Muscle Part 2 POWERPOINT PDF

Anatomy & Physiology I 1 FACTORS AFFECTING CONTRACTION FORCE Contraction Type Muscle Stretch Motor Unit Recruitment Fiber Types Frequency of Contraction 2 ALL OR NONE PRINCIPLE When an individual muscle f...

Anatomy & Physiology I 1 FACTORS AFFECTING CONTRACTION FORCE Contraction Type Muscle Stretch Motor Unit Recruitment Fiber Types Frequency of Contraction 2 ALL OR NONE PRINCIPLE When an individual muscle fiber is exposed to a threshold stimulus, it contracts to its fullest extent, for the conditions at that time – i.e. muscle fibers do not partially contract 3 However, the entire muscle organ may have varying degrees of contraction 4 TWO TYPES OF CONTRACTIONS Isotonic: movement Isometric: no movement 5 Isotonic there is shortening of the overall muscle that results in movement 6 2 Types of isotonic contractions Concentric: – contraction w/ muscle shortening – e.g. picking up a book Eccentric: – contraction w/ muscle lengthening – e.g. putting the book down 7 Isometric: no muscle shortening or movement However, overall muscle tension ↑↑↑ e.g. holding a book, posture Occurs when muscle attempts to move a load greater than the force the muscle can hold 8 RECRUITMENT OF MOTOR UNITS An entire muscle organ may have graded contractions Muscle is composed of many motor units: 1 motor neuron + its associated muscle fibers 9 The # of motor units varies with the muscle type postural muscle: 1 neuron: _________ myocytes eye muscles: 1 neuron: _________ myocytes 10 Relative % brain regions devoted to muscle movement 11 motor unit recruitment ↑ the # of motor units activated in a muscle will ↑ contraction force or range of motion 12 motor unit recruitment In a given muscle organ, some fibers are contracting; others are relaxing or extending Allows movement to be more or less forceful 13 motor unit recruitment & fiber size Note: same goes for # of fibers recruited 14 FREQUENCY OF CONTRACTION 15 MYOGRAM: A record of a muscle contraction Isolate muscle and attach to a tension meter Stimulate with electric shock 16 Graph contraction force (Y) vs. time (X) Twitch: a rapid single muscle contraction due to a single stimulus 17 Don’t confuse with the action potential! 18 Latent Period: lag time between time of stimulation and initiation of contraction why? → 19 Why a latent period? 20 Reason: impulse not yet propagated from PM → T tubules →SR 21 Refractory Period: Time when muscle cannot respond to a 2nd stimulus reason → Na+ still moving in 22 Contraction Period: time from initial contraction to max. contraction force Relaxation Period: muscle fibers begin return to original position 23 Contraction period varies with fiber type 24 Wave Summation Application of 2nd stimulus before complete relaxation Results in ↑ contraction strength Appears to violate the "all or none" principle Explanation → Increased availability of Ca+2 25 Treppe / Staircase effect Basis of the "warm up“ When muscle is simulated to contract several times in a row (w/ relaxation), each force of contraction becomes greater (to a point) – why? Same reason as wave summation 26 Tetany Sustained contraction resulting from successive stimulation Results in ↑ contraction strength 27 Incomplete / unfused tetany: there is partial relaxation before next contraction 28 Complete / fused tetany: lacks partial relaxation 29 Clostridium tetani: an anaerobic bacterium secretes a neurotoxin that results in continuous stimulation of muscle* result: tetanus etc. "lock-jaw” * Blocks GABA which inhibits motor nerves: motor nerves keep firing resulting in spastic paralysis. 