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3 types: 1) skeletal-pulls on bones to cause movement 2) cardiac-pumps blood thru circulatory system 3) smooth-pushes fluids & solids thru body, regulates.

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Presentation on theme: "3 types: 1) skeletal-pulls on bones to cause movement 2) cardiac-pumps blood thru circulatory system 3) smooth-pushes fluids & solids thru body, regulates."— Presentation transcript:


2 3 types: 1) skeletal-pulls on bones to cause movement 2) cardiac-pumps blood thru circulatory system 3) smooth-pushes fluids & solids thru body, regulates blood vessel diameter

3 Skeletal Muscle: Functions: a) Produce skeletal movements -contract & tendons pull on bones

4 b) Maintain posture & position b) Maintain posture & position -constant tension keeps head in position & body over feet c) Soft tissue support -muscles lining abdomino- pelvic cavity support weight of organs & offer protection

5 d) Guard entrances & exits -closes openings in digestive & urinary tracts e) Produce heat -contractions require energy that is converted into heat to maintain temp.

6 f) Nutrient reserve storage -proteins in muscles are broken down to provide amino acids for enzymes & energy

7 Organization -3 connective tissue layers 1) Epimysium: -surrounds entire muscle -separates muscle from other tissues/organs

8 2) Perimysium: -divides muscle into compartments -each contains a fascicle- bundle of muscle fibers -each receives a branch of blood vessels & nerves

9 3) Endomysium: -surrounds individual muscle fibers (cells)

10 Collagen fibers from each layer join to form a tendon (connects muscle to bone) or aponeurosis (broad sheet that connects muscle to bone)

11 Microscopic structure -cells can be 30 cm long & 100 µm (.1 mm)diameter -very large compared to most cells -multinucleate -may be 100’s/cell -lie just below membrane

12 -Sarcolemma-plasma membrane of muscle fiber -Sarcoplasm-cytoplasm

13 -Transverse (T) tubules- narrow tubes, continuous w/ sarcolemma that extend thru sarcoplasm -fluid-filled -contain same electrical charge as sarcolemma -send impulse to entire fiber so it all contract together

14 -Myofibrils- cylindrical structures that run the length of a fiber -made of myofilaments: thin strands/filaments of protein -2 types 1)Thin filaments-actin 2)Thick filaments-myosin

15 -can shorten & are responsible for muscle contracting -anchored to ends of sarcolemma which eventually becomes a tendon which pulls on bone -space filled w/ mitochondria & glycogen

16 -Sarcoplasmic reticulum- membrane complexs, similar to smooth ER -surround each myofibril between T-tubules -terminal cisternae- expanded, fused chambers where SR meets T-tubule

17 -triad-2 terminal cisternae & a T-tubule -cells pump CA 2+ ions out of cells, they also transport them into the terminal cisternae -may have 1000x higher concentration of free Ca 2+

18 -calsequestrin (protein) binds Ca 2+ -total Ca 2+ may be 40,000x greater -contractions begin when Ca 2+ ions are released into sarcoplasm


20 -Sarcomere- repeating, individual contractile units in myofibrils -1 myofibril can have 10, components:

21 1) Thick filaments-myosin w/ associated titin (elastic filaments) 2) Think filaments-actin 3) Stabilizing proteins 4) Regulating proteins -create banded/striated appearance

22 I-band-light band (only actin) A-band-dark (myosin & actin) H-zone- only myosin

23 M-line-proteins that stabilize position of thick bands Zone of overlap-thin filaments between thick -6 thin surround a thick -3 thick surround a thin p. 289

24 Z-line-boundary between sarcomeres -proteins that connect thin filaments -titin proteins extend from thick filaments & attach to Z-line -helps filament alignment

25 -Surrounded by 2 T-tubules & triads located at zones of overlap

26 -Thin filaments: -each contains 4 proteins -active site: area where myosin can bind -covered by troponin- tropomyosin complex when a muscle is relaxed

27 -in resting muscle, intracellular Ca 2+ concentrations are very low & binding site is empty -Troponin-tropomyosin complex must move in order for contraction to occur -calcium triggers process

28 -Thick filaments -contain 300 twisted myosin molecules -tail-where molecules are bound to each other -head-projects toward actin -made of 2 globular protein subunits

29 -interact w/ active site to form cross-bridges -hinge that allows head to pivot freely -arranged so tails point toward M-line -core contains titin that extends past fiber & attaches to Z-line

30 ContractionEvents: 1)H-zones & I-bands get smaller 2)Zones of Overlap get larger 3)Z-lines get closer together 4)A-band width stays constant

