Topics and Speakers Stephen Rayport, MD, PhD
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Synopsis
In this lecture, Dr Stephen Rayport exhaustively limns the basic anatomical elements and physical properties of neurons and glia. He ends the lecture with examples of how insults to this anatomy results in neurological and neurodegenerative disorders.
The brain is composed of two kinds of cells: neurons and glia. Neurons are composed of a cell body (known as the soma, which encloses the nucleus), dendrites (which receive information from other neurons), an axon (which is covered by a myelin sheath to speed up the passage of the message received from the dendrite), and the bouton (or the "foot" of the neuron, which also receives information from other neurons since it contains dendrites). Two of the neurons showed for their anatomy are pyramidal cells and Purkinje cells. Cytoskeletal structures that differentiate neurons from other body cells, such as the invagination of neuronal membranes and neurotransmission, are discussed via freeze-fracture microscopy.
Dr Rayport also stresses that there are three main differences between axons and dendrites. The first one is that there is only one axon, whereas dendrites are typically many, since they are tree-like and branch out. Secondly, neurofilaments identify axons whereas microtubule-associated proteins define dendrites. Thirdly, the dendrites are restricted to the brain region, whereas the axon, which has to carry information over long distances from different parts of the body, can extend over large distances (up to 3 feet).
Attention is then focused to glial cells. There are two types of glial cells: macroglia and microglia. Macroglia include astrocytes and oligodendrocytes. The microglia are the macrophages of the brain; they originate in the bone marrow and make up part of the central nervous system.
For a long time it was believed that glial cells had no discernible role in the brain. This has turned out to be far from the truth, as it has been discovered that glial cells provide multifarious functions and can also multitask. Some of these functions-such as providing trophic support to neurons, participating in neurotransmission by getting rid of excess neurotransmitters, and giving rise to the myelin sheath that covers axons-are just a few of the important roles these cells perform. Other functions are responding to brain injury caused by neurodegenerative diseases such as HIV encephalitis and Alzheimer's.
With the mention of such diseases, the lecture concludes with an interesting example of how insults to the anatomy of neurons can result in Parkinson's disease. The hallmark of this disease is the presence of Lewy bodies, "clumps of neurofilaments which have gotten backed up." These clumps take over the cell body and literally choke it. Of course, Lewy bodies are formed when the neuron has degenerated in a certain way. Current research is focusing on the development of these Lewy bodies and what kind of pharmacology is needed to slow down such development.
