Chapter 10Muscle Tissue

Alternating contraction and relaxation of cells

Chemical energy changed into mechanical energy

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3 Types of Muscle TissueSkeletal muscle

attaches to bone, skin or fasciastriated with light & dark bands visible Multi-nucleatevoluntary control of contraction & relaxation

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Skeletal muscle Cells

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3 Types of Muscle TissueCardiac muscle

striated in appearanceforkedinvoluntary controlAutorhythmic (fire themselves)

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3 Types of Muscle TissueSmooth muscleattached to hair follicles in skinin walls of hollow organs -- blood vessels & GInonstriated in appearanceinvoluntary

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Smooth Muscle

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The Muscular SystemThe Muscular System refers mainly to

skeletal muscles, which are…

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Organization of Skeletal Muscles

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Muscle OrganizationMuscles are made up of units, which are

made up of smaller units, which are made up of even smaller units….etc.

Make an analogy: Muscles are like…because…

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Muscle Fiber (cell) DrawingsPage 159 in the textbook has a good diagram

showing the organization of muscles.Use it as a guide to draw a copy for your

notes. Label the following: Muscle fiberSarcolemaMyofibril/fibrilSarcomere

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Drawings (pg 159)******Draw A, B, C ******Label:Muscle fiberSarcolemaMyofibril/fibrilSarcomereMyosin (thick) filamentActin (thin) filament

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Functions of Muscle TissueProducing body movementsStabilizing body positionsRegulating organ volumes

bands of smooth muscle called sphinctersMovement of substances within the body

blood, lymph, urine, air, food and fluids, spermProducing heat

involuntary contractions of skeletal muscle (shivering)

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Properties of Muscle TissueExcitability

respond to chemicals released from nerve cellsConductivity

ability to propagate electrical signals over membrane

Contractilityability to shorten and generate force

Extensibilityability to be stretched without damaging the tissue

Elasticityability to return to original shape after being

stretched17

Skeletal Muscle -- Connective TissueSuperficial fascia is loose connective tissue &

fat underlying the skinDeep fascia = dense irregular connective

tissue around muscleAll these connective tissue layers extend beyond

the muscle belly to form the tendon

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Nerve and Blood Supply Each skeletal muscle is supplied by a nerve, an

artery, and two veins.

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Fusion of Myoblasts into Muscle Fibers

Every mature muscle cell developed from 100 myoblasts that fuse together in the fetus. (multinucleated)

Mature muscle cells can not divideMuscle growth is a result of cellular

enlargement & not cell division20

Muscle Fiber or Myofibers

Muscle cells are long, cylindrical & multinucleated Sarcolemma = muscle cell membrane

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Myofibrils & Myofilaments

Muscle fibers are filled with threads called myofibrils

Myofilaments (thick & thin filaments) are the contractile proteins of muscle

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Filaments and the SarcomereThick and thin filaments overlap each other

in a pattern that creates striations (light I bands and dark A bands)

The I band region contains only thin filaments.

They are arranged in compartments called sarcomeres, separated by Z discs.

In the overlap region, six thin filaments surround each thick filament

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Thick & Thin Myofilaments

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25Dark(A) & light(I) bands visible with an electron microscope

The Proteins of MuscleMyofibrils are built of 3 kinds of protein

contractile proteins myosin and actin

regulatory proteins which turn contraction on & off troponin and tropomyosin

structural proteins which provide proper alignment, elasticity and extensibility titin, myomesin, nebulin and dystrophin

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The Proteins of Muscle -- Myosin

Thick filaments are composed of myosin each molecule resembles two golf clubs twisted

togethermyosin heads extend toward the thin filaments

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The Proteins of Muscle -- Actin

Thin filaments are made of actin.From one Z line to the next is a sarcomere.

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Sliding Filament Mechanism Of Contraction Myosin cross bridgespull on thin filaments

Thin filaments slide inward

Z Discs come toward each other

Sarcomeres shorten.The muscle fiber shortens. The muscle shortens

Notice :Thick & thin filaments do not change in length

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Contraction CycleRepeating sequence of events that cause the thick & thin filaments to move past each other.

4 steps to contraction cycleATP hydrolysis (ATP ADP + P)attachment of myosin to actin to form

crossbridgespower strokedetachment of myosin from actin

Cycle keeps repeating as long as there is ATP available

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Steps in the Contraction Cycle

Notice how the myosin head attaches and pulls on the thin filament with the energy released from ATP

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ATP and MyosinMyosin heads are activated by ATPActivated heads attach to actin & pull (power

stroke)ADP is released. (ATP released P & ADP &

energy)Thin filaments slide past the thick filamentsATP binds to myosin head & detaches it from

actinAll of these steps repeat over and over

if ATP is available

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Sarcomere ModelYou will create a model of a sarcomere with

an assigned group.Requirements:

Must be anatomically correct Must be functional (have contraction mechanism) Must include following parts:

ATP Myosin Actin

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Model PresentationYou will present your models to the class

with a full explanation of what each part is, what the model looks like before contraction & what the model looks like after contraction.

