Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download some of Chapter 25 - Concordia College
Document related concepts
no text concepts found
Transcript
Chapter 10 Muscle Tissue (Mostly Skeletal Muscle) Muscle tissue: skeletal bones cardiac heart smooth “hollow organs” Muscle tissue: skeletal muscle functions move skeleton maintain balance/posture support soft tissues guard entrances/exits maintain body temp store nutrients Muscle tissue: muscle contains muscle cells connective tissue nerves (axons) blood vessels muscle (and connective tissue) surrounded by epimysium subdivided into fascicles surrounded by perimysium fascicles contain myofibers surrounded by endomysium fig. 10-1 three connective tissues: epimysium perimysium endomysiyum blend into each other, and the end of the muscle blend into the tendon three connective tissues: contain: blood vessels and nerves that supply the muscle skeletal muscle voluntary muscle although many are also controlled subconsciously too skeletal muscle formation and structure fig. 10-2 myoblast fuse forming large multinucleated cells (myofibers) myofibers cell membrane sarcolemma cytoplasm sarcoplasm filaments organized into myofibrils T-tubules (transverse) -extensions of the sarcolemma to the interior of the cell -surround myofibrils fig. 10-3 sarcoplasmic reticulum (SR) •modified sER (smooth endoplasmic reticulum) •also surrounds myofibrils •expanded ends called terminal cisternae •gather and store Ca2+ fig. 10-3 myofibril tc T tc myofibers: contain myofibrils myofibrils: contain myofilaments thin filaments thick filaments actin myosin Thin filaments: G actin (globular) F actin (filamentous) Other components: Troponin (covers active site) Tropomyosin Nebulin Thin filaments: fig. 10-7b fig. 10-7a, b Thick filaments: myosin head tail Thick filaments: binds to active site on thin filaments fig. 10-7d fig. 10-7c, d fig. 10-7c, d to here Monday 2/5 lec # 13 fig. 10-6 muscle fascicles myofibers myofibrils thick & thin filaments fig. 10-4 A band I band Z line A band I band Z line A muscle structure terms sarcomere from Z line to Z line A band where myosin is M line center of A band H zone where actin isn’t center of A band I band where myosin isn’t Z line in center overlap actin and myosin tc T tc triad titin fig. 10-5 when muscle contracts: A band I band H zone Z lines overlap same shrinks shrinks closer increases sliding filament theory fig. 10-8 The contraction of skeletal m. background physics: tension compression pull towards push away overcome resistance muscle cells only pull (produce tension) generate force by getting shorter OVERVIEW motorneuron AP release nt AP in myofiber release Ca2+ thick/thin interact contraction tension fig. 10-9 control of skeletal muscle motorneurons in CNS synapse with myofiber neuromuscular junction aka myoneural junction aka motor end plate (mep) each myofiber is innervated by a myelinated motorneuronfig. 10-9 neuromuscular junction (nmj) axon terminal with ACh synaptic cleft postsynaptic membrane (aka sarcolemma) junctional folds AChR and AChE fig. 10-10 neuronal AP myofiber AP contraction ? Excitation-Contraction Coupling myofiber AP (depolarization of sarcolemma) depolarization of the T-tubules release of Ca2+ from sacroplasmic reticulum release of Ca2+ from sacroplasmic reticulum Ca2+ interacts with troponin (on thin filaments) exposing active site (myosin will now bind) remember structure: fig. 10-7b fig. 10-5 myosin heads fig. 10-11 Now we are ready for the contraction cycle (almost) fig. 10-7 fig. 10-12 AP AP Ca2+ 2 1 expose active site fig. 10-12 form cross-bridges “POWER STROKE” 4 3 cross bridge detachment re”energize” the myosin fig. 10-12 5 re energize myosin fig. 10-12 As long as Ca2+ is present… power stroke re-energize power stroke re-energize sarcomere shortens ~1%/cycle tug-of-war energize reach cross-bridge grab power stroke pull release release tug-of-war repeat cycle reach grab pull release what if everybody released at the same time? actin myosin Z line sarcomere Z line cross bridge formation power stroke release energize cross bridge formation power stroke release energize cross bridge formation power stroke release energize cross bridge formation power stroke to here 2/7 lec # 14 with contraction cycle… each sarcomere get shorter… …each myofiber is lots of sarcomeres end to end… …myofiber gets shorter… …muscle gets shorter As muscle gets shorter… …it generates tension (pulls) Skeletal muscles are attached to bone at both ends origin insertion actions action: flex at elbow origin insertion fig. 11-2 How long will muscle contract ? As long as: continued stimulus at nmj + free Ca2+ in sarcoplasm + ATP to energize myosin… …muscle will keep contracting If stimulus disappears: ACh broken down by AChE sarcolemma returns to RP Ca2+ is reabsorbed by SR active