NEUR 255: Brain Cells and How They Communicate

Vocabulary practice flashcards covering brain cell anatomy, resting membrane potentials, action potential generation and propagation, synaptic transmission, classical neurotransmitters, and synaptic plasticity.

Neurons

Specialized cells responsible for carrying information back and forth within the brain and between the brain and the body, numbering approximately $100\text{ billion}$ in the human brain.

Glial Cells

Non-neuronal support cells that make up approximately $90\%$ of all cells in the brain, historically named after the Greek word for "glue."

Motor Neurons

Neurons that convey motor instructions and information from the brain and spinal cord to muscles and bodily organs.

Sensory Neurons

Neurons that bring sensory information from the body and the surrounding environment into the brain and spinal cord.

Soma

The cell body of a neuron, containing organelles suspended in cytoplasm and a nucleus that houses DNA encoding genetic instructions.

Dendrites

Branching extensions projecting from the soma that receive incoming information from other neurons, with individual neurons receiving inputs from up to $10{,}000$ to $100{,}000$ sources.

Axon

A tail-like process extending from the soma that propagates outgoing electrical signals over short or long distances toward other target cells.

Multipolar Neuron

A structural category of neuron characterized by an axon and multiple dendrites extending outward in several directions from the soma, characteristic of motor neurons.

Bipolar Neuron

A neuron with a soma that gives rise to an axon on one end and a dendritic process on the opposite end.

Unipolar Neuron

A neuron characterized by a single short stalk exiting the soma that subsequently splits into two functional branches.

Terminal Boutons

Specialized swellings (boutons terminaux) at the terminal ends of axon branches that store and release neurotransmitters across synapses.

Myelin

A fatty insulating sheath produced by specialized glial cells that wraps around neuronal axons, accelerating electrical conduction and giving white matter its characteristic color.

Oligodendrocytes

Glial cells responsible for forming and maintaining myelin sheaths around axons within the central nervous system (CNS).

Schwann Cells

Glial cells responsible for producing and maintaining the myelin sheath around axons in the peripheral nervous system (PNS).

Nodes of Ranvier

Unmyelinated gaps along an axon between adjacent myelin segments where ion channels are concentrated and action potentials occur.

Resting Membrane Potential

The steady electrical voltage across an unstimulated neuronal membrane, typically measured at approximately $-70\,\text{mV}$ inside relative to outside.

Electrostatic Force

The electrical attraction or repulsion acting on ions, which drives them toward regions with opposite charge and repels them from regions with like charge.

Diffusional Force

The physical chemical tendency of ions and molecules to move passively down their concentration gradient from an area of higher concentration to lower concentration.

Organic Anions ($\text{A}^-$)

A collective group of large, negatively charged intracellular proteins and particles that cannot cross the cell membrane.

Sodium-Potassium Pump

An active transport protein that uses metabolic energy to pump three $\text{Na}^+$ ions out of the neuron for every two $\text{K}^+$ ions moved in, consuming roughly $40\%$ of total brain energy.

Threshold

The critical membrane potential (typically around $-40\,\text{mV}$) at which voltage-gated sodium channels open and an action potential is triggered.

Voltage-Gated Sodium Channels

Membrane protein channels that selectively open when the membrane potential reaches approximately $-40\,\text{mV}$, allowing rapid inward flow of $\text{Na}^+$ ions.

Depolarization

A shift in a neuron's membrane potential toward a more positive value, reaching approximately $+40\,\text{mV}$ during the rising phase of an action potential.

Repolarization

The phase of the action potential where the membrane rapidly returns to a negative potential due to the closure of $\text{Na}^+$ channels and the opening of voltage-gated $\text{K}^+$ channels.

Undershoot

The brief hyperpolarization phase following repolarization where the membrane potential becomes more negative than the standard resting potential (around $-85\,\text{mV}$) before stabilizing.

Action Potential

A rapid, transient electrical impulse across the membrane featuring all-or-none depolarization, repolarization, and a brief undershoot phase.

All or None Law

The physiological principle stating that an action potential fires completely at full strength once threshold is reached or does not fire at all.

Saltatory Conduction

The rapid propagation of an action potential along a myelinated axon, where the impulse leaps from one node of Ranvier to the next.

Tetrodotoxin

A potent neurotoxin found in the Japanese pufferfish ("fugu") that selectively blocks voltage-gated sodium channels, preventing action potential generation.

Axon Hillock

The cone-shaped transition zone connecting the soma to the axon where incoming postsynaptic potentials summate to initiate an action potential if threshold is reached.

Synapse

The functional junction consisting of a presynaptic terminal, a synaptic cleft, and a postsynaptic membrane through which neurons communicate.

Synaptic Cleft

The microscopic extracellular space separating the presynaptic terminal bouton from the postsynaptic cell membrane.

Synaptic Vesicles

Membrane-bound spheres within the presynaptic terminal that store neurotransmitters prior to exocytosis.

Voltage-Gated Calcium Channels

Ion channels located on presynaptic terminals that open in response to action potential depolarization, allowing $\text{Ca}^{2+}$ influx that triggers vesicle fusion and neurotransmitter release.

Postsynaptic Receptors

Membrane-bound proteins on the recipient cell that bind specific neurotransmitters, undergoing conformational changes that gate ion channels or trigger intracellular cascades.

Gamma-Aminobutyric Acid (GABA)

The primary inhibitory neurotransmitter of the central nervous system, which acts on $\text{GABA}_{\text{A}}$ and $\text{GABA}_{\text{B}}$ receptors to open chloride channels and hyperpolarize postsynaptic neurons.

Glutamate

The principal excitatory neurotransmitter in the brain and spinal cord, binding NMDA and AMPA receptors to open sodium channels and promote depolarization.

Acetylcholine

A neurotransmitter acting on nicotinic and muscarinic receptors that triggers skeletal muscle contraction in the periphery and mediates learning and memory within the hippocampus.

Dopamine

A monoamine neurotransmitter binding $\text{D}_{1}$ and $\text{D}_{2}$ receptor families, critical for movement initiation, habit learning, motivation, and reward processing.

Norepinephrine

A neurotransmitter (also known as noradrenaline) binding $\alpha$ and $\beta$ adrenergic receptors that regulates heart rate in the periphery and controls mood, alertness, and attention in the CNS.

Serotonin

A neurotransmitter acting on $\text{5-HT}$ receptors that regulates blood pressure peripherally and modulates mood, sleep, and arousal centrally.

Spatial and Temporal Summation

The integration of synaptic inputs arriving at different anatomical locations on a neuron (spatial) or arriving closely spaced in time at the same input (temporal).

Neuroplasticity

The biological process by which synaptic pathways and neuronal circuits modify their structure or strength in response to experience and learning.

Cell Assembly

A theoretical concept proposed by Donald Hebb in the 1940s describing a newly formed network of interconnected neurons whose strengthened synaptic connections represent a memory trace.

Entorhinal Cortex

A temporal lobe brain structure closely linked with the hippocampus that serves as a primary model for investigating how neurotransmitters modulate synaptic strength and memory formation.

Multiple Sclerosis

An autoimmune disorder in which the body's immune system attacks and damages myelin sheaths throughout the nervous system, impairing axonal conduction.