actions that normally occur when agonists develop concentric tension. E.g. ◦ When the biceps brachii develops concentric tension, it produces both flexion at the elbow & supination of the forearm. If only elbow flexion is desired, the pronator teres act as a neutralizer to counteract the supination of the forearm. Performance of human movements typically involves the cooperative actions of many muscle groups acting sequentially & in concert. 37
  38. 38. Factors Affecting Muscular Force Generation The magnitude of the force generated by muscle is also related to: Velocity of muscle shortening Length of the muscle when it is stimulated Period of time since the muscle received a stimulus Factors affecting: Force-Velocity relationship Length-Tension Relationship Electromechanical Delay (EMD) 38
  39. 39. Force-Velocity Relationship for muscle tissue When the resistance (force) is negligible, muscle contracts with maximal velocity.  As the load progressively increases, concentric contraction velocity slows to zero at isometric maximum.  As the load increases further, the muscle lengthens eccentrically. Maximall y activated muscle FVR does NOT imply that it is impossible to move a heavy resistance at a fast speed.  The stronger a muscle, the greater the magnitude of maximum isometric tension FVR also does NOT imply that it is impossible to move a light load at a slow speed. 39
  40. 40. Length-Tension Relationship The total tension present in a stretched muscle is the sum of the active tension provided by the muscle fibers & the passive tension provided by the tendons & muscle membranes. Total tension = active tension (muscle fibers) + passive tension (tendons & muscle membranes) Within the human body, force generation capability increases when the muscle is lightly stretched.  Parallel-fibered muscles produce maximum tensions at just over resting length.  Pennate-fibered muscles generate maximum tension at between 120% & 130% of resting length.  This phenomenon is due to the contribution of the elastic components of muscle (primarily the SEC), which add to the tension present in the muscle when the muscle is stretched. 40
  41. 41. Electromechanical Delay (EMD) When a muscle is stimulated, a brief period of time elapse before the muscle begins to develop tension. ED- time between the arrival of neural stimulus and tension development by the muscle 41
  42. 42. EMD where the period of time is believed to be needed for the contractile component of the muscle to stretch the SEC. During this time, muscle laxity is eliminated. Once the SEC is sufficiently stretched, tension development proceeds. Researchers have found shorter EMDs produced by muscles with high percentages of FT fibers as compared to muscles with high percentages of ST fibers. 42
  43. 43. Muscular Strength, Power & Endurance Muscular Strength The maximum amount of force a muscle can produce in a single effort Muscular Power The product of muscular force and the velocity of muscle shortening Muscular Endurance The ability of a muscle to exert a sub-maximal force repeatedly over time 43
  44. 44. What is the effect of muscle temperature (warm up) ? The speeds of nerve and muscle functions increase. Normal body temperature Elevated body temperature velocity With warm-up, there is a shift to the right in the force-velocity curve, with higher maximum isometric tension and higher maximum velocity of shortening possible at a given load. force 44
  45. 45. Common Muscle Injuries Strains - overstretching of muscle tissue Contusions - compressive forces sustained during impacts Cramps - electrolytes imbalance, deficiencies in calcium & magnesium, dehydration Delayed-Onset Muscle Soreness (DOMS) ◦ occurs after some period of time following unaccustomed exercise. ◦ arises 24 – 72 hours after participation in a long or strenuous bout of exercise. 45