sites covered by troponin What happens to the muscle when contraction stops ? muscle cannot lengthen on its own muscles are “paired” agonist muscle that does action antagonist has opposite action (stretches agonist) Muscle cannot lengthen on its own… …it has to be stretched. death no nutrients to muscle ATP gets used up Ca2+ pumps quit myosin binds to actin “freezes” muscle rigor mortis rigor mortis occurs after a few hours last for 15-25 hrs until lyzozymal enzymes start to break down muscle proteins Have covered: Muscle architecture Mechanism of contraction Still to come: Tension Production Energy Use Muscle Performance cardiac muscle smooth muscle Tension production by myofibers by muscles Tension production by myofibers: Amount of tension produced depends on number of “power strokes” happening Tension production by myofibers: Cannot vary the amount of tension produced by a myofiber by varying number of sacromeres being used. Tension production by myofibers: A single myofiber is either stimulated “on” or relaxed (off) Tension production by myofibers: but… “tension production at the level of the individual cell does vary” frequency of stimulation resting length of fiber Tension production by myofibers: resting length vs. tension in myofibers Amount of tension produced depends on number of power strokes happening resting length vs. tension in myofibers the number of cross-bridges forming will depend on the degree of overlap between the thin and thick filaments (zone of overlap) only those myosin molecules that can form cross-bridges will produce tension tension produced resting length vs. tension in myofibers length of sarcomere fig. 10-14 Tension production by myofibers: frequency of stimulation resting length of fiber frequency of stimulation single stimulus (AP) single contraction (twitch) 7-100 msec frequency of stimulation a single twitch has phases latent phase contraction phase relaxation phase Stimul fig. 10-15 myogram fig. 10-15 What if we stimulated a muscle cell, let it contract and relax, and then stimulated it again? tension time fig. 10-16a What if we stimulated a muscle cell, let it contract and relax (but not all the way), and then stimulated it again? tension time fig. 10-16b tension wave summation time fig. 10-16b tension time fig. 10-16c tension incomplete tentanus time fig. 10-16c tension complete tentanus time fig. 10-16d twitch cycle stimulation rate < stimulation rate > twitch cycle stimulation rate stimulation rate > twitch cycle latent p + contraction p > treppe 1st 2nd fig. 10-15 Don’t play around rusty nails ! Don’t run around barefoot outside! Have you had your tetanus shot ? What is tetanus ? Tetanus prolonged contraction of muscle Why rusty nails ? puncture wound closes very quickly very little bleeding Clostridium tetani live is soil (low O2 levels) If it gets into the body: divide release tetanospasmin (powerful neurotoxin) carried to CNS by retrograde transport disables GABA-releasing neurons (inhibitory nt) overstimulation of motorneurons If it gets into the body: overstimulation of motorneurons sustained, powerful contraction of skeletal muscle throughout body “lockjaw” Sir Charles Bell ,1809 Not much of a problem in developed nations… immunizations & booster shots DTP 5X (diptheria, tetanus, pertussis) to here 2/9 lec # 15 Tension production by myofibers myofiber length stimulation rate by muscles Tension production by muscles tension from myofibers # myofibers stimulated “The amount of tension produced by a muscle as a whole is the sum of the tensions generated by the individual muscle fibers,” (pg 304) Tension production •each muscle - 1000’s of fibers •muscle fibers - controlled by neurons •motorneurons - control many myofibers all the fibers controlled by a single neuron… …motor unit size of motor unit… (how many myofibers/unit) …indication of how precisely the muscle is controlled for example eye muscles 4-6 fibers/unit leg muscles 1000-2000 within the muscle myofibers are intermingled fig. 10-17 think… …move muscle activate smallest motor units keep thinking… …move muscle activate larger motor units… smooth, steady increase in tension smooth, steady increase in tension recruitment peak tension is produced when all motor units are in complete tetany (can’t do it for long) in sustained contractions: rotate which motor units are being activated asynchronous motor unit summation (can’t do it at max. tension) fig. 10-17 Key (pg 305) “All voluntary muscle contractions and intentional movements involve sustained contractions of skeletal muscle fibers. The force exerted can be increased by increasing the frequency or motor neuron action potentials or the number of stimulated motor units (recruitment).” muscle tone resting muscle… …always has some fibers contracting don’t produce enough tension to cause movement, but