Download Skeletal muscle cells

Muscle Tissue
• Characteristics
– Cells are referred to as fibers
– Contracts or shortens with force when stimulated
– Moves entire body and pumps blood
• Types
– Skeletal:attached to bones
– Cardiac: muscle of the heart.
– Smooth: muscle associated with tubular
structures and with the skin. Nonstriated and
involuntary.
Muscular
Tissue
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Functions of Muscle Tissue
• Producing body movements
• Stabilizing body positions
• Regulating organ volumes
– bands of smooth muscle called sphincters
• Movement of substances within the body
– blood, lymph, urine, air, food and fluids, sperm
• Producing heat
– involuntary contractions of skeletal muscle
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Special functional characteristics of
muscle
 Contractility
 Only one action: to shorten
 Shortening generates pulling force
 Excitability
 Nerve fibers cause electrical impulse to travel
 Extensibility
 Stretch with contraction of an opposing muscle
 Elasticity
 Recoils passively after being stretched
Muscle Tissue
I. Striated Muscle - regularly arranged contractile units
A. Skeletal Muscle - long, cylindrical multinucleated cells with
peripherally placed nuclei. Contraction is typically quick and vigorous
and under voluntary control. Used for locomotion, mastication, and
phonation.
B. Cardiac Muscle - elongated, branched cells with a single centrally
placed nucleus and intercalated discs at the ends. Contraction is
involuntary, vigorous, and rhythmic.
II. Smooth Muscle - possesses contractile machinery, but it is irregularly
arranged (thus, non-striated). Cells are fusiform with a central nucleus.
Contraction is involuntary, slow, and long lasting.
Muscle Regeneration and Growth
Skeletal Muscle
• Increase in size (hypertrophy)
• Increase in number (regeneration/proliferation)
• Satellite cells are proposed source of regenerative cells
Smooth Muscle
• Increase in size (hypertrophy)
• Increase in number (regeneration/proliferation)
• Smooth muscle cells are proliferative
(e.g. uterine myometrium and vascular smooth muscle)
Heart Muscle
• Increase in size (hypertrophy)
• Formerly thought to be non-proliferative
• Post-infarction tissue remodeling by fibroblasts
(fibrosis/scarring)
FROM THE OUTSIDE IN
MUSCLE STRUCTURE
EPIMYSIUM
FIBROUS CONNECTIVE TISSUE
BINDS BUNDLES OF FIBERS TOGETHER
PERIMYSIUM
FIBROUS CONNECTIVE TISSUE
COVERS FASCICLES
FASCICLES
BUNDLES OF MUSCLE FIBERS
ENDOMYSIUM
FIBROUS CONNECTIVE TISSUE
COVERS MUSCLE FIBERS
MUSCLE FIBER
MUSCLE CELL
ALSO KNOWN AS A MYOFIBER
TENDON
ALL FIBROUS CONNECTIVE TISSUE EXTENDS BEYOND THE MUSCLE FIBERS
KNOWN AS A TENDON OR APONEUROSIS
http://training.seer.cancer.gov/module_anatomy/unit4_2_muscle_structure.html
Formation of a skeletal muscle fiber (muscle cell)
Skeletal muscle cells (fibers) develop from the fusion of myoblasts, resulting in large, multinuclear
cells. The cells then assemble their contractile machinery in the cytoplasm. These come in the form
of myofibrils, which have an alternate dark-light banding pattern when viewed from the side. The
fact that the cell is chock-full of these myofibrils pushes the nuclei to the periphery of the cell.
Muscle Fiber or Myofibers
• Muscle cells are long, cylindrical & multinucleated
• Sarcolemma = muscle cell membrane
• Sarcoplasm filled with tiny threads called myofibrils &
myoglobin (red-colored, oxygen-binding protein)
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Microscopic anatomy of a skeletal
muscle fiber
Nuclei
Fiber
(a)
Sarcolemma
Mitochondrion
Myofibril
(b)
Dark
A band
Light
I band
Nucleus
Z disc
H zone
Z disc
Thin (actin) filament
Thick (myosin)
filament
(c)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Microscopic anatomy of a skeletal muscle fiber
Z disc
H zone
Z disc
Thin (actin) filament
Thick (myosin)
filament
(c)
I band
Thin (actin) filament
Z disc
A band
Sarcomere
M line
I band
M line
Z disc
Elastic (titin)
filaments
Thick (myosin)
filament
(d)
(e)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
I band
thin filaments
only
H zone
M line
Outer edge of
thick filaments thick filaments linked
A band
only
by accessory proteins thick and thin
filaments overlap
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle
I band
A band
I band
Z disc
H zone
Z disc
M
line
Part of a skeletal
muscle fiber (cell)
Sarcolemma
Triad
Mitochondrion
Myofibrils
Myofibril
Tubules of
sarcoplasmic
reticulum
Sarcolemma
Terminal cisterna
of the sarcoplasmic
reticulum
T tubule
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Cardiac Muscle
Tissue Features:
• Striated (same contractile machinery)
• Self-excitatory and electrically coupled
• Rate of contractions modulated by autonomic nervous system
– innervation is neuroendocrine in nature (i.e. no “motor end plates”)
Cell Features:
• 1 or 2 centrally placed nuclei
• Branched fibers with intercalated discs
• Numerous mitochondria (up to 40% of cell volume)
• Sarcoplasmic reticulum & T-tubules appear as diads at Z lines
– T tubules are about 2x larger in diameter than in skeletal muscle
• transport Ca2+ into fibers
Cardiac Muscle (longitudinal section)
Cardiac muscle is composed of smaller, branched muscle cells, which are
connected to each other by intercalated discs. These intercalated disks,
which are unique to cardiac muscle tissue, include adherent junctions for
cell-cell strength, as well as gap junctions to allow electrical synchrony (so
the cells contract at the same time). Similar to skeletal muscle, cardiac
muscle fibers are packed with myofibrils, which are in-register, and give the
tissue a striated appearance. Each cardiac muscle cell has a single nucleus
that is centrally located.
Smooth Muscle
• Fusiform, non-striated cells
• Single, centrally-placed nucleus
• Contraction is non-voluntary
• Contraction is modulated in a
neuroendocrine manner
• Smooth muscle tissue is
composed of many smooth
muscle cells. Although there are
connective tissue elements (e.g.
collagen) between the cells,
smooth muscle is much more
cellular than connective tissue.
6 major locations:
1. inside the eye 2. walls of vessels 3. respiratory
tubes
4. digestive tubes 5. urinary organs 6. reproductive
organs