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
10-2
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
10-3
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)
• Vascular pericytes can also provide source of smooth muscle
Heart Muscle
• Increase in size (hypertrophy)
• Formerly thought to be non-proliferative
• Post-infarction tissue remodeling by fibroblasts (fibrosis/scarring)
• New evidence suggests mitotic cardiomyocytes and regeneration
by blood or vascular-derived stem cells
Skeletal Muscle Investments
Epimysium dense irr. c.t.
Perimysium less dense irr. c.t.
Endomysium basal lamina and
reticular fibers
ALL MUSCLE
CELLS HAVE
BASAL LAMINAE!
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.
Composition of thick and thin filaments
Thick filament
Tail
Thin filament
Heads
Flexible hinge region
(a) Myosin molecule
(d) Longitudinal section of filaments within
one sarcomere of a myofibril
Thin filament (actin) Myosin heads Thick filament (myosin)
Myosin head
(b) Portion of a thick filament
Troponin complex
Tropomyosin
(c) Portion of a thin filament
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Actin
(e) Transmission electron micrograph of part
of a sarcomere
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Filaments and the Sarcomere
• Thick and thin filaments overlap each other in
a pattern that creates striations (light I bands
and dark A bands)
• They are arranged in compartments called
sarcomeres, separated by Z discs.
• In the overlap region, six thin filaments
surround each thick filament
10-14
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.
Connective tissue sheaths of skeletal muscle
Epimysium
Tendon
Muscle fiber
in middle of
a fascicle
Epimysium
Endomysium Endomysium
(between
fibers)
(b)
Perimysium
Muscle fiber
(cell)
Bone
(a)
Perimysium
Blood
Fascicle
(wrapped by vessel
perimysium)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Blood vessel
Endomysium
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. In
addition, smooth muscle cells are smaller than
cardiac and skeletal muscle cells. These
features result is a tissue that has lots of
nuclei. Depending on the orientation of the
cells, the nuclei are slightly elongated in
longitudinally-oriented cells (L), or round in
transverse (cross) -sections (T).
6 major locations:
1. inside the eye 2. walls of vessels 3. respiratory tubes
4. digestive tubes 5. urinary organs 6. reproductive organs
, p. 296.
Spinal cord
Motor
unit 1
Motor
unit 2
Axon terminals at
neuromuscular junctions
Nerve
Motor neuron
cell body
Muscle
Motor neuron
axon
Muscle fibers
Muscle
fibers
Branching axon
to motor unit
(a)
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
(b)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
The cross bridge cycle
Myosin head
(high-energy
configuration)
ADP
Pi
1 Myosin head attaches to the actin
myofilament, forming a cross bridge.
Thin filament
ATP
hydrolysis
ADP
ADP
Thick filament
Pi
4 As ATP is split into ADP and Pi, the myosin
head is energized (cocked into the high-energy
conformation).
2 Inorganic phosphate (Pi) generated in theprevious
contraction cycle is released, initiating
the power (working) stroke. The myosin head
pivots and bends as it pulls on the actin filament,
sliding it toward the M line. Then ADP is released.
ATP
ATP
Myosin head
(low-energy
configuration)
3 As new ATP attaches to the myosin head, the link between
Myosin and actin weakens, and the cross bridge detaches.
Human Anatomy and Physiology, 7e
by Elaine Marieb & Katja Hoehn
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
--Skeletal muscle cells have the largest diameter, cardiac muscle cells are smaller, and smooth muscle cells
have the smallest diameter.
--The diameter of skeletal muscle is very consistent between cells. Cardiac muscle cells are somewhat
consistent in diameter (but vary in shape), while the smooth muscle cell profiles vary depending on whether the
cell is sectioned through the middle (with nucleus) or near the periphery of the cell (without nucleus).
--Skeletal muscle nuclei are near the plasma membrane, while cardiac and smooth muscle nuclei are centrally
located.
--In cuts through the nucleus of a cell, there is significant cytoplasm in skeletal and, to a lesser extent, cardiac
muscle, while smooth muscle has a small rim of cytoplasm around the nucleus.
--In ideal sections, stippling can be seen in skeletal and cardiac muscle, but not smooth muscle.
skeletal muscle 320X
cardiac muscle 480X
smooth muscle 320X