they tense and firm the muscle muscle tone •holds bones in place •keeps body balanced(position) •prevent sudden movements •shock absorption •a muscle with good tone will burn more Calories than one with poor muscle tone contractions isotonic isometric contractions isotonic (equal tension) rise in tension leads to change in the muscle length fig. 10-18 isotonic contractions concentric muscle shortens (overcomes resistance) eccentric muscle lengthens (control) contractions isometric (equal measure) •muscle length does not change •doesn’t produce enough tension to overcome resistance isometric fig. 10-18 isometric contractions although whole muscle does not shorten… individual fibers do isometric contractions when would it be used? …hold head up …carrying books …maintaining posture Resistance and speed of contraction inversely related lighter resistance… …faster speed of contraction heavier resistance… …slower speed of contraction Returning a muscle to resting length can’t actively lengthen muscle can stretch it opposing muscle elastic forces gravity Energy use and Muscle activity single myofiber: may have 15 billion thick filaments each thick filament: uses 2500 ATP molecules/sec ~ bazillion Energy use and Muscle activity muscle need lots of ATP but ATP is for short-term storage hot $ ? Energy use and Muscle activity ATP + creatine ADP + creatine phosphate (CP) Energy use and Muscle activity myosin (unenergized): ATP ADP + P myosin (energized): Energy use and Muscle activity (as muscle uses ATP it makes ADP) ATP ADP + P creatine ADP + phosphate ATP + creatine TABLE 10-2 Energy use and Muscle activity (as muscle uses ATP it makes ADP) ATP ADP + P creatine ADP + phosphate CPK ATP + creatine Energy use and Muscle activity CPK (or CK) creatine phosphokinase if muscle is damaged, CK leaks out of the cell into the blood ( high [CK] = muscle damage) Energy use and Muscle activity Aerobic metabolism (living with oxygen) Most ATP demands (at rest) are met through TCA and ETS organic molecules from cytoplasm TCA CO2 O2 ETS ATP Energy use and Muscle activity during contraction swtiches to pyruvate as entry point into TCA Where does pyruvate come from? glycolysis Energy use and Muscle activity during contraction What do we need to do glycolysis? glucose What does glucose come from? glycogen in myofibers Energy use and Muscle activity at rest low demand for ATP use fatty acids for C source lots of O2 available extra ATP --->CP glycogen is stored at rest fig. 10-20 Energy use and Muscle activity moderate activity higher demand for ATP if enough of O2 available mitochondria can supply ATP via cellular respiration fig. 10-20 Energy use and Muscle activity high activity anaerobic enormous demand for ATP no enough O2 delivered (ETS will not work fast enough) cells use ATP from glycolysis make pyruvate converted to lactic acid pH fig. 10-20 Energy use and Muscle activity muscle fatigue when the muscle can no longer perform at the required level Energy use and Muscle activity muscle fatigue •depletion of energy reserves •damage to cell membrane, etc •decline in pH of myofibers (decrease Ca2+ binding) Energy use and Muscle activity normal muscle function needs: •intracellular energy reserves •normal blood supply •normal O2 levels •normal blood pH interfere with any one of them… …premature muscle fatigue Energy use and Muscle activity recovery period: time needed for muscle to return to pre-exertion conditions moderate activity peak activity hours days-week to here 2/12 lec # 16 review 1 muscles cells contract… or ……don’t vary tension by: muscles have motor units: vary tension by: maximum tension is called ?? review 2 isotonic contraction: concentric ? isometric contraction: Energy use by muscles need ATP stored as ? ? review 3 Energy use by muscles at rest fatty acids moderate work aerobic metab. heavy work anaerobic (leads to build up of ?) recovery period Energy use and Muscle activity removal of lactic acid (LA) with O2, can be converted back to pyruvate liver can convert LA to glucose which goes back to the muscle Cori cycle Energy use and Muscle activity Oxygen debt supply O2 to tissues and allow for restoring pre-exertion levels of ATP, CP, glycogen,… Energy use and Muscle activity Heat production ~58 % of energy produced is lost as heat only 42% goes to producing ATP Energy use and Muscle activity Hormones GH and testosterone stimulate synthesis of muscle tissue TSH stimulate energy consumption by muscle tissue Energy use and Muscle activity Hormones epinephrine stimulate muscle metabolism and contraction Muscle Performance How much force can be produced tension produced by a muscle or group of muscles How long can the muscle continue endurance Muscle Performance Two factors influence performance types of muscle fibers physical conditioning Muscle Performance Two