Physiology Midterm Study Guide: Foundational Concepts, Action Potentials & Muscle Physiology

Comprehensive vocabulary flashcards covering foundational physiological mechanisms, cell membrane transport, bioelectrical properties, synaptic signaling, excitation-contraction coupling, and autonomic divisions.

Physiology

The study of how body parts work and maintain life.

Homeostasis

The maintenance of a relatively stable internal environment despite changing conditions.

Negative Feedback

A physiological control mechanism in which a response reverses the original change; examples include body temperature and blood glucose regulation.

Positive Feedback

A physiological control mechanism in which a response amplifies the original change until an endpoint is reached; examples include labor contractions and blood clotting.

Intracellular Fluid

Fluid located inside cells, accounting for about two-thirds of total body water in a typical adult.

Extracellular Fluid

Fluid located outside cells, comprising interstitial fluid and blood plasma.

Set Point

A target range monitored by a physiological control system that can change with circumstances.

Phospholipid Bilayer

The fundamental structure of the cell membrane, consisting of hydrophilic heads facing water and hydrophobic tails facing inward.

Diffusion

The net movement of particles from an area of higher concentration to lower concentration without using ATP.

Facilitated Diffusion

Movement of substances down a concentration gradient through a membrane channel or carrier without using ATP.

Active Transport

The movement of substances against an electrochemical gradient using energy directly or indirectly.

Sodium-Potassium Pump

A membrane transport protein that uses ATP to export $3\,\text{Na}^+$ and import $2\,\text{K}^+$ per cycle to maintain ion gradients.

Osmosis

The net movement of water across a selectively permeable membrane toward a higher effective solute concentration.

Hypotonic Solution

An external solution with a lower solute concentration than the cell, causing water to enter, swell, and potentially lyse an animal cell.

Hypertonic Solution

An external solution with a higher solute concentration than the cell, causing water to leave and the animal cell to shrink.

Isotonic Solution

A solution that produces no net water shift, allowing cell volume to remain approximately constant.

Membrane Potential

The electrical voltage difference measured across the inside and outside of a cell membrane.

Resting Membrane Potential

The electrical voltage across the membrane of an unstimulated cell, typically around $-70\,\text{mV}$ in many neurons.

Depolarization

A shift in membrane potential making it less negative, often caused by $\text{Na}^+$ influx during an action potential.

Repolarization

The return of the membrane potential toward a negative resting value, often driven by $\text{K}^+$ exiting the cell.

Hyperpolarization

A condition where the membrane potential becomes more negative than its normal resting potential.

Threshold

The critical membrane voltage at which enough voltage-gated $\text{Na}^+$ channels open to initiate an action potential.

All-or-None Principle

The property stating that once threshold is reached, an action potential fires at full characteristic amplitude; stronger stimuli raise firing frequency rather than spike height.

Absolute Refractory Period

The timeframe during which a second action potential cannot fire because most voltage-gated $\text{Na}^+$ channels are inactivated.

Relative Refractory Period

The timeframe following an action potential during which a stronger-than-usual stimulus is required to initiate another spike.

Saltatory Conduction

The rapid propagation of action potentials along a myelinated axon as the impulse jumps between nodes of Ranvier.

Dendrites

Branching neuron processes whose primary role is to receive incoming signals.

Axon

A neuronal projection specialized to conduct action potentials away from the cell body toward synaptic terminals.

Synapse

A specialized junction where an electrical or chemical signal is transmitted from one cell to another.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization of the postsynaptic membrane that brings the neuron closer to threshold and makes firing more likely.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization of the postsynaptic membrane that makes action potential firing less likely.

Temporal Summation

The integration of postsynaptic potentials generated by repeated signals occurring close together in time.

Spatial Summation

The integration of postsynaptic potentials originating simultaneously from multiple distinct synaptic sites.

Acetylcholine (ACh)

The primary neurotransmitter released by somatic motor neurons at the neuromuscular junction.

