MUSCLE TISSUE - Page |1 Muscular System I I Functions of...

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Muscular System I
I. Functions of muscular system :
A. movement of the skeleton (body parts)
B. maintenance of posture -due to skeletal muscles being in a partially contracted
state (muscle tonus).
C. maintenance of body temperature by heat production or shivering!!
II. Important physiological properties or characteristics of muscle:
III. Anatomy of skeletal muscle :
A. Connective tissue (CT) components of skeletal muscle.
1. deep fascia -CT which holds groups of skeletal muscles together
2. epimysium- CT which surrounds an entire skeletal muscle.
3. perimysium -CT which surrounds a bundle of muscle fibers ( fasciculus or fascicle ).
4. endomysium -CT which covers each individual muscle fiber (myofiber).
5. tendon -cord of dense CT which attaches muscle to bone. Ex. Achilles tendon!!
Note: Each of these CT coverings contain many blood vessels, nerves, and lymphatic vessels.
B. skeletal muscle gross anatomy à microscopic anatomy (from bigger to smaller):
1. whole muscle
2. muscle fasciculus or bundle
3. muscle fiber (cell)=myofiber
4. myofibril
5. myofilaments
Myosin: thick filament

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Actin: thin filament - remember the microfilaments of the cytoskeleton?
IV. Structure of skeletal muscle fibers (muscle cells or myofibers) :
A. sarcolemma - the cell membrane of a muscle cell.
B. sarcoplasm- the cytoplasm of a muscle cell. There are numerous nuclei, mitochondria,
and large number of myofibrils that are oriented lengthwise in a skeletal muscle cell.
C. sarcoplasmic reticulum - specialized form of SER in muscle cells that stores calcium.
D. transverse (T) tubules -invaginations of the sarcolemma that extend all the way through the fiber.
These tubules are continuous with, and are filled with, extracellular fluid.
E. each T-tubule is situated between two cisternae(sacs) of sarcoplasmic reticulum near the
region where actin and myosin fibers overlap. This arrangement is very important in
muscle contraction and is called a triad or triplet. The heart muscle has DIAD
F. myofibrils - each muscle cell is made up of numerous myofibrils that run lengthwise and
parallel to each other.
1. myofibrils are composed primarily of two overlapping myofilaments that are responsible for the
striated appearance of skeletal muscle:
i. actin filaments -thin filaments that are anchored at Z-lines .
ii. myosin filaments- thick filaments that are anchored at M-line .
2. myofibrils are made up of numerous sarcomeres that are attached end-to-end.
A sarcomere is a segment of a myofibril that extends from one Z-line to the next.
Structure of a sarcomere :
A-band : extends from one end of the myosin filaments to the other. The A-band contains myosin and
overlapping actin filaments.
I-band : the region between the Z-line and the A-band that contains actin filaments only
Z-Lines : actin filaments are anchored here by a network of proteins.