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75 Cards in this Set
- Front
- Back
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How does Muscular Tissue contribute to Homeostasis?
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1. Producing body movements
2. Moving substances through the body 3. Producing heat to maintain normal body temperature |
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What is myology?
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Scientific study of muscles
muscles make up 40-50 % of the total adult body weight |
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What is Muscular Strength?
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Muscular strength reflects the primary function of muscle - the transformation of chemical into mechanical energy
to generate force, perform work, and produce movement |
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What are the functions of muscle tissue?
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Stabilize body position - maintaining posture, contraction of skeletal muscles stabilizes joints & posture
Produce body movements - whole body and localized Generate Heat - shivering (involuntary contractions of skeletal muscle to increase rate of heat, known as thermogenesis) Propel fluids and food matter through various body systems - 3 ways: Cardiac muscle contraction of heart pumps blood through blood vessels of body Smooth muscle moves substances in the digestive tract, contracts sphincters for temporary storage of urine or food |
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What are the two ways to elecrically excite muscle cells (produce action potentials)?
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Electrical signals - autorhythmic, heart's pacemaker
Chemical stimuli - neurotransmitters, hormones, or changes in pH |
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What is contractility in muscles?
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Ability to contract when stimulated by action potential
Generates tension when it contracts If tension > resistance, muscle shortens and movement occurs |
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What are extensibility and elasticity in muscles?
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Extensibility - ability of muscle to stretch w/o being damaged, smooth muscle stretches the most.
ex. stomach, heart (cardiac muscle) Elasticity - ability to return to original length and shape after contraction or extension |
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What are properties of skeletal muscle tissue?
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made up of hundreds to thousands of long cells called muscle cells
muscle - bundles of fibers (fascicles) are bound to connective tissue |
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What are some properties of connective tissue of skeletal muscle?
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surround and protect the muscle tissue
superficial fascia - separates skin from muscle and contains areolar CT and adipose tissue allows free movement of muscles and carries nerves, blood vessels, and lymphatic vessels, fills spaces between muscles |
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What is Fascia?
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dense sheet of dense irregular connective tissue that lines body walls and limbs, holds muscles with similar functions together
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What are the 3 layers of CT that protect and strengthen skeletal muscle?
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Epimysium - dense irregular CT outer layer, surrounds entire muscle
Perimysium - dense irregular CT that surrounds 10-100 muscle fibers and separates them into bundles called fascicles Endomysium - areolar CT, separates muscle fibers from one another |
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What is a tendon and an aponeurosis?
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Tendon - dense regular connective tissue composed of parallel bundles of collagen fibers attaching muscle to bone
Aponeurosis - flat, broad layer of tendon |
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What are Tendon sheaths?
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also known as Synovial sheaths
enclosed by tubes of fibrous connective tissue (ex. tendons in wrist and ankle) visceral layer - inner layer attached to surface of tendon parietal layer - outer layer attached to bone |
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What are Somatic Motor Neurons?
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Neurons that stimulate skeletal muscles to contract
each muscle fiber is in close contact with one or more capillaries |
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What do blood capillaries do?
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provide nutrients and oxygen to muscle fibers and remove heat and waste products of muscle metabolism
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What are Myoblasts?
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small mesodermal cells that when fused together during embryonic development create muscle fibers
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What are some properties of skeletal muscles?
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diameter of mature muscle fiber ranges from 10-100 micrometer and length is 10 cm
100 or more nuclei amitotic after fusion # of skeletal muscle fibers set before birth and last a lifetime, hormone-induced hypertrophy is responsible for muscle growth after birth undergo fibrosis - replacement of msucle fibers by fibrous scar tissue |
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What do satellite cells do in skeletal muscle?
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retain ability to regenerate functional muscle fibers from the damaged ones
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What are the A band and H zone?
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A band - extends the entire length of thick filaments
H zone - narrow zone in the middle of each A band which contains only thick filament |
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What are sarcomeres?
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basic structural and functional unit of the myofibrils/muscle fibers
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What is a Z disc?
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narrow plate-shaped region which separates one sarcomere from the next
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What is the I Band?
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lighter, less dense area, contains rest of thin filaments, but no thick filaments
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What is the M Line?
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middle of the sarcomere, it is made by supporting proteins which hold the thick filaments together at the center of the H zone
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What are the 3 types of muscle proteins?
