Neurophysiology and Synaptic Transmission Vocabulary

Vocabulary flashcards reviewing concepts in neurophysiology, glia, synaptic transmission, action potentials, local potentials, and neurotransmitter properties from Dr. Banzuela's lecture notes.

Many-to-one synapses

A synaptic arrangement where many presynaptic neurons converge onto a single postsynaptic element, such as in spinal motor neurons.

Excitatory Post-Synaptic Potentials (EPSPs)

Local potentials that depolarize the postsynaptic cell membrane, bringing it closer to threshold, typically caused by $\text{Na}^+$ influx.

Inhibitory Post-Synaptic Potentials (IPSPs)

Local potentials that hyperpolarize the postsynaptic cell membrane, pushing it further from threshold, typically caused by $\text{Cl}^-$ influx.

Spatial Summation

The integration of two or more excitatory inputs arriving at the postsynaptic membrane at the exact same time ($A + B + C$).

Temporal Summation

The integration of two or more excitatory inputs arriving at the postsynaptic membrane in rapid succession ($A \dots A \dots A$).

Acetylcholine (ACh)

A neurotransmitter synthesized from Acetyl CoA and Choline by Choline Acetyltransferase, uniquely degraded by Acetylcholinesterase in the synapse prior to reuptake, and found decreased in Alzheimer dementia and Huntington dementia.

Norepinephrine (NE)

The primary neurotransmitter released by post-ganglionic sympathetic neurons, synthesized inside synaptic vesicles in the locus coeruleus of the pons with a short half-life of $2\,\text{minutes}$.

Epinephrine (EPI)

A neurotransmitter/hormone secreted mainly by the adrenal medulla with greater $\beta_2$ receptor activity than NE, capable of relieving bee sting symptoms by relaxing airway smooth muscle.

Dopamine

A neurotransmitter produced in the substantia nigra (modulating movement) and hypothalamus (inhibiting prolactin), which is decreased in Parkinson Disease and exhibits increased $D_2$ activity in Schizophrenia.

Serotonin

A neurotransmitter synthesized from tryptophan in the median raphe of the brainstem, converted to melatonin, and associated with depression when present at low levels.

Nitric Oxide (NO)

A permeant gas synthesized from arginine by NO synthase that functions as an inhibitory non-adrenergic, non-cholinergic neurotransmitter and potent vasodilator.

Glycine

The primary inhibitory neurotransmitter in the spinal cord that acts by increasing $\text{Cl}^-$ influx.

GABA

The primary inhibitory neurotransmitter in the brain that increases $\text{Cl}^-$ influx via $\text{GABA}_A$ receptors or $\text{K}^+$ efflux via $\text{GABA}_B$ receptors.

Glutamate

The main excitatory neurotransmitter in the brain, formed from the reactive amination of $\alpha\text{-ketoglutarate}$.

Microglia

Tissue macrophages of the central nervous system that act as scavenger cells to remove debris from injury, infection, or neurodegenerative disease.

Oligodendrocytes

Macroglial cells responsible for forming the myelin sheath around axons in the Central Nervous System (CNS).

Schwann Cells

Macroglial cells that form the myelin sheath and assist in regeneration and remyelination in the Peripheral Nervous System (PNS).

Astrocytes

Macroglia that envelop synapses, help form the blood-brain barrier (BBB), regulate extracellular ion concentrations, and perform reuptake of glutamate and GABA.

Initial Segment

The unmyelinated region of the neuron located at the axon hillock where action potentials are first generated.

Nodes of Ranvier

Unmyelinated gaps along a myelinated axon containing the highest concentration of $\text{Na}^+$ channels per square micrometer, where action potentials are regenerated.

Terminal Boutons

Distal tips of an axon containing voltage-gated calcium channels (VGCC) that trigger neurotransmitter exocytosis upon action potential arrival.

Lambert-Eaton Myasthenic Syndrome

An autoimmune disease characterized by autoantibodies against voltage-gated calcium channels, preventing acetylcholine release into the neuromuscular junction.

One-to-one synapses

A synaptic arrangement where one presynaptic neuron connects to a single postsynaptic element, such as at neuromuscular junctions (NMJ).

Orthodromic Transmission

Conduction of a nerve impulse in the normal direction from synapse/soma along the axon toward the terminal.

Threshold

The membrane potential at which an action potential is inevitable, occurring when net inward current exceeds net outward current ($\text{Na}^+$ inward current > $\text{K}^+$ outward current).

Overshoot

The brief portion of an action potential peak where the membrane potential rises above $0\,\text{mV}$.

Undershoot

The phase of an action potential (after-hyperpolarization) where the membrane potential falls below the normal resting membrane potential.

Absolute Refractory Period (ARP)

The period during an action potential when no second action potential can be elicited regardless of stimulus size due to closed $\text{Na}^+$ inactivation gates.

Relative Refractory Period (RRP)

The period following the ARP during which a new action potential can be triggered only by a larger-than-normal stimulus due to prolonged opening of $\text{K}^+$ channels.

Accommodation

A state in which a cell membrane is depolarized slowly, causing $\text{Na}^+$ inactivation gates to close without firing an action potential (e.g., in hyperkalemia).

Saltatory Conduction

The rapid propagation of an action potential jumping electronically from one Node of Ranvier to the next along a myelinated axon.

Nernst Potential

The equilibrium potential that exactly balances or opposes the concentration gradient driving an ion's diffusion across a cell membrane.

Goldman-Hodgkin-Katz Equation

An equation used to calculate overall equilibrium potential when a membrane is permeable to multiple ions simultaneously ($\text{Na}^+$, $\text{K}^+$, $\text{Cl}^-$).

All-or-None Response

The characteristic of excitable cells where reaching threshold produces a full-sized, identical action potential, while failing to reach threshold yields no action potential.

m Gate

The activation gate of voltage-gated $\text{Na}^+$ channels that opens during depolarization to allow $\text{Na}^+$ influx.

h Gate

The inactivation gate of voltage-gated $\text{Na}^+$ channels that closes during repolarization to stop $\text{Na}^+$ influx.

Reflection Coefficient (\sigma)

A measure of solute membrane penetration ranging from $1$ (impermeable/effective osmole) to $0$ (completely permeable/ineffective osmole).

Gibbs-Donnan Effect

The unequal distribution of diffusible charged ions across a semi-permeable membrane resulting from the presence of non-diffusible charged particles like proteins.