BIOL 651 Chapter 1-4 Content Review Set

EQUILIBRIUM POTENTIAL

This potential is the electrical potential difference across a cell membrane that exactly balances the concentration gradient for a specific ion.

Reversal potential

The potential at which the ion changes its direction of flow, which is the same as the equilibrium potential for that ion.

MEMBRANE POTENTIAL

This potential is a weighted average of the equilibrium potentials for all ions to which the membrane is permeable.

Measurement of membrane potential

What does this accomplish?: one electrode is placed inside the cell and the other outside the cell.

Sodium-potassium pump (Na+/K+ pump)

Contributes to the resting potential but does not solely determine it; the resting potential is mainly determined by the movement of ions (especially K+) through leak channels.

Concentration gradient

The difference in the concentration of a specific ion across the cell membrane.

Macrophages

these are larger immune cells, not glial cells.

Microglia

These are glial cells that act as the resident immune cells of the central nervous system.

Schwann Cells

Glial cells that provide myelination to peripheral neurons.

Astrocytes

A type of glial cell involved in supporting neurons and maintaining the blood-brain barrier.

Oligodendrocytes

Glial cells that myelinate neurons in the central nervous system.

Voltage Clamp Technique

allows membrane potential to be changed when measuring ion currents.

Synaptic Potential

Neurons experience them when neurotransmitters bind to their receptors.

Threshold Potential

The potential that must be reached to trigger an action potential.

Membrane Potential

A reasonable value for the membrane potential in the axon at a location 1 mm away from the point of current injection is -60 mV.

Nernst Constant

+58 mV is only a simplified approximation under standard temperature conditions, not a fundamental constant like the others.

Equilibrium Potential for Calcium Ions

Is measured at +145 mV in a squid giant axon.

Rising phase

This is initiated when the membrane potential reaches the threshold potential, causing voltage-gated Na+ channels to open. Na+ ions rush into the cell, causing the membrane potential to become more positive (depolarization).

Overshoot phase

As the membrane potential becomes more positive than 0 mV, it overshoots, reaching its peak. At this point, the inside of the neuron is more positively charged compared to the outside.

Falling phase

After the overshoot, voltage-gated Na+ channels close, and voltage-gated K+ channels open. K+ ions exit the cell, causing repolarization, or a return to a more negative membrane potential.

Undershoot phase

This occurs when the membrane potential briefly becomes more negative than the resting membrane potential due to the continued efflux of K+. Eventually, K+ channels close, and the membrane potential returns to its resting state.

K+ selective permeability

If the membrane suddenly becomes selectively permeable to K+ (but not Cl-), K+ will begin to move down its concentration gradient into the other compartment, leaving Cl- behind. This will generate a membrane potential, with the compartment where KCl was initially added becoming negatively charged relative to the other compartment.

Effect of KCl on resting potential

Adding KCl to the external medium will increase the concentration of K+ outside the neuron. Since K+ plays a major role in establishing the resting membrane potential, increasing external K+ will reduce the gradient for K+ efflux, leading to a less negative (depolarized) resting potential.

Effect of NaCl on resting potential

Adding NaCl to the external medium will have less of an effect on the resting potential because the membrane is relatively impermeable to Na+ at rest.

Reason for negative resting potential

Neurons have a negative resting membrane potential because there is an unequal distribution of ions across the membrane. Specifically, K+ ions tend to leak out of the cell due to the high internal concentration, while the membrane is less permeable to Na+, which is concentrated outside.

Action potentials vs. synaptic potentials

Action potentials are 'all-or-none' responses, meaning they either occur fully or not at all once the threshold is reached. In contrast, synaptic potentials are graded, meaning their size is proportional to the strength of the stimulus.

Stimulus strength encoding in graded potentials

Stimulus strength is encoded by the amplitude of the potential: a stronger stimulus results in a larger change in membrane potential.

Stimulus strength encoding in action potentials

stimulus strength is encoded by the frequency of the potentials: a stronger stimulus leads to more frequent action potentials.

Electrochemical equilibrium

occurs when the electrical and chemical forces driving ion movement across a membrane are equal and opposite, resulting in no net movement of ions.

Active transporters

Proteins that use energy (typically from ATP) to move ions against their concentration gradient.

Equilibrium potential

The membrane potential at which the net flow of a particular ion is zero, as calculated by the Nernst equation.

