The Muscular System

Comprehensive practice flashcards covering the functions, classification, anatomy, and mechanical properties of the human muscular system based on the lecture transcript.

Electrical excitability

The ability of muscular tissue to respond to certain stimuli by producing electrical signals called action potentials.

Contractility

The ability of muscular tissue to contract forcefully when stimulated by an action potential.

Extensibility

The ability of muscular tissue to stretch without being damaged.

Elasticity

The ability of muscular tissue to return to its original length and shape after contraction or extension.

Fascia

A dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body.

Epimysium

The outermost layer of connective tissue, encircling the entire skeletal muscle.

Perimysium

Connective tissue that surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles.

Fascicles

Bundles of muscle fibers wrapped in perimysium.

Endomysium

A thin sheath of areolar connective tissue penetrating the interior of each fascicle and separating individual muscle fibers from one another.

Aponeurosis

A broad, flat layer formed when the connective tissue elements (epimysium, perimysium, and endomysium) extend beyond the muscle fibers.

Sarcolemma

The plasma membrane wrapping a single, long, cylindrical, and multinucleated muscle fiber (cell).

Sarcoplasm

The cytoplasm of a muscle fiber, which contains numerous mitochondria, glycogen, and myoglobin.

Myofibrils

Long, rod-like structures within the muscle fiber made of repeating contractile units responsible for muscle contraction.

Sarcomeres

The functional, repeating units of the myofibrils, running from one Z-line to the next, containing thick and thin filaments.

Sarcoplasmic Reticulum

A specialized type of smooth endoplasmic reticulum that surrounds the myofibrils and stores and releases $Ca^{2+}$ essential for muscle contraction.

Transverse (T)-tubules

Invaginations of the sarcolemma that penetrate deep into the muscle fiber to transmit action potentials from the sarcolemma to the sarcoplasmic reticulum.

Triad

A structure formed by a transverse tubule and the two terminal cisterns on either side of it.

Satellite cells

Quiescent stem cells within skeletal muscles that become active to repair and regenerate muscle tissue in response to injury or exercise.

Z discs

Narrow, plate-shaped regions of dense material that separate one sarcomere from the next.

A band

The dark, middle part of the sarcomere extending the entire length of the thick filaments and overlapping thin filaments.

I band

The lighter, less dense area of the sarcomere containing the rest of the thin filaments but no thick filaments.

H zone

A narrow region in the center of each A band that contains thick filaments but no thin filaments.

M line

A region in the center of the H zone containing proteins that hold thick filaments together at the center of the sarcomere.

Origin

The stationary or more fixed end of a muscle, usually proximal in the limbs.

Insertion

The more moveable end of a muscle, usually distal in the limbs.

Prime movers (Agonists)

The main muscle(s) responsible for a particular movement, such as the biceps brachii for elbow flexion.

Antagonists

Muscles that perform the opposite action of the prime mover, often relaxing to allow movement.

Synergists

Muscles that help the prime mover by adding extra force, stabilizing joints, or preventing unwanted movements.

Fixators

A special type of synergist that stabilizes the origin of the prime mover to allow it to produce more force.

Lever

A rigid structure that can move around a fixed point called a fulcrum (F).

Effort (E)

The force exerted by muscular contraction causing movement in a lever system.

Load (L)

The weight of the body part that is moved, which opposes movement in a lever system.

First class lever

A lever category where the fulcrum is positioned between the effort and the load ($EFL$).

Second class lever

A lever category where the load is positioned between the fulcrum and the effort ($FLE$).

Third class lever

A lever category where the effort is positioned between the fulcrum and the load ($FEL$); this is the most common type in the body.

Rectus

A muscle naming term describing fascicles that are parallel to the midline.

Transverse

A muscle naming term describing fascicles that are perpendicular to the midline.

Oblique

A muscle naming term describing fascicles that are diagonal to the midline.

Vastus

A muscle naming term meaning huge, such as the vastus lateralis.

Biceps

A muscle naming term indicating two tendons of origin.

Triceps

A muscle naming term indicating three tendons of origin.

Quadriceps

A muscle naming term indicating four tendons of origin.

Peristalsis

The result of alternate contraction of circular and longitudinal smooth muscle in the intestine.