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HISTOLOGY1.11: MUSCULAR TISSUES
Muscular tissues are specialized to perform directed organized movements.
The tissues are composed of elongate spindle shape cells, or elongated
muscle fibers (different from the CT fibers!).
Cells/fibers are arranged in bundles surrounded by CT sheats.
Origin: mesodermal (except the head region).
Blood supply: densely capillarized.
Innervation: dense (sensory and motor endings).
Classification:
striated
non-striated
skeletal muscle
cardiac muscle
smooth muscle
Skeletal muscle
Cardiac muscle
Smooth muscle
Tissue unit:
non-branching
multinucleated
fibers
Y-shaped cells
form fibers
spindle-shaped
cells form fibers
Functional
properties:
quick contraction
easily fatigues
quick contraction
no fatigue
slow contraction
no fatigue
Impulse
generation:
motor endplate
specialized
cardiac muscle
vegetative
plexus
Occurrence:
locomotor
organs(muscles)
heart
wall of visceral
organs
Skeletal muscle
Skeletal myofibers vary from 10 to 120 mm.
Origin: fusion of many mononuclear myoblast cells.
Morphology:
1./Longitudinal section: elongated nuclei at subsarcolemmal position
transverse striation as regular cross-banding pattern
2./Cross-section:
polygonal-shaped profiles
no-cross-striation
1
2
Organization of the muscles:
Individual myofibers surrounded
by endomysium (fine reticular CT)
Primary bundles/fascicles
ensheathed by perimysium (dense
collagen fibers with blood vessels
and nerves)
The whole muscle is
ensheathed by the epimysium
(thick dense collagenous CT)
Sensory innervation of the skeletal muscle:
Morphology of the muscle spindle
LM image of muscle spindle
Schematic drawing of the
components
Motor innervation of the
skeletal muscle:
Light micrograph of the
motor endplate
Schematic drawing of the
Motor endplate
CARDIAC MUSCLE
Cardiac myofibers are organized for pumping the blood in the circulatory
system.
Myofibers are formed by individual cells that branch and anasotomose.
Morphology:
cylindrical, or Y-shaped cells
centrally located single nucleus
very dense capillary network
cell borders: Eberth’s line (discus intercalaris) (arrows)
Longitudinal section
Cross-section
Comparison of the cardiac
muscle types:
The smaller slender fibers with
more contractile elements
are engaged with contraction,
the larger with more sarcoplasm
are responsible for impulse
generation and conduction
CARDIAC MUSCLE
Model drawing of the cardiac muscle cells
and their attachment to each other by the
Eberth’s lines (blue lines)
Cardiac myocytes :
Purkinje fibers
Isolated cell A bundle with Discus intercalaris formed by
capillaries
desmosomes (D) and gap junctions (N)
SMOOTH MUSCLE:
Smooth muscle myofibers are formed by small mononucleated spindle-shaped
cells of 10 mm in diameter. Length varies between 20-500 mm.
No cross-striation is visible. No perimysium.
Rod-like nucleus is in the center of the cell.
Longitudinal section
N
Cross-section
Organization of smooth muscle cells
into fiber bundles and their innervation
Contraction of smooth muscle cells