Goldman equation

A mathematical formula used to calculate the membrane potential based on the relative permeabilities and concentrations of multiple ions.

Nernst equation

An equation used to calculate the equilibrium potential for a single ion based on its concentration inside and outside the cell.

Receptor potentials

Graded changes in membrane potential in response to a stimulus, typically occurring at sensory receptors.

Saltatory conduction

The process by which action potentials jump from one node of Ranvier to the next along a myelinated axon.

Squid giant axons

Conduct action potentials faster primarily because of their large diameter, which reduces internal resistance to the flow of current.

Propagation direction of action potentials

Typically propagates in one direction because they originate at one end of the axon and Na+ channels become refractory after activation.

Conduction velocities in neurons

Large-diameter axons generally outperform small ones due to lower internal resistance.

Type Aα neurons

Tend to have longer internodes compared to Aβ neurons.

Tetraethylammonium ions

A chemical that blocks potassium channels, used experimentally to study the role of K+ in action potentials.

Tetrodotoxin (TTX)

A toxin that blocks sodium channels, preventing action potentials, often used to study Na+ currents.

Voltage clamp technique

A method used to maintain a set membrane voltage to study the role of different ions in generating action potentials.

PATCH CLAMP

The patch clamp method allows the study of ion channels in small patches of membrane, offering more localized control compared to the classic voltage clamp, which measures currents across the entire cell membrane.

VOLTAGE CLAMP

A technique that measures total ionic currents across the entire cell membrane.

Cell-attached patch clamp

Used for studying ion channels without disturbing the intracellular environment.

Whole-cell patch clamp

Allows measurement of the electrical properties of the entire cell.

Inside-out patch clamp

A technique that allows researchers to manipulate and study the internal environments of the ion channel.

Outside-out patch clamp

A technique that allows researchers to manipulate and study the external environments of the ion channel.

ION PUMP

Actively transports ions across a membrane using energy, usually from ATP, moving ions against their concentration gradient.

ION ANTIPORTER

A type of cotransporter that moves two or more ions in opposite directions without direct energy expenditure, often relying on the gradient of one ion to drive the movement of another.

CO-TRANSPORTER

Moves ions or molecules across the membrane simultaneously, often using the concentration gradient of one ion to transport another ion or molecule.

Sodium-Calcium Exchanger Function

It removes excess Ca2+ from a neuron.

Na+/Ca2+ Exchanger Mechanism

The Na+/Ca2+ exchanger uses the sodium gradient to expel calcium from the neuron.

Nicotinic Acetylcholine Receptor Effect

The cell would be excited (more likely to produce an action potential).

ATPase pumps

Transporters that hydrolyze ATP to pump ions (e.g., Na+/K+ pump).

Ligand-gated ion channels

Channels that open or close in response to binding of a chemical ligand.

Macroscopic currents

Ion currents measured across large regions of membrane, reflecting the activity of many ion channels.

EPP (End-Plate Potential)

A local depolarization at the neuromuscular junction that occurs when acetylcholine binds to its receptor on the postsynaptic membrane, leading to the opening of ion channels and a subsequent influx of sodium ions.

IPSP (Inhibitory Postsynaptic Potential)

A postsynaptic potential that makes the neuron less likely to fire an action potential, usually caused by the influx of Cl⁻ or the efflux of K⁺.

EPSP (Excitatory Postsynaptic Potential)

A postsynaptic potential that increases the likelihood of a neuron firing an action potential, generally caused by Na⁺ influx.

Reversal Potential

The membrane potential at which there is no net flow of a particular ion through its channel. At this potential, the electrical force driving the ion in one direction is exactly balanced by the concentration gradient driving it in the opposite direction.

SNARE Proteins

Proteins involved in the docking and fusion of vesicles at the membrane for neurotransmitter release.

Synaptotagmin

A calcium sensor that triggers vesicle fusion but is not a SNARE protein.

Connexons

Part of gap junctions in electrical synapses, whose conductance can vary depending on factors such as voltage, pH, or calcium concentration.

Vesicle Docking

The process by which synaptic vesicles attach to the presynaptic membrane in preparation for neurotransmitter release.

Clathrin

A protein found at chemical synapses involved in vesicle recycling.

Coated pits

Regions involved in endocytosis and vesicle recycling, found at chemical synapses.