Download 5-1 Muscular Tissue

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, spindleshaped 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
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