Muscle Types pgs. 181-185Microscopic Anatomy of Skeletal Muscle

pgs. 185-187*emphasis will be placed on

skeletal muscle

• Functions: –body movement (of any kind)–Posture/position–Stability–Generate heat–Protection

• Three basic muscle types:1.Skeletal muscle2.Cardiac muscle3.Smooth muscle

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• Skeletal and smooth muscle cells are elongated (muscle cell muscle fiber)

• Microfilaments cause muscle contraction– Via shortening of the muscle fibers

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Skeletal◦ Elongated◦ Multinucleic◦ Striated◦ Banded◦ Attach to

skeleton

Cardiac◦ Branching◦ One nucleus◦ Striated◦ Intercalated

discs Gap

junctions

◦ Found only in heart

•Smooth

-Fusiform

-One nucleus

-No striations-found in hollow visceral organs like stomach, bladder

skeletal cardiac smooth

•differences in contraction between the three types of muscle fibers:

•Skeletal: has no rhythm, and the speed can vary; you control•Cardiac : has rhythm, and the rate is slow•Smooth: has variations in rhythm, depending on the process, and very slow contractions

Most are attached by tendons to bones Multinucleate Striated—have visible banding Voluntary—subject to conscious control

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• Endomysium—encloses a single muscle fiber• Perimysium—wraps around a fascicle (bundle)

of muscle fibers• Epimysium—covers the entire skeletal muscle

• Fascia—outermost layer; covers the epimysium– Fascia is a dense connective tissue found covering

muscles, groups of muscles, and large vessels and nerves• It binds structures together like plastic wrap• Fasciitis is an inflammation of the fascia or a

muscle/organ

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Blood vessel

Perimysium

Musclefiber(cell)

Fascicle(wrapped byperimysium)

Endomysium(betweenfibers)

Tendon

Bone

Epimysium(wraps entire muscle)

Epimysium blends into a connective tissue attachment◦ Tendons—cordlike structures

Mostly collagen fibers Often cross a joint because of their toughness and

small size◦ Aponeuroses—sheetlike structures

Attach muscles indirectly to bones, cartilages, or connective tissue coverings

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Sites of muscle attachment◦ Bones◦ Cartilages◦ Connective tissue coverings

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Sarcolemma—specialized plasma membrane◦ Surrounds each fiber◦ Multiple nuclei reside just beneath this membrane

Myofibrils—long organelles inside muscle cell◦ These create Light (I) bands and dark (A) bands to

give the muscle its striped appearance

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Figure 6.3a Anatomy of a skeletal muscle fiber (cell).

Sarcolemma

Myofibril

NucleusDark(A) band

Light(I) band

(a) Segment of a muscle fiber (cell)

Sarcomere—contractile unit of a muscle fiber

The light and dark bands are myofilaments

They are organized in a pattern that give the muscle fiber a banded look

These are protein filaments of different widths:

Thick filaments myosin filaments Thin filaments actin filaments

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Figure 6.3b Anatomy of a skeletal muscle fiber (cell).

Z discZ disc H zone

Thin (actin)myofilamentThick (myosin)myofilament

Myofibril or fibril (complex organelle composed of bundlesof myofilaments)

I band A band M lineI bandSarcomere

(b)

I band light band◦ Contains only thin filaments◦ Z disc is only a midline interruption

A band dark band ◦ Contains the entire length of the thick filaments◦ H zone is a lighter central area◦ M line is in center of H zone

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Z discZ disc H zone

Thin (actin)myofilamentThick (myosin)myofilament

Myofibril or fibril (complex organelle composed of bundlesof myofilaments)

I band A band M lineI bandSarcomere

(b)

Composed of the protein myosin

◦ Contain ATPase enzymes◦ Possess myosin heads

◦ Heads are known as cross bridges when they link thick and thin filaments during contraction

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Composed of the contractile protein actin◦ Actin is anchored to the Z disc

At rest, within the A band there is a zone that lacks actin filaments ◦ Called the H zone

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Figure 6.3c Anatomy of a skeletal muscle fiber (cell).

Thin (actin)myofilament

Thick (myosin)myofilament

Sarcomere (contractile unit of a myofibril)

Z disc M line Z disc

Sarcomere

(c)

H Zone

• I band: thin (light) filaments (actin)• A band: thick (dark) filaments (myosin)• Z disc: dark area; the boundary at each

end of the sarcomere– Actin attaches at the Z disc (a network of

proteins)• H zone: central part of A band where no

thin filaments occur• M line: center of the H zone

– Myosin attaches to the M line via protein rods

Sarcoplasmic reticulum (SR) • Specialized smooth endoplasmic reticulum• Stores and releases calcium• Surrounds the myofibril in a tubule

arrangement

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