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Muscle MetabolismProduction of ATP in Muscle FibersMuscle uses ATP at a great rate when activeATP supply is limited.

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Anaerobic Cellular Respiration

-Occurs when oxygen is not present.

-Byproduct is lactic acid, which builds up in the muscles (causes soreness)

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Aerobic Cellular Respiration

ATP for any activity lasting over 30 seconds if sufficient oxygen is available, pyruvic acid enters

the mitochondria to generate ATP, water and heatfatty acids and amino acids can also be used by the

mitochondria

Provides 90% of ATP energy if activity lasts more than 10 minutes 37

Muscle FatigueInability to contract after prolonged

activitycentral fatigue is feeling of tiredness and a

desire to stop (protective mechanism)Factors that contribute to muscle fatigue

insufficient oxygen or glycogenbuildup of lactic acid and ADP

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Oxygen Consumption after Exercise

Muscle tissue has two sources of oxygen.diffuses in from the bloodreleased by myoglobin inside muscle fibers

Aerobic system requires O2 to produce ATP needed for prolonged activityincreased breathing effort during exercise

Recovery oxygen uptakeelevated oxygen use after exercise (oxygen debt)lactic acid is converted back to pyruvic acidelevated body temperature means all reactions

faster

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Classification of Muscle Fibers

Slow oxidative (slow-twitch)red in color (lots of mitochondria, myoglobin & blood vessels)prolonged, sustained contractions for maintaining posture

Fast oxidative-glycolytic (fast-twitch A)red in color (lots of mitochondria, myoglobin & blood vessels)split ATP at very fast rate; used for walking and sprinting

Fast glycolytic (fast-twitch B)white in color (few mitochondria & BV, low myoglobin)anaerobic movements for short duration; used for weight-

lifting40

Fiber Types within a Whole MuscleMost muscles contain a mixture of all three

fiber typesProportions vary with the usual action of the

muscleneck, back and leg muscles have a higher

proportion of postural, slow oxidative fibersshoulder and arm muscles have a higher

proportion of fast glycolytic fibersAll fibers of any one motor unit are same.Different fibers are recruited as needed.

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Anabolic SteroidsSimilar to testosteroneIncreases muscle size, strength, and enduranceMany very serious side effects

liver cancerkidney damageheart diseasemood swingsfacial hair & voice deepening in femalesatrophy of testicles & baldness in males

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Regeneration of MuscleSkeletal muscle fibers cannot divide after 1st year

growth is enlargement of existing cellsrepair

satellite cells & bone marrow produce some new cells if not enough numbers---fibrosis occurs most often

Cardiac muscle fibers cannot divide or regenerateall healing is done by fibrosis (scar formation)

Smooth muscle fibers (regeneration is possible)cells can grow in size (hypertrophy)some cells (uterus) can divide (hyperplasia)new fibers can form from stem cells in BV walls

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Aging and Muscle TissueSkeletal muscle starts to be replaced by fat

beginning at 30 “use it or lose it”

Slowing of reflexes & decrease in maximal strengthChange in fiber type to slow oxidative fibers may be

due to lack of use or may be result of aging

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Myasthenia GravisProgressive autoimmune disorder that blocks the

ACh receptors at the neuromuscular junction The more receptors are damaged the weaker the

muscle. More common in women 20 to 40 with possible

line to thymus gland tumorsBegins with double vision & swallowing difficulties

& progresses to paralysis of respiratory muscles Treatment includes steroids that reduce antibodies

that bind to ACh receptors and inhibitors of acetylcholinesterase

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Muscular Dystrophies Inherited, muscle-destroying diseases Sarcolemma tears during muscle contractionMutated gene is on X chromosome so problem

is with males almost exclusivelyAppears by age 5 in males and by 12 may be

unable to walkDegeneration of individual muscle fibers

produces atrophy of the skeletal muscleGene therapy is hoped for with the most

common form = Duchenne muscular dystrophy

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Abnormal ContractionsSpasm = involuntary contraction of single

muscleCramp = a painful spasmTic = involuntary twitching of muscles

normally under voluntary control--eyelid or facial muscles

Tremor = rhythmic, involuntary contraction of opposing muscle groups

Fasciculation = involuntary, brief twitch of a motor unit visible under the skin

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