unimaginable heights. Golgi believed in the reticular theory of the brain,
but Cajal was able to show that the brain was instead comprised of billions
of nerve cells. (It is widely accepted that the brain is formed by one
hundred billion cells, and that each brain cell can connect to tens of
thousands of other cells.) Cajal is the unquestioned father of neuroscience:
the titan who paved the way in demonstrating the stunning pathways and
conduits that nerves travel throughout the brain, spinal cord, and body.
Quite opposite of seeing the brain as a blob of gelatinous material,
Cajal envisioned the tissue as “the hum of the restless beehive which we
all have within us.”^12 Even the most naïve student of medicine can
recognize that cells are infinitesimally small, of course not visible to the
human eye. But Cajal, and those who followed in his footsteps, were able
to point to an astounding fact: between the outermost layer of the brain,
the cortex, where the impulse to move is initiated, and the muscle it
moves, say the thumb flexor muscle, there are only two nerve cells.
Microscopically tiny, the upper motor neuron (UMN) starts in the brain
cortex, and sends its axon, the spiny appendage that carries the electrical
signal, down through the brain and toward the brain stem. Here, it crosses
(“decussates”) and descends down the spinal cord. This same axon fiber
tendril continues on the opposite side of the spinal cord, until it synapses
with the lower motor neuron (LMN) in the neck. This nerve cell travels
from the spinal cord, out the nerve root between neck vertebrae, and down
the arm to the thumb muscle in the forearm. The axon for this LMN is
over two feet long in a regular-sized adult! It simply boggles the mind that
something so unimaginably slender can be so long. And it’s inconceivable
that any scientist figured out that the thinner-than-spider-silk axon fiber
runs the entire length of the connection from the spinal cord to the muscle.
(It also explains the near-impossible task of reconnecting every axonal
gossamer strand following a spinal cord injury, and why there is no
surgery to recouple the shredded ends ... yet.)
“When we look at his [Cajal’s] drawings today, we see not diagrams or
arguments, but the first clear picture of that remote frontier, drawn by the
man who traveled farthest into its endless reaches.”^13 Santiago Ramón y
Cajal ignited an investigation into the labyrinth of the brain and the mind.
He, like Golgi, lived to eighty-two years of age, still exploring, even on his
deathbed. Decades would pass before CT scans and MRI imaging
elucidated the live function of the brain, but Cajal was the voyager who