The Muscular SystemThe Muscular SystemThere are ~650 muscles in the There are ~650 muscles in the

human body.human body.

TerminologyTerminology

Myology: scientific study of musclesMyology: scientific study of muscles Striated: stripedStriated: striped Muscle tone: firmness of a muscle that Muscle tone: firmness of a muscle that

results from motor units being activatedresults from motor units being activated Atrophy: deterioration of muscle fibersAtrophy: deterioration of muscle fibers Hypertrophy: bulking up of muscle Hypertrophy: bulking up of muscle

fibersfibers Oxygen debt: the amount of oxygen Oxygen debt: the amount of oxygen

you owe your body after exerciseyou owe your body after exercise

3 types of muscle3 types of muscle

SmoothSmooth SkeletalSkeletal CardiacCardiac

Muscle ClassificationMuscle Classification

Striated vs. NonstriatedStriated vs. Nonstriated Voluntary vs. InvoluntaryVoluntary vs. Involuntary

Remember this??Remember this??

5 Muscle Functions5 Muscle Functions

Produce body movementProduce body movement Stabilize body positionsStabilize body positions Regulate organ volumeRegulate organ volume Movement of substances within bodyMovement of substances within body Producing heatProducing heat

– Ever gone to bed hot at night and woke Ever gone to bed hot at night and woke up cold?up cold?

Muscle CharacteristicsMuscle Characteristics

Excitability: responsiveness to nerve Excitability: responsiveness to nerve impulsesimpulses

Contractility: ability to contractContractility: ability to contract Extensibility: ability to stretch and Extensibility: ability to stretch and

not tearnot tear Elasticity: ability to return to original Elasticity: ability to return to original

shape after contractionshape after contraction

Smooth MuscleSmooth Muscle

NonstriatedNonstriated InvoluntaryInvoluntary Found in internal organs and blood Found in internal organs and blood

vesselsvessels Spindle-shaped cells with one Spindle-shaped cells with one

nucleusnucleus

Cardiac MuscleCardiac Muscle

Striated with intercalated discsStriated with intercalated discs InvoluntaryInvoluntary Found in heart onlyFound in heart only Branched cells with one nucleusBranched cells with one nucleus

The average heart beats about 75 times per minute.

There are LOTS of mitochondria in cardiac muscle.

Skeletal MuscleSkeletal Muscle

StriatedStriated VoluntaryVoluntary Cylindrical cells with many nuclei per cellCylindrical cells with many nuclei per cell Attached to bones by tendonsAttached to bones by tendons

– Largest = Achilles tendon in heelLargest = Achilles tendon in heel At least 2 attachment sites of each At least 2 attachment sites of each

musclemuscle– Origin: stationary site of attachmentOrigin: stationary site of attachment– Insertion: movable site of attachmentInsertion: movable site of attachment

Histology of muscle tissueHistology of muscle tissue

Muscle cells = muscle fibersMuscle cells = muscle fibers Fibers are held together by fasciaFibers are held together by fascia

– Superficial fascia: under skin/on top of Superficial fascia: under skin/on top of musclemuscle

– Deep fascia: holds individual fibers Deep fascia: holds individual fibers togethertogether

Think about eating roast beef.Think about eating roast beef.

Think about cleaning a chicken breast.Think about cleaning a chicken breast.

Bundles of fibers are called fasciclesBundles of fibers are called fascicles

More histology…More histology…

Actin (thin protein) + Myosin (thick Actin (thin protein) + Myosin (thick protein) protein) filaments* filaments* myofibril myofibril muscle fiber muscle fiber fascicle fascicle

**Where filaments overlap is called the sarcomere: the basic Where filaments overlap is called the sarcomere: the basic functioning unit of musclefunctioning unit of muscle

Think of a large rope that can be unraveled.Think of a large rope that can be unraveled.

Sliding Filament Theory/Mechanism is the Sliding Filament Theory/Mechanism is the description of how muscles move when description of how muscles move when actin and myosin move over and past one actin and myosin move over and past one another at the sarcomere, thus allowing another at the sarcomere, thus allowing the filaments to shorten causing the filaments to shorten causing contractioncontraction

A look at muscle histologyA look at muscle histology

Another look…Another look…

Muscle contractionMuscle contraction

Occurs after a motor neuron Occurs after a motor neuron stimulates itstimulates it

One motor neuron plus all the muscle One motor neuron plus all the muscle fibers it stimulates = 1 motor unitfibers it stimulates = 1 motor unit

Remember the pathway from chapter 1??Remember the pathway from chapter 1??

