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Note: Prefixes myo, mys, and sarco refer to muscle
The Muscular System
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Naming Skeletal Muscles
Direction of muscle fibers Rectus: The muscles fascicles are parallel to the long axis of the body or limb. Transverse: The muscles fascicles are perpendicular to the long axis of the body or limb. Oblique: The muscles fascicles are aligned at an angle to the long axis of the body or limb. Location Location of a muscle Size Maximus: Large muscle Minimus: Small muscle Longus: Long muscle Brevis: Short muscle Number of origins: the end of the muscle that does not move. Biceps: Two origins Triceps: Three origins Quadriceps: Four origins Shape (ie. Deltoid is triangular) Origin (proximal less movable end) & insertion (Insertion: the end of the muscle that moves) Action (What a muscle does when it contracts)
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Shapes of skeletal muscles:
Parallel or fusiform: fibers run parallel to each other contract over a great distance good endurance but are not very strong. Examples: Sartorius muscle and rectus abdominus muscle. Convergent: muscle fibers converge on the insertion to maximize the force of muscle contraction Examples: Deltoid muscle and Pectoralis Major muscle. Pennate: many fibers per unit area. strong but they tire quickly. There are three types of pennate muscle. unipennate bipennate multipennete Circular: Muscle fibers surround an opening to act as a sphincter. Examples: Orbicularis oris and Orbicularis oculi muscles.
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Do Now: Grab your Clicker!
Review your charts and diagrams for names and locations of skeletal muscles
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Id the Masseter 1 2 3 4 5 6 7 8 9
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Id the buccinator 1 2 3 4 5 6 7 8 9
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Id the orbicularis oris
1 2 3 4 5 6 7 8 9
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Id the frontalis 1 2 3 4 5 6 7 8 9
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Id the deltoid 1 2 3 4 5 6 7 8. 9
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Id the sternocleidomastoid
1 2 3 4 5 6 7 8. 9
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Id the external obliques
1 2 3 4 5 6 7 8. 9
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Id the serratus anterior
1 2 3 4 5 6 7 8. 9
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Id the rectus abdominis
1 2 3 4 5 6 7 8. 9
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Id the gastrocnemius 1 2 3 4 5 6 7
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Id the biceps femoris 1 2 3 4 5 6 7
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Id the semimebranosis 1 2 3 4 5 6 7
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Id the soleus 1 2 3 4 5 6 7
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Id the semitendonosis 1 2 3 4 5 6 7
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ID the trapezius 1 2 3 4 5 6
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ID the infraspinatus 1 2 3 4 5 6
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ID the lattisimus dorsi
1 2 3 4 5 6
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ID the teres minor 1 2 3 4 5 6
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ID the brachioradialis
1 2 3 4 5 6 7 8 9
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Id the sartorius muscle
1 2 3 4 5 6 7
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Id the vastus lateralis
1 2 3 4 5 6 7
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Id the rectus femoris 1 2 3 4 5 6 7
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Why do you think that muscle- enhancing supplements (steroids, creatine) are so popular at all levels of fitness and athletics (high school, college, pro, etc.) and do you see any problems with this?
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Muscle Tissues Cardiac Smooth Skeletal Involuntary striated muscle
Dinucleated Communicate via intercalated disks Natural contraction cycle determined by pacemaker cells Smooth Lines blood vessels, digestive organs, urinary system, and parts of respiratory system Involuntary nonstriated muscle Ca+ triggers contractions differently (lacks sarcomeres) Skeletal Voluntary striated muscle Multinucleated cells called muscle fibers Controlled by motor nerve cells 40% of your body mass!
