Neurophysiology: Neurons at Rest, Action Potentials, and Synaptic Transmission

Comprehensive vocabulary flashcards covering neurophysiology lecture topics, including ionic basis of resting membrane potential, ion channel types, action potential mechanics and propagation, synaptic transmission, and neurotransmitter systems.

Synaptic transmission

The process by which neurons communicate across distances by releasing chemical messengers called neurotransmitters from their axon terminals to bind receptors on another cell.

Current

The physical movement or flow of charged particles (ions) from one location to another.

Electrical potential

The difference in net total charge between one region and another, also referred to as voltage.

Resting membrane potential

The baseline electrical voltage across a neuronal membrane when at rest, typically measuring approximately $-65\,mV$, indicating the intracellular space is more negative than the extracellular solution.

Diffusional force

The force purely driven by relative particle concentrations that pushes ions down their concentration gradient from regions of high concentration to regions of low concentration until evenly distributed.

Electrostatic force

The electrical attraction or repulsion acting on ions based on charge, causing opposite charges to attract and like charges to repel.

Driving force

The net combination of diffusional and electrostatic forces acting on a specific ion; its strength increases the farther an ion is from its equilibrium point.

Phospholipid bilayer

The structural basis of the neuronal membrane composed of two opposing layers of hydrophilic phosphate heads and hydrophobic lipid tails, which acts as a barrier impermeable to ions on its own.

Leak channels

Membrane-spanning protein channels that remain constitutively open, allowing passive passage of specific ions across the membrane.

Voltage-gated channels

Ion channels that remain closed until the interior of the neuron reaches a specific threshold voltage.

Ligand-gated channels

Ion channels that remain closed until a specific chemical messenger (ligand) binds to the receptor on the channel protein.

Mechanically-gated channels

Ion channels that open only when physically deformed or moved in a way that mechanically opens the pore.

Equilibrium potential ($E_{\text{ion}}$)

The specific membrane potential at which the diffusional and electrostatic forces on a given ion are equal and opposite, resulting in zero net driving force and no net ion flow.

Nernst equation

The mathematical formula used to calculate the equilibrium potential of an ion: $E_{\text{ion}} = 2.303\,\frac{RT}{zF}\,\log\left(\frac{[\text{ion}]_o}{[\text{ion}]_i}\right)$.

Action potential

A rapid and dramatic redistribution of electrical charges across the neuronal membrane (also called a 'spike') that serves as the primary signal for communication between neurons.

Depolarization

A shift in membrane potential making the interior of the cell less negative and moving it closer to zero relative to the extracellular space.

Hyperpolarization

A shift in membrane potential making the interior of the cell more negative, increasing the difference from the extracellular space.

Threshold of excitation

The critical membrane potential—approximately $-55\,mV$—that triggers the opening of voltage-gated sodium channels and initiates an action potential.

Delayed rectifier potassium channels

Voltage-gated potassium channels that open in response to depolarization after a $1\,ms$ delay to rectify and restore the membrane potential back to negative values.

Rising phase

The initial depolarizing upstroke of an action potential triggered at threshold by the opening of voltage-gated sodium channels and the rapid influx of $Na^+$ down its strong electrochemical gradient.

Overshoot phase

The peak segment of the action potential where the membrane potential passes $0\,mV$ toward the $Na^+$ equilibrium potential ($+60\,mV$) before voltage-gated sodium channels inactivate.

Falling phase

The repolarization phase of the action potential during which voltage-gated sodium channels are inactivated and potassium rapidly exits through open delayed rectifier potassium channels.

Undershoot phase

The transient hyperpolarization following an action potential where the membrane potential drops below resting levels, approaching the potassium equilibrium potential of $-80\,mV$.

Absolute refractory period

The period following an action potential during which voltage-gated sodium channels are inactivated and cannot be reopened, preventing another spike from firing and enforcing unidirectional propagation.

Sodium-potassium pump

An active membrane transporter that uses ATP to export $3\,Na^+$ ions and import $2\,K^+$ ions against their concentration gradients, consuming approximately $70\%$ of the brain's ATP.

Rate coding

The neural communication principle stating that neurons convey stimulus strength by changing their frequency or rate of action potential firing, rather than changing the size or shape of individual spikes.

Axon hillock

The specialized conical region at the base of the neuronal soma where action potentials are initiated.

