anatomy let 2- Electrical Signals: Generation, Propagation, and Neurotransmission

Comprehensive vocabulary flashcards covering neuron anatomy, resting membrane potentials, graded vs. action potentials, propagation mechanisms, synapses, and neurotransmitter classes.

Cell body (perikaryon/soma)

The region of a typical neuron that houses the nucleus and essential cellular organelles.

Dendrites

Branch-like extensions of a neuron (literally 'little trees') that receive incoming input signals.

Axon hillock

The cone-shaped region of a neuron where nervous impulses (action potentials) are initially generated.

Myelin sheath

An insulating covering produced by Schwann cells in the peripheral nervous system (PNS) that increases the conduction velocity of nervous impulses.

Synaptic end bulbs

Dilated terminal endings of an axon that contain synaptic vesicles and serve as the site of neurotransmitter release.

Graded potentials

Small, localized, and short-lived deviations from resting membrane potential with variable amplitudes, utilized for short-distance communication.

Action potentials

Rapid, brief reversals of membrane potential that operate on an all-or-none principle and propagate along excitable membranes for long-distance communication.

Ion channels

Transmembrane proteins containing a pore that allow specific ions to pass across the plasma membrane down their electrochemical gradient.

Electrochemical gradient

The dual driving force acting on ions across a membrane, comprising an electrical (charge) gradient and a chemical (concentration) gradient.

Resting membrane potential (RMP)

The voltage difference across an excitable cell membrane at rest, typically ranging from $-40\,mV$ to $-90\,mV$ ($-70\,mV$ on average in neurons), where the interior is negatively charged relative to the exterior.

Immobile anions

Intracellular negatively charged molecules that cannot cross the plasma membrane, notably including phosphates bound to molecules and amino acids in proteins.

$$\text{Na}^+/\text{K}^+\text{ ATPase}$$

An electrogenic primary active transport pump that consumes $1\,\text{ATP}$ to pump three $\text{Na}^+$ ions out of the cell for every two $\text{K}^+$ ions brought in, contributing approximately $-3\,mV$ to the resting membrane potential.

Decremental conduction

The progressive loss of amplitude of a graded potential as it spreads locally over a few micrometers from the point of stimulus before completely dying out.

Spatial summation

The additive integration of simultaneous graded potentials occurring close to one another in physical space across the neuronal membrane.

Temporal summation

The additive integration of multiple graded potentials occurring closely spaced in time at the same membrane location.

Absolute refractory period

The period during an action potential when voltage-gated $\text{Na}^+$ channels are either open or inactivated, making the generation of a second action potential impossible regardless of stimulus strength.

Relative refractory period

The period following an action potential during which voltage-gated $\text{K}^+$ channels remain open and voltage-gated $\text{Na}^+$ channels have reset, requiring a suprathreshold stimulus to trigger a second action potential.

Continuous conduction

The step-by-step sequential depolarization and repolarization of adjacent segments of the plasma membrane occurring along unmyelinated axons and muscle fibers.

Saltatory conduction

The rapid form of action potential propagation along myelinated axons in which the electrical impulse leaps from one myelin sheath gap (node) to the next.

Electrical synapse

A junction where action potentials conduct directly between the plasma membranes of adjacent cells via gap junctions, enabling rapid communication and synchronization in tissues like cardiac muscle, visceral smooth muscle, and the brain.

Chemical synapse

A junction where presynaptic and postsynaptic cells are separated by a fluid-filled synaptic cleft, across which neurotransmitters diffuse to trigger postsynaptic graded potentials after a synaptic delay of approximately $0.5\,\text{msec}$.

Excitatory postsynaptic potential (EPSP)

A depolarizing postsynaptic graded potential that brings the membrane closer to threshold, typically triggered by the opening of cation channels such as $\text{Na}^+$ channels.

Inhibitory postsynaptic potential (IPSP)

A hyperpolarizing postsynaptic graded potential that drives the membrane further away from threshold, typically caused by the opening of $\text{K}^+$ or $\text{Cl}^-$ channels.

Ionotropic receptor

A type of neurotransmitter receptor that contains a neurotransmitter binding site and an intrinsic ligand-gated ion channel that directly opens upon ligand binding.

Metabotropic receptor

A neurotransmitter receptor that lacks an intrinsic ion channel and is coupled via a G-protein to open or close separate ion channels directly or via second messengers.

Acetylcholinesterase

A synaptic cleft enzyme that rapidly terminates cholinergic neurotransmission by breaking down acetylcholine into acetate and choline.

Monoamine oxidase (MAO)

An enzyme that slowly degrades biogenic amine neurotransmitters—specifically epinephrine, norepinephrine, and dopamine—into inactive forms.

Biogenic amines

A category of small-molecule neurotransmitters possessing an amino functional group ($\text{R-NH}_2$), including catecholamines (dopamine, norepinephrine, epinephrine), serotonin, and histamine.

Nitric oxide (NO)

A lipid-soluble, small-molecule excitatory neurotransmitter produced in neural tissues for memory and learning, which signals through cGMP and causes vasodilation and anti-platelet aggregation in peripheral vessels.

Neuropeptides

Neurotransmitters composed of chains of 3 to 40 amino acids that bind metabotropic receptors and can also function systemically as endocrine hormones.

Substance P

An 11-amino-acid neuropeptide neurotransmitter involved in transmitting pain sensations to the central nervous system.

Enkephalins and endorphins

Endogenous opioid neuropeptides that function as natural analgesics by inhibiting the release of substance P.

Cholecystokinin (CCK)

A neuropeptide localized in the brain and small intestine that regulates feeding behavior as a 'stop eating' signal while functioning as a gastrointestinal endocrine hormone.

Oxytocin

A cyclic nonapeptide released from the pituitary gland that modulates emotional bonding, sexual pleasure, uterine contractions during labor, and milk let-down.