30 MUSCLE STRETCH 31 Contraction force is greatest when actin & myosin overlap is maximum i.e. greatest # of cross linkages Max overlap & highest tension occurs when muscle slightly stretched 32 Tension is lowest when: sarcomeres are excessively stretched - why? b/c there less overlap / cross bridging 33 Tension is also lowest when: the sarcomere is too short - why ? b/c opposing actins overlap & can’t X-bridge 34 Not a big issue with skeletal muscle (why?) b/c muscle length is determined by origin & insertion Crucial to cardiac muscle 35 Stretch & cardiac muscle - FYI – Next semester 36 SKELETAL MUSCLE FIBER TYPES 37 Most muscle are a mixture of these Slow Oxidative / Slow Twitch/ Red Fibers Fast Glycolytic / Fast Twitch / White Fibers Fast Oxidative / Partly glycolytic / Pink Fibers / Intermediate Fibers – thought to be largely genetically determined (esp. the fast type) 38 SLOW OXIDATIVE / SLOW TWITCH RED Compared to fast white fibers, they have Slow, prolonged contraction without fatigue Express / have slow myosin ATPase Fast Glycolytic White Fast Oxidative Pink Slow Oxidative Red 39  Small fiber diameter ____myoglobin content (appear red) Well vascularized (appear red) 40 SLOW OXIDATVE / SLOW TWITCH RED Many __________ w/ ↑ aerobic capacity Low glycogen content, like to burn fatty acids Examples: Endurance muscle: – Hamstrings – Posture muscle 41 Comparison of fiber types 42 FAST GLYCOLYITC / FAST TWITCH WHITE compared to slow twitch red fibers contact quickly: – express / have fast myosin ATPase – release Ca++ quickly and have a large ____ 43  larger fiber diameter; very strong 44 Fast white fibers have ↑ capacity for anaerobic respiration - therefore → _____ mitochondria _____ glycogen content to fuel _______________ _____ vascularization _____ myoglobin content fatigue easily; likely due to the ___ availability issue examples: eye muscles, fingers, forearms, calf 45 FAST OXIDATIVE (PINK) or INTERMEDIATE FIBERS similar to slow-twitch red but have fast myosin ATPase intermediate in most other respects 46 Muscle types in various individuals 47 Summary of Fiber Types Red Pink White 48 MUSCLE TONE / TONUS Force with no net movement Slight tension of muscle that keeps the body upright: important to posture Loss of consciousness leads to loss of posture: collapse The muscle organ, as a whole, is in a state of partial contraction and overall stationary 49 Some motor units are in tetany, others relax or extend waves of contractions prevent fatigue coordinated by reflexes postural muscles tend to be ______________ 50 CARDIAC MUSCLE Located exclusively in the heart Single nucleus per cell - amitotic Organized myofilaments - striated 51  Many mitochondria - highly dependent on O2 SR is small - less Ca+2 is stored in the ICF Large T tubules Much of the Ca+2 comes from the ECF VIP: calcium channel blocker drugs 52 cells are joined at intercalated disks Desmosomes help transmit force of contraction through the myocardium 53 Gap junctions (in intercalated disks) allow Ca+2 to diffuse between cells facilitates rapid transmission of the muscle impulse allows heart muscle to contract in unison = electrical synapse 54 pacemaker cells Initiate contraction ~72X per minute by spontaneously producing an action potential (pacemaker potential) Regulation via the ANS & endocrine systems 55  Remains refractory until relaxation occurs Cardiac Skeletal 56 Long refractory period prevents _____________ 57 Muscle stretch (via filling of heart chambers) is important! See 132! 58 SMOOTH MUSCLE Short cells with a single nucleus ↑ mitotic capability vs. skeletal or cardiac Actin & myosin are randomly arranged (smooth!) – sarcomeres not present 59 Lacks T-tubules and has a small SR much Ca+2 is extracellular and in caveolae contraction is similar to skeletal muscle  Ca+2, ATP & sliding filament mech. Contracted 60 Contraction differs from skeletal muscle: Uses signal transduction / 2nd messenger systems / hormones & NTs 61  lacks troponin - calmodulin binds Ca+2 62  Calmodulin activates myosin ATPase / kinase, which activates the thick filament  contraction 63  Slow, sustained contractions - last several seconds 20-200 msec 400 msec > 1000 msec 64 Summary of Smooth Muscle Contraction 65 Single & Multiunit Smooth Muscle 66 Single Unit / Unitary / Visceral Smooth Muscle Most common - located in the walls of hollow organs, e.g. GI tract, BV, etc. 67  Gap junctions allow cell to cell impulse transmission and the organ contracts as a unit 68  Uses a pacemaker potential – initiates the impulse – control via ANS and endocrine system 69 G.I. tract arrangement: outer longitudinal layer inner circular layer 70 peristalsis: rhythmic wave-like contraction of smooth muscle to propel "food" along