Transcript Ch 6 Overview of Muscle and Microscopic Anatomy pgs. 181-187

Muscle Types pgs. 181-185
Microscopic Anatomy of Skeletal Muscle
pgs. 185-187
*emphasis will be placed on skeletal
muscle
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Functions:
– body movement (of any kind)
– Posture/position
– Stability
– Generate heat
– Protection
Three basic muscle types:
1. Skeletal muscle
2. Cardiac muscle
3. Smooth muscle
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Skeletal and smooth muscle cells are
elongated (muscle cell  muscle fiber)
Microfilaments cause muscle contraction
– Via shortening of the muscle fibers
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Skeletal
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Elongated
Multinucleic
Striated
Banded
Attach to
skeleton
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Cardiac
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Branching
One nucleus
Striated
Intercalated
discs
 Gap junctions
◦ Found only
in heart
•Smooth
-Fusiform
-One nucleus
-No striations
-found in hollow
visceral organs
like stomach,
bladder
skeletal
cardiac
smooth
•differences in contraction between the three types of muscle fibers:
•Skeletal: has no rhythm, and the speed can vary; you control
•Cardiac : has rhythm, and the rate is slow
•Smooth: has variations in rhythm, depending on the process, and
very slow contractions
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Most are attached by tendons to bones
Multinucleate
Striated—have visible banding
Voluntary—subject to conscious control
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Endomysium—encloses a single muscle fiber
Perimysium—wraps around a fascicle (bundle) of
muscle fibers
Epimysium—covers the entire skeletal muscle
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Fascia—outermost layer; covers the epimysium
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– Fascia is a dense connective tissue found covering
muscles, groups of muscles, and large vessels and
nerves
• It binds structures together like plastic wrap
• Fasciitis is an inflammation of the fascia or a muscle/organ
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Muscle
fiber
(cell)
Blood vessel
Perimysium
Epimysium
(wraps entire
muscle)
Fascicle
(wrapped by
perimysium)
Endomysium
(between
fibers)
Tendon
Bone
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Epimysium blends into a connective tissue
attachment
◦ Tendons—cordlike structures
 Mostly collagen fibers
 Often cross a joint because of their toughness and
small size
◦ Aponeuroses—sheetlike structures
 Attach muscles indirectly to bones, cartilages, or
connective tissue coverings
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Sites of muscle attachment
◦ Bones
◦ Cartilages
◦ Connective tissue coverings
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Sarcolemma—specialized plasma membrane
◦ Surrounds each fiber
◦ Multiple nuclei reside just beneath this membrane
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Myofibrils—long organelles inside muscle cell
◦ These create Light (I) bands and dark (A) bands to
give the muscle its striped appearance
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Figure 6.3a Anatomy of a skeletal muscle fiber (cell).
Sarcolemma
Myofibril
Light
Dark
Nucleus
(A) band (I) band
(a) Segment of a muscle fiber (cell)
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Sarcomere—contractile unit of a muscle fiber
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The light and dark bands are myofilaments
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They are organized in a pattern that give
the muscle fiber a banded look
These are protein filaments of different
widths:
 Thick filaments  myosin filaments
 Thin filaments  actin filaments
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Figure 6.3b Anatomy of a skeletal muscle fiber (cell).
Z disc
H zone Z disc
Thin (actin)
myofilament
Thick (myosin)
myofilament
I band
A band I band
Sarcomere
M line
(b) Myofibril or fibril (complex organelle composed of bundles
of myofilaments)
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I band  light band
◦ Contains only thin filaments
◦ Z disc is only a midline interruption
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A band  dark band
◦ Contains the entire length of the thick filaments
◦ H zone is a lighter central area
◦ M line is in center of H zone
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Z disc
H zone Z disc
Thin (actin)
myofilament
Thick (myosin)
myofilament
I band
A band I band
Sarcomere
M line
(b) Myofibril or fibril (complex organelle composed of bundles
of myofilaments)
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Composed of the protein myosin
◦ Contain ATPase enzymes
◦ Possess myosin heads
◦ Heads are known as cross bridges when they link
thick and thin filaments during contraction
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Composed of the contractile protein actin
◦ Actin is anchored to the Z disc
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At rest, within the A band there is a zone that
lacks actin filaments
◦ Called the H zone
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Figure 6.3c Anatomy of a skeletal muscle fiber (cell).
Sarcomere
Z disc
M line
Thin (actin)
myofilament
Thick (myosin)
myofilament
(c) Sarcomere (contractile unit of a myofibril)
H Zone
Z disc
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I band: thin (light) filaments (actin)
A band: thick (dark) filaments (myosin)
Z disc: dark area; the boundary at each end of
the sarcomere
– Actin attaches at the Z disc (a network of proteins)
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H zone: central part of A band where no thin
filaments occur
M line: center of the H zone
– Myosin attaches to the M line via protein rods
Sarcoplasmic reticulum (SR)
• Specialized smooth endoplasmic reticulum
• Stores and releases calcium
• Surrounds the myofibril in a tubule
arrangement
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