1 CH 11 muscle tissue types of muscles microscopic anatomy of muscles how muscles work

2 three kinds of muscles skeletal – voluntary smooth – involuntary cardiac - involuntary

3 where do muscles come from - progenitor muscle cells go through myogenesis - form myoblasts multiple myoblasts unite to form multinucleated cell - myoblasts become myocytes - myocytes align in parallel arrangement - myocytes (muscle) become parallel thick & thin myofibrils which interact to form fibers, fascicles, & a muscle

4 muscles are/have excitability – generate electrical changes conductivity – wave of excitability contractility – shortens extensibility – can stretch without breaking elasticity – move back to zero point

5 - a muscle is a complex structure - it has an origin and an insertion - it has a function which is to move a bone or structure or to stabilize or protect a bone or structure - a muscle consists of many fascicles - a fascicle consists of many muscle fibers - a muscle fiber consists of many long & thin myofibrils - the functional unit of a myofibril is a sarcomere - a myofibril has many sarcomeres - a sarcomere consists of many thick and thin myofilaments - a sarcomere is able to contract and return to normal length

6

7 -many myofilaments and associated organelles form a myofibril -each myofibril is surrounded by a sarcoplasmic reticulum -T tubules penetrate deep into the endomysium covered myofibril a group of myofibrils surrounded by a sarcolemma = muscle fiber -groups of muscle fibers surrounded by perimysium form fascicles -numerous fascicles surrounded by epimysium form a muscle a muscle fiber has a very developed SR so a muscle contains many thousands of SR

8

9

10

11

12

13 sliding filament theory thick filaments – myosin heads (light and heavy) in an inactive form each attached to a long twisted tail with a flexible portion and a longer portion linked to other longer tails, heads are able to hydrolyze ATP and release the energy needed to allow the myosin head to change position and link to troponin on thin filament

14 thin filaments - two intertwined strands of globular actin - two strands of tropomyosin which cover the active sites on the globular actin - calcium binds to troponin on tropomyosin causing exposure of active sites on globular actin

15

16 the whole process - when a nerve impulse arrives -calcium rushes into synaptic knob - ACh released which binds to sarcolemma receptor – opens Na/Ca channels in sarcolemma and polarity is reversed – creating an action potential which reaches T tubules - where Ca is released and enters muscle fiber – and binds to troponin on thin filament – thin fiber changes shape and active sites on actin are exposed – myosin ATPase on myosin splits ATP - and released energy allows myosin head to bind to actin - and bends into a high energy position - ready for a power stroke

17 power stroke myosin releases ADP + P- myosin bends into a low energy position, - picks up ATP, & releases actin = recovery stroke – energy from ATP used to attach to actin – same happens over and over by thousands of myosin heads all acting at the same time & in a coordinated fashion resulting in the Z lines coming closer = a contraction nerve impulse stops - AChE breaks Ach - Ca reabsorbed by sarcoplasmic reticulum - active sites covered - no more contraction

18

19 - plasma membrane of muscle fiber = sarcolemma - cytoplasm of muscle fiber = sarcoplasm - the protein cords which make up the sarcomeres = myofibrils - muscle fibers are rich in glycogen & myoglobin - some myoblasts remain as = satellite cells (stem cells) - smooth endoplasmic reticulum is called the sarcoplasmic reticulum - sarcoplasmic reticulum has channels called terminal cisternae which cover the myofibrils from side to side - the sarcolemma sends a tube called transverse (T) tubules associated with two terminal cisternae which travel with the terminal cisternae from side to side - the sarcoplamic reticulum is a reservoir for Ca needed for sarcomere contraction

20

21

22

23

24

25

26 myosin & actin = contractile proteins tropomyosin & troponin = regulatory proteins I band = isotropic A band = anisotropic

27

28 smooth muscle no striations, 1 nucleus, no T tubules, no Z discs, no sarcomeres, no myofibrils, no motor end plates scant sarcoplasmic reticulum small groups of myocytes for fine control autonomic (not always innervated) NE sym & ACh parasym synaptic vesicles have multiple varicosities receptors spread over muscle surface slow response long to fatigue very energy efficient mitosis, hyperplasia, move things, hold things

29

30

31

32

33

34 contraction and relaxation NE or ACh bind to receptors and open Ca channels Ca binds to calmodulin on myosin activates myosin light chain kinase adds phosphate to regulatory protein and activates ATPase myosin performs repetitive power stroke and recovery stroke thick pull thin in & attached cytoskeleton and dense bodies cause muscle cell to shorten and twist removal of Ca is slow so contractions long latch mechanism holds cell contracted without more energy

35 cardiac muscle heart – regular rhythm – non stop – resists fatigue cells contract in unison – contract long enough to pump blood striated – short and thick cardiocytes – gap junctions intercalated discs (tight junctions) – small SR – large T tubules pacemaker – ANS stim= ↑or ↓ of contr. and/or strength mostly aerobic, myoglobin↑, glycogen↑, large mito,

36

37

38 nerve muscle relationship some muscles contract spontaneously but most muscle fibers contract as a response to a nerve stimulation the nerves which stimulate a muscle are called somatic motor fibers whose cell bodies are in the brainstem and spinal cord

39 a neuron has a few to many terminal branches which end on individual muscle fibers all of the muscle fibers innervated by the terminal branches of a neuron are called a motor unit small(fine control) = large(coarse) = average 200

40 100 neurons innervate 1000 muscle fibers 1 neuron innervate 1000 muscle fibers different groups of fibers within a muscle are innervated by different motor units this allows for continued contraction as one group of fibers fatigue others continue to function