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Contractile - generate force during contraction. ex. actin & mysosin
Regulatory - help to regulate 'on and off' of contraction process. ex. troponin & tropomyosin Structural - maintain the proper alignment of thick and thin filaments, give the myofibril elasticity & extensibility, link the myofibrils to the sarcolemma and extracellular matrix. ex. titin, myomesin, nebulln, dystrophin |
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What are some properties of Myosin?
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thick filaments
in all 3 types of muscles achieve movement by converting chemical energy to ATP to mechanical energy of motion or force in skeltal muscle, 300 for one thick filament shaped like 2 golf clubs twisted together |
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What are the myosin tail and myosin head?
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tail - points toward the M line in the center of the sarcomere
head - two projections of each myosin molecule, project outward in spiraling fashion |
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What are some of the properties of Actin?
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thin filaments, anchored by Z discs
globular proteins in helix formation cross-bridges for myosin head in relaxed muscle, myosin is blocked from binding to actin |
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What are Tropomyosin and Troponin?
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both are regulatory proteins that are part of thin filament (actin)
tropomyosin covers the myosin-binding sites and are held in place by troponin |
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What role does Calcium ion have in muscle contraction?
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binds to troponin
troponin moves tropomyosin away from myosin-binding sites allows muscle contraction to begin as myosin binds to actin |
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What are some properties of Titin?
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large protein, 3rd most abundant in skeletal muscle
in relaxed state, spans half a sarcomere from Z discs to M line, and anchors thick filament to both a Z disc and M line stabilizes myosin and accounts for much of elasticity and extensibility of myofibrils prevents overextension and maintains central location of A band |
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What are Alpha-actinin, myomesin, and nebulin?
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Alpha actinin - binds to actin and titin
Myomesin - forms M line and binds to titin, connects adjacent thick filaments Nebulin - non elastic protein, surrounds thin filament, anchors thin filaments to Z discs |
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What are some properties of Dystrophin?
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cytoskeletal protein
reinforces sarcolemma and transmits tension generated by sarcomeres to the tendons |
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What is the Sliding Filament Mechanism?
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Myosin head attaches to and "walks" along thin filaments at both ends of a sarcomere, progressively pulling the thin filaments toward the center of the sarcomere (M Line)
Z discs come closer together and sarcomere shortens but thick/thin filaments DO NOT change in length this causes shortening of entire muscle |
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What are the 4 steps of the contraction cycle?
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started by the caclium binding to troponin
1. ATP Hydrolysis - reorients and energizes myosin head. 2. Formation of Cross-Bridges - Pi group released by myosin head binding to site 3. Power stroke - crossbridge rotates and releases ATP, sliding thin filament toward center of sarcomere (M line) 4. Detachment of Myosin from Actin - as next ATP binds to myosin head, myosin head detaches from actin |
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What are the factors to keep the contraction cycle going?
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ATP available
Ca levels sufficiently high |
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What do the crossbridges do?
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refers to myosin head attaching to actin during contraction
applies force to draw Z discs toward each other, sarcomere shortens Z disc then pulls neighboring sarcomeres, shortening whole muscle |
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What is Excitation-Contraction Coupling?
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increase in Ca starts contraction, decrease in Ca stops it
action potential causes Ca to be released from SR into muscle cell Calcium moves tropomyosin, allowing crossbridges to form Calcium pumps return Ca back to SR quickly, as Ca level drops muscle relaxes |
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What are the events in Muscle contraction?
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1. Motor neuron releases Ach
2. Ach diffuses across synaptic gap at NMJ 3. Muscle fiber membrane stimulated, sending impulse through T tubles to SR 4. Ca influx into Sarcoplasm from terminal cisterns of SR 5. Actin-Myosin binding 6. Myosin pulls actin inward 7. Muscle fiber shortens as contraction occurs |
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What are the events in Muscle Relaxation?
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1. Ach esterase decomposes Ach
2. Ca back to SR 3. Actin-Myousin link breaks 4. Actin-Myosin slide apart 5. Muscle fiber relaxes |
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What is Rigor Mortis?
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state of rigidity 3-4 hours after death
calcium leaks out of SR which allows myosin to bind to actin since ATP synthesis is stopped after death, cross bridges can't detach from actin and muscles remain rigid disappears as proteolytic enzymes from lysosomes digest cross-bridges |
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What is Muscular Hypertrophy?
