Transport of Substances Through the Cell Membrane and Action Potentials (BMS 595)

Vocabulary flashcards covering key terms related to membrane transport, membrane potentials, and action potentials as presented in the lecture notes.

Passive transport

Movement of substances across a membrane without energy input, down their concentration gradient.

Active transport

Movement that requires energy (usually ATP) to move substances against their concentration gradient.

Diffusion

Net movement of molecules down their concentration gradient due to kinetic energy; no ATP required.

Facilitated diffusion

Passive diffusion through membrane proteins (channels or carriers) down a concentration gradient.

Osmosis

Diffusion of water across a semipermeable membrane toward higher solute concentration.

Filtration

Movement of water and solutes driven by a hydrostatic pressure gradient.

Endocytosis

Bulk transport into the cell via vesicle formation.

Exocytosis

Bulk transport out of the cell via vesicle fusion with the membrane.

Phagocytosis

Endocytosis of solid particles (cell eating).

Pinocytosis

Endocytosis of liquids (cell drinking).

Na+/K+-ATPase

Sodium-potassium pump; uses ATP to move 3 Na+ out and 2 K+ in, helping maintain resting potential.

Resting membrane potential

Baseline voltage across the cell membrane, typically about -70 to -90 mV, mainly due to K+ gradient and Na+/K+-ATPase activity.

Equilibrium potential

Membrane potential at which there is no net ion flux for a given ion.

Nernst equation

Relation used to calculate the equilibrium potential for a specific ion.

Potassium gradient

The concentration gradient of K+ across the membrane; major determinant of resting potential.

Sodium gradient

Higher Na+ concentration outside the cell than inside.

Chloride gradient

Distribution of Cl- across the membrane; generally a smaller influence on resting potential.

Organic anions

Negatively charged intracellular components that cannot cross the membrane and contribute to intracellular negativity.

Action potential

Rapid, large change in membrane potential that travels along the membrane; all-or-none.

Depolarization

Phase of an action potential when Na+ influx makes the interior more positive.

Repolarization

Phase following depolarization where Na+ channels inactivate and K+ channels open, restoring negative potential.

Hyperpolarization

Membrane potential becomes more negative than resting due to continued K+ efflux.

Threshold potential

Critical depolarization level needed to trigger an action potential.

All-or-none

Property that an action potential has a consistent amplitude; its occurrence is not dependent on stimulus strength.

Voltage-gated channels

Ion channels opened or closed by changes in membrane potential (e.g., Na+ and K+ channels during AP).

Channel proteins

Proteins that form pores for ions to pass; can be gated.

Carrier proteins

Proteins that bind and transport substances by changing shape during translocation.

Sodium-glucose symporter

Secondary active transporter using Na+ gradient to move glucose into the cell (symport).

Antiporter

Secondary active transporter moving two different substances in opposite directions.

Graded potential

Small, variable changes in membrane potential; amplitude declines with distance from the source.

Membrane potential

Voltage difference across the cell membrane.

Fluid-mosaic model

Structure of the plasma membrane as a fluid phospholipid bilayer with embedded proteins.

Plasma membrane components

Phospholipids, cholesterol, and proteins that compose the membrane.

Extracellular fluid (ECF)

Fluid outside cells; includes plasma and interstitial fluid; about one-third of body fluids.

Intracellular fluid (ICF)

Fluid inside cells; about two-thirds of body fluids.

Interstitial fluid

Fluid between the circulatory system and cells; ~75% of the ECF.

Permeable vs impermeable

Permeable membranes allow passage of substances; impermeable membranes do not.

Membrane potential

Electrical potential difference across the cell membrane; usually negative inside.

Threshold and action potential frequency

AP frequency encodes stimulus intensity when amplitude is fixed by the all-or-none law.