factors influence performance types of muscle fibers fast fibers intermediate fibers slow fibers Muscle Performance fast fibers contract very quickly after stimulation large diameter packed with myofibrils large glycogen reserves few mitochondria fatigue easily aka “white muscle fibers” Muscle Performance slow fibers slower rate of contraction 1/2 diameter of fast fibers more mitochondria (and what they need) good blood supply contain abundant myoglobin more for extended contractions aka “red muscle fibers” Muscle Performance intermediate fibers in between look like fast fibers little myoglobin (pale) but… better blood supply than fast more resistant to fatigue than fast table 10-3 Muscle Performance skeletal muscle can have different percentages of the different fiber types hand/eye fast back/calf slow genetically determined can be altered with exercise Muscle Performance skeletal muscle growth repeated, exhaustive stimulation more mitochondria more glycolytic enzymes more myofibrils more filaments cells get bigger hypertrophy Muscle Performance skeletal muscle growth non-stimulated muscles get smaller loose muscle tone become weaker atrophy Muscle Performance skeletal muscle growth atrophy temporary immobilization (leg in a cast) initially reversible in extreme cases: permanent physical therapy Muscle Performance Physical conditioning improve power (ability to generate tension) improve endurance Muscle Performance Physical conditioning anaerobic endurance how long the muscle can work supported by glycolysis and stored ATP and CP Muscle Performance Physical conditioning anaerobic endurance limited by: amount of ATP and CP stored [glycogen] available tolerance to lactic acid sprint work, pole vault, short events Muscle Performance Physical conditioning anaerobic endurance training: frequent, brief, intense workouts stimulate hypertrophy Muscle Performance Physical conditioning aerobic endurance how long the muscle can work supported by mitochondrial activity Muscle Performance Physical conditioning aerobic endurance limited by: availability of substrates for aerobic respiration dependent on blood supply jogging, distance running, swimming, etc., don’t require peak tension production Muscle Performance Physical conditioning aerobic endurance improvement changing characteristics of fibers fast fibers can take on intermediate characteristics improving CV performance increased capillarity accelerate blood flow Muscle Performance Physical conditioning aerobic endurance improvement does not promote hypertrophy cross-training combination aerobic and anaerobic exercise for benefits of both Cardiac Muscle like skeletal: striated (organized myofibrils) unlike skeletal: smaller cells no triads SR lacks terminal cisternae dependent on aerobic metabolism special cell-cell junctions Cardiac Muscle intercalated discs junctions to hold the cells together (adhering junctions) junctions allowing for cell-cell communication (gap junctions) functional syncytium (fused cells) Cardiac Muscle functional specializations: •contract without neural stimulation (beat is intrinsic) •nervous system can alter “pace” and adjust tension produced •contractions are slower than skeletal •wave summation and tetany don’t occur fig. 10-22 Smooth Muscle forms sheets, bundles or sheaths skin: blood vessels regulate blood flow to surface (thermoregulation) cardiovascular:blood distribution blood pressure respiratory: change airways / airflow Smooth Muscle forms sheets, bundles or sheaths digestion: move material through urinary: urine production, transport… reproduction: gamete movement labor Smooth Muscle structure small, single cells, central nucleus no organized myofibrils (no striations) have thick and thin filaments connected to neighbors to here 2/14 lec # 17 Smooth Muscle functional differences: 1. excitation-contraction coupling calcium enters cells at stimulation binds to calmodulin activates an enzyme to permits cross-bridges to form Smooth Muscle functional differences: 2. length-tension relationship plasticity ability to contract over a wide range of lengths Smooth Muscle functional differences: 3. control of contractions multiunit similar to skeletal iris m., arrector pili m., …. visceral contraction spreads in waves (peristalsis in gut) Smooth Muscle functional differences: 4. smooth muscle tone neural and hormonal control table 10-4 fig. 10-23 Muscle strains (pulls, tears) sprain injury to a ligament strain injury to a muscle to tendon Muscle cramps (via wikipedia) There are two basic causes of cramping. One is inadequate oxygenation of muscle, and the other is lack of water or salt. Electrolyte disturbance may cause cramping and tetany of muscles, particularly hypokalemia (a low level of potassium) and hypocalcemia (a low level of calcium). (postive feedback-next chapter)
