Electrical Signals and Cell-to-Cell Communication in Neurons

Vocabulary flashcards covering determinants of axon conduction velocity, electrical activity alteration, synaptic transmission, neurocrines, and receptor signaling pathways based on the lecture.

Axon Diameter

A physical parameter determining conduction velocity, where a larger axon diameter offers less internal resistance to current flow, bringing adjacent membrane regions to threshold faster.

Membrane Resistance

The resistance of the axon membrane to ion leakage; myelin insulation prevents current loss through leak channels, allowing current to spread faster to adjacent membrane sections.

Squid Giant Axon

A large unmyelinated axon measuring $0.8\,\text{mm}$ in diameter, historically used to study neuronal conduction parameters.

Saltatory Conduction

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

Nodes of Ranvier

Uninsulated gaps along a myelinated axon that contain an abundance of voltage-gated $\text{Na}^+$ channels necessary for saltatory conduction.

Demyelination

The loss of the myelin sheath leading to current leakage out of uninsulated regions, increasing the likelihood that depolarization becomes subthreshold before reaching the next node.

Normokalemia

Normal plasma $\text{K}^+$ concentration ranging between $3.5\,\text{mM}$ and $5\,\text{mM}$, maintaining normal resting membrane potential where subthreshold potentials do not fire action potentials.

Hyperkalemia

An increased blood $\text{K}^+$ concentration that depolarizes the resting membrane potential closer to threshold, allowing normally subthreshold stimuli to trigger action potentials.

Hypokalemia

A decreased blood $\text{K}^+$ concentration that hyperpolarizes the membrane potential, making neurons less likely to fire an action potential in response to normal stimuli.

Electrical Synapse

A synapse where ions flow directly from one cell to another through gap junctions, present in cardiac muscle, smooth muscle, and some CNS neurons.

Chemical Synapse

A synapse where electrical signals in the presynaptic cell are converted into neurocrine signals that cross the synaptic cleft and bind to postsynaptic receptors.

Neurocrine

A chemical substance released from neurons used for cell-to-cell communication, including neurotransmitters, neuromodulators, and neurohormones.

Neurotransmitter

A neurocrine chemical released to act on a nearby postsynaptic cell, producing a rapid, short-acting postsynaptic response.

Neuromodulator

A neurocrine chemical released to act on a nearby postsynaptic cell, causing slow synaptic potentials and long-term cellular effects.

Neurohormone

A neurocrine chemical secreted into the bloodstream to act on distant target tissues throughout the body.

Ionotropic Receptor

A ligand-gated ion channel that undergoes a conformational change upon ligand binding to open an ion channel, mediating fast postsynaptic responses.

Metabotropic Receptor

A G-protein coupled receptor (GPCR) that mediates slow postsynaptic responses by activating G proteins that alter ion channel states or activate membrane-bound enzymes.

GPCR-Phospholipase C Pathway

A signal transduction pathway where G protein activates phospholipase C (PLC) to convert membrane phospholipids into diacylglycerol (DAG) and inositol trisphosphate ($\text{IP}_3$), inducing $\text{Ca}^{2+}$ release from the endoplasmic reticulum.

GPCR-Adenylyl Cyclase Pathway

A signal transduction pathway where G protein activates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), which activates protein kinase A (PKA) to phosphorylate proteins.

Acetylcholinesterase (AChE)

An enzyme present in the synaptic cleft that rapidly breaks down acetylcholine into choline and acetate.

Acetylcholine Synthesis and Recycling

The metabolic process in which acetylcholine (ACh) is synthesized from choline and acetyl CoA, released into the cleft, degraded by AChE, and choline is cotransported back into the terminal with $\text{Na}^+$.

Excitatory Postsynaptic Potential (EPSP)

A depolarizing postsynaptic potential created by opening $\text{Na}^+$ channels or closing $\text{K}^+$ channels, moving the membrane potential closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarizing postsynaptic potential created by opening $\text{K}^+$ or $\text{Cl}^-$ channels, moving the membrane potential further from threshold.

Voltage-Gated Ca2+ Channel

Presynaptic channels that open in response to axon terminal depolarization, allowing $\text{Ca}^{2+}$ entry that triggers exocytosis of synaptic vesicles containing neurocrines.