Muscle System - Anatomy

The Muscular System Chapter 10 - ebook Musculoskeletal system – integrated system of bones, muscles and joints Orthopedics – disorders of musculoskeletal system Myology – scientific study of muscle ALL muscle have - Excitability – send electrical wave - Elasticity – recoil back to original length - Extensibility – can stretch - Contractility – pull on points with force - Types of Muscular Tissue Skeletal muscle tissue - attached to bones - movement - striations (dark and light lines) - voluntary – conscious control - limited regeneration – most can’t undergo cell division Cardiac muscle tissue - heart wall - striated - in voluntary - can regenerate under certain conditions Smooth muscle tissue - walls of hollow organs o blood vessels, airways digestive organs - digestion and regulation of blood pressure - nonstriated - involuntary - can regenerate but not to epi. Extent Functions of Muscular Tissue ( not in ebook) 1. Producing body movement 2. Stabilizing body position Contractions stabilize joints Postural muscles contract continuously - awake 3. Regulating organ volume Sphincters – ring-like bands of smooth; prevent overflow – hollow organs Storage of food in stomach; urine in bladder 4. Moving substances within the body Cardiac pumps blood Smooth adjust blood vessel diameter Move food thru GI Skeletal muscle aids getting blood back to heart 5. Producing heat Contractions produce heat Shivering increase heat Skeletal Muscle Tissue (FIGURE 10.3 page 535) Connective tissue components - fascia – sheet or band of fibrous connective tissue beneath skin or around muscles and other organs - around muscles are deep fascia – dense irregular connective (figure 10.3 page 535) o Epimysium § surrounds entire muscle o Perimysium § Surrounds 10 -100 muscle fibers (cells) called Fasciles o Endomysium § Surrounds each muscle fiber - all three extend to form tendon - Connective tissue can form broad sheets called aponeurosIs o attach muscle to bone Nerve and Blood Supply - need to supply blood and oxygen and eliminate waste Histology (microscopic structure) – figure 10.4 page 536) - muscle fiber – elongated cylindrical cell - multinucleated o Sarcolemma – plasma membrane o Sarcoplasm – cytoplasm – many mitochondria o Transverse Tubules – extensions of sarcolemma – pass thru fiber side to side o Sarcoplasmic reticulum – fluid filled tubules that store Ca o Myoglobin – reddish brown molecule that store Oxygen o Myofibrils – extend along length on muscle § Thin filaments § Thick filaments Sarcomere (not in book order) (figure 10.5 page537) - basis contractile unit of muscle - made of myofibrils – consist of two proteins o thin filament § actin • twisted helix • contains myosin – binding site § tropomyosin and troponin • cover myosin – binding site o thick filament § myosin • form crossbridges • resemble golf club - extend Z disc to Z disc (figure 10.10 page 543) o inside: § A band • Darker area – length of thick filament § H zone • At center of A • Thick and thin overlap § I band • Lighter color • Either side of A • Composed of thin filaments Contraction and Relaxation of Skeletal Muscle – out of order from book Sliding-Filament Mechanism - during contraction filaments do not shorten - filaments slide between each other o head of thick filaments pull thin o I and H band becomes thinner Physiology of Contraction - need Ca and ATP When relaxed - Ca stored in sarcoplasmic reticulum and t-tubules o Contain Ca active transport pumps - Low Ca in sarcoplasm When receive “signal” to contract - Ca pumps open in S.R. membrane - Ca moves into sarcoplasm - Ca binds to troponin o Changes shape and exposes myosin-binding site - Contraction cycle begins (p.544 interactive 10.1) o 1. Splitting ATP § Myosin head contains ATPase § Splits ATPàADP +P § Energy goes to myosin head § ADP and P stay attached o 2. Forming crossbridges § Myosin head attaches to actin § Release Phosphate group o 3. power stroke § Started by release of P § Myosin head rotates and swivels • Releases ADP § Slides thin pass thick o 4. Binding ATP and detaching § Remain attached until ATP binds § Then detaches - contraction cycle continues as long as ATP and Ca are available o Rigor Mortis § Ca leaks out triggers contraction § No ATP there to attach so remains contracted § Lasts about 24 hours - relaxation o Ca returns to sarcoplasmic reticulum and return to relaxed state Signal to Contract comes from Neuromuscular Junction (figure 10.8 and 10.9 pages 541 and 542) - delivered by motor neuron - stimulated by electrical signal – muscle action potential - motor unit – all fibers neuron stimulates o contract all in unit o some few – precise – fewer than 10 o some many – biceps – up to 2000 - Axon terminals approach sarcolemma – no touch o Ends in synaptic end bulbs § Contain synaptic vesicles § Filled with neurotransmitter o Motor end plate – region of sarcolemma near axon o Synaptic cleft – space between motor end plate and axon terminals o Everything – Neuromuscular junction (NMJ) - Steps o 1. Release of acetylcholine § Impulse arrives at end bulbs à release NT acetylcholine (Ach) à diffuses in cleft o 2. Activation of Ach receptors § Receptors in end plate bind ACh à then allow ion channels to open (Na) o 3. Generation of muscle action potential § This moves Ca out into sarcoplasm § Each impulse will activate steps 2 and 3 again o 4. Breakdown of Ach § Broken down rapidly by acetylcholinesterase (AChE) - How some toxins work o Botulism toxin (botox) § Blocks release of ACh – no muscle contraction § Death by paralyzing diaphragm § Medically – used to stop crossed-eyes, uncontrollable blinking, and relax muscles o Curare § Used in blow darts § Binds and blocks ACh receptors § In surgery can be used to relax skeletal muscle Muscle atrophy - progressive loss of myofibrils - disuse