Neuroanatomy I: Basics of Cellular Anatomy

Introduction

The Nervous System. It is one of the most complicated puzzles for scientists to study our body, an entity responsible for everything from blinking to critical thinking. The history of neuroanatomy dates back to ancient Egypt, where a manuscript known as the Edwin Smith Papyrus was found to be the oldest written evidence of neural study. As time progressed, many Greek and Roman scientists began theorizing about the role of the brain in our body. A significant figure in this field would be Galen, a Roman physician who believed anatomy was the fundamental of all medical knowledge. While the Greek and Roman eras mainly focused on philosophy or religion to solve scientific mysteries, the Renaissance period resulted in a large growth in scientific and medical research. In 1664, Thomas Willis published the Cerebri Anatome and coined the term Neurology. This text provided the foundation for neuroanatomical research. In 1894, Santiago Ramón y Cajal, one of the Founding Fathers of Modern Neuroscience, was able to provide a three-dimensional map of the avian brain by using silver nitrate staining techniques. Similarly, many future scientists continued to study neuroanatomy and made their revolutionary contributions that helped the world understand the brain in more depth. This passage will outline the key concepts of neuroanatomy including the types of cells in the nervous system, the parts of the brain and much more.

Neurons

Figure 1 displays the parts of a basic neuron, the primary components of the Nervous System. The dendrites are located at the front end of the cell, and they act as the receiving end of electrical and/or chemical signals from other neurons. At the other end of the neuron, there is the axonal terminal, the part responsible for sending the signal out to the next neuron in line. The axon is what connects these two elements, and allows for the quick transmission of signals. This system is similar to a charger for a laptop; the dendrites act as the input plug that is inserted into the wall outlet. The wire is the axon that conducts the energy to the output and finally, the axon terminal is represented by the output end of the charger. Schwann cells are key figures in the production of the myelin sheath. The myelin sheath plays a huge role in the transfer of information between neurons by helping signals to transmit from fifteen to three hundred times faster than it would have without a sheath. When referring to the laptop charger analogy provided earlier, the myelin sheath acts as the protective rubber insulation around the wire (axon), helping with transmitting the energy to the laptop. The cell body (or soma) is the part of the cell that holds the nucleus (a part of the neuron that instructs the cell to conduct necessary functions to survive and fulfill its purpose). Lastly, the Nodes of Ranvier are unmyelinated nodes covered in ion channels involved in regenerating any lost energy during action potential (the process of transporting signals from the dendrites to the axon terminal through a series of chemical reactions).

The Neuronal Cell Membrane

Though Figure 2 may seem a little intricate, the concept behind it is simple to understand. The neuron’s cell membrane is made up of two major parts, phospholipids and ion channels. Firstly, phospholipids are what make up the general structure of the neuronal bilayer. This layer is formed by two types of phospholipids known as phosphoglycerides (located on the outer membrane) and sphingolipids (locates=d on the inner membrane). Secondly, ion channels are responsible for regulating the entry and exit of ions when conducting action potential. They are made up of proteins that attach themselves onto the membrane in the early stages of development.

Glial Cells

Glial Cells in the nervous system play a vital role in maintaining neural health. There are four types of glia that can be found in the Central Nervous System (CNS) and two types in the Peripheral Nervous System (PNS). Firstly, the Ependymal Cells form in the ventricles, and they play an important role in the production of Cerebrospinal Fluid (CSF). The CSF helps the brain’s hemispheres communicate with each other, and it plays a key role in transporting signals from the peripheral nervous system to the brain via the spinal cord. Next on the list are Oligodendrocytes (CNS) and Schwann cells (PNS). These cells are responsible for the action of myelination, the process in which the myelin sheath is formed. Additionally, Astrocytes help with cellular metabolism. Cellular metabolism is the function in which cells generate energy through a series of chemical reactions that happen either aerobically or anaerobically. Microglia, on the other hand, are key in clearing out waste products from metabolic and non-metabolic reactions. Finally, Satellite cells are found in the PNS on sensory, sympathetic and parasympathetic ganglion cells. These cells are responsible for forming a protective layer around these ganglia and maintaining functionality.

References

Hamilton, L. (1976, January 01). A Brief History of the Study of Neuroanatomy. Retrieved October 13, 2020, from https://link.springer.com/chapter/10.1007/978-1-4684-2247-4_1

History of Neuroscience. (n.d.). Retrieved October 13, 2020, from https://youthneuro.org/media/myelin/slides/1.02__History_of_Neuroscience_1.pdf

Introduction to Neuroanatomy. (n.d.). Retrieved October 13, 2020, from https://youthneuro.org/media/myelin/slides/1.06__Introduction_to_Neuroanatomy.pdf