What is the diameter of a typical neuron cell body (soma)?

• A. ~2 µm
• B. ~20 µm
• C. ~200 µm
• D. ~0.2 µm

Answer: (B)

Neurons need a cell body large enough to house the nucleus and the machinery for making proteins, while still allowing long processes (dendrites and axons) to extend from it. For most neurons, the soma sits in the tens of micrometers range, with about 20 micrometers being a representative diameter. This size is just right to accommodate the nucleus, rough endoplasmic reticulum, mitochondria, and other organelles without making the cell impractically large.

A diameter of about 2 micrometers is far too small to contain a nucleus and the full set of organelles needed by a neuron. A diameter of 0.2 micrometers is on the scale of individual organelles or large macromolecules, not a whole cell. A diameter of 200 micrometers would be unusually large for a typical neuron soma, though a few exceptional cells can be larger. Therefore, the typical neuron soma is around 20 micrometers in diameter.