Muscular System Vocab I

Introduction, Macroanatomy of Skeletal Muscle, Microstructure of Skeletal Muscle

Excitability

Receives and responds to stimuli; one of the characteristics of muscle tissue

Contractibility

Can shorten when stimulated; one of the characteristics of muscle tissue

Extensibility

Can stretch when pulled; one of the characteristics of muscle tissue

Elasticity

Can return to its original shape after contraction or extension; one of the characteristics of muscle tissue

Skeletal (striated)

a type of muscle tissue that is under voluntary control; attached to bones

Visceral (smooth)

a type of muscle tissue that is involuntary; responsible for the movements of the internal organs

Cardiac

a type of muscle tissue that is striated and involuntary; causes the heartbeat and is self-generating (myogenic)

Muscle fibers (cells)

Organized into functional units called muscles

Fascia

A thin sheet of fibrous connective tissue that surrounds each skeletal muscle and cell; reinforces the muscle, provides a passageway for nerves and blood vessels, and participates in muscle attachment

Epimysium

a sheet of dense irregular tissue that surrounds the entire muscle

Perimysium

An inward fold of epimysium surrounding a fasciculus (bundle of muscle fibers); there are many

Endomysium

An inward fold of perimysium around a single muscle fiber, but separated from the cell membrane by an interstitial space

Direct attachment

Epimysium connects directly to the periosteum of the bone

Indirect attachment

Extensions of the perimysium from tendons and aponeurosis that anchor the muscle to bone, fascia, or cartilage of other bones

Series-elastic component

The various connective tissue elements; not excitable of contractile, but it is extensible and elasticInte

Internal tension

The force muscle creates first when contracting, stretching the series-elastic components

External tension

Once fully contracted, continued shortening of the muscle exerts this force; causes its eventual movement

Sarcolemma

The muscle fiber membrane; it maintains cell potential and receives the contraction signal

Sarcoplasm

The cytoplasm of the muscle fiber

Sarcoplasmic reticulum

A modified ER, primarily involved with calcium storage and release during the contraction cycle

Terminal cisternae

Enlargements of the SR where most of the calcium is stored

Transverse (T) tubules

A deep protrusion of the sarcolemma that forms a penetrating tubular system; the lumen contains extracellular fluid

Triad

The association of terminal cisternae and a T-tubule; demarks the beginning and ending of each sarcomere

Myofibrils

Hundreds or thousands of these that make up a muscle fiber

Myofilaments

Protein filaments that also make up myofibril

Thin filaments

Composed primarily of fibrous (F) action which in turn is formed from multiple globular (G) actin molecules end to end

Thick filaments

Constructed primarily of myosin which can interact with attachment sites on each G actin

Troponin

The site where calcium ions bond; contributes to muscle contraction

Tropomyosin

Covers the actin active sites preventing cross-bridge formation with the myosin heads; contributes to muscle contraction

Striations

The spatial arrangement of various elements producing shading patterns

Sarcomeres

Functional units in which myofilaments are organized; they are stacked end to end in the cell

Z disc

The ends of the sarcomere; a protein structure connected to the thin (actin) filaments directly and indirectly to the thick (myosin) filament via the elastic filament

Motor neurons

Supply the neural stimulation needed to initiate contraction

Neuromuscular junction

A specialized junction formed between the neuron and the skeletal muscle cell

Synaptic cleft

The small interstitial space between the ending of the motor neuron and the cell membrane

Motor unit

Made up of fibers (~150) controlled by one neuron; contract simultaneously