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increase in total muscle mass
results from repetitive muscle activity ex. strength training |
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What are hyperplasia?
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increase in actual number of muscle fibers
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What is the Neuromuscular Junction (NMJ)?
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a single muscle fiber only has 1 NMJ
axon has many motor unit - motor neuron and all skeletal muscles supplied by that one axon synaptic end bulbs - motor axons divided at NMJ synaptic vesicles - membrane enclosed sacs in each bulb, contain Ach motor end plate - region of sarcolemma adjacent to bulbs, contains millions of Ach receptors |
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What is the sequence of muscle stimulation?
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1. Release of ACh - ACh diffuses through synaptic cleft and goes to motor end plate (after AP)
2. Activation of ACh receptors on muscle - action potential occurs at sarcolemma due to opening of ion channels 3. Production of muscle action potential - goes through sarcolemma into T tubules 4. Termination of ACh activity - ACh esterase degrades ACh into acetyl and choline |
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What is Botullinum toxin?
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blocks release of ACh from synaptic vesicles, can cause death by paralyzing respiratory muscles
used as Botox |
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What is Curare?
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plant poisoning on arrows that causes muscle paralysis by blocking ACh receptions inhibiting Na+ ion channels
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What is an Anti ACh esterase agent?
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slows removal of ACh
ex. Neostigmine - used for Myasthenia Gravis, antidote for curare posioning |
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What are the 3 ways muscle fibers produce ATP?
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1. Creatine Phosphate
2. Anaerobic cellular respiration 3. aerobic cellular respiration |
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What is Creatine Phosphate?
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energy-rich molecule found only in muscle fibers
during muscle contraction, tranfers its high energy phosphate group to ADP regnerating new ATP creatine kinase (CK) catalyze both reactions synthesized in body and also derived from milk, red meat, and fish provides 15 seconds of muscle activity |
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What is anaerobic respiration?
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glycolysis: each glucose split into two pyruvic acids which forms 4 ATP
if enough oxygen, pyruvic acid enters aerobic respiration if low oxygen, converted to lactic acid 1/2 as rapid as phosphagen system provides energy for 30-40 secs of muscle activity |
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What is aerobic respiration?
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each molecule of glucose produces 36 ATP, lasts more than half a minute of muscle activity
oxygen comes from hemoglobin or myoglobin provides 90 % of needed ATP for activities more than 10 minutes |
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What is central fatigue?
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protective mechanism by CNS that gives person desire to stop an activity due to feeling of tiredness
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What are some factors that contribute to muscle fatigue?
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inadequate release of Ca+ from SR
depletion of creatine phosphate insufficient oxygen depletion of glycogen and other nutrients building of lactic acid and ADP failure of motor neuron to release enough ACh |
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What is oxygen debt?
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additional oxygen that is taken into body after exercise
also called recovery oxygen uptake |
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What does oxygen debt do?
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additonal oxygen that is used:
1. converts lactic acid to glycogen 2. synthesize creatine phosphate and ATP 3. replace the oxygen removed by myoglobin |
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What are the factors involved in muscle tension?
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rate at which nerve impulse arrives
amount of stretch before contraction nutrient and oxygen availability size of motor unit |
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What is a twitch contraction?
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brief contraction of all the muscle fibers in a motor unit in response to a single action potential
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What are the events in a myogram?
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Latent Period - 2 msec
brief delay between application of stimulus and beginning of muscular contraction, Ca released from SR after AP sweeps over sarcolemma Contraction period - (10-100 msec) Ca binds to troponin myosin-binding sites exposed cross-bridges form peak tension develops Relaxation Period - (10-100 msec) Ca back to SR myosin-binding site covered by tropomyosin myosin head detaches from actin Refractory Period when muscle fiber contracts, temporarily cannot respond to another AP; Cardiac muscle has much higher refractory period than skeletal muscle |
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What is wave summation?
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if a second stimulus occurs during the refractory period of the first stimulus but before the relaxation period, the effect of the two stimuli are summed up
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What is incomplete tetanus or clonus?
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if next successive stimulus occurs during the relaxation period it leaves an incomplete relaxation period
when skeletal muscle is stimulated at a rate of 20-30 stimuli/sec it produces incomplete tetanus |
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What is complete tetanus?