Control Center

Receptor Effector

Sensory neuron

Motor neuron

Movement typesMovement types

Small precise movements ie. writing, Small precise movements ie. writing, coloring (fine motor skills) use many coloring (fine motor skills) use many motor units with few numbers of motor units with few numbers of muscle fibersmuscle fibers

Large, powerful movements ie. Large, powerful movements ie. Jumping, lifting use few motor units Jumping, lifting use few motor units with large numbers of muscle fibers.with large numbers of muscle fibers.

Muscles and the Nervous Muscles and the Nervous SystemSystem

Neuromuscular Junction (NMJ): point Neuromuscular Junction (NMJ): point where a motor neuron excites a where a motor neuron excites a muscle fibermuscle fiber

Neurotransmitters: chemicals found Neurotransmitters: chemicals found within the NMJ that trigger within the NMJ that trigger contractioncontraction– Acetylcholine is one of the most importantAcetylcholine is one of the most important– Certain toxins and drugs can affect NMJ eventsCertain toxins and drugs can affect NMJ events

Muscle ContractionMuscle Contraction

RequiresRequires– High CalciumHigh Calcium– High ATPHigh ATP

Aerobic cellular respirationAerobic cellular respiration GlycolysisGlycolysis Creatine phosphate within musclesCreatine phosphate within muscles

– AcetylcholineAcetylcholine

Muscle relaxation requires the opposite.Muscle relaxation requires the opposite.

Muscles may become fatigued if the above mentioned Muscles may become fatigued if the above mentioned substances are not maintained at proper levels.substances are not maintained at proper levels.

Muscle movementsMuscle movements

Nerve impulses must reach a Nerve impulses must reach a threshold in order for there to be a threshold in order for there to be a response (movement).response (movement).

Twitch: brief contraction in response Twitch: brief contraction in response to 1 action potential = nerve impulseto 1 action potential = nerve impulse

Tetanus: sustained contraction in Tetanus: sustained contraction in response to several action potentialsresponse to several action potentials

Can be read with a myogram: Can be read with a myogram: graphical reading of muscle graphical reading of muscle contractionscontractions

MyogramMyogram

TetanusTetanus

Motor unit recruitmentMotor unit recruitment

Allows for smooth rather than jerky Allows for smooth rather than jerky movement.movement.

Allows for some units to be Allows for some units to be contracting while others are relaxingcontracting while others are relaxing

Prevents muscle fatiguePrevents muscle fatigue

Types of Types of contractions/exercisescontractions/exercises

IsotonicIsotonic– Causes movement due to muscle Causes movement due to muscle

shorteningshortening Walking, swimming, biking, runningWalking, swimming, biking, running

isometricisometric– Causes no movement due to muscle Causes no movement due to muscle

shorteningshortening Wall sits, bar hangsWall sits, bar hangs

Muscle dutiesMuscle duties

Movement occurs when several Movement occurs when several muscles act togethermuscles act together

Most muscles are arranged in Most muscles are arranged in opposing pairsopposing pairs– Ex: flexor – extensor; abductor – adductorEx: flexor – extensor; abductor – adductor

Prime mover: muscle causing main Prime mover: muscle causing main movementmovement

Synergist: complements prime moverSynergist: complements prime mover Antagonist: opposes prime moverAntagonist: opposes prime mover

Example of muscle dutiesExample of muscle duties

To flex the forearmTo flex the forearm– Prime mover: biceps brachiiPrime mover: biceps brachii– Synergist: brachialis & brachioradialisSynergist: brachialis & brachioradialis– Antagonist: triceps brachiiAntagonist: triceps brachii

Other helpful hints…Other helpful hints… Muscles are named based on Muscles are named based on

– Origin & insertion pointsOrigin & insertion points Ex: sternocleidomastoidEx: sternocleidomastoid

– ShapeShape Ex: trapezius, deltoidEx: trapezius, deltoid

– Number of originsNumber of origins Ex: bicep, tricep, quadricepEx: bicep, tricep, quadricep

– Size & lengthSize & length Ex: longus, brevis, maximus, minimusEx: longus, brevis, maximus, minimus

– Direction of fibersDirection of fibers Ex: rectus, oblique, transverseEx: rectus, oblique, transverse