Acetylcholinesterase

An enzyme present in the synaptic cleft that terminates signaling at the neuromuscular junction by hydrolyzing acetylcholine.

Muscle Fiber

A single, elongated, multinucleated skeletal muscle cell.

Myofibril

A rodlike cylindrical contractile element inside a muscle fiber composed of repeating sarcomeres.

Sarcomere

The functional contractile unit of striated muscle tissue, bounded between two Z discs.

Thick Filaments

Myofilaments primarily composed of the protein myosin.

Thin Filaments

Myofilaments composed of actin along with the regulatory proteins troponin and tropomyosin.

Sarcoplasmic Reticulum (SR)

A specialized smooth endoplasmic reticulum in muscle fibers that stores and releases $\text{Ca}^{2+}$ to initiate contraction.

T-Tubules (Transverse Tubules)

Invaginations of the muscle cell membrane (sarcolemma) that transmit action potentials deep into the muscle fiber interior.

A Band

The dark striation region of a sarcomere spanning the entire length of thick filaments, which maintains a constant length during contraction.

I Band

The light striation region of a sarcomere consisting exclusively of thin filaments, which narrows during muscle contraction.

Sliding Filament Model

The mechanism of muscle contraction whereby myosin heads pull thin filaments toward the sarcomere center, causing them to slide past thick filaments without shortening individual filaments.

Troponin

A regulatory protein complex on thin filaments that binds $\text{Ca}^{2+}$, causing a conformational shift in tropomyosin to unmask myosin-binding sites on actin.

Power Stroke

The mechanical step in cross-bridge cycling where the release of inorganic phosphate (and subsequently ADP) from energized myosin pulls the actin filament.

Rigor Mortis

Postmortem muscle stiffness caused by ATP depletion, which prevents the detachment of myosin heads from actin filaments.

Motor Unit

A single somatic motor neuron and all the skeletal muscle fibers it innervates.

Motor Unit Recruitment

The sequential activation of additional motor units by the nervous system to produce greater contractile force.

Summation (Muscle)

The increase in contractile force that occurs when successive stimuli arrive before the muscle fiber has completely relaxed.

Tetanus (Physiological)

A sustained, smooth maximal muscle contraction produced by high-frequency stimulation without intervening relaxation periods.

Isometric Contraction

A muscle contraction that develops internal tension while overall muscle length remains unchanged.

Isotonic Contraction

A muscle contraction where tension remains constant while muscle length changes, encompassing concentric and eccentric actions.

Concentric Contraction

An active isotonic contraction in which the muscle shortens while generating tension to overcome a load.

Eccentric Contraction

An active isotonic contraction in which the muscle lengthens while resisting or controlling an applied load.

Type I Muscle Fibers

Slow oxidative muscle fibers characterized by high fatigue resistance, abundant mitochondria, and specialization for endurance.

Type II Muscle Fibers

Fast muscle fibers capable of generating high power outputs that fatigue more rapidly depending on the specific subtype.

Intercalated Discs

Specialized cell junctions connecting branched cardiac muscle cells, containing gap junctions that permit rapid electrical transmission between cells.

Calmodulin

A cytoplasmic calcium-binding regulatory protein that activates myosin light-chain kinase (MLCK) to trigger contraction in smooth muscle.

Somatic Motor System

The motor division of the peripheral nervous system providing voluntary and reflex control over skeletal muscles.

Autonomic Nervous System

The visceral motor division regulating involuntary activities of cardiac muscle, smooth muscle, and glandular tissue.

Sympathetic Nervous System

The autonomic division responsible for fight-or-flight responses, characterized by elevated heart rate, bronchodilation, and energy mobilization.

Parasympathetic Nervous System

The autonomic division responsible for rest-and-digest responses, acting to lower heart rate and stimulate digestive processes.

Reflex Arc

The neural circuit underlying a reflex, typically ordered as: receptor, sensory neuron, integration center, motor neuron, and effector.

Graded Potentials

Local changes in membrane voltage that vary continuously in amplitude, can summate, and decay with distance along the membrane.