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The Muscular System part 2 Modified by J. Kalinowski 1/2015

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1 The Muscular System part 2 Modified by J. Kalinowski 1/2015
Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb The Muscular System part 2 Muscle Physiology Modified by J. Kalinowski 1/2015 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

2 Microscopic Anatomy of Skeletal Muscle
Sarcolemma – specialized plasma membrane of muscle fiber Cells are multinucleate Nuclei are just beneath the sarcolemma Sarcoplasm – cytoplasm of a muscle fiber Figure 6.3a Slide 6.9b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

3 Myoglobin Myoglobin is a common protein, which has the ability to store oxygen in muscle cells. The myoglobin has a high level of red pigment, so the more myoglobin the meat has, the redder it will be. The terms “red meat” and “white meat” are actually an indicator for the level of myoglobin.

4 Myoglobin Amounts

5 Myoglobin This protein is also the main reason that the red meat turns darker while you’re cooking it. During the heating process, iron atoms of the myoglobin lose electrons and they move up to a higher oxidation level. Thus, the meat turns from pinkish-red to brown.

6 Microscopic Anatomy of Skeletal Muscle
Myofibril - Long rod like organelles comprising 80% of cell volume Running parallel the entire length of the cells the myofibrils are aligned to give distinct bands A band = dark band Contains lighter central H Zone visible only in relaxed fiber I band = light band Contains Z disc/line at midpoint Slide 6.10a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7 Micro anatomy Banding patterns/striations reveal the working structure of muscle fiber


9 Microscopic Anatomy of Skeletal Muscle
Sarcomere Region of myofibril Contractile unit of a muscle fiber Region between 2 successive Z discs Figure 6.3b Slide 6.10b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings


11 Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere Thin filaments = actin filaments Contain troponin & tropomyosin to regulate attachment of myofilaments to each other Slide 6.11b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

12 Microscopic Anatomy of Skeletal Muscle
Thick filaments = myosin filaments Composed of the protein myosin with cross bridge heads Heads contain ATPase enzymes to split ATP & release energy for contraction Figure 6.3c Slide 6.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings


14 Twizzler analogy Many packages of Twizzlers = Fascicle
Find a Fascicle on your diagram.

15 Twizzler analogy 2 1 package of Twizzlers = Muscle fiber
The packaging = Sarcolemma

16 Twizzler analogy 3 1 bundle of twizzlers = myofibril

17 Twizzler analogy 4 1 Twizzler strand = Filament

18 Compare the Muscle Fiber to Pull and Peel Twizzlers
How amazing is that?

19 Sarcoplasmic Reticulum
Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum Function: Stores ionic calcium & releases it on demand

20 Sarcoplasmic Reticulum
Surrounds myofibrils At junction of A band and I band, sarcolemma forms hollow T-tubule to conduct stimulus deep into every sarcomere


22 How muscle knows WHEN to contract
Mechanism of contraction on a cellular level

23 Motor Unit One motor neuron and ALL the muscle cells that it stimulates Spread throughout muscle

24 Explanation - then see next slide!
Stimulation of one motor unit results in weak contraction of ENTIRE muscle Since a motor unit is spread throughout the muscle & not clustered together, it stimulation will activate cells scattered throughout the entire muscle This causes a weak contraction of the entire muscle Muscles requiring fine control have small motor units that only activate a few cells at a time.

25 Figure 6.4a Slide 6.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

26 Nerve Stimulus to Muscles
Neuromuscular junctions – association site of nerve and muscle Figure 6.5b Slide 6.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

27 Nerve Stimulus to Muscles
Each axon terminal forms junction with single muscle fiber Synaptic cleft – fluid filled gap between nerve and muscle Nerve and muscle do not make contact Importance: prevent continuous stimulation Figure 6.5b Slide 6.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

28 Transmission – know the steps
Vesicles in axon terminal filled with neurotransmitter – chemical released by nerve upon arrival of nerve impulse The neurotransmitter for skeletal muscle is acetylcholine (ACh) Neurotransmitter crosses synaptic cleft and attaches to receptors on the sarcolemma The Neuromuscular Junction video 2 Slide 6.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

29 Transmission – know the steps
Sarcolemma becomes temporarily permeable to sodium (Na+) Na+ ions rush into muscle cell which reverses electrical conditions Action potential is caused which moves along sarcolemma and down T tubules deep into muscle fiber Once initiated – action potential is unstoppable (all or none principle) resulting in full contraction of that particular muscle fiber (cell) Excitation-Contraction Coupling

30 Safeguard When nerve stimulation stops:
Ach is destroyed by acetylcholinesterase (AChE) to prevent continued contraction Substances such as certain organophosphates found in pesticides and fertilizers destroy AChE causing convulsions