41 where a nerve fiber synapses with a muscle fiber it is called a neuromuscular junction

42

43

44

45

46 words we need to remember and understand somatic motor fiberswords we need to remember and understand somatic motor fibers motor unit synapse neuromuscular junction motor end plate synaptic knob synaptic cleft Schwann cell synaptic vesicle acetylcholine (ACh) ACh receptors junctional folds acetylcholinesterase(AChE)

47 nerves and muscle cells are described as electrically excitable this is based on the difference in concentrations between the intercellular fluid ions compared to the extracellular fluid ions the inside of the cell has more negative ions than the outside of the cell

48 this difference in polarity is referred to as a resting membrane potential the inside of the muscle cell compared to the fluid outside of the cell is -90 mV (milli volts)

49 stimulation of a nerve or muscle causes - channels open in the plasma membrane - Na rushes in from high to low concentration - the positive Na ions depolarize the cell (goes from – to +) - Na channels close and K channels open - K leave the cell and repolarizes and hyperpolarizes the cell - this cycle of de and re polarization is an action potential - so much K enters the cell that the RMP drops to more than mV and the cell becomes refractory (cannot initiate another action potential until RMP returns to -90mV)

50

51

52

53 muscle relaxation - as the local potential becomes an action potential - there is no more need for calcium at the initial site - but there is still a need for calcium - until the nerve stops firing - at this point the calcium channels close - calcium is reabsorbed by the sarcoplasmic reticulum - and large amounts of calcium are stored in the - sarcoplasmic reticulum bound to a protein calsequestrin and - stored in the sarcoplasmic reticulum without Ca precipitation

54 length strength relationship too contracted = weak response to stimulation too stretched = weak response to stimulation optimum length = strong response to stimulation at optimum length the body maintains partial contraction known as muscle tone

55 not all stimuli result in an action potential or muscle contraction too much or too little stretch = less than maximum contraction fatigued muscle = less than maximum cold muscle = less than maximum too little hydration = less than maximum long stimuli intervals = less than maximum

56 intensity vs frequency a weak stimulus activates a twitch with weak or no contraction stronger stimulus activates more fibers = weak or no contraction stronger stimulus activates more fibers = weak or small contraction strong stimulus activates more fibers = small to strong contraction stronger stimulus activates more fibers = strong contraction as the stimulus increases more motor units are recruited and more muscle fibers are stimulated resulting in stronger contractions known as MMU multiple motor unit summation

57 low frequency stimulation = muscle relaxes completely before next stimulus higher frequency stimulation = before one twitch comes to rest the next stimulus adds to the previous twitch – strength can build quickly to more than a single twitch very high frequency = no relaxation, twitches fuse to tetanus

58

59

60

61

62 isometric and isotonic scientists describe 4 different types of contractions isometric - isotonic - concentric - eccentric isometric = contraction without a change in length isotonic = contraction with a change in length but no change in tension concentric = muscles shorten as it maintains tension eccentric = muscle lengthens as it maintains tension tension = a state of contraction, muscle tone (tension) is a good thing, muscle tension due to stress is a bad thing

63

64

65

66

67 where do muscles get the energy to do the work that they all dowhere do muscles get the energy to do the work that they all do? ATP aerobic and anaerobic with oxygen or without oxygen resting = aerobic respiration using fatty acids during exercise = anaerobic, short term, & long term

68 - at start of exercise = myoglobin & oxygen (but used up quickly) - then shifts to myokinase & creatine kinase( phosphagen system) - myokinase = takes P from ADP & adds it to ADP to form ATP + AMP - creatine kinase = creatine phosphate donates P to ADP to form ATP - above is good for 1 minute of brisk walking or 6 seconds sprinting - if activity continues = glycogen to glucose to lactic acid from fermentation – good for about 40 seconds (short term energy)

69 - if still active = homeostasis catches up & oxygen becomes available & aerobic respiration takes over (long term energy) - the body accommodates over 3 to 4 minutes & energy production levels off at a steady state – 90% of energy is aerobic for exercise of more than 10 min – up to 30 minutes energy is from glucose & fatty acids and then only fatty acids after glucose stores depleted

70 fatigue K concentration ADP/P accumulation lactic acid accumulation fuel depletion ** - glucose and glycogen depletion electrolyte loss ** - too much sweat, too little intaske central fatigue ** - NH3 accumulation inhibits CNS signals

71 XS post exercise oxygen consumption (oxygen debt) oxygen is required for synthesize ATP ATP needed to regenerate creatinine phosphate regeneration of myglobin liver need oxygen to destroy lactic acid raised body temperature increases need for oxygen

72 slow and fast twitch muscles slow = small motor units, long duration of twitch, excitable, weak strength, aerobic, fatigue resistance, many organelles, many BV, slow ATP hydrolysis, slow oxidative, red color fast = large motor units, short duration of twitch, less excitable, strong contraction, anaerobic, easy fatigue, fewer organelles, white color, rapid ATP hydrolysis, fast glycolytic, few BV, extensive sarcoplasmic reticulum, much glycogen, high CP, most muscles have both types in various amounts type of muscles you have may determine choice of activity

73

74

75 muscle strength depends on size = thickness fascicles = arrangement/orientation of fibers motor units = larger generate more strength multiple summation = involve more motor units temporal summation = increased frequency increases strength stretch = optimum stretch results in optimum strength fatigue = more rest produces more strength

76 resistance exercise = contraction against a load, results in more and thicker myofibrils, does not increase endurance endurance exercise = improves resistance against fatigue, more organelles, better use of oxygen, more BV, increases skeletal strength, does not increase strength to increase both strength and endurance requires cross training

77

78