The Muscular System

The Muscular System

Note: Prefixes myo, mys, and sarco refer to muscleNaming Skeletal MusclesDirection of muscle fibersRectus: The muscles fascicles are parallel to the long axis of the body or limb.Transverse: The muscles fascicles are perpendicular to the long axis ofthe body or limb. Oblique: The muscles fascicles are aligned at an angle to the long axis of the body or limb. LocationLocation of a muscleSizeMaximus: Large muscleMinimus: Small muscleLongus: Long muscleBrevis: Short muscleNumber of origins: the end of the muscle that does not move.Biceps: Two originsTriceps: Three originsQuadriceps: Four originsShape (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)

Shapes of skeletal muscles:Parallel or fusiform: fibers run parallel to each othercontract 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.unipennatebipennatemultipenneteCircular: Muscle fibers surround an opening to act as a sphincter. Examples: Orbicularis oris and Orbicularis oculi muscles.Do Now:Grab your Clicker! Review your charts and diagrams for names and locations of skeletal musclesId the Masseter

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Id the buccinator

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Id the orbicularis oris

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Id the frontalis

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Id the deltoid

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Id the sternocleidomastoid12345678.9

Id the external obliques12345678.9

Id the serratus anterior12345678.9

Id the rectus abdominis12345678.9

Id the gastrocnemius

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Id the biceps femoris

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Id the semimebranosis

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Id the soleus

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Id the semitendonosis

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123456ID the brachioradialis

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Id the sartorius muscle1234567

Id the vastus lateralis1234567

Id the rectus femoris1234567

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?

Muscle TissuesCardiac Involuntary striated muscleDinucleatedCommunicate via intercalated disksNatural contraction cycle determined by pacemaker cellsSmoothLines blood vessels, digestive organs, urinary system, and parts of respiratory systemInvoluntary nonstriated muscleCa+ triggers contractions differently (lacks sarcomeres)Skeletal Voluntary striated muscleMultinucleated cells called muscle fibersControlled by motor nerve cells40% of your body mass!

Functions of Skeletal MuscleExcitableReceive and respond to stimulusContractible Produce MovementPull on tendons and move bonesMaintain posture and body positionContinuous contractions maintain postureStabilize & strengthen jointsSupport/protect soft tissuesAbdominal wallFloor of pelvic cavityGuard entrances and exitsVoluntary control of swallowing, defecation, and urinationMaintain body tempSome energy from contractions lost as heatExtensibilityCan stretch beyond its resting lengthElasticityRecoils to resume resting length

Muscle AttachmentsMost muscles attach to bones in 2 placesInsertion- movable boneOrigin immovable/less movable bone

Direct AttachmentsEpimysium of muscle fused to periosteum of bone

Indirect Attachments (more common)Tendons connect skeletal muscle to periosteum of bonesAponeurosis layers of tendons that form a sheet

Organization of Skeletal Muscle: Gross AnatomyEach elongated cell is called a muscle fiberContains several tissuesConnective Tissue SheathsEpimysium dense irregular connective tissue surrounding entire musclePerimysium divide skeletal muscles into bundles of fibers (fascicles)Endomysium areolar tissue that surrounds ea/fiberBlood vessels 1 artery & 1+ veinsNumerous cross-linked capillariesNervesTypically 1 nerve ending per muscle fiberSkeletal muscleSee next page for details.Connective tissue coverings of a skeletal muscle listed from superficial to deep are

Endomysium, perimysium, epimysiumEndomysium, epimysium, perimysium, Epimysium, Endomysium, perimysium, Epimysium, perimysium, Endomysium, Microanatomy of Skeletal MuscleSarcolemma plasma membraneT tubules transverse invaginationsSarcoplasm cytoplasmIncreased myoglobinIncreased gylcosomes Myofibrils bundles of myofilaments parallel to cellThin filaments actin proteinsThick filaments myosin proteinsUsed for contractionSarcoplasmic reticulum smooth ER (stores Ca+)Sarcomeres repeating units of myofilaments

Sarcomere: functional contractile unit of a muscle fiberSarcomere- 2m 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)

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 proteinsTropomyosin spirals around actin to block myosin binding sites in relaxed muscle

Troponin inhibitory helps position tropomyosin on actin and binds to Calcium ions

Sarcoplasmic Reticulum & T TubulesSarcoplasmic 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

