Understanding The Life And Death Of A Neuron

For many years, most neurologists believed that we were born with all the neurons we would ever carry in our brains. As children, we can develop new neurons to help create the pathways, known as neural circuits, that function as information pathways between different regions of the brain. However, scientists believed that after a neural circuit was created, the development of any new neurons could interrupt the flow of information and disable the brain's communication system.

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Introduction to Brain Basics

In 1962, scientist Joseph Altman questioned this belief when he saw evidence of neurogenesis, as the birth of neurons, in a region of the brain of an adult rat known as the hippocampus. He then reported that newborn neurons migrated from their birthplace in the hippocampus to other regions of the brain. In 1979, another scientist, Michael Kaplan, proved Altman's findings in the rat brain and in 1983 Kaplan found neural progenitor cells in the forebrain of an adult monkey.

In the early 1980s, a scientist tried to explain how birds learn how to sing, suggesting that neuroscientists need to analyze neurogenesis in the adult brain and begin to determine how it can make sense. In several experiments, Fernando Nottebohm and his team revealed that the number of neurons in the prehensals of male canaries increased enormously during the mating season. This was the same time when the birds had to learn new songs to attract females.

Why, however, did this bird resin create new neurons at such a life-saving time in learning? Nottebohm believed it was because new neurons helped to maintain new song patterns in the neural tissues of the forebrain, as the region of the brain that regulates complex behavior. These new neurons made learning possible. As birds develop new neurons to help them remember and learn new singing patterns, Nottebohm believed that mammalian brains can do the same.

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Elizabeth Gould discovered evidence of newborn neurons in another region of the brain in monkeys. Fred Gage and Peter Eriksson also demonstrate that the adult human brain develops new neurons in a similar region. For several neuroscientists, neurogenesis in the adult brain is still an unproven theory. However, other neuroscientists believe that the evidence provides interesting possibilities associated with the role of adult-generated neurons in memory and learning.

Architecture of the Neuron

The central nervous system, which includes the brain and spinal cord, consists of two primary types of cells: the neurons and the glia. Glia are more than neurons in different regions of the brain, however, neurons are the major structures in the brain. Neurons are information providers. They use electrical impulses and chemical signals to transmit information between different regions of the brain and between the brain and the rest of the nervous system. Everything we think, feel and do would be impossible without the use of neurons and the glial cells, known as astrocytes and oligodendrocytes.

Neurons have three primary parts, including a cell body and two extensions, known as an axon and a dendrite. Within the cell body is a nucleus, which regulates the activities of the cell and contains the genetic material of the cell. The axon is characterized by a very long tail and it transmits messages from the cell. Dendrites are equally characterized as those of the branches of a tree and they receive messages from the cell. Neurons communicate with each other by sending chemicals, known as neurotransmitters, over a very small area, known as a synapse, found between the axons and the dendrites of adjacent neurons.

There are three types of neurons:

• Sensory neurons: Transfer information from the sensory organs, such as the eyes and ears, to the brain.
• Motor neurons: Manage voluntary muscle activity and transmit messages from nerve cells in the brain to muscles.
• All other neurons are known as Inter-neurons .

Scientists believe that neurons are the most varied type of cell in the human body. Within these three types of neurons are hundreds of different types of neurons, each with specific capacities for message transmission. The way these neurons interact with each other through making connections is ultimately what makes people unique in how we think, feel and act.

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Birth of the Neuron

The range in which new neurons are made in the brain has been a controversial topic among neuroscientists for many years. Meanwhile, although almost all neurons are present in our brains by the time we are born, there is recent evidence to support that neurogenesis, as the scientific word used to describe the birth of neurons, is a lifelong procedure.

Neurons are born in regions of the brain that are filled with neural progenitor cells, known as neural stem cells. These cells have the potential to develop all, if not all, of the different types of neurons and glia found in the brain. Neuroscientists have discovered how neural progenitor cells function in the laboratory. While this may not be exactly how these cells behave when they are in the brain, it does give us data on how they can function when they are in the brain's environment.

The science of stem cells is still very recent and could eventually change with further discoveries. Researchers, however, have discovered enough evidence to support, such as to demonstrate how neural stem cells make up the other cells of the brain. Neuroscientists refer to this as the stem of a stem cell and it is basically the same as the concept of a pedigree.

