Fundamentals of Neuroscience
Santiago Ramón y Cajal is considered by many to be the father of modern neuroscience. What many do not know is that as a charismatic and fervent young man, his true passion was not for the sciences but rather for the arts. While familial pressure resulted in him entering the field of medicine, his romantic and poetic spirit never ceased. His journey towards birthing modern neuroscience began when he came across a 14 year old technique termed the Golgi (Silver Nitrate) stain in a textbook. This technique had revolutionized microscopic investigations of the nervous system, as it allowed for intricate staining of entire cell bodies as well as the fibrous branches which shot out from them. He was captivated, almost hypnotized, by what he saw. When he learnt how to set up the stain in his lab, he became consumed with the task of improving its resolution, and succeeded in doing so. Throughout this obsession, he created thousands of hand-made drawings depicting what he saw under the microscope. In his autobiography, he states “Look, here I am pursuing a goal of great interest to painters: appreciating line and color in the brain.” He termed the cell bodies “mysterious butterflies of the soul” which reside in a “flower garden of grey matter.”
With these images, Cajal was able to make one of the most foundational discoveries in the field of neuroscience. Up until that point, experts had postulated that the entire nervous system was a continuous network of fatty tissue; an uninterrupted web of nodes and wires, completely fused like one large pipe system. People knew that nerves conduct electricity, and at the time, the only known way to propagate such a spark was through continuous, uninterrupted copper wiring. With his imaging, Cajal was the first to suggest that there exists a tiny space between every one of the billions of neurons in this network, which we now know as the synapse. He inferred that electricity was somehow jumping past this space, from neuron to neuron, in chains of communication. Set in the 1800s, this theory he sketched was unbelievably bold, and completely counterintuitive to existing conjectures. However, it was empirically supported by his massive collection of drawings. Many years later, his ideas were confirmed by electron microscopy. This is a recurring theme throughout science; observation trumps intuition every day of the week.
While this discovery is his most famous, it is not the only contribution that Cajal made. He was the first to predict that these cells are “dynamically polarizable” and “adaptable”, referring to the characteristic restructuring of neural connections with development and experience. This would later be termed plasticity. He was also able to infer that these electrical signals must travel in one way only, which was later confirmed, and will be discussed in great molecular detail in this chapter.
Cajal is an inspiration to neuroscientists around the world not just for his brilliance and incredible intuition, but also for the wonder, marvel, and passion that translated through each of his works. He cuts through the stereotype that science is only made for the rigorous and the quantitative. His devotion to the beauty of the brain is what allowed him to see so much where people saw so little. As Dr. Elle O’Brian puts it “Perhaps only an artist’s eye could have seen so much in a slice of the brain.” As you mature into a neuroscientist, you will sometimes be bogged down by the molecular and anatomical details which have to be memorized. In these times, you must never forget that to study the brain is to study human nature. It is to inquire about what makes us think, behave and feel the way we do. It allows for discoveries regarding the basis of friendship, hatred, war, love, addiction, intelligence and so much more. It is awe striking that we are the only species with the capabilities of modelling ourselves. There is a saying that “if a tree fell in the middle of a forest and no one could hear it, did it really fall?”. Dr. Jeff Hawkins extends this saying to the brain; “if a universe came in and out of existence but there was no brain to discover its wonders, then did that universe ever truly exist?”
In this unit, we will be introducing the structure and molecular function of these darkly stained cells, which we now call neurons. In addition, we will be discussing other types of cells, termed glial cells, which cannot be seen via silver stain but are extremely important nonetheless. Lastly, we will discuss how neurons conduct electrical signals, how these signals are converted into a chemical cascade within the synapse, and how this then allows that electrical signal to “jump” to the next neuron.
