Galvani’s suggestion that neural signaling was electrical in nature
continued to catch on. Around 1850, the German physician and physi-
cist Hermann von Helmhotz (1821-1894) measured the speed of an
electrical signal moving along a nerve fiber, finding it to be about 100
kilometers per hour in the preparation of frog leg muscle he used. He
later obtained a similar speed for nerve conduction in humans. A few
years later, Walt Whitman (1819-1892) wrote a famous poetic line: “I
sing the body electric.”What are nerve fibers? Nerve cells have a basic construction and
biochemistry very similar to all cells for all of life on Earth. There are
chromosomes containing genetic information, coded into the molec-
ular structure of DNA. There are structures involved in the synthesis
of proteins and their transport to desired locations within the cell.
There are structures dedicated to the generation of cellular energy.
All this is enclosed by a cell membrane, the structure that forms the
boundary of the cell. Within the cell there is also elaborate molecular
scaffolding, composed of protein polymers called microfilaments and
microtubules. Far from being a bag of disorganized fluid protoplasm, a
living cell is a highly ordered system of vast complexity.
Nerve cells are further characterized as having additional parts—
dendrites and axons—specialized for the communication of signals
from one cell to another (see Fig. 2.15). What we have been calling
nerve fibers—the thread-like structures connecting the brain with
various parts of the body, and observed by Vesalius and Descartes in
their dissections—consist mainly of bundles of axons.
Microscopic analyses of the brain revealed it to consist of densely
packed neurons and glial cells. The elaborate interconnectivity of
nerve cells in the brain was gorgeously illustrated in the drawings of
two great pioneers of neuroscience, Camillo Golgi (1843-1926) and