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Functions of Skeletal Muscle
Excitable Receive and respond to stimulus Contractible – Produce Movement Pull on tendons and move bones Maintain posture and body position Continuous contractions maintain posture Stabilize & strengthen joints Support/protect soft tissues Abdominal wall Floor of pelvic cavity Guard entrances and exits Voluntary control of swallowing, defecation, and urination Maintain body temp Some energy from contractions lost as heat Extensibility Can stretch beyond its resting length Elasticity Recoils to resume resting length
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Muscle Attachments Most muscles attach to bones in 2 places
Insertion- movable bone Origin – immovable/less movable bone Direct Attachments Epimysium of muscle fused to periosteum of bone Indirect Attachments (more common) Tendons – connect skeletal muscle to periosteum of bones Aponeurosis – layers of tendons that form a sheet
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Organization of Skeletal Muscle: Gross Anatomy
Each elongated cell is called a “muscle fiber” Contains several tissues Connective Tissue Sheaths Epimysium – dense irregular connective tissue surrounding entire muscle Perimysium – divide skeletal muscles into bundles of fibers (fascicles) Endomysium – areolar tissue that surrounds ea/fiber Blood vessels 1 artery & 1+ veins Numerous cross-linked capillaries Nerves Typically 1 nerve ending per muscle fiber Skeletal muscle See next page for details….
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Connective tissue coverings of a skeletal muscle listed from superficial to deep are
Endomysium, perimysium, epimysium Endomysium, epimysium, perimysium, Epimysium, Endomysium, perimysium, Epimysium, perimysium, Endomysium,
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Microanatomy of Skeletal Muscle
Sarcolemma – plasma membrane T tubules – transverse invaginations Sarcoplasm – cytoplasm Increased myoglobin Increased gylcosomes Myofibrils – bundles of myofilaments parallel to cell Thin filaments – actin proteins Thick filaments – myosin proteins Used for contraction Sarcoplasmic reticulum – smooth ER (stores Ca+) Sarcomeres – repeating units of myofilaments
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Sarcomere: functional contractile unit of a muscle fiber
Sarcomere- 2µm region of myofibril between two Z-discs (Z-lines) Striations - repeating units of dark A bands and light I bands H zone – light stripe in the middle of the A band, with dark vertical M line Z disc or Z line in the I band All banding patterns are due to myofilaments: Actin – thin filament (blue) Myosin – thick filament (tan)
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Actin (thin filaments) & Myosin (thick)
Myosin – globular heads that face outwards to cross-bridge (link) to actin, and contain ATPase Myosin tails form central part of molecule Cross bridges – act as motors to generate tension Regulatory proteins Tropomyosin – spirals around actin to block myosin binding sites in relaxed muscle Troponin – inhibitory… helps position tropomyosin on actin and binds to Calcium ions
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Sarcoplasmic Reticulum & T Tubules
Sarcoplasmic Reticulum (SR) – elaborate smooth ER like a sleeve along myofibril w/ perpendicular cross channels called terminal cisternae T Tubules – protrude deep into cell encircling each sarcomere
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Sliding Filament Model of Contraction
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Sliding Filament Theory
ACh (Acetylcholine) – neurotransmitter that released at neuromuscular junction (1 per muscle fiber) SR & T-tubules release Ca+2 into sarcoplasm Ca+2 binds to troponin, removing blocking action of tropomyosin Myosin heads attach to actin (cross bridge is formed) Power Stroke: myosin pulling actin towards midline of sarcomere powered by hydrolysis of ATP ADP + Pi Acetylcholinesterase – enzyme that breaks down Ach to prevent continued contraction Ca+2 recaptured by SR, tropomysoin blocks binding site Myosin heads release actin relaxing sarcoemre
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The command to contract is distributed deep into the muscle fiber by
Sarcolemma Sarcomere Transverse tubules myofibrils
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Homework: Compare Pallor mortis, Algor mortis,, Rigor mortis, Liver mortis, and putrification Describe how this relates to the muscular system Cite your source (informal URL is fine) -OR- Draw a diagram depicting stages of muscle contraction and relaxation labeling structural components
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Do Now: What is Rigor Mortis?