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when the successive stimulus falls before the relaxation phase it will produce sustained, smooth and forceful contraction, without any relaxation period
80-100 stimuli/sec = complete tetanus |
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Characteristics of tetanus
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occur due to release of additional Ca from the SR in already elevated levels
due to build up of Ca the peak tension produced in complete tetanus is 4-5 times greater than a single twitch stretch of elastic components also plays a major role |
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What is muscle tone?
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keeps skeletal muscles firm
small amt of tension due to weak involuntary contractions of motor units smooth muscle tone helps maintain BP, keeps head from slumping forward on chest |
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What are the types of muscle contraction?
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Isotonic - movement
concentric: muscle shortens eccentric: muscle lengthens ex. picking a book up off a table isometric - no movement ex. holding a book steady using an outstretched arm |
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What are the 3 types of skeletal muscle fibers?
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1. Slow oxidative fibers - smallest and least powerful, dark red, generate ATP by aerobic respiration, slow speed of conduction (100-200 msec twitch), resistant to fatigue, in most skeletal muscles represent half of fibers
ex. running a marathon and maintaining posture 2. Fast oxidative-glycolytic fibers - dark red lots of myoglobin, aerobic respiration & some anaerobic glycolysis (less than 100 msec twitch) ex. walking and sprinting 3. Fast glycolytic fibers - largest and most powerful, low myoglobin (white color), ATP by glycolysis, fatigue quickly ex. weight lifting or throwing ball |
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What are some characteristics of Cardiac muscle tissue?
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tissue in heart wall
intercalated discs connect cardiac muscle fibers gap junctions allow muscle APs to spread between cardiac muscle fibers autorhythmic contraction, longer contractions than skeletal muscles no epimysium mitochondria are large and numerous aerobic respiration but uses lactic acid produced by skeletal muscle fibers for ATP |
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What are characteristics of smooth muscle tissue?
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involuntary
gap junctions for APs stimulated by hormones, neurotransmitters, and autorhythmic signals |
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What are the two types of smooth muscle?
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Visceral - autorhythmic, found in walls of small arteries and veins and walls of stomach, intestines, uterus, urinary bladder
Multiunit - few gap junctions, found in walls of large arteries, airway to lungs, hair follicle muscles, lens of eye, and muscles of iris |
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What are some microscopic characteristics of smooth muscle?
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not arranged in orderly sarcomeres
not striated no T tubules small amt of SR for storage of Ca filaments attach to dense bodies (function like Z discs) |
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Differences in Smooth muscle compared to Cardiac and Skeletal
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slower but longer contractions
more stretching and shortening small amounts of SR No T tubules, takes longer for Ca ions to reach center of fiber to trigger contraction calmodulin - binds calium in cytosol (behaves like troponin), activates myosin light chain kinase myosin light chain kinase - uses ATP to add Pi to myosin head which allows binding to actin for contraction to occur |
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Properties of Muscle Regeneration
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growth is due to hypertrophy (in all 3)
satellite cells assist in repair of damaged fibers skeletal muscles can only regenerate to a limited extent |
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How is muscle developed?
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from mesoderm
somites - columns of mesoderm 3 regions of somites: 1. myotome - skeletal muscles of head, neck and limbs 2. dermatome - CT, including dermis of skin 3. Sclerotome - gives rise to vertebrae |
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What is Myasthenia Gravis?
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autoimmune disorder of the NMJ
causes chronic, progressive damage of NMJ block ACh receptors at NMJ muscles become fatigued and weak (mostly face and neck), double vision, difficulty in chewing and talking thymic abnormalities are main predisposing factor Anti ACh esterase drugs are used (pryidostigmine and neostigmine), steroids like prednisone, and thyectomy |
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What is Duchenne's Muscular Dystrophy?
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most common type
inherited X-linked recessive (only affects males) appears between ages 2-5, have difficulty running, jumping, and hopping other symptoms include poor balance, calf pain, inability to walk, drooping eyelids, scoliosis gene that codes for protein dystrophin is mutated this absence of dystrophin leads to tear of sarcolemma during muscle contraction, leading to ruptured muscle fibers no cure but treated by physical, speech, and occupational therapy |
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What is Fibromyalgia?
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painful, nonarticular rheumatic disorder
affects fibrous CT symptoms include pain, tenderness, stiffness of muscles |