31 Sliding Filament Theory-thin filaments slide toward M-line moving across thick filaments, causing sarcomere to shorten & muscles to contract

32 -When muscles contract they put tension on attached tendons

33 Control of Muscle Activity -nerves from central nervous system (brain & spinal cord) control contractions -Neuromuscular junction: area where nerve connects/ communicates w/ muscle fiber -1/fiber

34 -ends w/ synaptic terminal -filled with acetylcholine (Ach)-a neurotransmitter that is released by the neuron from the synaptic terminal, attaches to muscle fiber & alters the permeability of the sarcolemma

35 -Synaptic cleft: space between synaptic terminal & muscle sarcolemma -Motor end plate: sarcolemma opposite synaptic terminal that houses receptors where Ach binds -folded to  surface area

36 -Acetylcholinesterase: (AChE)-enzymes that breaks down ACh, found in synaptic cleft & sarcolemma


38 -Steps of Stimulation 1) Action potential: (electrical impulse to signal release of ACh) reaches synaptic terminal 2) ACh is released thru exocytosis into synaptic cleft

39 3) ACh binds to motor end plate receptors & changes permeability to Na + ions, which move into sarcoplasm until AChE removes ACh from receptor sites

40 4) Na + movement creates an action potential in sarcolemma, moves inward thru T-tubules 5) ACh broken down by AChE & system is ready for another action potential

41 Excitation-Contraction Coupling: process that uses the stimulus from an action potential to create a muscle contraction -occurs at triads

42 -action potential causes cisternae to release Ca 2+ ions into sarcoplasm at a sarcomere’s zone of overlap -action potential causes cisternae to release Ca 2+ ions into sarcoplasm at a sarcomere’s zone of overlap -normally troponin (enzyme) covers the active site of actin strands, Ca 2+ causes troponin to release & allow for myosin heads to bond

43 -begins the contraction cycle

44 Contraction cycle: 1) Troponin removed & active sites available 2) Myosin head binds to active site forming a cross-bridge (requires 1 ATP)

45 3) Myosin heads pivot from being pointed away from the M-line to being pointed towards it (power stroke) 4) Cross-bridges detach (myosin head lets go of active site)

46 5) Another ATP is split to re- energize free myosin head which causes it to pivot back to its original position -Cycle begins again as long as Ca 2+ is present & ATP is available -Cycle begins again as long as Ca 2+ is present & ATP is available -Each power stroke shortens the sarcomere by 1%

47 -Length of contraction depends on: 1) Length of stimulation at neuromuscular junction 2) Availability of free Ca 2+ ions in sarcoplasm 3) Availability of ATP

48 -ACh binding occurs only briefly, so action potentials must continue to be applied in rapid succession to maintain a contraction -Once action potential ends, sarcoplasmic reticulum permeability changes & absorbs Ca 2+, active site is recovered

49 -sarcomere slowly returns to original length

50 -at death, no more nutrients/ oxygen cycles, Ca 2+ enters sarcoplasm which triggers contraction. Cross-bridges can’t detach because there’s no ATP-causes rigor mortis- constant contraction of skeletal muscles at death, lasts hours until autolytic enzymes break down Z-lines & titin

51 Tension: -amount of tension depends on number of pivoting cross- bridges -level at muscle fibers depends on: a) resting length & size of zone of overlap b) frequency of stimulation

52 -sarcomere length must be optimal for good tension -allows for max. # of cross- bridges to form & pull on fibers -extreme stretching/ compression is prevented by muscle arrangement, connective tissue, & bones -titin fibers also help prevent extreme stretching

53 -stimulation frequency -single contraction lasts milliseconds -this can be extended by repeated stimulation & sustained contractions which  tension

54 -Twitch: single stimulus- contraction-relaxation sequence in a muscle fiber -time varies

55 -3 phases 1) Latent period: action potential releases ACh & SR releases Ca 2+ -no tension produced (2 msec)

56 2) Contraction phase: tension rises to a peak, Ca 2+ binds to troponin, active sites exposed, cross- bridges form (2-15 msec)

57 3) Relaxation phase: Ca 2+ levels fall, active sites covered w/ tropomyosin & cross-bridges decrease, tension falls (15-40 msec)


59 -Treppe: second stimulation is applied immediately after relaxation period ends, tension increases w/ each stimulus until max. tension is reached (after stimulations) -results from gradual  in Ca 2+ because SR can’t reabsorb all