31 End of stimulation K+ ions leaves cell rapidly to restore electrical balance Then Na-K pump restores ions to original positions for relaxation of muscle fiber

32 Sliding Filament Theory
HOW a muscle contracts

33 Sliding Filament Theory
The thin filaments slide past the thick filaments so the overlap increases This shortens the muscle fiber and thus the entire muscle

34 The Sliding Filament Theory
Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament Myosin heads then bind to the next site of the thin filament Figure 6.7 Slide 6.17a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

35 The Sliding Filament Theory of Muscle Contraction
This continued action causes a sliding of the myosin along the actin The result is that the muscle is shortened (contracted) Figure 6.7 Slide 6.17b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

36 What causes the filaments to slide?
Cross bridge attachment: in presence of Ca ions, high energy myosin cross bridge binds to actin binding site Power Stroke: energy from ATP is used to bend cross bridge and pull actin toward center of sarcomere 1% shortening for each power stroke

37 Neuromuscular junction animation
Focus Questions: What is the name of the stimulus that travels down the axon to the muscle fiber? An action potential Does the terminal (end) of the axon enter the muscle fiber? No. There is a gap between the two. Does acetylcholine enter the muscle fiber? No. What chemical does enter the muscle fiber, resulting in an action potential through the muscle fiber? Sodium

38 Sliding Filament theory
Boat = Myosin (thick filament) Oar = Myosin side arm Water = Actin (thin filament) Life ring = Calcium

39 Resting ATP is bound to myosin side arm.
ATP cleaves into ADP + P (high energy)

40 Step 1 Action potential A nerve action potential releases acetylcholine into the synaptic cleft opening the Na+ channels. Action potential spreads across sarcolemma releasing Ca into sarcoplasma

41 Step 2 Myosin-actin binding
Ca binds to troponin. A shape change in troponin moves tropomyocin out of the way of actin binding site. Actin and myosin bind using energy from cleaved ATP.

42 Step 3 Power Stroke Side arm pivots so myosin and actin slide by each other shortening the sarcomere. ADP and P released (low energy)

43 Step 4 ATP Binding Actin-myosin release
A different ATP molecule binds to active site. Actin released

44 Step 5 ATP cleavage Return to high energy state
Cycle will repeat if Ca still available.

45 Think it over The boat (myosin) does not move far in one cycle, can a muscle contraction occur with one cycle? No If a muscle is contracted what happens if a new molecule of ATP is not available? Muscle stays contracted- cramps Why does rigor mortis occur? (Hint: What chemical is no longer available to the body?) ATP is not available to control Ca release so contractions are continuous 6-8 hours after death. Body relaxes hours as enzymes break down contractile structures. Myofilament Contraction

46 Sarcomere summary

47 Sliding Filament Theory
Focus questions: What happens to the length of the sarcomere during a contraction? The sarcomere shortens.

48 Sarcomere Contraction

49 Sliding Filament Animation
Focus Questions: What chemical exposes the binding site for actin and myosin? Ca What is the source of energy for a contraction? ATP What is the name of the step in which the actin filament is actively contracted? Powerstroke What chemical must be present in order for the actin and myosin filaments to separate?

50 Muscle contraction at the macroscopic level
Place your fingers along the angle of your jaw just in front of your ear. Grit your teeth and fell what happens to the hardness of the masseter muscle. During muscle contraction the muscle becomes ________________________.

51 With your thumb and little finger of one hand, span the opposite arm’s bicep’s from the elbow to as close to the shoulder as possible. Bend the arm and observe the change in the length of the muscle. During muscle contraction the muscle ___________________ in length.

52 Wrap a string around your extended upper arm and determine the circumference.
Clench your fist tightly and flex your arm to contract the muscle. During muscle contraction the diameter of the muscle _____________________.

53 Types of Muscle Contractions
Isotonic (same tension) contractions Myofilaments are able to slide past each other during contractions The muscle shortens & movement occurs Isometric (same length) contractions Tension in the muscles increases The muscle does not shorten & no movement occurs Most movements involve both types of activity Slide 6.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings


55 Developmental Aspects
Progresses superior to inferior direction Baby can lift head before walking Progresses proximal to distal Baby can move arm before grasping object This is due to the way that neural pathways are built in your brain.

56 Men vs. women Women’s skeletal muscles make up 36 % of body weight
Men’s is 42 % due to effects of testosterone Muscle strength per unit mass is equal

57 Building Muscle Mass Type of joint involved in motions
Direction of muscle fibers (contained in fascicle) Anatomy of the muscle Angles of body parts In order to work a muscle effectively & to minimize risk of injury, the above factors must be considered. Number of reps and amount of weight depends on purpose of exercise (building vs. toning).

