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