PSY 106: Action Potentials, Synapses, and Neurotransmitters

Comprehensive vocabulary flashcards covering action potential phases, propagation, synaptic mechanisms, and major neurotransmitter systems based on Lectures 4, 5, and 6.

Tetrodotoxin (TTX)

A toxin that completely blocks voltage-gated sodium ($Na^+$) channels, preventing nerves from firing; it is found in puffer fish and is $1,200 \times$ more potent than cyanide.

Action Potential

A rapid and dramatic change in charge across the membrane, also known as a "spike," which represents an all-or-nothing event used for neuronal communication.

Depolarization

A change in membrane potential where the cell becomes less negative, moving the potential closer to zero.

Hyperpolarization

A change in membrane potential where the cell becomes more negative, moving the potential farther from zero.

Threshold of excitation (Threshold potential)

The membrane potential value, usually around $-55\,mV$, that must be reached to trigger the opening of voltage-gated sodium channels and initiate an action potential.

Voltage-Gated Sodium Channels

Channels that open immediately when the threshold potential is reached, allowing an influx of $Na^+$; they stay open for approximately $1\,ms$ before entering an inactivation period.

Absolute Refractory Period

A brief period (~1 ms) following the opening of voltage-gated sodium channels during which they are inactivated and cannot be reopened, preventing further action potentials.

Rising Phase

The stage of the action potential characterized by the rapid influx of positively charged sodium ions, making the membrane potential less negative.

Overshoot

The phase where the membrane potential becomes positive, exceeding $0\,mV$, as sodium continues to enter the neuron.

Falling Phase (Repolarization Phase)

The stage where sodium channels close and voltage-gated potassium ($K^+$) channels open, causing $K^+$ to rapidly exit the cell and restore the negative membrane potential.

Undershoot (Hyperpolarization Phase)

The phase where the membrane potential becomes more negative than its resting state because voltage-gated potassium channels are slow to close.

Relative Refractory Period

A period during the undershoot phase when the cell is hyperpolarized, requiring a stronger-than-usual depolarization to reach the threshold and trigger another action potential.

Axon Hillock

The base of the axon where the initiation of the action potential occurs.

Sodium-Potassium Pump

An active transport mechanism that requires ATP to move $3\,Na^+$ out of the cell and $2\,K^+$ into the cell, accounting for ~70% of total ATP expenditure in the brain.

Nodes of Ranvier

Naked sections of the axon between myelin segments where voltage-gated $Na^+$ channels are highly concentrated.

Saltatory Conduction

The process by which an action potential "jumps" from one Node of Ranvier to the next, speeding up conductance.

Synapse

The tiny gap between the end of one neuron’s axon terminal and the dendrite of another neuron.

Presynaptic

The side of the synapse that sends information, typically the axon terminal.

Postsynaptic

The side of the synapse that receives information, typically the dendrite.

Electrical Synapse

A type of synapse where neurons directly transmit electrical signals via gap junctions made of proteins called connexons; these are fast, simple, and uncommon.

Chemical Synapse

A synapse where action potentials are translated into chemical signals through the release of neurotransmitters.

Vesicle

A membrane bubble inside the cell used for storing neurotransmitters.

Exocytosis

The process initiated by calcium ($Ca^{2+}$) influx where vesicles fuse with the axon terminal membrane to release neurotransmitters into the synaptic cleft.

Ligand

Any molecule that binds to a receptor.

Agonist

A ligand that binds to and activates a receptor.

Antagonist

A ligand that binds to a receptor and blocks its activation.

Affinity

A measure of how well a ligand fits and attaches to a specific receptor.

Inverse Agonist

A ligand that binds to a receptor and produces the reverse effect of an agonist, actively suppressing baseline activity.

Ionotropic Receptors

Ligand-gated ion channels that open to allow ion flow immediately when a ligand binds.

Metabotropic Receptors

Receptors coupled to G-proteins (GPCRs) that, when bound by a ligand, initiate an intracellular signaling cascade of events.

Autoreceptor

A receptor located on the presynaptic membrane.

Reuptake

A method of neurotransmitter elimination where the molecules are transported back into the presynaptic cell through transporters.

Degradation

A method of neurotransmitter elimination where enzyme proteins in the synaptic cleft break down the transmitter.

Postsynaptic Potential (PSP)

A change in membrane potential in the postsynaptic cell caused by receptor activation, categorized as either excitatory (EPSP) or inhibitory (IPSP).

Spatial Summation

The summing of simultaneous inputs from multiple different neurons at the axon hillock.

Temporal Summation

The summing of multiple inputs from a single neuron that occur over time.

Glutamate (GLU)

The primary excitatory and most abundant neurotransmitter in the brain; it binds to AMPA, NMDA, and kainate ionotropic receptors.

Excitotoxicity

A condition where neurons die due to excessive stimulation, often caused by overstimulation of glutamate receptors.

GABA

The primary inhibitory neurotransmitter in the brain, synthesized from the precursor glutamate.

Positive Allosteric Modulators (PAMs)

Drugs (such as alcohol and benzodiazepines) that enhance the activation of $GABA_A$ receptors without directly activating them.

Dopamine (DA)

A diffuse modulatory neurotransmitter involved in reward, motivation, motor control, and learning; its receptors are purely metabotropic.

Dopamine Synthesis Structures

The three specific brain regions where Dopamine is synthesized: the substantia nigra, ventral tegmental area, and hypothalamus.