Chapter 10 - Muscle Tissue PDF

CHAPTER 10 - MUSCLE TISSUE Chemical energy  mechanical energy to 1 generate force, perform work, produce movement Myology Prefixes – myo, mys, & sarco all refer to muscle 5 FUNCTIONS OF MUSCLE TISSUE 1. Body movement 2. Maintenance of posture 3. Pro...

CHAPTER 10 - MUSCLE TISSUE Chemical energy  mechanical energy to 1 generate force, perform work, produce movement Myology Prefixes – myo, mys, & sarco all refer to muscle 5 FUNCTIONS OF MUSCLE TISSUE 1. Body movement 2. Maintenance of posture 3. Protection & Support 4. Storage & Movement of materials Peristalsis taking place in the Heat production intestine of a horse. Viewed during 5. laparoscopic surgery. 2  5 SPECIAL PROPERTIES OF MUSCLE TISSUE 1. Excitability 2. Conductivity (Action potentials) 3. Contractility 4. Extensibility 5. Elasticity 3 3 TYPES OF MUSCLE TISSUE 1. Skeletal muscle –  attaches to bone, skin or fascia  striated  voluntary control of contraction & relaxation http://www.cretin-derhamhall.org/Departmental/Science/AFroehle/skeletal_muscle2.gif 4 http://www.css.edu/users/tboone2/asep/dexp/anatpics.htm 3 TYPES OF MUSCLE TISSUE 2. Cardiac muscle http://www.cretin-derhamhall.org/Departmental/Science/AFroehle/cardiac4.gif striated involuntary autorhythmic (pacemaker) 5 3 TYPES OF MUSCLE TISSUE 3. Smooth muscle  Arrector pili  Wallsof hollow organs  Non-striated  Involuntary 6 GROSS ANATOMY OF SKELETAL MUSCLE: CONNECTIVE TISSUE A muscle = one organ  Hypodermis  Fascia  Connective tissue sheaths include:  epimysium  perimysium  endomysium 7  Tendon GROSS ANATOMY OF SKELETAL MUSCLE: NERVE AND BLOOD SUPPLY  Skeletal muscle supplied by nerves, arteries & veins  Somatic motor neuron  Neuromuscular junction 8 FUSION OF MYOBLASTS INTO MUSCLE FIBERS  Maturemuscle developed from > 100 myoblasts  Mature muscle cells can not divide  Satellitecells retain ability to regenerate new cells 9 MUSCLE FIBER OR MYOFIBERS  Sarcolemma  Sarcoplasm filled w/ myofibrils & myoglobin 10  Muscle organization: Muscle  muscle fibers (cells)  myofibrils  sarcomere  myofilaments (actin & myosin) SARCOMERE  Smallest contractile unit of a muscle  region of myofibril between 2 successive Z discs  Composed of myofilaments made up of contractile proteins  Myofilaments: thick (myosin) & thin (actin) 11 Muscle organization: Muscle  muscle fibers (cells)  myofibrils  sarcomere  myofilaments (actin & myosin) MYOFIBRILS & MYOFILAMENTS  Myofibrils separated by SR  Myofilaments = contractile proteins of muscle 12  SARCOPLASMIC RETICULUM (SR)  System of tubular sacs (sER) encircles myofibril  Regulates Ca+2 levels  Stores Ca+2 in relaxed muscle (attached to calmodulin & calsequestrin), Ca+2 pump  releases Ca+2 during contraction via voltage gated Ca+2 channels 13  TRANSVERSE TUBULES  Invaginations of the sarcolemma into cell  Filled w/ extracellular fluid  Carry AP down into cell  Mitochondria lay near muscle proteins that use ATP 14 FILAMENTS & SARCOMERE  Striations = I bands & A bands  Overlap region  Supporting proteins  M line, titin & Z disc anchor thick & thin filaments in 15 place REGIONS OF A SACROMERE OF A MYOFIBRIL 16  THE PROTEINS OF MUSCLE Myofibrils built of 3 kinds of protein: 1. Contractile= myosin & actin 2. Regulatory = troponin & tropomyosin 3. Structural = titin, myomesin, nebulin & dystrophin 17 THICK FILAMENTS - COMPOSED OF MYOSIN 18 