Node of Ranvier

Periodic unmyelinated gaps along an axon where the neuronal membrane is exposed and enriched with voltage-gated sodium channels to regenerate action potentials.

Saltatory conduction

The rapid transmission of an action potential along a myelinated axon, where depolarization jumps from one Node of Ranvier to the next.

Tetrodotoxin

A neurotoxin that completely blocks voltage-gated sodium channels, abolishing the initiation and propagation of action potentials throughout the nervous system.

Electrical synapse

A direct neuronal junction where gap junction channels (formed by connexons) physically link adjacent cells, enabling immediate, bidirectional passive ion passage without chemical messengers.

Chemical synapse

A specialized junction where an action potential triggers the exocytotic release of neurotransmitters across a synaptic cleft to bind postsynaptic receptors.

Synaptic vesicles

Small membrane-bound spheres located in the presynaptic terminal that store neurotransmitter molecules prior to release.

Exocytosis

The calcium-dependent mechanism whereby synaptic vesicle membranes fuse with the presynaptic terminal plasma membrane to release neurotransmitter contents into the synaptic cleft.

Reuptake

The process of clearing neurotransmitters from the synaptic cleft by pumping them back into the presynaptic terminal via specialized plasma membrane transporters.

Ionotropic receptor

A neurotransmitter receptor that contains an intrinsic ion channel (transmitter-gated ion channel) that rapidly opens upon ligand binding, allowing immediate ion flow.

Metabotropic receptor

A G-protein-coupled receptor (GPCR) that, upon ligand binding, activates intracellular G-proteins and secondary messengers to indirectly modulate ion channels and enzymes through multi-step cascades.

Excitatory postsynaptic potential (EPSP)

A transient depolarization of the postsynaptic membrane produced when neurotransmitters open cation-permeable channels, moving the membrane potential closer to threshold.

Inhibitory postsynaptic potential (IPSP)

A transient hyperpolarization of the postsynaptic membrane typically caused by chloride ion ($Cl^-$) influx, moving the membrane potential further from threshold.

Spatial summation

The additive integration of simultaneous postsynaptic potentials generated from multiple different synaptic inputs across the dendritic tree.

Temporal summation

The integration of sequential postsynaptic potentials arriving in rapid succession from a single presynaptic terminal over time.

Glutamate

The primary excitatory neurotransmitter in the brain; synthesized from glutamine by glutaminase, packaged into vesicles by VGLUT, and cleared by excitatory amino acid transporters (EAATs).

Glutamate excitotoxicity

Cellular injury or death caused by excess accumulation of glutamate in the synaptic cleft, leading to toxic overstimulation of postsynaptic receptors.

GABA (gamma-aminobutyric acid)

The primary inhibitory neurotransmitter in the central nervous system; synthesized from glutamate by glutamate decarboxylase (GAD) and packaged into vesicles by VIAAT.

Acetylcholine (ACh)

A neurotransmitter synthesized from choline and acetyl CoA by choline acetyltransferase (ChAT), broken down by acetylcholinesterase, and responsible for muscle contractions at neuromuscular junctions and cognitive processing in the CNS.

Serotonin (5-HT)

A biogenic amine neurotransmitter synthesized from tryptophan via 5-HTP by tryptophan hydroxylase and aromatic L-amino acid decarboxylase; cleared via SERT and involved in mood, appetite, and wakefulness.

Dopamine (DA)

A catecholamine neurotransmitter synthesized from tyrosine via L-DOPA by tyrosine hydroxylase and DOPA decarboxylase; degraded by MAO or COMT and essential for motor control, motivation, and reward.

Nigrostriatal pathway

A dopaminergic pathway originating in the substantia nigra and projecting to the striatum, which is essential for voluntary motor function.

Mesolimbic pathway

A dopaminergic projection running from the ventral tegmental area (VTA) to the nucleus accumbens, central to processing reward, motivation, and salience.

Mesocortical pathway

A dopaminergic circuit extending from the ventral tegmental area (VTA) to the prefrontal cortex, participating in cognition, working memory, and emotional regulation.

Norepinephrine (NE)

A catecholamine synthesized from dopamine inside synaptic vesicles by the enzyme dopamine beta-hydroxylase; regulates arousal, sleep-wake cycles, and cognitive processing.