58 Aerobic vs. Anaerobic 3 main factors affect your respiration type:
Your nutrition Your respiratory efficiency Your cardiovascular fitness IMPORTANT NOTE TO UNDERSTAND: The type of respiration that is happening depends on what is going on in a particular muscle at a particular time. You will have some muscles doing aerobic and others doing anaerobic AT THE SAME TIME!


60 Aerobic Respiration Is the most efficient type of respiration – producing the most ATP per glucose molecule Glucose + oxygen produce ATP + carbon dioxide + water It is slower and requires continuous delivery of oxygen & nutrients to the muscle

61 Aerobic Respiration Duration of energy produced can be hours
This type of energy production is used for activities that require endurance rather than power Jogging, marathon running, walking, etc

62 Anaerobic Respiration
Muscle uses up oxygen faster than circulatory and respiratory systems can deliver it Glucose gets converted to lactic acid in that muscle Lactic acid will get converted to pyruvic acid and enter aerobic mechanism when oxygen becomes available

63 Anaerobic Respiration
Circulatory and respiratory system cannot deliver oxygen as fast as muscles are using it up. This leads to lactic acid buildup - when oxygen is again available – lactic acid is converted to pyruvic acid and oxidized

64 Anaerobic Respiration
For muscle to be restored to resting state: Oxygen stores must be replenished Lactic acid converted to pyruvic acid Glycogen stores replaced ATP & creatine phosphate reserves replenished Liver must reconvert the pyruvic acid produced to glucose or glycogen ALL of these processes require oxygen

65 Oxygen Debt The amount of oxygen that must be taken into the body to provide for these restorative processes The difference between amount of oxygen needed for totally aerobic respiration during muscle activity AND the amount that is actually used. All nonaerobic sources of ATP used during muscle activity contribute to this debt

66 Oxygen Debt Repaid by rapid, deep breathing (hyperventilation) triggered by change in pH from lactic acid) after exertion is ended Breathing pure oxygen does not help recovery time – oxygen has to have time to get to the muscles that require it. There are limitations due to your circulatory and respiratory systems.


68 Efficiency of Oxygen Use
Athlete: ~10 % greater rate and efficiency of oxygen use than normal person Marathon runner: ~45 % greater Working your muscles, heart, lungs, etc out on a regular basis increases your efficiency Things like smoking, poor nutrition, too much sugar, etc. decreases your efficiency

69 Disorders

70 Muscle Strain Commonly called a “pulled muscle”
Is excessive stretching & possible tearing of muscle due to overuse/abuse Injured muscle becomes painful & inflamed (myositis) Treatment: adjacent joints are usually immobilized

71 Muscle Strain Factors contributing
Degree of stretch (more flexible at a joint the less likely you are to strain a muscle than someone who’s “tight” Speed of stretch

72 Contusions A bruise or bleeding within a muscle
Caused by impact to muscle When already injured muscle is repeatedly struck, a more serious condition, myositis ossificans, can develop

73 Myositis Ossificans Involves formation of a calcium mass with the muscle over a period of 3-4 weeks After 6-7 weeks the mass usually begins to dissolve and is reabsorbed by the body. In rare cases, a bony lesion can remain in the m


75 Muscle Cramps Moderate to severe muscle spasms that cause pain
Possible causes Electrolyte imbalance Ca, Mg or K deficiency dehydration

76 DOMS (Delayed Onset Muscle Soreness)
Follows participation in a long or strenuous activity Soreness begins hours after activity Involves multiple microscopic tears in muscle tissue & causes inflammation, pain, swelling & stiffness

77 Muscle Disorders Torticollis – a twisting of the neck which causes rotation and tilting of the head to one side – caused by injury to one of the sternocleidomastoid muscles Pulled groin muscles – Strain or stretching of adductor muscles (magnus, longus, brevis) Foot drop – paralysis of anterior muscles in lower leg – caused by injury to the peroneal nerve

78 Torticollis

79 Muscle disorders Shin splints – inflammation of the anterior muscle group of the lower leg (& the periosteum they pull on)– caused by trauma or strain – usually felt on the medial &/or anterior borders of the tibia


81 Muscle Disorders Charley horse – officially a trauma induced tearing of muscles followed by bleeding into the tissues (NOT just a cramp)

82 Halux valgus – permanent displacement of the great toe – caused by wearing pointy toed shoes

83 Duchenne Muscular Dystrophy
Page 194 Genetic – affects primarily males – X linked trait Dystrophin protein not produced correctly – leads to muscle fiber degeneration & atrophy Progresses from extremities upward Generally do not live beyond young adulthood


85 Myasthenia gravis Probably autoimmune
Shortage of neurotransmitter receptors in muscle Muscles not stimulated properly & grow progressively weaker Death occurs when respiratory muscles fail to function

86 Drooping of eyebrow & eyelid called Ptosis
Myasthenia Gravis

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