MUSCLULAR TISSUES

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MUSCLULAR TISSUES The flesh of the body also bulk
of wall (hollow organs) Muscle cells elongate
elements Contraction ? long axis of cell Muscle
cell is a MUSCLE FIBER Protoplasm
SARCOPLASM Cell membrane SARCOLEMMA Endoplas
mic reticulum SARCOPLAMIC RETICULUM
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Contractile elements MYOFIBRILS Composed of
MYOFILAMENTS
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CLASSIFICATION STRUCTURAL and FUNCTIONAL Functiona
l Voluntary or Involuntary Structural Striated
or Smooth Combined Smooth involuntary muscle
smooth muscle Striated involuntary muscle
cardiac muscle Striated voluntary muscle
skeletal muscle
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Muscle tissue building material (smooth,
cardiac) Muscle tissue as an organ skeletal
muscle
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SMOOTH MUSCLE Occurrence Walls hollow viscera,
ducts, blood vessels Skin, spleen, penis, broad
ligament, visceral pleura Shape Elongate,
tapering spindles Size Length varies ? 18 to 200
µ Pregnant uterus 70 to 500 µ Diameter ? 3 to 8
µ
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Structure Nucleus Elongate (ovoid, cigar
shaped) fiber length Midway fiber
(longitudinal section) Center (cross
section) Cytoplasm Cell membrane
indistinct Homogeneous (light microscope) EM
shows myofilaments, organelles Unspecialized
sarcoplasm
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Fiber arrangement Solitary fibers Loose
network of fibers Common functional unit
fascicle (bundle) Economy of space ? thick middle
to thin end
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Isolated bundle Erector pili muscles Aggregated
bundles (sheets) Well defined layers intestine,
ductus deferens Ill-defined layers stomach,
urinary bladder, uterus
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Fibers surrounded with reticular and elastic
net Bundles/sheets surrounded with Areolar
C.T. One fibers pulls on another one fascicle
pulls on another unified action Contraction is
slow Contraction nodes if wave passes along
fiber Constant muscular contraction tone
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Blood supply moderate Capillaries in C.T.
surrounding fibers bundles Capillaries do not
invade bundles Capillary network follows axis
of layer/fibers Nerves Autonomic nerve fibers
(sympathetic and parasympathetic) add enteric
ANS fibers for digestive tube
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SKELETAL MUSCLE Voluntary/striated Muscle fiber
very long and thick, mutltinucleated Fiber
generally cylindrical Fibers gradually taper
near ends Bifurcation near end tongue/ skin of
face Fiber dozens to hundreds of
myofibrils Nuclei around periphery of cytoplasm
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Size Length ? 1 t 40 mm longer in nontapering
muscles (sartorius) Diameter ? 10 to 100
µ Varies with muscle type and within
muscle Gluteus coarse Ocular msucles
fine Increases with age, exercise, male
hormone Adult fiber up to 10Xs that at
birth
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Nuclei Numerous 35 per mm. (total depends on
length of fiber) Sarcolemma May appear as a
sharp outline Elastic Sarcoplasm Undifferentiat
ed between myofibrils Amount varies with fiber
type Coarse fibrils rich in sarcoplasm
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Color categories Red and White Rabbit has
both dark muscles rich in sarcoplasm white
muscles poor in sarcoplasm Most mammals
(including humans) red and white fibers mingle
in same muscle
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Myofibrils Unbranched, parallel
filaments thickness varies 1 and 2
µ thinnest 0.2 µ Fibrils often bundled
(Koellikers columns) In cross section
Koellikers columns Cohnheims area
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Myofibrils Chains of long protein
molecules Actin thin filament extend
into dark band Myosin thick
filament extend throughout light band
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Myofibrillar banding 300 per mm. Dark Band
Anisotropic (A disk) Strongly refractile
live Doubly refractive (anisotropic) polarized
light Middle of A disk is an H disk H
means helle (clear) also called Hensens
disk Actin absent
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Myofibrillar banding Light Band Isotropic disk
(I disk) Poorly refractile pale
(live) Singly refractile (isotropic) Only
actin in I disk
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Myofibrillar banding Other bands Z membrane (Z
for zwischenscheibe) bisects I disk web-like
set of threads actin inserts on Z disk M line
(M for mittelscheibe) bisects H disk N line (N
for nebenscheibe) crosses I disk between Z and A
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Sarcomere Functional unit of muscle From Z disk
to Z disk Functional Correlations Skeletal
muscle faster contracting than smooth Fatigues
easier action less sustained Smaller stimulus
sets off contraction Contraction consumes more
energy More red fibers slower to fatigue
(ocular, respiratory and masticatory msucles
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White fibers greater numbers quicker
contraction more powerful contraction richer
in myofibrils Fatugues sooner Digital
muscles, biceps
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Endomysium
Nucleus
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Endomysium
Perimysium
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Muscle as an organ Aggregated muscle
fibers Groups of skeletal muscle fibers
fascicle Groups can be large (coarse
grain) Gluteus maximum deltoid Fine grain
(small bundles) Ocular muscles May not extend
length of muscle (common)
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• C.T. surrounds fibers, fascicles, muscle
• Endomysium around muscle fiber (delicate C.T.)
• Perimysium around fascicle (fibrous)
• Epimysium around entire muscle (fibrous)
• Fibers arrangement in muscle
• entire length of muscle
• attach one end of fascicle other terminates
  freely
• entirely within fascicle does not attach to
  ends

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Blood vessels and Nerves Blood vessels follow
connective tissue into muscle rich capillary
network in endomysium around each
fiber Lymphatics only in epimysium and
perimysium Nerves Sensory muscle spindles
(muscle sensibility) Motor activity motor end
plates
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MOTOR END PLATES Motor fibers branch
repeatedly Terminal twig midpoint muscle
fiber Axonal branch ends in crow foot One
to every muscle fiber
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CARDIAC MUSCLE Involuntary, striated Heart, root
of vessels from heart Short columns, united into
meshwork Column composed on discrete
cells Cells arranged in single row Cells
(muscle fibers) branch Endomysium pronounced only
in mammals
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Fiber diameter 9 to 22 µ Nuclei Ovoid (oriented
to long axis) Central position in cell One per
cell Sarcolemma Appears more delicate than in
skeletal muscle
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Sarcoplasm Abundant Embeds nucleus extends
beyond - spindle Mitochondria abundant Numerous
fat droplets Myofibrils Distinct, less robust
than skeletal muscle Fibrillar striping like
skeletal muscle closer and fainter Koellikers
columns Cohnheims arears sometimes seen
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Intercalated disk Distinctive feature of cardiac
muscle blackened with silver nitrate A tight
junction between cells Functional syncytium
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nucleus
Intercalated disk
branch
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Purkinje fibers Specialized cardiac muscle
cells Arranged in column Thick fibers with
abundant sarcoplasm Fibrils scant and
peripheral impulse conduction system Close
to endocardium Most prominent system ?
atrio-ventricular bundle
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Blood vessels and Nerves Blood capillaries 2Xs
greater than in skeletal muscle Lymphatic
capillaries in endomysium Autonomic nerves
simple brushes on cardiac muscle fibers
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