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Muscular Tissue

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Types of Muscle Tissue

skeletal cardiac smooth

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Skeletal attached to bones, skin, deep fascia, or

other muscles voluntary control striated , alternating light and dark bands

along length of myofibrils many nuclei Functions:

- movement - posture - respiration

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Skeletal Muscle

Nuclei

Striation

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Cardiac located only in the heart striated, single nucleus, branched fibers with

intercalated discs involuntary control by autonomic nervous

system regulation of heart rate is primarily due to

hormones and neurotransmitters no regeneration capability propels blood through blood vessels

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Cardiac Muscle

intercalated disc

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Smooth

located in hollow organs, skin attached to hair follicles, etc.

no striations, single nucleus, spindle-shaped fibers

involuntary control by autonomic nervous system

some regeneration

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Functions of Smooth Muscles

mix and propel food though GI tract regulate flow of blood by changing diameter of

lumen contraction of urinary bladder, gallbladder,

and spleen, expels urine, bile and blood control sphincter muscles control muscles of eye contraction of arrector pili muscles

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Types of Smooth Muscles

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Multiunit Smooth

muscle fibers are not well organized occur as separate fibers rather than

sheets found in irises of eye, walls of blood

vessels

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Visceral Smooth

composed of sheets of spindle-shaped cells

in contact with one another more common type found in hollow visceral organs capable of stimulating each other display rhythmicity due to self-exciting

fibers - responsible for peristalsis

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Peristalsis

wavelike motion occurs in various tubular organs helps force contents of these organs

along their lengths

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Contraction of Smooth Muscles

acetylcholine and norepinephrine also affected by hormones slower to contract - slower to relax can maintain a forceful contraction longer

than skeletal with same amount of ATP can change length without changing

tautness

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Smooth Muscle

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Muscle Fibers

many muscle fibers are enclosed in a delicate connective tissue sheath called endomysium

several sheathed fibers are wrapped in perimysium in bundles called fascicles (10 -100 fibers)

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Muscle Fibers (cont.)

many fascicles are joined together by even tougher covering called epimysium

fascia covers entire muscles which lead into tendons which attach to bones

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Individual Muscle Fiber (single cell)

sarcolemma

- plasma membrane covering of muscle cell

sarcoplasm

- cytoplasm of a skeletal muscle cell

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Individual Muscle Fiber (cont.)

sarcoplasmic reticulum

- network of membranous channels

- within sarcoplasm (corresponds to endoplasmic reticulum)

- surrounds each myofibril

- channels run parallel to myofibril

- stores calcium which is necessary for muscle contraction

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Individual Muscle Fiber (cont.)

transverse tubules

- fingerlike inward invaginations or channels of sarcolemma

- extend from membrane and pass through the fiber

- open to outside of the muscle fiber

- contain extracellular fluid

- carry action potentials to sarcoplasmic reticulum

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Individual Muscle Fiber (cont.)

cisternae

- enlarged portions of sarcoplasmic reticulum

- lie on either side of transverse tubules

- near region where actin and myosin overlap

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Individual Muscle Fiber (cont.)

myofibrils

- long ribbon-like organelles

- lie parallel to one another myofilaments

- thread-like structures within myofibrils (contain two types of protein filaments)

actin (thin & light) and myocin (thick & dark)

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Actin and Myosin

appear as light (thin) and dark (thick) bands

arrangement of these fibers produces the characteristic striations of a skeletal muscle fiber

slide past each other causing muscle cells to contract

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Myosin

located within the dark portions of the striations (A bands)

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Actin

located primarily within light areas (I bands) during muscle contraction actin filaments slide

farther into A bands attached to the Z lines at end of I bands Z lines extend across muscle fiber enabling

adjacent myofibrils to lie side by side segment between two Z lines is called a

sarcomere

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Sarcomeres

repeating units composed of filaments inside myofibrils

do not extend the entire length of the muscle fiber

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Muscle Activity

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Characteristics of Muscle Tissue

excitability contractility extensibility elasticity

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Excitability(irritability)

ability to respond to stimuli generate action potentials or impulses stimuli that initiate action potentials in

muscles are neurotransmitters neurotransmitters are released by axon

terminals of neurons

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Contractility

ability to contract and shorten to generate a force

muscles contract in response to action potentials

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Extensibility

ability to be stretched or extended when pulled

with pairs of skeletal muscles - one muscle is contracted while the opposing one is usually stretched

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Elasticity

ability to return to original shape after contraction or extension