BIO 201: Neurons and Stimulus-Response Pathway

Comprehensive vocabulary flashcards covering neuron anatomy, structural and functional classifications, glial cell types, action potential mechanics, and the stimulus-response pathway.

Neuron (Nerve Cell)

The fundamental structural and functional unit of the nervous system, specialized for receiving, processing, and propagating electrical and chemical signals.

Soma (Cell Body)

The central body of a neuron that contains the nucleus and the majority of major organelles, where incoming graded potentials gather.

Processes

Any cellular extensions projecting from the neuron's plasma membrane, encompassing both dendrites and axons.

Dendrites

Branching extensions of the neuronal cell membrane that detect incoming stimuli and receive signals from other neurons at specialized junctions called synapses.

Axon Hillock

The specialized, tapering region of the soma where the axon originates; the site where graded potentials accumulate until threshold is reached to initiate an action potential.

Axon

A single long cylindrical nerve fiber emerging from the cell body that conducts action potentials toward target cells and may branch repeatedly.

Neuronal Polarity

The property describing the strictly unidirectional flow of electrical information through a neuron, typically directed from dendrites and soma down toward the axon terminal.

Myelin Sheath

An insulating lipid-rich covering wrapped around axons by glial cells that protects the fiber and significantly accelerates nerve impulse conduction speed.

Nodes of Ranvier

Unmyelinated gaps along an axon between adjacent glial cells where voltage-gated ion channels are concentrated, permitting saltatory conduction.

Saltatory Conduction

The rapid form of action potential propagation occurring in myelinated axons, where the electrical depolarization jumps from one node of Ranvier to the next.

Continuous Conduction

The relatively slow wave of sequential depolarization and repolarization that travels down the entire uninterrupted length of an unmyelinated axon.

Axon Terminal (Synaptic End Bulb)

The distal endpoint of an axon branch containing synaptic vesicles that releases neurotransmitters across the synaptic cleft toward a target cell.

Synaptic Cleft

The narrow extracellular fluid-filled space at a synapse between the presynaptic neuron's axon terminal and the postsynaptic target membrane.

Multipolar Neuron

A structural class of neuron characterized by three or more processes (one axon and multiple dendrites); constitutes approximately $99\%$ of all neurons in the body.

Bipolar Neuron

A structural neuron type having only two processes projecting from opposite sides of the cell body (one dendrite and one axon); found in the olfactory epithelium, retina, and inner ear cochlea.

Unipolar Neuron

A structural class possessing a single short process originating from the soma that divides T-like into proximal and distal branches; characteristic of most vertebrate sensory neurons.

Sensory (Afferent) Neurons

Neurons that convey incoming electrical impulses from sensory receptors in the skin or visceral organs toward or into the central nervous system.

Interneurons (Association Neurons)

Neurons situated entirely within the central nervous system that integrate, process, and interpret incoming sensory information; account for $99\%$ of all CNS neurons.

Motor (Efferent) Neurons

Typically multipolar neurons that carry outgoing motor commands away from the central nervous system to target effector tissues, such as muscles and glands.

Glial Cells (Neuroglia)

Non-neuronal helper and supporting cells in both the central and peripheral nervous systems that maintain homeostasis, form myelin, and protect neurons.

Astrocyte

A star-shaped CNS glial cell that regulates the extracellular chemical environment, recycles neurotransmitters, and associates with cerebral capillaries to support the blood-brain barrier.

Oligodendrocyte

A CNS glial cell whose membrane extensions wrap around and insulate multiple axon segments across one or more neurons to form myelin.

Microglia

Phagocytic glial cells of the CNS derived from macrophage precursors that engulf cellular waste, damaged cells, and invasive pathogens.

Ependymal Cells

Ciliated glial cells lining the ventricles of the brain and central canal of the spinal cord that filter blood components to synthesize and circulate cerebrospinal fluid ($\text{CSF}$).

Choroid Plexus

A specialized vascular structure in the brain ventricles where ependymal cells interact directly with capillary beds to filter blood and produce cerebrospinal fluid.

Schwann Cell

A glial cell of the peripheral nervous system ($\text{PNS}$) that wraps around a single axon segment to form myelin.

Satellite Cell

A supporting glial cell of the peripheral nervous system that surrounds neuron cell bodies within sensory and autonomic ganglia, performing functions analogous to CNS astrocytes.

Resting Membrane Potential

The baseline electrical charge differential across an unstimulated neuronal membrane, maintaining a net positive charge outside and a net negative charge inside via differential concentrations of $Na^+$ and $K^+$.

Depolarization

The phase of an action potential during which voltage-gated $Na^+$ channels open, causing a massive influx of positively charged sodium ions that flips the membrane polarity from negative to positive internally.

Repolarization

The phase following depolarization in which voltage-gated $Na^+$ channels close and voltage-gated $K^+$ channels open, allowing potassium ions to exit the cell and restore the internal negative charge.

Hyperpolarization

A slight, transient overshoot at the completion of an action potential where the intracellular potential becomes even more negative than the resting membrane potential due to lingering $K^+$ outflow.

Sodium-Potassium Pump ($Na^+/K^+$ ATPase)

A primary active transport membrane mechanism that moves $Na^+$ ions outward and $K^+$ ions inward against their concentration gradients to fully restore resting ionic baselines.

Primary Afferent Axon Classification

Sensory nerve fiber categorizations organized by size and velocity: $A\alpha$ ($13-20\,\mu m$, $80-120\,m/s$), $A\beta$ ($6-12\,\mu m$, $35-75\,m/s$), $A\delta$ ($1-5\,\mu m$, $5-35\,m/s$), and unmyelinated $C$ ($0.2-1.5\,\mu m$, $0.5-2.0\,m/s$).

Dorsal Root Ganglion

An enlargement along the dorsal root of each spinal nerve housing the cell bodies of unipolar sensory neurons.

Thalamus

A central brain structure in the sensory pathway that serves as an essential sensory relay station, routing incoming signals from the spinal cord to the cerebral cortex.

Cerebral Cortex

The outermost mantle of gray matter in the cerebrum responsible for conscious perception, integration of multiple sensory inputs, memory, and cognitive processing.

Precentral Gyrus

The region of the frontal lobe cortex that plans and dispatches voluntary motor commands through upper motor neurons.

Upper Motor Neuron

A motor neuron originating in the cerebral cortex whose axon descends through the CNS to synapse with lower motor neurons in the spinal cord gray matter.

Lower Motor Neuron

An efferent neuron located in the ventral horn of the spinal cord whose axon exits into peripheral nerves to directly stimulate skeletal muscle contraction.

Neuromuscular Junction

The specialized chemical synapse formed between the terminal of a lower motor neuron and the motor end plate of a target skeletal muscle fiber.