The Internal Structure of Neurons - Introduction to Psychobiology (Part 2)

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Internal Structures

In the previous post, we explored the structure of a neuron. Now, we will take a look at its internal components starting from the outermost part of the soma and ending in the nucleus. 

First, we have the membrane, which is composed of a lipid bilayer that forms a border between the intra and extracellular space.  It allows small molecules, like water, to enter the cell, but regulates the entrance/exit of molecules based on their size and charge.  A  molecule's ability to cross the membrane is known as permeability. In the case of neurons, their membranes are semipermeable and are highly permeable to potassium (K+) and slightly permeable to Chloride (Cl−) and Sodium (Na−). Outside of the neuron, there is a balance between the high concentration of Na and Cl. Inside of it, there is a high concentration of K. This is relevant in understanding how neurons communicate, but we will explore this relationship later on.
The neuron
Then we have the cytoplasm, which is a semi-liquid substance inside of the cell (1) that contains the organelles. These are sub-units that are responsible for specific  functions within a cell. One type of organelles is ribosomes. These are produced by the nucleolus and are responsible for the production of proteins (2). 

DNA, which contains the genetic material of an organism, is usually found in the nucleus, but can also be found in the mitochondria of a cell(4). The latter, also known as the powerhouse of the cell, are organelles that convert oxygen and nutrients into adenosine triphosphate (ATP(6)), which aids with energy metabolism. Moreover, mRNA carries the genetic codes from the DNA in the nucleus to ribosomes ((5) in order to translate it into proteins.  


More organelles include the Golgi apparatus, which is responsible for transporting proteins and it's located close to the endoplasmic reticulum (7). The latter has two forms: smooth and rough endoplasmic reticulum. It is a membrane that has several functions, three of them include the transportation, synthesis, and modification of proteins (8). The Golgi apparatus also produces lysosomes, which are sacs full of enzymes, which aid in the breaking or uniting of chemicals by acting as a catalyst. Finally, there is the nucleus, which as previously stated contains DNA. Additionally, it contains the nucleolus and chromosomes (1). It usually has a round shape and it is found at the center of the cell, protected by the nuclear membrane (1).

Here is a picture of an axon terminal that was cut open taken from an electron microscope. 
This has to be one of my favorite pictures!


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References

1. "Physiology of Behavior" by Neil Carson

2. http://rna.ucsc.edu/rnacenter/ribosome.html

3. https://www.genome.gov/26524120/chromosomes-fact-sheet/

4. https://ghr.nlm.nih.gov/primer/basics/dna

5. http://www.britannica.com/science/messenger-RNA

6. https://micro.magnet.fsu.edu/cells/mitochondria/mitochondria.html

7. http://www.britannica.com/science/Golgi-apparatus

8. http://www.britannica.com/science/endoplasmic-reticulum

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