the GI tract 71 Multi-Unit Smooth Muscle Cells are more randomly organized Locaton: – large airways – large arteries – eye – arrector pili, etc. Lacks pacemaker cells & gap junctions 72  contraction is mediated mainly by the ANS, hormones & reflexes 73  Review 74 Comparison of muscle types 75 Comparison of Skeletal, Cardiac & Smooth Muscle II 76 Comparison of Skeletal, Cardiac & Smooth Muscle III 77 Comparison of Skeletal, Cardiac & Smooth Muscle IV 78 DISORDERS & MYOPATHIES 79 Flaccidity reduction of tonus usually neurological, e.g. spinal cord damage muscles no longer contract properly flaccid paralysis and atrophy develop 80 Spasticity excessive tone that leads to rigidity = spastic paralysis e.g. late stage Parkinson’s disease 81 Myalgia Muscle pain resulting from any muscle disorder – e.g. fibromyalgia: tendons, ligaments & affects mainly women fascia exhibit great pain – accompanied with fatigue, depression, etc. 82 Spasm: sudden involuntary twitch cause unclear - may be mild or severe 83 Tic: spasmodic contraction of a muscle often affects eye, face; psychological? 84 Cramp: painful spasmodic contraction without relaxation 85 Fasciculation: An involuntary and uncoordinated contraction of a muscle visible under the skin http://www.youtube.com/watch?v=N64LPt5cXVw In ALS http://www.youtube.com/watch?v=u421daHAgpY 86 Fibrillation: uncoordinated contraction of a muscle not visible under the skin often used to refer to cardiac muscle - accompanies MI 87 Tendinitis: inflammation of a tendon 88 Strain: “pulled muscle” excessive stretching or tearing of a muscle fiber resulting in inflammation and pain 89 Fibromyositis: inflammation of muscle fibers, CT coverings, tendons and joint capsules associated with pain (fibromyalgia), stiffness, soreness 90 Charley Horse: fibromyositis of the quadriceps femoris due to a contusion slang definition: leg cramp 91 Botulism: food poisoning caused by Clostridium botulinum toxin prevents ACh release & action, causing paralysis 92 Convulsions: violent involuntary muscle contractions many causes 93 Myofascial Trigger Points / Muscle Knots Irritable area of fascia surrounding taught muscles Idiopathic; possibly due to overload, stress, homeostatic imbalance Treat with massage, etc. 94 Amyotrophic Lateral Sclerosis: ALS aka Lou Gehrig's Disease progressive loss of motor function due to destruction of motor neurons does not affect mental capacity 30,000 in US 95  some forms genetic - most “sporadic” linked to free radical damage Steven Hawking 96 Muscular Dystrophy a group of genetic disorders progressive muscle weakness & degeneration 97 Dystrophin: the mutant gene/protein stabilizes the sarcolemma during contraction 98 duchenne MD: sex / X linked disorder characterized by weakness and shortening of muscles XDXd X XDY Also: Beckers is X-Linked 99  starts by age 3, wheelchair bound by age 12 100 myotonic MD: autosomal slower progression & affects fewer muscles 101 Myasthenia Gravis: autoimmune disease affects ♀ age 30-50 characterized by weak fatigued muscles cause: auto-antibodies to the ACh receptor Progressive Rx: ______________ antagonists / blockers 102 Aging muscle may atrophy & strength may ↓ up to 50% by age 80 muscle lost is replaced by dense CT / = fibrosis = sarcopenia 103 EXERCISE EFFECTS ON MUSCLE Endurance Exercise: e.g. cycling or running increases muscle (probably all fiber types) vascularization # mitochondria levels of EZs for Krebs cycle & ETS also ↑ respiratory and circulatory system capacity 104 Strength Exercise e.g. weight lifting Results in hypertrophy: ↑ fiber diameter – not due to increase mitosis of myocytes! Due to the  # of myofibrils to meet activity demands 105 Muscle soreness & repair due to micro-tears & muscle damage repair via growth hormone / IGF-1 pathways ↑ glycogen storage 106 anabolic steroids Testosterones / androgens that ↑ muscle mass Serious side effects: – liver damage & CA – testicular atrophy – baldness – aggression – prostate enlargement and CA Females: – ↓ in breast & reproductive organ size – menstrual irregularities, etc. Colbert – Androgel 1.6 - http://www.cc.com/video-clips/q3aiti/the-colbert-report-low-t---low-o 107