BSC 215 Lecture Notes - Lecture 20: Endoplasmic Reticulum, T-Tubule, Myocyte
11 Jun 2018
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Connective Tissue Associated with Muscle Tissue
A skeletal muscle consists of numerous muscle cells called muscle fibers.
Three layers of connective tissues surround these fibers to form a muscle.
These and other connective tissues associated with muscles follow:
• The endomysium is the connective tissue that surrounds each muscle
fiber (cell).
• The perimysium encircles a group of muscle fibers, forming a fascicle.
• The epimysium encircles all the fascicles to form a complete muscle.
• A tendon is a cordlike extension of the preceding three linings. It
extends beyond the muscle tissue to connect the muscle to a bone or
to other muscles.
• An aponeurosis is a flat broad extension of the three muscle linings
and serves the same function as a tendon.
• Fascia is a term for a layer or sheet of connective tissue.
• The deep fascia surrounds the epimysium and encloses or lines other
nearby structures such as blood vessels, nerves, and the body wall.
• The superficial fascia (hypodermis or subcutaneous layer) lies
immediately below the skin. The superficial fascia merges with the
deep fascia where the surfaces of the skin meet.
Structure of Skeletal Muscle
A muscle fiber (cell) has special terminology and distinguishing characteristics:
• The sarcolemma, or plasma membrane of the muscle cell, is highly invaginated by transverse
tubules (T tubes) that permeate the cell.
• The sarcoplasm, or cytoplasm of the muscle cell, contains calcium‐storing sarcoplasmic
reticulum, the specialized endoplasmic reticulum of a muscle cell.
• Striated muscle cells are multinucleated. The nuclei lie along the periphery of the cell, forming
swellings visible through the sarcolemma.
• Nearly the entire volume of the cell is filled with numerous long myofibrils. Myofibrils consist of
two types of filaments, shown in Figure 1:
• Thin filaments consist of two strands of the globular protein actin arranged in a double helix.
Along the length of the helix are troponin and tropomyosin molecules that cover special binding
sites on the actin.
• Thick filaments consist of groups of the filamentous protein myosin. Each myosin filament forms a
protruding head at one end. An array of myosin filaments possesses protruding heads at
numerous positions at both ends.
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Document Summary
A skeletal muscle consists of numerous muscle cells called muscle fibers. Three layers of connective tissues surround these fibers to form a muscle. The superficial fascia merges with the deep fascia where the surfaces of the skin meet. The nuclei lie along the periphery of the cell, forming swellings visible through the sarcolemma: nearly the entire volume of the cell is filled with numerous long myofibrils. Myofibrils consist of two types of filaments, shown in figure 1: thin filaments consist of two strands of the globular protein actin arranged in a double helix. Along the length of the helix are troponin and tropomyosin molecules that cover special binding sites on the actin: thick filaments consist of groups of the filamentous protein myosin. Each myosin filament forms a protruding head at one end. An array of myosin filaments possesses protruding heads at numerous positions at both ends. Within a myofibril, actin and myosin filaments are parallel and arranged side by side.