Sliding Filament Model of Contraction

Sliding Filament TheoryACh (Acetylcholine) neurotransmitter that released at neuromuscular junction (1 per muscle fiber)SR & T-tubules release Ca+2 into sarcoplasmCa+2 binds to troponin, removing blocking action of tropomyosinMyosin heads attach to actin (cross bridge is formed)Power Stroke: myosin pulling actin towards midline of sarcomere powered by hydrolysis of ATP ADP + PiAcetylcholinesterase enzyme that breaks down Ach to prevent continued contractionCa+2 recaptured by SR, tropomysoin blocks binding siteMyosin heads release actin relaxing sarcoemreThe command to contract is distributed deep into the muscle fiber by

SarcolemmaSarcomereTransverse tubulesmyofibrilsHomework:Compare Pallor mortis, Algor mortis,, Rigor mortis, Liver mortis, and putrificationDescribe 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

Do Now: What is Rigor Mortis? Stiffness of DeathBegins 3-4 hours after death, peaks at 12 hours postmortem and slowly dissipates over the next 48-60 hoursCalcium influx into muscle cells promotes cross-bridge formationATP is no longer produced, therefore detachment is impossibleCreates 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.

Energetics of Muscle ActivityActive Skeletal Muscle fiber requires 600 trillion ATP/sec! Stored ATP- lasts 4-6 secondsQuickly regenerated by: Creatine Phosphate (CP)ADP + Creatine-P ATP + creatineLasts 15 sec (replenishes during inactivity)

Aerobic Metabolism (Glycolysis Krebs Oxidative Phosphorylation)Provides 30% of ATP needed during peak exertion, 95% of ATP during prolonged exertionGlycogen, blood glucose, after 30 mins fatty acidsHigh yield ATP (38 ATP), but slow

Anaerobic Metabolism (glycolysis)Main E sourceLactic acid builds up (gone 30 mins after exercise stops)Faster but ineffective only 2ATP

Muscle Fatigue physiological inability to contract despite stimulationlactic acid build upIoinc imbalancesRecovery Period returns to pre-exertion levelsPlease make your selection...

Choice OneChoice Two

Aerobic RespirationEPOC: Excess Postexcercise Oxygen ConsumptionOxygen debtextra O2 needed by body to restore all nonaerobic sources of ATPReplenish O2 reserves in myoglobin Liver must convert lactic acid to pyruvic acidGlycogen stores must be replacedATP and creatine-P reserves must be resynthesizedOnly 25-40% of energy released is used for work, remainder is released as heat

Muscle MechanicsMotor unit - # muscle fibers controlled by singe motor neuronFine control of movement determined by size of motor unitEx. Eye vs. Leg musclesDuring sustained contraction motor units activated on a rotating basis (some rest/some contract)Muscle tone -slightly contracted relaxed muscles to maintain posture and stabilize jointsMuscle 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+2Contraction phase (peak) (10-100 msec) cross bridges activeRelaxation phase (10-100 msec) reuptake of Ca+2 sarcomere returns to original length

Types of ContractionsIsotonic ContractionsConcentric muscle shortens and does workEccentric muscle generates force as it lengthens

Isometric ContractionsTension builds but muscle neither shortens or lengthensMaintains postureMuscle ToneTone resting tension (slightly contracted)Spinal reflexes alternate contractions of motor unitsStabilizes the position of your joints and maintains postureAny skeletal muscle not stimulated on a regular basis will atrophy fibers become smaller and weakerDecreases 5% per day of inactivity!Initially atrophy is reversibleExtreme atrophy is permanentParalyzed muscle may be reduced by 25% of its initial size

Muscle PerformanceForce and endurance depends on: Types of muscle fibers (most muscles contain a mixture of both but genetic variation)

Fast Twitch (white)Powerful rapid contractionsGlycogen used quicklyFatigue rapidly (few mitochondria)Anaerobic, few mitochondriaLittle myoglobinLactic acid builds up quickly

Slow Twitch (red)Slow contractionAerobic, high enduranceMany mitochondriaExtensive capillary supplyMyoglobin - binds O2 reserves in muscle cellExerciseAnaerobic (Resistance)Frequent, brief intense workoutsWeightlifting, isometric exerciseResults inHypertrophy of muscle fibersMore mitochondriaMore myofilaments and myofibrilsStore more glycogen

Aerobic (Endurance)Sustained low levels of activityWalking, swimming, biking, joggingResults in:Increases # capillariesIncreases # mitochondriaIncreases myoglobin synthesisCarb-load the day before; drink glucose rich sports drinks

An activity that would require anaerobic endurance is

50-meter dashPole vaultWeight lifting competitionAll of the above