Tuesday, April 19, 2016

Introduction to Psychobiology Part 3 (Supporting Cells)

Anterograde and Retrograde Axoplasmic Transport

For more information about biopsychology, please check out "Physiology of Behavior" by Neil Carson

Before I start I want to cover axoplasmic transport

If you saw the pictures from part 2 (http://hbookreviews.blogspot.com/2016/04/introduction-to-psychobiology-part-2.html), there was something called microtubules that we did not cover. They are a bundle of protein filaments with two main functions (1). One of them is to form the cytoskeleton, which gives each neuron its shape. The other function is to engage in axoplasmic transport. This is the process in which substances are transported along the axon. Kinesin, which is a protein, carries the substance. If the movement is from the body of the cell towards the terminal buttons, the process is called anterograde and if it is from the terminal buttons to the soma it's called retrograde transport (Antero- means towards and retro means backwards).

Supporting Cells

Most people think that neurons are the only type of cells on the brain. This is not true. There are cells such as glial cells that support the neurons in different ways. For example, the type of cell mentioned above holds neurons together (glia means glue) and provides nutrients (2). 

There are three main types of glial cells. they are astrocytes, oligodendrocytes, and microglia (3). The first cell got its name because of its shape (astrocyte means star cell) and it is responsible for delivering nutrients, as well as controlling the development of neurons (4). Another function is to engage in a process known as phagocytosis. This procedure involves astrocytes cleaning up any cell in the central nervous system (CNS) that dies. 

The second type of cells, which are oligodendrocytes, produce an insulating sheath called myelin that covers the axons of neurons (5). The points at which the axon is not insulated are called nodes of Ranvier. 

The last cell is microglia. They also engage in phagocytosis (did you remember that this was the process of cleaning up dead cells?), as well as acting as one of the parts of the immune system in the CNS (6). If you paid close attention, you noticed that we have only covered supporting cells in the CNS, well, not anymore. In the peripheral nervous system (PNS) Schwann cells perform the same functions as oligodendrocytes cells (7) from the CNS (remember that the central nervous system is encompassed by the brain and the spinal cord).

The Blood Brain Barrier

An important thing to mention is the blood brain barrier. This refers to the barricade that separates the brain and the vascular system (8). The BBB is semipermeable, this means that some substances are able to pass through it (2). The barrier has some gaps were substances are able to come in and out of the vascular system. Another part, besides the small gaps, where substances can travel through the barrier is the postrema, which is the section responsible for vomiting. In this area, neurons can detect poison in the blood and thus induce vomit (9).

Feel free to leave comments, questions, concerns, or suggestions.

1. http://www.ruf.rice.edu/~bioslabs/studies/invertebrates/microtubules.html

2. "Physiology of Behavior" by Neil Carson.

3. http://www.ncbi.nlm.nih.gov/books/NBK10869/

4. http://www.networkglia.eu/en/astrocytes

5. http://www.britannica.com/science/oligodendrocyte

6. http://www.networkglia.eu/en/microglia

7. http://www.britannica.com/science/Schwann-cell