Neuroscience: Neuronal Structure, Signaling, and Neurotransmitters

Comprehensive vocabulary flashcards covering neuron anatomy, cellular electrical signaling, synaptic transmission, and neurotransmitter classifications.

Soma (Cell Body)

The central body of a neuron that synthesizes macromolecules and integrates electrical signals; typically possesses one axon and may have one, two, or many dendrites.

Dendrites

Tapered extensions branching from the neuron cell body whose primary function is to collect information from other neurons.

Axon

A single, cylindrical neuronal extension that may be myelinated or unmyelinated, can reach many centimeters in length, and conducts information to other neurons.

Axon Terminals (Presynaptic Terminals / Synaptic Boutons)

Vesicle-filled appositions located at the ends of axon branches that transmit information across the synapse to other neurons.

Synapse

An intercellular junction where fast, highly localized transmission of chemical and electrical signals occurs, comprising presynaptic and postsynaptic membranes along with the synaptic cleft.

Neurotransmitters

Chemical messengers synthesized and stored in synaptic vesicles and released from the axon terminal of a sending neuron to transmit signals across the synaptic cleft.

Synaptic Cleft

The microscopic gap separating the presynaptic membrane from the postsynaptic membrane across which neurotransmitters diffuse.

Bipolar Neuron

A neuron structural classification defined by having two distinct processes extending from the cell body—one dendrite and one axon—as exemplified by the retina bipolar cell.

Unipolar Neuron

A neuron structural classification featuring a single extension branching into dendrites and axon terminals, typically found in invertebrates.

Resting Membrane Potential

The difference in electrical charge across the neuronal membrane when it is not firing; the inside of the neuron is approximately $70\,\text{mV}$ more negative than the outside ($-70\,\text{mV}$).

Threshold

The specific voltage level (approximately $-55\,\text{mV}$) that a neuron must reach to trigger an action potential that propagates down the axon.

Depolarization

A shift in membrane potential making the inside of the neuron less negative, occurring when $\text{Na}^+$ rushes into the cell and driving the membrane voltage up to approximately $+40\,\text{mV}$.

Repolarization

The stage following peak action potential where $\text{Na}^+$ channels close and $\text{K}^+$ channels open, allowing $\text{K}^+$ efflux down its electrochemical gradient and causing the membrane voltage to fall.

Hyperpolarization

An overshoot in repolarization where excess positive ions ($\text{K}^+$) leave the cell, temporarily making the inside of the membrane more negative than its normal resting potential.

Action Potential

A rapid electrical impulse triggered when threshold is met that propagates down the axon to stimulate neurotransmitter release at the terminals.

Absolute Refractory Period

The brief recovery duration during and immediately following an action potential during which the neuron cannot fire a second time under any circumstance, even with a very strong stimulus.

Relative Refractory Period

The period following the absolute refractory period where the neuron can fire again, but requires a stronger-than-usual stimulus to reach threshold.

Postsynaptic Potential (PSP)

A graded voltage shift across the receptor sites of a postsynaptic cell membrane resulting from neurotransmitter binding.

Excitatory Postsynaptic Potential (EPSP)

A positive ($+$) voltage shift that depolarizes the membrane toward the $-55\,\text{mV}$ threshold, increasing the probability that the postsynaptic neuron will fire an action potential.

Inhibitory Postsynaptic Potential (IPSP)

A negative ($-$) voltage shift that hyperpolarizes the membrane further away from the $-55\,\text{mV}$ threshold, decreasing the probability that the postsynaptic neuron will fire an action potential.

Reuptake

The reabsorption process by which released neurotransmitter molecules are taken back up from the synaptic cleft into the presynaptic membrane for reuse.

Agonist

A chemical substance that binds to a neurotransmitter's receptor site and mimics or turns on the biological actions of that neurotransmitter.

Antagonist

A chemical substance that binds to a neurotransmitter's receptor site and blocks or inhibits the normal action of that neurotransmitter.

Acetylcholine (ACh)

A neurotransmitter released by motor neurons to control skeletal muscles; contributes to attention, arousal, and memory; its receptors are stimulated by nicotine and its deficiency is linked to Alzheimer's disease.

Dopamine (DA)

A monoamine catecholamine neurotransmitter that controls voluntary movement and mediates medial forebrain reward pathways; degeneration of DA neurons causes symptoms of Parkinson's disease.

Serotonin (5-HT)

A monoamine indolamine neurotransmitter that regulates sleep, wakefulness, eating, and aggression, and whose circuits are modulated by antidepressant drugs such as Prozac.

Norepinephrine (NE)

A monoamine neurotransmitter and hormone (also called noradrenaline) involved in brain arousal, mood, hunger, sleep, and sexual behavior, with levels elevated by amphetamines.

GABA (Gamma-Aminobutyric Acid)

The primary inhibitory amino acid neurotransmitter in the brain that contributes to the regulation of anxiety and sleep/arousal, targeted by anti-anxiety medications like Valium.

Glutamate

The principal excitatory amino acid neurotransmitter in the nervous system, playing key roles in learning and the transmission of sensory information.

Anandamide

An unconventional endocannabinoid neurotransmitter named from the Sanskrit word for joy or bliss; binds to the same receptors as THC and regulates eating, memory, motivation, sleep, and pain.

Endorphins

Endogenously produced opioid neuropeptides that function as natural analgesics (painkillers) by inhibiting the transmission of pain signals in the spinal cord.

Endocrine System

A bodily communication system composed of glands that secrete chemical regulatory messengers directly into the bloodstream.

Hormones

Chemical substances synthesized and released into the blood circulation by endocrine glands to coordinate physiological functions across the body.