Chapter 2: Homeostasis, Bioenergetics, and Skeletal Muscle Physiology

Vocabulary flashcards covering core concepts of homeostasis, bioenergetics, metabolic pathways, nerve activation, muscle microanatomy, excitation-contraction coupling, fiber types, and dynamic muscle actions.

Homeostasis

The dynamic physiological process by which a living system maintains a relatively constant internal environment despite changes in the external environment.

Claude Bernard

The 19th-century French physiologist who noted that warm-blooded animals establish and protect an internal environment that is more hospitable to cells than the outside environment.

Walter Cannon

The American physiologist who coined the term "homeostasis" and authored the 1932 book The Wisdom of the Body.

Negative Feedback Loop

The primary mechanism of homeostatic regulation in which a change in a controlled variable triggers physical and conceptual mechanisms that reverse or minimize the initial variation.

Sensor

The tangible physical component of a negative feedback loop that detects or senses the actual value of a regulated variable.

Integrator

The physical component of a negative feedback loop (the brain in biological systems) that interprets sensor input and sends corrective instructions to the effector.

Effector

The physical component of a negative feedback loop that receives signals from the integrator and acts directly to change or restore the regulated variable.

Set Point

The conceptual baseline or target value that a homeostatically controlled system works to maintain.

Error Signal

The conceptual parameter representing the deviation between the actual value of a variable and its target set point value.

Threshold

The conceptual limit representing the amount of deviation from a set point required before the integrator signals an effector to act.

Stressor

Any internal or external condition or process with the potential to push a homeostatically controlled variable beyond its acceptable physiological limits.

Steady-state

A condition in which a physiological parameter remains constant over a period of time, regardless of whether that parameter is homeostatically regulated.

ATP (Adenosine Triphosphate)

The universal chemical energy currency of the body, composed of an adenine molecule, a ribose sugar, and three linked phosphate groups.

Karl Lohmann

The scientist who discovered ATP in 1929.

Glycogen

The polysaccharide molecule that serves as the storage form of carbohydrates in animals, located primarily in the liver and skeletal muscle.

Triglyceride

The storage form of fat in plants and animals, consisting of three fatty acid molecules attached to a single glycerol molecule.

De-amination

The enzymatic removal of nitrogen from an amino acid, required before protein can be utilized as a metabolic energy source.

Creatine Phosphate

A high-energy molecule stored in skeletal muscle cells that rapidly donates a phosphate group to ADP to synthesize ATP anaerobically.

Glycolysis

The enzymatic pathway that breaks down glucose or stored glycogen into two three-carbon pyruvic acid molecules, yielding a net of $2\,\text{ATP}$.

Lactate Dehydrogenase

The enzyme that catalyzes the reversible conversion of pyruvic acid to lactic acid.

Gluconeogenesis

The metabolic process carried out exclusively by the liver that converts non-carbohydrate precursors, such as lactate, back into glucose.

Krebs Cycle

The mitochondrial metabolic cycle that oxidizes acetyl-CoA, producing carbon dioxide, electrons, and the reducing equivalents $\text{NADHH}^+$ and $\text{FADH}_2$.

Electron Transport Chain

A sequence of electron-carrier molecules embedded in the inner mitochondrial membrane that uses oxygen as the final electron acceptor to drive aerobic ATP synthesis.

Octet Rule

The chemical principle stating that atoms interact in ways that achieve eight electrons in their outer valence shell.

Afferent Nerves

Sensory nerves in the peripheral nervous system that conduct impulses from peripheral receptors toward the central nervous system.

Efferent Nerves

Motor nerves in the peripheral nervous system that conduct impulses away from the central nervous system to target effectors.

Somatic Motor Nerves

Efferent motor nerves that innervate voluntary skeletal muscles.

Autonomic Motor Nerves

Efferent motor nerves that supply involuntary tissue structures, including cardiac muscle, smooth muscle, and glands.

Motor Unit

A functional unit consisting of a single somatic motor neuron and all the individual skeletal muscle fibers innervated by its axon branches.

Neuromuscular Junction

The specialized synapse or communication site between a somatic motor neuron axon terminal and a skeletal muscle cell membrane.

Acetylcholine (ACH)

The specific neurotransmitter released by somatic motor neurons to initiate electrical stimulation of skeletal muscle fibers.

Depolarization

A rapid electrical shift across a cell membrane from a negative internal potential to a positive potential caused by an influx of sodium ions ($\text{Na}^+$).

Sarcolemma

The plasma membrane surrounding an individual skeletal muscle cell or fiber.

T-tubules

Transverse invaginations of the sarcolemma that extend deep into the muscle fiber to allow action potentials to penetrate the entire cell.

Sarcoplasmic Reticulum

The smooth endoplasmic reticulum of a muscle cell that acts as a specialized internal storage depot for calcium ions ($\text{Ca}^{2+}$).

Sarcomere

The fundamental repeating contractile unit of a myofibril, defined as the region from one Z-line to the next adjacent Z-line.

Actin

The primary globular protein that polymerizes into double-stranded filaments to form the thin structural filaments of a sarcomere.

Myosin

The motor protein that forms the thick filaments of a sarcomere, containing functional heads that bind to actin to exert pulling force.

Tropomyosin

A ribbon-like regulatory protein associated with thin filaments that obstructs myosin-binding sites on actin during muscle relaxation.

Troponin

A calcium-binding regulatory protein attached to actin and tropomyosin that shifts tropomyosin away from actin binding sites when bound to $\text{Ca}^{2+}$.

Cross-bridge Cycling

The repetitive cyclic mechanism where myosin heads bind actin, perform a power stroke, detach using ATP, and re-cock to produce muscle contraction.

Type I Muscle Fibers

Slow oxidative skeletal muscle fibers with high mitochondrial content, superior aerobic capacity, and maximum resistance to fatigue.

Type IIa Muscle Fibers

Intermediate fast oxidative-glycolytic skeletal muscle fibers possessing fast contraction speeds, moderate aerobic capacity, and mixed metabolic qualities.

Type IIx Muscle Fibers

Fast glycolytic skeletal muscle fibers that exhibit the fastest contraction speed and highest force production, but possess low endurance and few mitochondria.

Hypertrophy

An increase in muscle mass caused by the enlargement of individual muscle cell cross-sectional area in response to resistance training or overload.

Atrophy

A decrease in individual muscle cell size and overall muscle mass resulting from disuse, bed rest, casting, or neural injury.

Concentric Contraction

A dynamic muscle contraction in which the muscle active force production causes the overall muscle length to shorten.

Eccentric Contraction

A dynamic muscle contraction in which the muscle active force production occurs while the overall muscle length is forced to extend or lengthen.

Isometric Contraction

A muscle contraction where active force is developed within the muscle without any change in overall muscle length or joint motion.

Sarcopenia

The progressive, age-related loss of skeletal muscle mass, strength, and function.

Force-velocity Curve

The fundamental physiological property showing that as the velocity of muscle shortening increases, the maximum force capability decreases.