Muscular and Skeletal Systems Review

Types of Muscle Tissue Diagram

Visual categorization showing cardiac muscle (striated, branching, centrally located nucleus, intercalated discs), skeletal muscle (striated, multinucleated, myofibrils), and smooth muscle (nonstriated, spindle-shaped cells).

Masseter Muscle

Located in the jaw, this is the strongest muscle in the human body by weight, capable of reaching a maximum force of $200\text{ PSI}$.

Gluteus Maximus

Located in the buttocks, this is the largest muscle in the human body by volume.

Skeletal Muscle

Voluntary, striated muscle tissue composed of multinucleated cells governed by the Central Nervous System (CNS) and attached to bones to produce movement.

Smooth Muscle

Involuntary, nonstriated muscle tissue made of spindle-shaped cells controlled by the Autonomic Nervous System; located in vessel walls and digestive and respiratory tracts.

Cardiac Muscle

Involuntary, striated muscle tissue composed of $H$ or $Y$-shaped cells found exclusively in the heart.

Muscle Irritability (Excitability)

The capacity or property of muscle tissue to receive and react to a stimulus.

Muscle Contractility

The ability of muscle cells to contract or shorten, thereby exerting a force.

Muscle Elasticity

The ability of a muscle fiber to return to its original shape after contracting.

Muscle Extensibility

The ability of muscle tissue to stretch.

Fascicles

Bundles of parallel contractile fibrous muscle cells (fibers) that aggregate to form a whole muscle.

Epimysium

The outermost layer of fascia connective tissue that covers the entire muscle.

Perimysium

The connective tissue layer that separates muscle tissue into individual bundles of fascicles.

Endomysium

The inner layer of connective tissue that wraps around each individual muscle fiber (cell).

Sarcolemma

The plasma cell membrane surrounding an individual muscle fiber, located directly beneath the endomysium.

Sarcomere

The smallest functional contractile unit of a muscle fiber, composed of actin and myosin myofilaments.

Myosin

The thick protein myofilament within a sarcomere that makes up nearly $50\%$ of total muscle tissue.

Actin

The thin protein myofilament within a sarcomere that is pulled across myosin during muscle contraction.

Sliding Filament Theory

The contraction model where thin actin filaments slide across thick myosin filaments toward the M line, narrowing the I band and drawing Z lines closer together.

Sarcoplasmic Reticulum

A network of membranous channels within a muscle cell that stores and releases calcium ions to trigger muscle contraction.

Neuromuscular Junction (NMJ)

The anatomical site where a motor neuron's terminal branch meets the motor end plate of a muscle fiber.

Acetylcholine (ACh)

The primary chemical neurotransmitter released at the NMJ that changes the membrane potential of the muscle fiber to produce an action potential.

All-or-None Response

The principle stating that all muscle fibers within a single motor unit contract to their fullest extent, or not at all, when stimulated.

Motor Unit Recruitment (Graded Response)

The mechanism by which the nervous system regulates contraction force by altering the number of active motor units.

Aerobic Respiration

ATP production process taking place in cell mitochondria that requires glucose and oxygen to generate sustained muscular energy.

Anaerobic Respiration

Energy pathway operating without oxygen that converts glucose into pyruvic acid and then lactic acid when available oxygen is depleted.

Oxygen Debt

The deficit incurred during intense exercise due to lactic acid accumulation, requiring subsequent oxygen intake to transport lactic acid to the liver for conversion back to glucose.

Type I Muscle Fibers (Slow Twitch)

Red muscle fibers with slow contraction velocity, high fatigue resistance, and rich supplies of myoglobin, capillaries, and mitochondria; common in postural muscles.

Type II Muscle Fibers (Fast Twitch)

White muscle fibers with high-velocity contraction power that fatigue rapidly and rely on stored glycogen and creatine phosphate; common in phasic muscles.

Postural Muscles

Stabilizing muscles with a high proportion of Type I fibers that support the body against gravity and tend to tighten or shorten under stress.

Phasic Muscles

Movement-producing muscles containing a high proportion of Type II fibers that respond rapidly and tend to become inhibited or weakened under stress.

Muscle Origin

The tendon attachment site anchored to a relatively immovable or stable skeletal section, usually located proximal or closer to the midline.

Muscle Insertion

The tendon attachment site anchored to a more movable section of the skeleton where action is produced, usually located distally.

Isometric Contraction

A muscle contraction that generates tension and force without changing muscle length or producing joint movement.

Isotonic Contraction

A muscle contraction that alters muscle length and produces movement, subdivided into concentric and eccentric actions.

Prime Mover (Agonist)

The main muscle primarily responsible for generating a specific joint movement.

Antagonist

A muscle that performs the opposite movement of the agonist, relaxing and lengthening while the agonist contracts.

Synergist

A muscle that assists the agonist in executing smooth, coordinated, and graceful movements.

Fixator (Stabil