NEUR 5300 - Action Potentials and Synaptic Transmission

Vocabulary flashcards covering electrical activity of axons, action potentials, ion channel gating, synaptic transmission, and neurotransmitters based on Parker University NEUR 5300 Week 2 Module 2.

Resting Membrane Potential (RMP)

The potential voltage difference across a cell membrane at rest, largely created by negatively charged organic molecules inside the cell and the limited diffusion of positively charged inorganic ions.

Excitability

The ability of a cell, such as a neuron or muscle cell, to produce and conduct electrical impulses in response to a stimulus.

Depolarization

A change in membrane potential that reduces the potential difference across the cell membrane, making the inside of the cell more positive.

Repolarization

The return of the membrane potential to the resting membrane potential after a depolarization event, making the inside of the cell more negative again.

Hyperpolarization

An increase in the potential difference across the cell membrane, causing the membrane potential to become more negative than the resting membrane potential.

Voltage-Gated Ion Channels

Ion channels comprised of integral membrane proteins that open or close in response to changes in the membrane potential.

Action Potential (AP)

A rapid, all-or-none reversal in membrane potential from $-70\,\text{mV}$ to $+30\,\text{mV}$ triggered by depolarization to threshold, mediated by sequential opening of voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels.

All-or-None Law

The principle that once depolarization reaches threshold, a maximum potential change occurs with a constant amplitude ($+30\,\text{mV}$) and fixed duration regardless of stimulus strength.

Recruitment

The activation of additional axon fibers with higher thresholds of depolarization in response to stronger stimuli.

Absolute Refractory Period

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

Relative Refractory Period

The period following an action potential during which open voltage-gated $\text{K}^+$ channels hyperpolarize the membrane, requiring a stronger-than-normal stimulus to elicit another action potential.

Cable Properties

The ability of a neuron to transmit electrical charge through its cytoplasm, which is relatively poor in axons due to high internal resistance and charge leakage across the membrane.

Saltatory Conduction

The rapid mode of action potential conduction along a myelinated axon, where the impulse leaps from one Node of Ranvier to the next.

Gap Junctions

Protein channels composed of $12$ connexin proteins that directly connect adjacent cells in electrical synapses, allowing direct passage of electrical charge.

Synaptic Cleft

The narrow fluid-filled space separating the presynaptic terminal bouton from the postsynaptic cell membrane across which neurotransmitters diffuse.

Synapsins

Proteins that, upon phosphorylation by protein kinase (activated by $\text{Ca}^{2+}$-calmodulin), aid in the fusion of synaptic vesicles with the presynaptic membrane for neurotransmitter release.

Excitatory Postsynaptic Potential (EPSP)

A graded depolarization of the postsynaptic membrane caused by neurotransmitter binding, bringing the membrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A graded hyperpolarization of the postsynaptic membrane caused by neurotransmitter binding, moving the membrane potential further away from threshold.

Nicotinic ACh Receptor

A ligand-operated ion channel containing $5$ polypeptide subunits ($2$ of which bind acetylcholine) found in autonomic ganglia and skeletal muscle fibers that allows influx of $\text{Na}^+$ to produce EPSPs.

Muscarinic ACh Receptor

A G-protein-coupled acetylcholine receptor found in smooth muscle, cardiac muscle, and gland cells that operates separate ion channels via G-protein subunit dissociation.

Acetylcholinesterase (AChE)

An enzyme present on or near the postsynaptic membrane that rapidly inactivates acetylcholine by cleaving it into acetate and choline to terminate synaptic signaling.

Monoamine Oxidase (MAO)

An enzyme in the presynaptic terminal responsible for the degradation of monoamine neurotransmitters that have undergone reuptake.

Catechol-O-methyltransferase (COMT)

An enzyme located in the postsynaptic membrane responsible for degrading catecholamine neurotransmitters.

Adenylate Cyclase

An enzyme activated by the dissociated G-protein alpha subunit during monoamine signaling that converts ATP to cyclic AMP ($\text{cAMP}$).

SSRIs (Serotonin-Specific Reuptake Inhibitors)

Antidepressant medications that inhibit the reuptake and destruction of serotonin in the synaptic cleft, prolonging its action.

Nigrostriatal Dopamine System

A dopaminergic pathway originating in the substantia nigra and projecting to the corpus striatum that is involved in initiating skeletal muscle movement.

Mesolimbic Dopamine System

A dopaminergic pathway originating in the midbrain and projecting to the limbic system that is involved in behavior and reward mechanisms.

Glutamic Acid

A major excitatory neurotransmitter in the central nervous system whose NMDA receptor subtype plays a crucial role in memory storage.

Glycine

An inhibitory neurotransmitter in the spinal cord that opens $\text{Cl}^-$ channels in the postsynaptic membrane to produce IPSPs and help control skeletal movements.

GABA (Gamma-Aminobutyric Acid)

The most prevalent inhibitory neurotransmitter in the brain that hyperpolarizes postsynaptic membranes to regulate motor functions in the cerebellum.

Substance P

A polypeptide neurotransmitter involved in mediating sensations of pain.

Endogenous Opioids

Brain-produced analgesic peptides, including beta-endorphin, enkephalins, and dynorphin, that block the synaptic release of substance P.

Neuropeptide Y

The most abundant neuropeptide in the brain that inhibits glutamate release in the hippocampus and acts as a powerful stimulator of appetite.

Endocannabinoids

Endogenous lipid neurotransmitters that bind to THC receptors, act as analgesics, and function as retrograde neurotransmitters.

Spatial Summation

The convergence and summation of excitatory postsynaptic potentials from multiple presynaptic axon terminals firing simultaneously at different locations on a single postsynaptic neuron.

Temporal Summation

The summation of postsynaptic potentials occurring when a single presynaptic axon fires successive waves of neurotransmitter release rapidly over time.

Long-Term Potentiation (LTP)

A persistent strengthening of synaptic efficacy following high-frequency stimulation along frequently used neural pathways, mediated by glutamate and NMDA receptors in the hippocampus.

Presynaptic Inhibition

A mechanism wherein a second neuron synapses onto a presynaptic axon terminal, reducing the amount of excitatory neurotransmitter released by that terminal.