Neural stem cells increase by dividing into two and creating two new stem cells, two early progenitor cells, as one of each. If a stem cell divides to make another stem cell, it is believed to renew itself. This new cell has the potential of making more stem cells. If a stem cell divides to make an early progenitor cell, it is said to be distinct. Differentiation is when a new cell is more technical in structure and function. An early progenitor cell does not have the potential of a stem cell to produce several different types of cells. It can only make cells in its alternating line. Some progenitor cells can self-renew or go one of two ways. One type will develop astrocytes. The other type will develop neurons or oligodendrocytes.

Migration of the Neuron

Once a neuron is born, it must move to the region of the brain where it will function. But, how does a neuron understand where it should go? And, what does it help to get there? Neuroscientists have determined that neurons use two different methods to travel:

• Several neurons migrate by following the long fibers of cells, known as radial glia. These fibers move from the inner layers to the outer layers of the brain. Neurons glide and the fibers until they reach their destination.
• Neurons also travel by using chemical signals. Scientists have found special molecules on the surface of neurons, known as adhesion molecules, that bind to similar molecules on nearby glial cells as nerve axons. These chemical signals will also eventually help guide the neuron to its final destination in the brain.

Not all neurons are successful in their journey. Scientists believe that only one-third of these neurons will reach their destination. Some cells die during the process of neuronal growth. Some neurons may also survive, but end up where they do not belong. Mutations in the genes that regulate migration create areas of wrong or abnormal neurons that can cause disorders, such as epilepsy. Scientists believe that schizophrenia is partly caused by improperly guided neurons.

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Differentiation of the Neuron

When a neuron reaches its destination, it must begin with its initial function. This last measure of differentiation is one of the most misunderstood sections of neurogenesis. Neurons are responsible for the transmission and uptake of neurotransmitters, as chemicals that provide information between cells. Depending on their location, a neuron may perform the role of a sensory neuron, a motor neuron, or an interneuron, sending and receiving specific neurotransmitters.

In brain development, a neuron depends on molecular signals from other cells, including astrocytes, to determine the shape and location, the type of transmitter it makes, and with which other neurons it can connect. These newborn cells establish neural circuits, as data pathways that connect from neuron to neuron, which is determined during adulthood. However, in the moderate brain neural circuits have already developed and neurons need to find a way to fit. When a new neuron settles, it starts to look like cells are trapped. It then develops an axon and dendrites and begins to communicate with its neighbors.

Death of the Neuron

Although neurons are the longest living cells in the human body, large numbers often die during migration and differentiation. The lives of some neurons can sometimes take unexpected turns. Several health problems associated with the brain, spinal cord, and nerves are the result of the unnatural deaths of neurons and supporting cells.

• In Parkinson's disease, neurons that make the neurotransmitter dopamine die to the basal ganglia, a region of the brain that controls body movements. This causes difficulty initiating movement.
• In Huntington's disease, a genetic mutation causes the overproduction of a neurotransmitter, known as glutamate, that kills neurons in the basal ganglia. As a result, angry and cruel individuals are uncontrollable.
• In Alzheimer's disease, unhealthy proteins build up in and around neurons in the neocortex and hippocampus, sections of the brain that control memory. When these neurons die, people lose their ability to remember and perform regular tasks. Physical damage to the brain and other regions of the central nervous system can also kill nerves.
• Injury to the brain, when damaged by a stroke, can completely kill nerves or slowly die from the oxygen and nutrients they need to survive. Spinal cord swelling can interfere with the communication between the brain and nerves as they lose their germination to axons located under the site of injury. These neurons survive but they can lose their ability to communicate.

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Conclusion for Brain Basics

Scientists hope that by understanding more about the life and death of neurons, they could develop treatment options and perhaps even cure brain disease and disorders that eventually affect the lives of many people in the United States.

Most current research studies suggest that neural stem cells can generate many, if not all, of the different types of neurons located in the brain and nervous system. Determining how to control these laboratory stem cells in specific types of neurons may develop a new brain supply to replace those that have been damaged or dead.

Treatment approaches can also be made to take advantage of growth factors and other signaling mechanisms in the brain, which tells precursor cells to create new neurons. This will make it easy to fix, resize and refresh the brain from within.
A neuron is characterized as a nerve cell that is considered the basic building block of the central nervous system. Neurons are similar to other cells in the human body, however, neurons are responsible for transmitting and transmitting information through the brain. As mentioned above, there are also several different types of neurons that are responsible for a variety of functions. Understanding the life and death of neurons is essential to help understand the mechanisms of neurological diseases and hopefully their treatment and cure.