Nervous System Structure, Physiology, and Neuroglia

Vocabulary flashcards covering the structural components of neurons, membrane potential physiology, conduction of action potentials, neuroglial cell types in the CNS and PNS, and neurotransmitter actions.

Neurons

Excitable cells of nervous tissue that transmit electrical signals through the properties of excitability, conductivity, and secretion.

Neuroglia (Glial Cells)

Non-excitable support cells of nervous tissue that perform diverse protective and metabolic functions and fill the space between neurons.

Soma (Cell Body)

The main biosynthetic and metabolic center of a neuron that contains the nucleus, mitochondria, cytoskeleton, and other cellular organelles.

Nissl Bodies

Specialized clusters of ribosomes and rough endoplasmic reticulum found within the cell body (soma) of a neuron.

Dendrites

Short, receptive branching processes extending from the neuronal soma that receive stimuli and convey incoming electrical messages toward the axon; they contain chemical (ligand)-gated and mechanically-gated ion channels.

Axon

A single long process extending from the cell body that conducts nerve impulses toward axon terminals; its membrane contains $Na^+/K^+$ pumps as well as voltage-gated $Na^+$ and $K^+$ channels.

Axon Hillock

The cone-shaped transition zone connecting the neuronal soma to the axon, where action potentials are typically initiated.

Axon Terminals

The repetitive, distal branches of an axon that end in rounded swelling structures called synaptic knobs.

Synapse

Round knobs at the end of axon terminals that house voltage-gated $Ca^{2+}$ channels and synaptic vesicles; they store neurotransmitters and transmit nerve impulses across a synaptic cleft to an adjacent neuron, muscle, or gland.

Resting Membrane Potential (RMP)

The stable polarized electrical potential across a neuron plasma membrane at rest (typically $-70\,\text{mV}$), characterized by a higher concentration of $Na^+$ in the extracellular fluid and a higher concentration of $K^+$ and negative proteins inside the cytosol.

$Na^+/K^+$ Pump

An active transport membrane protein that maintains resting membrane potential by consuming ATP to pump $3\,Na^+$ out of the cell and $2\,K^+$ into the cell against their electrochemical gradients.

Threshold

The critical membrane potential (typically $-55\,\text{mV}$) that a stimulus must reach to trigger the opening of voltage-gated $Na^+$ channels along the axon, initiating an all-or-none action potential.

Action Potential

A rapid, all-or-none, unidirectional reversal of membrane polarity propagating along an axon, in which membrane potential reaches up to approximately $+30\,\text{mV}$.

Depolarization

The phase of the action potential during which the opening of voltage-gated $Na^+$ channels allows $Na^+$ to enter the neuron, making the interior of the cell less negative and eventually positive.

Repolarization

The phase of the action potential in which voltage-gated $Na^+$ channels inactivate and voltage-gated $K^+$ channels open, allowing $K^+$ to exit the axon and restoring an internal negative charge.

Hyperpolarization (Undershoot)

A temporary state following repolarization where voltage-gated $K^+$ channels remain open, causing excessive $K^+$ outflow that drives the membrane potential down to approximately $-90\,\text{mV}$ before returning to RMP.

Refractory Period

The period following an action potential during which voltage-gated $Na^+$ channels are inactivated and the axon cannot respond to new stimuli, ensuring that nerve impulse transmission remains unidirectional.

Astrocytes

Central nervous system glial cells that anchor neurons to capillaries, facilitate the formation of the blood-brain barrier, regulate the extracellular environment, and repair damaged neural tissue.

Oligodendrocytes

Neuroglial cells that form insulating myelin sheaths around multiple axons within the central nervous system (CNS), featuring loose and even wrapping to speed electrical conduction.

Microglial Cells

Phagocytic neuroglia of the central nervous system that defend against invading pathogens, remove cellular debris, and clear metabolic waste.

Ependymal Cells

Ciliated glial cells lining the ventricles and central canal of the CNS that produce cerebrospinal fluid (CSF) and utilize their cilia to circulate CSF throughout the brain and spinal cord.

Schwann Cells (Neurolemmocytes)

Peripheral nervous system (PNS) neuroglia that myelinate a segment of a single peripheral axon by wrapping tightly around it, pushing their cytoplasm and nucleus outward to form the outer neurolemma.

Satellite Cells

Glial cells in the peripheral nervous system (PNS) that surround, support, and protect neuron cell bodies in ganglia, such as posterior root ganglia.

Nodes of Ranvier

Unmyelinated gaps along an axon between adjacent myelin segments where voltage-gated $Na^+$ and $K^+$ channels are clustered.

Saltatory Conduction

The rapid mode of nerve impulse propagation along myelinated axons in which depolarization jumps from one node of Ranvier to the next.

Continuous Conduction

The relatively slow method of action potential propagation along unmyelinated axons, requiring sequential opening and closing of voltage-gated channels along every point of the axolemma.

Synaptic Vesicles

Membrane-enclosed spheres inside the presynaptic axon terminal that store neurotransmitters and release them into the synaptic cleft by exocytosis upon $Ca^{2+}$ influx.

Acetylcholine (ACh)

A common excitatory neurotransmitter that triggers muscular contraction and neural excitation; its release and receptor binding can be altered by various neurotoxins.

Serotonin

An inhibitory neurotransmitter involved in regulation of memory, emotions, and sleep that undergoes rapid synaptic recycling and reuptake into the presynaptic neuron.

Dopamine

An inhibitory neurotransmitter that mediates pleasure, 'wanting', motivation, and behaviors associated with addiction and romantic attachment.

Endorphins

Inhibitory neurotransmitters that decrease neuronal signaling in pain pathways to alleviate pain perception.

GABA

A primary inhibitory neurotransmitter that decreases neuronal excitability and activity in the nervous system.

Botox

A pharmacological drug containing botulinum toxin from Clostridium botulinum that blocks acetylcholine receptors, resulting in local muscular paralysis.

Black Widow Spider Venom

A natural neurotoxin that abnormally increases the release of acetylcholine from presynaptic terminals, causing continuous neuronal firing and severe muscle cramping or paralysis.

Selective Serotonin Re-uptake Inhibitors (SSRIs)

Medications that block the reuptake of serotonin by the presynaptic neuron, allowing serotonin to remain in the synaptic cleft longer and prolong its inhibitory post-synaptic effects.