THIN FILAMENTS - ACTIN, TROPONIN, & TROPOMYOSIN  Myosin-binding site covered by tropomyosin in relaxed muscle  Thin filaments held in place by Z lines 19  OTHER STRUCTURA L PROTEINS  Titin anchors thick filament to M line & Z disc  Role in recovery of muscle from being stretched  M line (myomesin) - connects to titin & adjacent thick filaments  Nebulin - inelastic protein helps align thin filaments  Dystrophin - links thin filaments to sarcolemma & 20 transmits tension generated to tendon SLIDING FILAMENT MECHANISM OF CONTRACTION  Myosin cross bridges pull on thin filaments  Thin filaments slide inward  Z Discs come toward each other  Sarcomeres shorten  Muscle fiber shortens  muscle shortens 21 MUSCLE GROSS ANATOMY SUMMARY Myofibril Myofilament: Organelle Actin & Myosin 22 Muscle Fiber (Cell) Muscle fiber (cell) (organelles) 23 24 Myofilament: organelle 25  EXCITATION CONTRACTION COUPLING SUMMARY 1. Motor Neuron excites muscle cell at NMJ 2. AP spreads across sarcolemma & t-tubules 3. SR releases Ca++ into sarcoplasm 4. Ca++ enters myofibril organelles & binds to Troponin 5. Troponin removes tropmyosin from actin 6. Myosin heads attach to actin beads 7. Sarcomere, myofibril, muscle 26 fiber, fascicle, & muscle shorten -pull on tendon/bone CONTRACTION CYCLE  Repeating sequence of events that cause thick & thin filaments to move past each other (when ATP & Ca+2 available)  4 steps to contraction cycle 1. Cross bridge formation (attach) 2. Power stroke (pull) 3. Release of myosin head (cross-bridge detachment) 4. Reset (“cocking” of) myosin head 27  SEQUENTIAL Myosin head (high-energy EVENTS OF configuration) CONTRACTIO N 1 Myosin cross bridge attaches to actin myofilament Thin filament ADP +P (inorganic phosphate) released i Thick filament 4 2 Working stroke—myosin head pivots & bends as it pulls on the actin As ATP is split into ADP + P , cocking of myosin head i filament, sliding it toward M line occurs Myosin head (low-energy configuration) 28 3 As new ATP attaches to myosin head, cross bridge detaches 29 RIGOR MORTIS  State of muscular rigidity  3-4hours postmortem  Lasts about 24 hours  Afterdeath Ca+2 ions leak out of SR & allow myosin heads to bind to http://kadokami.hp.infoseek.co.jp/E.Sendoiji.htm actin  ATP synthesis has ceased  crossbridges cannot detach from actin until proteolytic 30 enzymes begin to digest decomposing cells NERVE STIMULUS OF SKELETAL MUSCLE  Motor neurons of somatic nervous system  Axons in nerves  muscle cells  Branch profusely as they enter muscles  Axonal branch forms neuromuscular junction w/ single muscle fiber  Neuromuscular junction is formed from:  Axonal endings  Motor end plate of a muscle  Synaptic cleft 31 STRUCTURES OF NMJ REGION  Synaptic end bulbs  Synaptic vesicles (Acetylcholine)  Motor end plate 32  Nerve signal events EXCITATION OF SKELETAL MUSCLE FIBER  nn 33 EXCITATION-CONTRACTION COUPLING 34 EXCITATION-CONTRACTION COUPLING 35 OVERVIEW OF SKELETAL MUSCLE CONTRACTION . 