The Structure of the Neuron
Neurons share some traits with other cells, so the structure of the neuron will, in some parts, be familiar. Since the function of neurons is quite specific, they do differ structurally from other cells in some ways. Different types of neurons are different from one another; however, you can get an idea of the structure of neurons by looking at a motor neuron in the central nervous system.
The soma or cell body contains a large nucleus and nucleolus. The nucleolus contains typical organelles associated with cell structure, including the Golgi complex and rough endoplasmic reticulum. Neurons have an extensive cytoskeleton, including neurofibrils that separate the endoplasmic reticulum into individual dark-stained regions called Nissl bodies. Nissl bodies are unique to neurons (Yale, n.d.). Neurons do not divide; there is no cellular mitosis in these cells.
Processes or extensions come off of the soma; these are dendrites. Dendrites receive signals from other neurons; depending upon the cell, there may be a few dendrites or a great many dendrites. Axons are nerve fibers that send signals to other neurons. Axons end in synaptic knobsremember discussing those in Lesson 10? Neurons are grouped or classed based on the number of processes extending from the soma:
Multipolar neurons have one axon and multiple dendrites.
Bipolar neurons have one axon and one dendrite.
Unipolar neurons have only one process extending from the soma.
Anaxonicneurons lack an axon.
All of the functions of the cell are performed in the soma; proteins and other materials must travel outward toward the axon, and back toward the soma for disposal. This is called axonal transport.
You have about a trillion neurons in your body, overall. Keep in mind, thats your entire supply; theres no cellular repair or replacement with neurons. Neurons make up a very small amount of the total mass of nerve cells. While theyre the key part of your nervous system, they are small in mass compared to neuroglia (Stufflebeam, 2008).
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