Skeletal Muscle Structure, Function, and Mechanics

Comprehensive vocabulary flashcards covering muscle tissue properties, connective tissue structure, sarcomere organization, sliding filament theory, Hill's muscle model, length-tension relationship, and types of muscle actions.

Moment (Torque)

The turning force produced across a joint when muscle force causes joint rotation.

Irritability

The property of muscle tissue to respond to stimulation by a chemical neurotransmitter ($\text{ACh}$).

Contractibility

The ability of muscle tissue to shorten ($50\text{--}70\%$), usually limited by joint range of motion.

Extensibility

The ability of muscle tissue to stretch or lengthen, corresponding to the stretching of the perimysium, epimysium, and fascia.

Elasticity

The ability of muscle tissue to return to its normal state after lengthening.

Epimysium

The outermost connective tissue layer covering the muscle as a whole, blending into the tendon to hold everything together.

Perimysium

The connective tissue layer that encases fascicles and contains larger blood vessels and nerves.

Endomysium

The connective tissue layer covering each individual muscle fiber, containing capillaries and small nerve fibers that nourish and activate the cell.

Sarcolemma

The muscle cell membrane located in between bundles, going around and underneath the endomysium.

Sarcomere

The basic contractile and functional unit of a muscle containing actin and myosin myofilaments.

Z-band

The structural border lines defining the boundaries of a single sarcomere.

I-band

The section of a sarcomere that contains only actin myofilaments.

A-band

The section of a sarcomere spanning from one end of a myosin filament to the other end.

H-Zone

The section of a sarcomere that contains only myosin myofilaments.

M-Band

The central vertical line of the sarcomere where myosin filaments attach.

Sliding Filament Theory

The model describing muscle contraction following neural activation through myosin crossbridge attachment, contraction, sliding of actin and myosin filaments past each other, sarcomere shortening, and force production.

Contractile Component (CC)

The active component in Hill's muscle model that produces active shortening of muscles through actin and myosin structures.

Parallel Elastic Component (PEC)

The passive elastic component in Hill's muscle model positioned parallel to the contractile elements.

Series Elastic Component (SEC)

The passive elastic component in Hill's muscle model positioned in series with the contractile elements, such as tendons.

Length-Tension Relationship

The principle stating that a muscle's ability to generate force depends on its length before contraction.

Active Tension

The force generated by actin and myosin crossbridge interactions when touching, which peaks at resting length ($2.0\text{--}2.25$).

Passive Tension

The resistance generated by elastic connective tissue when a muscle is stretched beyond resting length ($2.25\text{--}3.6$).

Concentric Muscle Action

A muscle action where the muscle shortens under tension because muscle force overcomes resistance ($F > R$), changing the joint angle in the direction of the applied force.

Eccentric Muscle Action

A muscle action where the muscle lengthens under tension because resistance exceeds muscle force ($R > F$), changing the joint angle in the direction of the resistance.

Isometric Muscle Action

A muscle action where total muscle length remains constant under tension because force equals resistance ($R = F$), resulting in no joint movement.

Isokinetic Muscle Action

An externally controlled muscle action performed at a constant fixed speed regardless of resistance (same speed, variable resistance).

Isotonic Muscle Action

A muscle action in which muscle tension remains constant throughout the entire range of motion (variable speed, same resistance).