60 -Wave summation: second stimulus begins before relaxation phase ends -create more powerful contractions -tension will rise to 4x treppe max. -rapid cycles that maintain max. level during wave summation-incomplete tetanus


62 -Complete tetanus: faster stimulations eliminates relaxation phase -SR can’t reabsorb Ca 2+ -creates continuous, strong contraction

63 Tension in Whole Muscle -dependent on tension in fibers & # of fibers contracting -twitch is ineffective for useful movement, treppe, or tetanus is used

64 -Motor unit: all muscle fibers controlled by a single motor neuron -fine motor areas have less fibers/neuron than gross motor

65 -smallest motor units are activated first during a contraction, larger units create faster more powerful movement -smallest motor units are activated first during a contraction, larger units create faster more powerful movement -recruitment: increasing # of motor units contracting based on movement

66 -all motor units contracting in complete tetanus creates peak tension can’t be sustained because ATP reserves run out -units usually take turns contracting so some have time to recover -asynchronous motor unit summation

67 -Muscle tone: resting tension in skeletal muscles -don’t cause motion -little tone=limp/flaccid muscle -motor units take turns contracting

68 -stabilizes & maintains body position, prevents sudden motions, & allows muscles to absorb sudden shock

69 Contraction classifications 1) Isotonic contraction: tension rises & length of muscle changes 2 types: a) Concentric contractions: muscle tension exceeds resistance & muscle shortens -e.g. flexion of elbow

70 b) Eccentric contraction: peak tension is less than load & muscle elongates due to pull of another muscle or gravity -e.g. controlled extension of elbow

71 2) Isometric contraction: contraction where muscle doesn’t change length because tension never exceeds resistance -fibers shorten, but connective tissue stretches

72 -after contraction, fibers return to original length because of elastic forces, opposing muscle contractions, & gravity

73 Fiber Types: 1. Fast Fibers: large fibers that contract quickly & forcefully -fatigue rapidly -”white meat” 2. Slow Fibers: smaller fibers that take longer to reach peak tension -more blood & myoglobin -difficult to fatigue -”red/dark meat”

74 Organization of the muscular system -muscle fibers in fascicle are parallel, but fascicle organization varies

75 Types 1. Parallel muscles: fascicles parallel to long axis -includes most skeletal muscles -e.g. sartorius -spindle-shaped w/ central body (belly) are called fusiform (e.g. biceps brachii)

76 2. Convergent muscle: fascicles extend over a broad area & converge at a common attachment site -shaped like fan or triangle w/ tendon at apex -e.g. pectoralis & trapezius

77 3. Pennate muscle: fascicles form a common angle w/ the tendon a. unipennate-muscle fibers on same side of tendon b. bipennate-fibers on both sides of tendon c. multipennate-tendon branches w/in pennate -e.g. deltoid

78 4. Circular muscle/sphincter: fascicles are concentrically arranged around opening -contraction decreases diameter -e.g. orbicular oris


80 Levers: rigid structure that moves on a fixed point (fulcrum) -moves when an applied force (AF) can overcome a resistance (R) -bone is lever, joint is fulcrum, & muscle is AF

81 -can change a. direction of applied force b. distance/speed of movement produced by AF c. effective strength of AF

82 Classes of Levers 1. 1 st class: seesaw -few in body -e.g.-extension of neck

83 2. 2 nd class: -small force can move a larger weight -e.g. ankle extension (plantarflexion)

84 3. 3 rd class: -most common in body -speed/distance ↑ at expense of effective force

85 Terminology Origin: place where fixed end of muscle attaches Insertion: site where movable end attaches to another structure Action: specific movement produced when a muscle contracts -based on movement from anatomical position -muscles work in groups for complex motions

86 Agonist: (prime mover) muscles that’s contracting to create a particular movement Antagonist: muscle whose action opposes the motion of the agonist e.g. biceps brachii vs. triceps brachii – functional opposites

87 Synergist: helps agonist work more efficiently, provide more pull, stabilize origin -fixators: synergists that stabilize origin by preventing movement in other joints

88 Naming 1. Location – Temporalis 2. Origin/Insertion – (1 st /2 nd ) – Sternocleidomastoid 3. Fascicle organization -Rectus (straight)-Rectus abdominis -Oblique/Transversus

89 4. Relative position -Superficialis/Externus-Internus/Profundus 5. Structure -Biceps (2 heads), Triceps (3 heads) -Trapezius (triangle) -Longus, Brevis, Maximus, Minimus, Major, Minor

90 6. Action -Flexor, Extensor, Pronator, Abductor, etc.

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