atrophy - denervation atrophy - eventfully can be replaced by fibrous connective tissue – cannot be reversed Muscle hypertrophy - produce more myofibrils - more myofibrils à more forceful contractions Muscle Tone - keep skeletal muscles firm - small number of motor unit in muscle contract involuntarily to produce sustained contraction - does not produce movement - sustained by motor neurons Metabolism Figure 10.11 page 546 Energy for Contraction - Three sources of ATP in muscle 1. creatine phosphate - only in muscle - made from excess ATP - ATP à ADP + P - P attaches to creatine - then can be reattached quickly to ADP à ATP - good for short burst of quick energy (max -15 secs) - creatine supplements ( creatine lost as creatinine in urine – increase muscle and performance Hard on kidneys and studies show that it may decrease ours from forming) 2. glycolysis - after 1 used up - glucose à 2 pyruvic acid + 2 ATP - glucose from blood or from breakdown of glycogen - anaerobic – no oxygen - 30-40 seconds of max activity If no oxygen then go to lactic acid fermentation If oxygen available then….. 3. aerobic cellular respiration - oxygen from blood or myoglobin - series of ATP production in mitochondria - begins with pyruvic acid and ends with ATP - one glucose à 36 ATPs - if activity last more than 10 minutes – use this - when oxygen is low converts to lactic acid fermentation Muscle Fatigue - inability of a muscle to contract forcefully after prolonged activity - less Ca released from SR à lower Ca in sarcoplasm - depletion of Creatine phosphate, oxygen, and glycogen - buildup of lactic acid and ADP (decrease pH) Oxygen Consumption after exercise - in Oxygen Debt or Recovery Oxygen Uptake o heavy breathing continues after exercise o glycogen needs to be replaced § some from diet later § some from lactic acid but most lactic acid is converted back to pyruvic acid and taken thru cellular respiration o increased body temp – increases chemical reaction § need more ATP o heart and muscles working harder – consume more ATP o tissue repair occurring o resynthesize creatine phosphate o replace oxygen in blood and myoglobin Control of Muscle Tension (figure10.13 page552) - studied by myogram – electrical impulse given and recording of contraction is made o # of impulse per second = frequency of stimulation - Twitch contraction o Brief delay in beginning – latent period § Ca ions going out and binding to troponin o Contraction period § Upward tracing o Relaxation period § Power stroke ceases § Ca back to SR - Frequency of Stimulation o Wave summation – seen when a second impulse is applied before first is relaxed § Stronger than first § 2nd begins at higher level of tension o Unfused (incomplete) tetanus § Stimulated repeatedly § Wavering contraction o Fused (complete) tetanus § Most like real contraction – works in relay § 90 stimuli / second § No relaxation Motor Unit Recruitment - process where number of contracting motor unit is increased - usually motor neurons in a muscle fire asynchronously - responsible for what appears to be smooth muscle movements - # recruited depends on load Types of Skeletal Muscle Fibers page 556 - Three types o Slow oxidative fibers (SO) § Small in diameter § Red - myoglobin( § Lots of mitochondria – oxidative § Contraction cycle slower § Resistant to fatigue – prolonged contraction o Fast oxidative fibers (FO) § Intermediate in diameter § Lots of mitochondria § Red – some Myoglobin § Store glycogen § Moderately high resistant to fatigue § Fast – contract and relax faster than SO o Fast glycolytic fibers (FG) § White fibers (low myoglobin and mitochondria) § Contain most myofibrils § Contractions powerful and more rapid § Lots of glycogen – glycolysis § Short duration - fatigue fast - most muscles made of mixture of all three - in a motor unit all are same - weak only SO - more force FO - Max – FG Exercise - ratio of SO and FG genetic - higher FG – weight lifting & sprinting - higher SO – long distance running - characteristics can change thru exercise - aerobic – FGà FO - Endurance exercise – increase heart and lung function – increased oxygen - Weights – increase size and strength of FG – more filaments Isometric and Isotonic Contractions (figure 10.12 page 549) - Isometric - no change in length – change in tension - important in posture and holding in fixed position - Isotonic - Change in length – none in tension - Lifting box or weights Origin and Insertion (figure 11.2 page 590) - skeletal muscle attached to two bones by tendons - Origin –at stationary bone - Insertion – movable bone - Belly – fleshy protion Group actions (page 591) - prime movers or agonist o desired movement muscle - antagonist o relaxes during main movement - synergists o help prime movers- reduce movement - fixators o stabilize origin of muscle - all can change roles Skeletal muscle names (section 11.2 page 596) - Table (end of power point in plus portals0 Cardiac Muscle (section 10.7 page 562) - striated involuntary - shorter and larger in diameter - single centrally located nucleus - intercalated discs – transverse thickenings of sarcolemma - fibers initiate contractions – built in pacemakers o called autorhythmicity o rates can change by hormones and neurotransmitters - more mitochondria than skeletal - can use lactic acid produced by Skeletal to make ATP Smooth Muscle ( section 10.8 page 564) - nonstriated (no regular pattern) involuntary - smaller and tapered at both ends - single nucleus - Two types o Visceral § Found in sheets in small arteries , veins and hollow organs § Autorhythmic – spreads to other fibers § Contract in unison o Multiunit § Contract one fiber only – own neuron § Found in large arteries, airways and arector pili - Ca released slower and contracts longer – tone - Can maintain pressure and stretch and still contract