Relative Sizes of Structures in the Brain

Linear measure- ments and dimensions generally are given in microns or micrometers (µm) (1 µm equals one- millionth of a meter) or nanometers (nm) (1 nm or millimicron equals one-billionth of a meter). About 240,000 µm equal one inch. As a reference, the following are the dimen- sions of some non-neural structures: human ovum, 100 µm; cross-section of a skeletal muscle fiber, 10-100 µm; erythrocytes, 8–10 µm; bacteria, 0.1–8 µm; and viruses, 0.15–0.5 µm. Cell bodies of neurons...

 Shorter People Live Longer

The study was conducted to evaluate one aspect of the entropy theory of aging, which hypothesizes that aging is the result of increasing disorder within the body, and which predicts that increasing mass lowers life span. The first evaluation of the impact of human size on longevity or life span in 1978, which was based on data for decreased groups of athletes and famous people in the USA, suggested that shorter, lighter men live longer than their taller, heavier counterparts. In 1990, a study...

 How Small are Atoms?

Why are atoms so small? ... Many examples have been devised to bring this fact home to an audience, none of them more impressive than the one used by Lord Kelvin: Suppose that you could mark the molecules in a glass of water, then pour the contents of the glass into the ocean and stir the latter thoroughly so as to distribute the marked molecules uniformly throughout the seven seas; if you then took a glass of water anywhere out of the ocean, you would find in it about a hundred of your marke...