Transmembrane Transport and Membrane Potential

A comprehensive set of vocabulary flashcards covering transmembrane transport mechanisms, types of diffusion, active transport, and the physiology of membrane potentials as described in the lecture notes.

Selective Permeability

The property of the cell membrane that allows it to regulate the bidirectional exchange of substances and the transfer of ions, favoring the appearance of electric currents.

Carrier Proteins (Cărăuși)

Membrane proteins involved in facilitated diffusion and active transport by changing their conformation to move substances across the membrane.

Passive Transport

Transmembrane movement that occurs without energy ($ATP$) consumption, including diffusion, osmosis, and facilitated diffusion.

Diffusion

The disordered and permanent movement of molecules or ions that favors the uniform distribution of substances in a solution or gas based on a concentration gradient.

Liposoluble Molecules

Non-polarized molecules that can traverse the cell membrane via diffusion, including oxygen ($O_2$), cortisol, estrogen, progesterone, testosterone, and aldosteron.

Osmosis

The process of diffusion of water (solvent) from a more dilute solution to a more concentrated solution through a semipermeable membrane.

Osmotic Pressure

The force applied to prevent osmosis, which is directly proportional to the number of dissolved particles in the solution.

Facilitated Diffusion

A specific, saturable, and competitive type of passive transport that moves large, polarized organic molecules along their concentration gradient with the help of carrier proteins.

Active Transport

Energy-consuming movement of molecules or ions against their concentration gradient, often involving the hydrolysis of $ATP$ into $ADP$ and $P_i$.

Primary Active Transport

A type of transport where the carrier protein (pump) consumes energy directly from the hydrolysis of $ATP$.

Secondary Active Transport (Cotransport)

A mechanism where the transfer of a molecule against its gradient is powered by the energy of another substance moving along its own concentration gradient.

Endocytosis

The process of engulfing external material into the cell within vesicles formed by the invagination of the plasmalemma; examples include phagocytosis and pinocytosis.

Exocytosis

The process by which intracellular content is captured in vesicles that fuse with the plasmalemma to release substances to the exterior of the cell.

Resting Membrane Potential

The unequal distribution of charges across the membrane in an unstimulated cell, typically ranging between $-65\,mV$ and $-85\,mV$.

Sodium-Potassium Pump ($Na^+/K^+$ Pump)

An active transporter that maintains constant ionic concentrations by reintroducing $2\,K^+$ ions into the cell in exchange for expelling $3\,Na^+$ ions.

Action Potential (AP)

A temporary modification of the membrane potential generated by electrical currents following the passage of ions through specific membrane channels.

Threshold Potential (Potențial prag)

The critical level to which the membrane potential must be reduced to trigger rapid, spontaneous depolarization and an "all or nothing" response.

Ascending Slope (Depolarization Phase)

The stage of an action potential caused by increased membrane permeability to $Na^+$ through voltage-dependent channels, changing the potential from $-65\,mV$ to $+40\,mV$.

Descending Slope (Repolarization Phase)

The return of the membrane potential toward its resting value, caused by the opening of voltage-dependent $K^+$ channels and the expulsion of $K^+$ from the cell.

Absolute Refractory Period (PRA)

The time interval during which no new action potential can be generated, regardless of stimulus strength, because $Na^+$ channels cannot be activated.

Relative Refractory Period (PRR)

An interval where a second action potential can be triggered by a sufficiently strong stimulus, though it will have a lower speed and amplitude.

Contractility

The property of muscle cells to transform the chemical energy of compounds into mechanical energy.

Secretory Activity

The process by which cells produce and export protein or lipid substances into the internal environment (endocrine) or external environment (exocrine).