“Stiffness of Death” Begins 3-4 hours after death, peaks at 12 hours postmortem and slowly dissipates over the next hours Calcium influx into muscle cells promotes cross-bridge formation ATP is no longer produced, therefore detachment is impossible Creates a state of muscular contraction until the breakdown of muscle tissue by enzymes (endogenous or bacterial) during decomposition. The myosin heads are eaten off by the enzymes, allowing the muscle contraction to release and the body to relax.
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Energetics of Muscle Activity
Active Skeletal Muscle fiber requires 600 trillion ATP/sec! Stored ATP- lasts 4-6 seconds Quickly regenerated by: Creatine Phosphate (CP) ADP + Creatine-P ATP + creatine Lasts 15 sec (replenishes during inactivity) Aerobic Metabolism (Glycolysis Krebs Oxidative Phosphorylation) Provides 30% of ATP needed during peak exertion, 95% of ATP during prolonged exertion Glycogen, blood glucose, after 30 mins fatty acids High yield ATP (38 ATP), but slow Anaerobic Metabolism (glycolysis) Main E source Lactic acid builds up (gone 30 mins after exercise stops) Faster but ineffective… only 2ATP Muscle Fatigue – physiological inability to contract despite stimulation lactic acid build up Ioinc imbalances Recovery Period – returns to pre-exertion levels
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Please make your selection...
Choice One Choice Two
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Aerobic Respiration
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EPOC: Excess Postexcercise Oxygen Consumption
Oxygen debt extra O2 needed by body to restore all nonaerobic sources of ATP Replenish O2 reserves in myoglobin Liver must convert lactic acid to pyruvic acid Glycogen stores must be replaced ATP and creatine-P reserves must be resynthesized Only 25-40% of energy released is used for work, remainder is released as heat
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Muscle Mechanics Motor unit - # muscle fibers 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 tone -slightly contracted relaxed muscles to maintain posture and stabilize joints Muscle twitch –response of motor unit to a single motor neuron (in lab) Each twitch has 3 phases: Latent period (2msec) – action pot. & release of Ca+2 Contraction phase (peak) ( msec) – cross bridges active Relaxation phase ( msec) –reuptake of Ca+2 sarcomere returns to original length
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Types of Contractions Isotonic Contractions Isometric Contractions
Concentric – muscle shortens and does work Eccentric – muscle generates force as it lengthens Isometric Contractions Tension builds but muscle neither shortens or lengthens Maintains posture
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Muscle Tone Tone – resting tension (slightly contracted)
Spinal reflexes alternate contractions of motor units Stabilizes the position of your joints and maintains posture Any skeletal muscle not stimulated on a regular basis will atrophy – fibers become smaller and weaker Decreases 5% per day of inactivity! Initially atrophy is reversible Extreme atrophy is permanent Paralyzed muscle may be reduced by 25% of its initial size
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Muscle Performance Force and endurance depends on:
Types of muscle fibers (most muscles contain a mixture of both but genetic variation) Fast Twitch (white) Powerful rapid contractions Glycogen used quickly Fatigue rapidly (few mitochondria) Anaerobic, few mitochondria Little myoglobin Lactic acid builds up quickly Slow Twitch (red) Slow contraction Aerobic, high endurance Many mitochondria Extensive capillary supply Myoglobin - binds O2 reserves in muscle cell
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Exercise Anaerobic (Resistance) Aerobic (Endurance)
Frequent, brief intense workouts Weightlifting, isometric exercise Results in Hypertrophy of muscle fibers More mitochondria More myofilaments and myofibrils Store more glycogen Aerobic (Endurance) Sustained low levels of activity Walking, swimming, biking, jogging Results in: Increases # capillaries Increases # mitochondria Increases myoglobin synthesis Carb-load the day before; drink glucose rich sports drinks
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An activity that would require anaerobic endurance is
50-meter dash Pole vault Weight lifting competition All of the above
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