Excitability
The ability to respond to a stimulus
Conductivity
Electrical changes travel along the plasma membrane, opening voltage-gated channels
Contractility
Contractile proteins within the muscle slide past one another (sliding filament)
Elasticity
The ability of a muscle to return to its original length
Extensibility
Lengthening of a muscle fiber
Functions of Skeletal Muscle
Body movement, maintenance of posture, protection & support, regulating elimination of materials, & heat production
Muscle Fiber
Muscle cell
Fascicle
Group of bound muscle fibers
Myofibril
Small tubules within the muscle fiber that contain the contractile unit (sarcomere)
Functions of Connective Tissue
Protection, site for distribution of blood vessels & nerves, & attachment to the skeletal system
Epimysium
Surrounds the whole muscle
Dense irregular tissue
Perimysium
Surrounds the fascicle, contains lots of blood vessels & nerves
Dense irregular tissue
Endomysium
Surrounds & electrically insulates each individual muscle fiber; contains reticular fibers to help bind together muscle fibers
Areolar tissue
Tendon
A thick cord-like structure formed by 3 layers of connective tissue; attaches muscle to bone
Aponeurosis
A thin, flattened sheet of dense irregular tissue; connects two muscle bellies
Myoblasts
Fuse together to form a single muscle fiber, leading to multiple nuclei in one cell
Satellite Cells
Myoblasts that do not fuse but remain in the muscle tissue to repair damaged muscle tissue
Sarcolemma
Specialized plasma membrane that can transmit electrical impulses
T-Tubules
Deep invaginations of the sarcolemma that extend into the skeletal muscle fiber to stimulate the sarcoplasmic reticulum
Sarcoplasmic Reticulum (SER)
Internal membrane complex that is similar to smooth ER
Terminal Cisternae
Sacs at the end of the SER that store calcium
Calcium Pumps
Move calcium into the SER
Calcium Channels
Move calcium out of the SER
Calmodulin & Calsequestrin
Proteins that bind with calcium in the SER
Myofibrils
Long, cylindrical structures that extend the length of the muscle fiber; 80% of the skeletal muscle volume; composed of myofilaments
Myofilaments
Contractile proteins that are bundled within the myofibrils
Myosin
Thick myofilament; globular head & elongated tail
Actin & ATP
Two binding sites on myosin globular head
Actin
Thin myofilament; two protein strands twisted around each other
F-Actin
Two strands twisted together
G-Actin
The individual bead; contains the myosin binding site
Tropomyosin
Regulatory protein that covers the myosin binding sites of actin until moved
Troponin
Regulatory protein that binds with calcium to move tropomyosin off the myosin binding sites of actin
Sarcomere
The contractile unit; repeating unites within the myofilaments
Z Disc
Proteins that are positioned perpendicular to the myofilaments & serve as anchors for the thin filaments; separates one sarcomere from another
I Bands
Extend in both directions of the Z disc; disappears during maximal contraction
A Band
Central region that contains the entire thick filament; does not change shape during contraction
H Zone
Most central portion of the A band; disappears during maximal contraction
M Line
Thin transverse protein meshwork in the center of the H zone
Connectin
Extends from the Z disc to the M line through the core of each thick filament
Dystrophin
A complex protein that anchors myofibrils to other proteins with within the sarcolemma that extend to the endomysium