Muscle Tissue and Naming Organization

Comprehensive vocabulary flashcards covering skeletal muscle anatomy, physiology, energetics, naming conventions, and specific muscle groups including smooth muscle differences.

Excitability

The ability to respond to a stimulus, which changes the electrical membrane potential.

Conductivity

The ability to conduct (send) an electrical signal along the muscle cell membrane.

Contractility

The ability of muscle fibers to shorten when actin and myosin filaments slide past one another, producing movement.

Extensibility

The ability of muscle tissue to be stretched without damage.

Elasticity

The ability of a muscle to return to its original length after stretching or shortening.

Epimysium

Dense irregular connective tissue that surrounds the entire skeletal muscle to protect it and maintain its shape.

Perimysium

Dense irregular connective tissue that surrounds each fascicle and contains blood vessels and nerves.

Endomysium

Areolar connective tissue that surrounds each individual muscle fiber, providing electrical insulation and supporting capillaries.

Fascicle

A bundle of muscle fibers organized and surrounded by perimysium.

Sarcolemma

The plasma (cell) membrane of a muscle fiber that contains voltage-gated ion channels and conducts action potentials.

T-Tubules (Transverse Tubules)

Deep invaginations of the sarcolemma that carry electrical signals deep into the muscle fiber to reach the sarcoplasmic reticulum.

Sarcoplasm

The cytoplasm of the muscle cell containing organelles, contractile proteins, glycogen, myoglobin, and mitochondria.

Myoglobin

A red, oxygen-binding protein found in the sarcoplasm that acts as an oxygen reserve for aerobic ATP production.

Glycogen

The stored form of glucose found in the sarcoplasm that serves as the muscle's energy reserve for making ATP.

Sarcomere

The functional unit of contraction within a myofibril, consisting of organized actin and myosin myofilaments.

Myosin

The thick filament consisting of protein bundles with heads that contain myosin ATPase and form crossbridges with actin.

Actin

The thin filament containing myosin-binding sites where myosin heads attach during contraction.

Tropomyosin

A regulatory protein that covers the myosin-binding sites on actin at rest to prevent contraction.

Troponin

A regulatory protein that binds $Ca^{2+}$ and changes shape to move tropomyosin away from actin's binding sites.

Sarcoplasmic Reticulum (SR)

The storage site for calcium ($Ca^{2+}$) in skeletal muscle cells.

Oxygen Deficit

The difference between the oxygen required during exercise and the oxygen actually available, which results in anaerobic metabolism.

Creatine Phosphate (CP)

A high-energy molecule in muscle fibers that quickly donates a phosphate group to ADP to regenerate ATP; provides energy for approximately $10–15$ seconds.

Anaerobic Glycolysis

The breakdown of glucose without oxygen that produces ATP quickly and results in the byproduct lactic acid (lactate).

Motor Unit

One somatic motor neuron and all the skeletal muscle fibers it controls.

Recruitment

The process of activating additional motor units to increase the force of muscle contraction.

All-or-None Principle

The concept that every muscle fiber in a motor unit contracts completely or not at all if the stimulus reaches threshold.

Muscle Twitch

The response of a muscle fiber to a single stimulus, consisting of latent, contraction, and relaxation phases.

Wave Summation

Increased muscle tension occurring when a second stimulus arrives before the muscle has completely relaxed from the first twitch.

Complete (Fused) Tetanus

A sustained, maximal contraction without any relaxation between stimuli due to very rapid repeated stimulation.

Isometric Contraction

A contraction in which the muscle develops tension but the length remains the same and no movement occurs.

Isotonic Contraction

A contraction in which muscle tension overcomes resistance, causing the muscle to change length and produce movement.

Concentric Contraction

A type of isotonic contraction where the muscle shortens while producing force.

Eccentric Contraction

A type of isotonic contraction where the muscle lengthens while still producing tension to control or slow movement.

Slow Oxidative (SO) Fibers

Type I (red) fibers that contract slowly, resist fatigue, and use aerobic respiration; suited for endurance and posture.

Fast Glycolytic (FG) Fibers

Type IIx (white) fibers that contract very quickly and powerfully but fatigue rapidly; rely on anaerobic metabolism.

Origin

The attachment site of a muscle on the less movable bone that remains relatively stationary during contraction.

Insertion

The attachment site of a muscle on the more movable bone that is pulled toward the origin during contraction.

Pennate

A feather-like fascicle arrangement where fibers attach obliquely to a tendon, producing greater force but less range of motion.

Calmodulin

The regulatory protein in smooth muscle that binds to calcium to initiate contraction, replacing the role of troponin.

Aponeurosis

A broad, flat sheet of dense regular connective tissue that attaches muscle to bone or other muscle.

Retinaculum

A thickened band of deep fascia that holds tendons close to bones as they cross joints, preventing "bowstringing."

Suprahyoid Muscles

A group of muscles (digastric, geniohyoid, mylohyoid, stylohyoid) located above the hyoid bone that elevate it during swallowing.

Infrahyoid Muscles

A group of muscles (omohyoid, sternohyoid, sternothyroid, thyrohyoid) located below the hyoid bone that depress it or the thyroid cartilage.

Anterior Forearm Compartment

The muscle compartment responsible for wrist and finger flexion and forearm pronation.

Posterior Forearm Compartment

The muscle compartment responsible for wrist and finger extension and forearm supination.

Lateral Rectus

An extraocular eye muscle innervated by the abducens nerve (CN VI) that moves the eye laterally (abduction).

Superior Oblique

An extraocular eye muscle innervated by the trochlear nerve (CN IV) that moves the eye down and out.