Neurons

Dendrites

Branching neuron structures lined with synaptic receptors that receive incoming signals from other neurons.

Dendritic Spines

Small outgrowth projections on dendrites that increase total surface area to receive more chemical inputs.

Cell Body (Soma)

The central processing structure (grey matter) of the neuron that contains the nucleus and organelles.

Axon Hillock

The cone-shaped region where the axon connects to the cell body and where the nerve impulse/action potential begins.

Axon

A long, thin nerve fiber extending from the soma that transmits electrical signals toward the terminal boutons.

Myelin Sheath

Fat and protein insulation surrounding vertebrate axons that speeds up signal conduction up to 10x without losing signal strength.

Nodes of Ranvier

Unmyelinated gaps along the axon where the axonal membrane depolarizes to propagate electrical signals.

Terminal Boutons

Presynaptic endpoints of an axon that release neurotransmitters into the synaptic gap to signal a target neuron.

Motor Neurons (Efferent)

Neurons with soma in the spinal cord that convey outgoing motor signals directly to muscle fibers.

Sensory Neurons (Afferent)

Neurons specialized to receive environmental stimuli (e.g., skin touch) and conduct incoming signals toward the CNS.

Astrocytes

Star-shaped glia in the CNS that absorb/release ions, clear cellular waste, regulate nutrient supply, and recycle glutamate.

Microglia

Tiny glial cells that act as immune defenders by clearing toxic materials and dead debris in injured brain areas.

Oligodendrocytes

Glial cells with "few branches" that produce and form myelin sheaths in the Central Nervous System (CNS).

Schwann Cells

Glial cells that produce and form myelin sheaths around peripheral nerves in the Peripheral Nervous System (PNS).

Radial Glia

Specialized glial cells that act as physical tracks to guide neuronal migration and axonal growth during early brain development.

Blood-Brain Barrier (BBB)

A protective vascular barrier made of endothelial tight junctions that blocks viruses, toxins, and harmful chemicals from entering the brain.

Passive BBB Transport

Unassisted movement of fat-soluble molecules, oxygen (O2), and carbon dioxide (CO2) directly across the blood-brain barrier wall.

Active BBB Transport

Energy-expending (ATP) protein pumps that actively pull glucose, amino acids, certain hormones, and vitamins across the BBB into the brain.

BBB Clinical Limitation

The barrier prevents standard pharmaceutical treatments (such as brain cancer chemotherapy drugs) from entering brain tissue.

Cerebellum Neuron Count

The brain region containing the vast majority of human neurons (~70 billion out of 86 billion total).