36  RELAXATION - ACETYLCHOLINESTERASE  1) Muscle end-plate potential ceases when  enzyme acetylcholinesterase (AchE) removes acetylcholine (Ach)  2) Muscle action potential ceases when  Na+ pumped out of cell with Na+/K+ ATPase pump  3) Cross-bridge cycling ceases when  Ca+2 release channels close & active transport pumps Ca+2 back into storage in sarcoplasmic reticulum  Ca+2 -binding protein (calsequestrin) helps hold Ca+2 in SR  In presence of ATP, Tropomyosin-troponin complex recovers 37 binding site on actin 38  PHARMACOLOGY OF THE NMJ  Botulinum toxin prevents Ach release  C. botulinum  Botulism  Curare  Blocks ACh receptors  Relaxes muscles during surgery  Neostigmine (Reversible acetylcholinesterase inhibitor)  Blocks removal of ACh from receptors  Antidote for curare  Pesticides & Nerve gas also ACh esterase inhibitors 39  MUSCLE METABOLISM : PRODUCTION OF ATP IN MUSCLE (10.4)  Muscle uses > ATP when active  3 sources of ATP production within muscle: 1. Immediate (5-6 sec): phosphagen system 1. ATPase, Myokinase, creatine kinase 2. Short-term (50-60 sec): anaerobic cellular respiration 3. Long-term (5-6 min): aerobic cellular respiration 40 IMMEDIATE SUPPLY OF ATP: PHOSPHAGEN SYSTEM 41 CREATINE PHOSPHATE  Excess ATP w/in resting muscle used to form creatine phosphate  Quick breakdown  ADP + CP  ATP  Creatine supplementation  decreases innate production 42 FERMENTATION: ANAEROBIC CELLULAR RESPIRATION  If no O2 present pyruvic acid is fermented  lactic acid  Lactic acid returns to liver where it’s turned into pyruvate when O2 available  About 2% as efficient as aerobic cellular 43 respiration ANAEROBIC VS AEROBIC CELLULAR RESPIRATION . 44 AEROBIC CELLULAR RESPIRATION  Production of ATP in mitochondria from pyruvic acid, FA’s & AA’s 45 MUSCLE FATIGUE (SECTION 10.7D)  Central fatigue - protective mechanism  Musclefatigue - Inability to contract after prolonged activity  Factors that contribute to muscle fatigue  Insufficient O2 or glycogen for aerobic cellular respiration  Buildup of lactic acid & phosphates  Insufficient release of ACh from motor neurons (reduced Ach or Ca+2 in neurons) 46  Na+, K+ imbalance in cell OXYGEN CONSUMPTION AFTER EXERCISE (10.4B)  Muscle tissue has two sources of O2:  Diffusesin from blood  Released by myoglobin inside muscle fibers  Aerobic system requires O2 to produce ATP needed for prolonged activity  Oxygen debt  elevated O2 use after exercise (O2 debt)  Hemoglobin & myoglobin  Glycogen stores  ATP & creatine phosphate stores  lactic acid is converted back to pyruvic acid to glucose  Elevated body temperature = > metabolic rate 47  bodyreactions release energy (~40% work & 60% lost as heat) SKELETAL MUSCLE FIBER TYPES (10.5)  3 fiber types present in each muscle to varying degrees  Differ with regards to ATP production & function  Know info. in red boxes (10.5B) 48 THE MOTOR UNIT (10.2C)  Motor unit = somatic motor neuron & skeletal muscle fibers it stimulates  Total strength of contraction depends on how many motor units are activated & how large motor units are 49 MOTOR UNIT RECRUITMENT (10.6B)  Motor units in a whole muscle fire asynchronously  Produces smooth muscular contraction  Precise movements require smaller contractions  Large motor units are active when large tension is needed 50 MUSCLE TONE (10.7A)  Involuntary contraction of a small # of motor units  Keeps muscles firm although they’re “relaxed”  Essential for maintaining posture (head upright)  Important in maintaining BP  Smooth muscle in blood vessels 51  WHAT TO FOCUS ON IN CH 10  Not Covering in Ch 10  USE POWER  Section 10.6a & 10.6c POINTS AS (on pages 354-356) OUTLINE  Get detailed  10.7b & 10.7c  10.8 information from lecture notes or text  10.9 & 10.10 – just what is in slides 4-6 52