The cells that compose the nervous system are extremely specialized. Due to their unique power and function within the body, the connections and pathways that are established between nervous centers are complicated and valuable.
When you look at humanity, with more than 7 billion humans on the planet, certain things unify us in terms of our basic needs and anatomical structure, but there are many other things that differentiate us, such as language, cultural background, profession, etc.
When you look at the cells that make up every human being on the planet, there is a similar dichotomy of unity and individuality. There are trillions of cells throughout the body, and hundreds of different types of cell that perform essential and specialized tasks. While cells do share some characteristics, not all cells are created equal. Some of the most uniquely specialized cells in the body are brain cells, more formally known as neurons, and there are about 100 billion of these that make up mankind’s greatest evolutionary achievement.
However, unlike the vast majority of cells in the body, neurons do not undergo mitosis – cell division. If these cells are so important, why don’t they have the ability to replicate?
Before we dig into that answer, we should talk a bit more about neurons, including their unique functions and structure.
What is a Neuron?
A neuron is a nerve cell/brain cell that has the ability to receive, manipulate and disseminate information through chemical and electrical signals. This provides neurons with the rather incredible ability to directly and rapidly communicate across long distances to other nerve cells throughout the body. Similar to a computer, which calculates and communicates at lightning-fast speed, your neurons are complex and highly specialized, with intricate connections and pathways for communication that allow your body to function normally.
These nerve cells have three main structural parts – axon, dendrites and soma – the explanation of which will help to shed some light on the function and importance of these cells.
Axon – This long structure within the cell can be likened to an electrical wire in an insulated cord. Electrochemical messages are carried along the length of the cell on an axon, which is often protected by a layer of myelin – composed of fat and protein. This myelin actually helps to increase the speed of electrochemical transmission, but certain nerve cells, such as those in the spinal cord, do not have this myelin sheath.
Soma – This is the primary area of a nerve cell, where the essential organelles are located, including the mitochondria, ribosomes and nucleus, among others. This part of a nerve cell is the most similar to other types of cells in the body.
Dendrites – These are small tendril-like projections on one or both side of a nerve cell, and they are the point of contact and communication between neurons. Dendrites are also referred to as nerve endings.
Why Do Cells Undergo Mitosis?
As mentioned earlier, almost all cells undergo mitosis – the act of replicating a cell’s genetic material, in the nucleus, and then dividing into two fully functional cells with the same specializations and characteristics. Reproductive cells undergo a slightly different process called meiosis, and there are some cell types that do not replicate, including neurons. For example, blood cells lack a nucleus, making it impossible to undergo cell division. Similarly, heart cells generally do not divide because they are constantly working; basically, if your heart cells die, they are not replaced.
Generally speaking, cell replication and division is performed to replace dead or damaged cells, ensuring full functionality in tissues and organs. Cells cannot live forever, although some do survive longer than others. With that in mind, it would logically follow that nerve cells – which possess a nucleus – would make the ability to replicate and replace damaged cells an evolutionary priority. Yet, that isn’t the case… why?
Why Don’t Nerve Cells Undergo Mitosis?
The cells that compose the nervous system are extremely specialized. Due to their unique power and function within the body, the connections and pathways that are established between nervous centers are complicated and valuable. Most of the cellular resources in a neuron are devoted to communicating and carrying electrochemical messages to other nerve cells. Similar to heart cells dedicating all their energy to pumping your blood, nerve cells don’t have time or resources to copy themselves and reproduce.
Furthermore, since these cells are so highly specialized and the intricate network of communication (between 100 billion different cells) is so complicated, the addition of new nerve cells could disrupt those pathways, affecting the normal function of the body, its muscles, and ability to communicate effectively.
Despite the fact that neurons contain a nucleus, they do not possess centrioles, which are essential for cell division. As nerve cells develop, they do not produce these key organelles, making replication impossible. For this reason, protecting your brain and spinal cord is of the utmost importance. Any potential damage or risk to your nervous system should be taken very seriously, as those cells won’t simply replicate overnight. That being said, recent research has revealed that there may be some hope for those worrying about the safety of their nerve cells…
Neuronal Stem Cells
There has long been a consensus in the scientific community that once nerve cells have died, there is no way to replace them. However, that isn’t entirely true. There are very specialized cells in the brain known as neuronal stem cells that can produce new neurons when old ones have died. This is seen as a partial explanation for the occasional recovery in patients with serious brain injuries. This process takes time, and is not a constant part of brain maintenance, so it is still important to avoid any damage to the brain and spinal cord at all costs.
These neuronal stem cells (neural stem cells, or NSC) are primarily active while the brain is initially developing as an infant, but many of them cease to function as we age. Some of the cells remain active throughout our lives, differentiating into different types of cells, including astrocytes, oligodendrocytes and neurons.
Neuronal stem cells are very intriguing for researchers, who are now isolating these cells and trying to determine their mechanism for turning their replication functions on and off. Researchers could potentially apply their findings to healing or treating the brain in ways we thought were impossible.
The nervous system is the seat of consciousness and control in the human body; understanding how it works, and what makes nerve cells different from other cells, provides yet another glimpse into the incredible complexity of our existence!
- University Of Florida
- UC Santa Barbara
- Arizona State University (Link 1)
- Arizona State University (Link 2)