The Muscular System
Dec 16, 2015
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Homework:Find and print a picture of your favorite
athlete (bathing suit preferred to see as many muscles as possible)
Hand label the visible muscles on their body using the muscles we discussed in class
Do Now:Grab your ClickerTake out your HW – athlete pic w/labeled
musclesReview names of muscles from hotlist &
diagram
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Id the serratus anterior1. 12. 23. 34. 45. 56. 67. 78. 89. 9
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Id the exterior obliques1. 12. 23. 34. 45. 56. 67. 78. 89. 9
Do Now: Why do you think that muscle-enhancing supplements (steroids, creatine, andro) are so popular at all levels of fitness and athletics (high school, college, pro, etc.) and do you see any problems with this?
Muscle TissuesCardiac
Involuntary striated muscleDinucleatedCommunicate via intercalated disksNatural contraction cycle determined by
pacemaker cellsSmooth
Lines blood vessels, digestive organs, urinary system, and parts of respiratory system
Involuntary nonstriated muscleCa+ triggers contractions differently (lacks
sarcomeres)Skeletal
Voluntary striated muscleMultinucleated cells called muscle fibersControlled by motor nerve cells
Functions of Skeletal MuscleProduce Movement
Contractions pull on tendons and move bonesMaintain posture and body position
Continuous contractions maintain postureSupport/protect soft tissues
Abdominal wallFloor of pelvic cavity
Guard entrances and exitsVoluntary control of swallowing, defecation, and
urinationMaintain body temp
Some energy from contractions lost as heat
Gross Anatomy of Skeletal Muscle
Each cell is called a “muscle fiber”
Contains several tissues:ConnectiveBlood vessels Nerves – control
contractionsSkeletal muscle
Microanatomy of Skeletal MuscleSarcolemma – cell
membraneSarcoplasm –
cytoplasmMyofibrils – bundles of
myofilaments Thin filaments – actin
proteinsThick filaments – myosin
proteinsSarcoplasmic
reticulum – smooth ER (stores Ca+)
Sarcomeres – repeating units of myofilaments
Classwork:Draw a flowchart or diagram showing how muscle contraction and relaxation occurs at a cellular level
Muscle Mechanics Muscle cells pull on collagen fibers
producing tension (can only contract!) Amount of tension dependent upon
Frequency of neural stimulation Latent period (2msec) – action
pot. & release of Ca+ Contraction phase (15msec) –
cross bridges form Relaxation phase (25msec) –
tension, cross bridges and Ca+ decrease
# of muscle fibrils activated Motor unit - # muscle fibrils
controlled by singe motor neuron Fine control of movement
determined by size of motor unit Ex. Eye vs. Leg muscles
During sustained contraction – motor units activated on a rotating basis (some rest/some contract)
Muscle ToneTone – resting tension Stabilizes the position of
your jointsAny skeletal muscle not
stimulated on a regular basis will atrophy – fibers become smaller and weaker
Initially atrophy is reversible
Extreme atrophy is permanent
Energetics of Muscle ActivityActive Skeletal Muscle fibril requires 600 trillion
ATP/sec! Sources of ATP
Stored (ADP + Creatine-P ATP)Lasts 15 sec
Aerobic Metabolism (Krebs Oxidative Phosphorylation)Provides 30% of ATP needed during peak exertion
Anaerobic Metabolism (glycolysis)Main E sourceLactic acid builds up Ineffective
Muscle Fatigue – no contraction despite stimulationLack of ATP or lactic acid build up
Recovery Period – returns to pre-exertion levels
Muscle Performance Force and endurance depends on: Types of muscle fibers
Fast Twitch (white) Powerful contractions Fatigue rapidly (few mitochondria)
Slow Twitch (red) Extended contraction (many
mitochondria) Extensive capillary network Myoglobin binds O2
Physical conditioning ( increase power and endurance)Anaerobic
Frequent, brief intense workouts (hypertrophy of muscle fibrils)
Aerobic Sustained low levels of activity Carb-load the day before; drink glucose
rich sports drinks
Muscle ReviewWhat muscle do you use to shrug your shoulders? What muscle would be well developed in a trumpet
player? What is the most likely cause of a muscle cramp? What muscle do you use to stand on your tippy-
toes? What muscle do you use to close your eye-lidsWhat muscle do you use when using a “butterfly”
machine? Compare “white” muscles to “red” musclesA friend wants to bulk up his arms. What would you
suggest to him? What are the 3 sources of energy for muscles?
What limits each?