Why Neurons Cannot Regenerate and How They Can Regrow After Injury

Neurons, or nerve cells, play a pivotal role in the functioning of our nervous system. They are responsible for processing and transmitting information. However, unlike many other cells in the body, neurons have a unique characteristic that sets them apart: they do not readily regenerate. This is partly due to the absence of centrioles in their cell bodies, which are crucial for cell division.

Why Neurons Cannot Regenerate

Among the reasons why neurons cannot regenerate is the lack of centrioles. Centrioles are essential for the formation of spindles during cell division, which help in the movement of chromosomes. Since neurons lack centrioles, they cannot undergo mitosis or meiosis, making regeneration a non-functional process for them.

Unlike the peripheral nervous system, which allows axons to regenerate at the distal portion when disconnected from the cell body, central nervous system (CNS) neurons have a significantly harder time regenerating their axons even from stumps. This means that when an axon in the CNS is damaged, the damaged part of the axon dies, leaving the neuron itself with a stump. The neuron itself may survive, but a new connection to another cell cannot be formed without a functional axon.

Neurogenesis: The Regeneration Process in Adult Brain

Contrary to the popular belief that neurons cannot regenerate, the adult brain does possess the capability to produce new neurons through a process called neurogenesis. This process has been observed in the subventricular area of the brain, where neural stem cells can differentiate into adult populations of neurons. This is a positive discovery for conditions where brain function can be compromised, such as after a stroke or injury to peripheral nerves.

During neurogenesis, neural stem cells divide and differentiate into neurons that can integrate into existing neural networks. However, the rate and extent of neurogenesis vary and are often limited, making it less effective in certain parts of the brain. This highlights the need for interventions that can enhance neurogenesis to boost brain function recovery.

Peripheral Nerve Regeneration

Seemingly, peripheral nerves are more capable of regenerating compared to the central nervous system. After injury, the proximal end of severed axons swells and degenerates retrogradely. However, subsequent clearance of debris allows for axonal sprouting, with growth cones appearing and far-reaching axon growth observed. The presence of Schwann cells in the endoneurium, also known as the endoneurial tube, facilitates this growth. The rate of human axon growth can reach up to 2 mm per day in small nerves and 5 mm per day in larger nerves.

While peripheral nerves can regenerate to a significant extent, the regrowth is limited compared to central nervous system neurons. The integrity of the neuron's cell body and its contact with Schwann cells are crucial for this process.

Conclusion: Enhancing Neurogenesis and Brain Plasticity

The findings regarding neurogenesis and nerve regeneration open up new avenues for developing treatments for brain injuries and neurological disorders. By enhancing neurogenesis, it may be possible to improve the plasticity of the brain, which could be instrumental in the recovery of functions lost due to conditions like stroke. Drugs or therapies that promote neurogenesis could play a crucial role in these advancements.

In summary, while neurons in the central nervous system generally cannot regenerate, peripheral nerves can regenerate to some extent. The process of neurogenesis in adult brains offers a pathway for the brain's plasticity and recovery from injuries. Further research and new technologies are needed to optimize these natural processes for better outcomes in neurological conditions.