5-1 Muscular Tissue
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Transcript 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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