Action Potentials and Synaptic Transmission

Vocabulary flashcards covering key concepts from NEUR 5300 Module 2 on action potentials, ion channel gating, axonal conduction, synaptic transmission, neurotransmitters, and synaptic integration.

Resting Membrane Potential (RMP)

The potential voltage difference across a cell membrane at rest, largely maintained by internal negatively charged organic molecules, limited diffusion of inorganic ions, and the $Na^+/K^+$ ATPase pump.

Depolarization

A change in membrane potential where the potential difference is reduced and the inside of the cell becomes more positive relative to the resting membrane potential.

Hyperpolarization

A change in membrane potential where the inside of the cell membrane becomes more negative than the resting membrane potential.

Voltage-Gated (VG) Channels

Ion channels located within the plasma membrane that open or close in response to changes in membrane potential.

Action Potential (AP)

A rapid, all-or-none reversal of membrane potential from $-70$ to $+30\,mV$ caused by inward diffusion of $Na^+$ through voltage-gated channels, followed by repolarization back to RMP via outward diffusion of $K^+$.

Absolute Refractory Period

The phase during an action potential when the axon membrane is completely incapable of producing another action potential due to inactivated voltage-gated $Na^+$ channels.

Relative Refractory Period

The period following an action potential when voltage-gated $K^+$ channels are open and an action potential can be produced only if a stronger stimulus is applied.

Saltatory Conduction

The rapid propagation of action potentials along a myelinated axon where electrical impulses leap from one Node of Ranvier to the next.

Nodes of Ranvier

Unmyelinated gaps in the myelin sheath along an axon that contain high concentrations of voltage-gated $Na^+$ and $K^+$ channels.

Gap Junctions

Structures composed of 12 connexin proteins that electrically couple adjacent cells in electrical synapses, allowing impulses to pass directly without interruption.

Synapsins

Proteins phosphorylated by protein kinase in response to intracellular $Ca^{2+}$ influx, aiding in the fusion of synaptic vesicles with the axon terminal membrane.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization of the postsynaptic membrane produced by neurotransmitter binding that brings the membrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization of the postsynaptic membrane produced by neurotransmitter binding that increases membrane potential away from threshold.

Nicotinic Acetylcholine Receptor

A ligand-operated channel consisting of 5 polypeptide subunits with 2 ACh binding sites, found in autonomic ganglia and skeletal muscle fibers.

Muscarinic Acetylcholine Receptor

A G-protein-operated acetylcholine receptor found in smooth/cardiac muscle cells and glands that indirectly opens or closes ion channels via G-protein subunit dissociation.

Acetylcholinesterase (AChE)

An enzyme located on or near the postsynaptic membrane that inactivates acetylcholine into acetate and choline to terminate synaptic stimulation.

Monoamine Oxidase (MAO)

An enzyme present in the presynaptic terminal responsible for the degradation of monoamine neurotransmitters after reuptake.

Catechol-O-Methyltransferase (COMT)

An enzyme present in the postsynaptic membrane responsible for the enzymatic degradation of catecholamines.

Nigrostriatal Dopamine System

A neural circuit originating in the substantia nigra and projecting to the corpus striatum, essential for the initiation of skeletal muscle movement.

Mesolimbic Dopamine System

A neural circuit originating in the midbrain and projecting to the limbic system, involved in emotional behavior and reward processes.

Gamma-Aminobutyric Acid (GABA)

The primary inhibitory neurotransmitter in the brain that hyperpolarizes postsynaptic membranes and plays a major role in cerebellar motor functions.

Substance P

A polypeptide neurotransmitter involved in transmitting sensations of pain.

Spatial Summation

The convergence and summation of postsynaptic potentials generated simultaneously at different presynaptic boutons on a single postsynaptic cell.

Temporal Summation

The cumulative effect of repetitive, successive waves of neurotransmitter release from a single presynaptic axon onto a postsynaptic membrane over time.

Long-Term Potentiation (LTP)

A persistent enhancement of synaptic transmission efficiency resulting from high-frequency stimulation, mediated by glutamate and NMDA receptors in the hippocampus.