BIOL 201 Exam 2: Membrane Potentials and Action Potentials

Vocabulary practice flashcards covering membrane potential concepts, neuron anatomy, local potentials, voltage-gated channel states, action potential events, refractory periods, and propagation.

Membrane potential

The electrical gradient caused by the separation of electrical charges across a cell membrane.

$Na^+/K^+$ pump

A cell membrane mechanism that maintains net $Na^+$ and $K^+$ ion concentrations by keeping high $Na^+$ outside the cell and high $K^+$ inside the cell.

Electrical gradient

A gradient created because the charge inside the cell is negative, causing opposite charges to attract into the cell and like charges to be repelled.

Chemical gradient

A concentration gradient where ions move across the membrane from an area of higher concentration to an area of lower concentration.

Electrochemical gradient

The net sum of the electrical gradient and chemical gradient acting on a specific ion.

Leak channel

A type of ion channel across the cell membrane that is always open.

Ligand-gated channel

An ion channel that opens or closes upon the binding of a specific chemical ligand.

Voltage-gated channel

An ion channel that opens or closes in response to changes in membrane potential (voltage).

Equilibrium potential

The specific membrane potential for an ion that creates an electrical gradient equal and opposite to its chemical gradient, resulting in an electrochemical gradient of $0$.

Sodium ($Na^+$) equilibrium potential

The equilibrium potential for sodium ions, which is equal to $+60\,mV$.

Potassium ($K^+$) equilibrium potential

The equilibrium potential for potassium ions, which is equal to $-94\,mV$.

Resting membrane potential

The membrane potential when a cell is not being stimulated, measured at $-70\,mV$ in resting neurons.

Cell body

The part of a neuron that carries out its metabolic functions.

Axon

The neuron structure that generates and conducts action potentials, usually carrying information away from the cell body.

Dendrite

The neuron structure that receives information from other neurons and carries information toward the cell body.

Myelin sheath

An insulating membrane surrounding an axon that speeds up the conduction of action potentials.

Myelin sheath gap

Gaps present between myelin sheaths surrounding an axon.

Axon terminal

The end structure of an axon that contains vesicles filled with neurotransmitters.

Axon hillock

The cone-shaped region of the neuron cell body where the axon originates.

Initial segment (trigger zone)

The region of a neuron where an action potential is generated.

Depolarization

A change in membrane potential that makes it more positive or less negative due to positive charges entering the cell.

Repolarization

A change in membrane potential that makes it more negative or less positive as positive charges leave or negative charges enter the cell.

Hyperpolarization

A change in membrane potential where the cell temporarily becomes more negative than its resting membrane potential.

Threshold

The level of membrane potential depolarization ($-55\,mV$) required to trigger an action potential.

Local potentials

Small, local, reversible changes in a cell's membrane potential used for short-distance signaling.

Resting state (voltage-gated channel)

The channel state in which the activation gate is closed.

Activated state (voltage-gated channel)

The channel state in which the activation gate is open.

Inactivated state (voltage-gated $Na^+$ channel)

The channel state unique to $Na^+$ channels in which the inactivation gate is closed even though the activation gate is open.

All-or-none principle

The rule that if membrane potential reaches threshold, an action potential fires completely, and if threshold is not reached, nothing happens.

Absolute refractory period

The timeframe during an action potential when no new action potential can occur because $Na^+$ channels are activated or inactivated.

Relative refractory period

The timeframe following the absolute refractory period during which an extra strong stimulus can trigger a new action potential.

Saltatory conduction

The process of action potential propagation along a myelinated axon where depolarization jumps from gap to gap.