Neurobiology is one of the most interesting, innovative, and ever-evolving scientific fields that is defined by the most complex organ of the human body, the brain. Historically, it has been an enigma, but in recent years many advancements have been made in this field allowing us to know more about the brain than ever before. Often called the master organ of the body, it dictates many key functions of life like: breathing, physical motor activity, behavior, thinking, and memory. Needless to say, without the brain, many of our everyday activities that we take for granted would become nearly impossible to accomplish.
Unfortunately, like all other human organs, the brain is heavily impacted by disease. Before taking a closer look into neurodegenerative diseases, it is important to first understand the basic components of the brain. It can be divided into three main parts: the forebrain, midbrain, and hindbrain. Each of these areas control vital functions. The forebrain is the largest part of the brain and where all of our critical thinking takes place. It controls our cognitive skills, auditory information, and visual information. Our memory is also stored in this area. The midbrain is part of the central nervous system, having control over our hearing, movement, pain, and sleep. The hindbrain controls involuntary functions like breathing and heart rate. While each part of the brain functions on its own, the complexity becomes evident when it is realized that each part is interconnected through networks.
To better understand how each part of the brain is connected with one another, we need to look in a little further into what makes up the tissue of the organ. The first are the cerebral arteries. These arteries provide blood flow throughout the brain, ultimately providing oxygen to this vital organ. Glial cells are non-neuronal cells that act as the main support system for the brain. These cells assist with development, repair, and even protect the neuronal cells of the brain. Some types of glial cells you might have heard of include: astrocytes, microglia, oligodendrocytes, and schwann cells. The rest of the brain and nervous system are made up of neuronal cells. It is said that there are about 80 to 100 billion neurons in the brain. Neurons have the ability to communicate with one another through electrical and chemical signals. These connections are made possible by synapses, which is a part of a neuron that allows signals to pass through. The three main types of neurons include: motor neurons, sensory neurons, and interneurons. These structures of the brain form into what is called the neural network.
Now that the connections between different areas of the brain have been established, we can discuss how disease impacts this complex network. It is now understood that different diseases impact different types of neurons, in different parts of the brain. For example: cerebrovascular diseases or strokes, are diseases that impact the arteries of the brain. Blood flow is often restricted in this type of disease, preventing oxygen from being readily available in the brain. This oxygen deprivation heavily affects the survival of neuronal cells in the brain. Infectious diseases also can affect the brain. These life-threatening diseases, like meningitis, attack both the blood vessels and neurons. Neurodegenerative diseases primarily impact the neuronal cells, where neuron cell death is common.
Let’s break down the term neurodegenerative. “Neuro” meaning nerves or nervous system and “degenerative” meaning to decline or deteriorate. This translates to the breakdown or deterioration of the nerve network. Both genetics and environmental factors play key roles in the development and onset of neurodegenerative diseases. A common feature of these diseases is the atrophy or shrinkage of the brain. The identification of disease genes has led to greater knowledge of disease pathways; however, cures and treatments remain limited as it has been difficult to reverse the progressive nature of these diseases.
Alzheimer’s is an irreversible disease characterized by progressive memory loss due to neuronal death. Neurons begin to deteriorate in the hippocampus, the part of the brain that helps in the formation of memories. Signs and symptoms usually start around age 65, and are unlikely to be present at earlier ages. The deterioration continues to get worse as time passes, eventually leading to very visible atrophy of brain tissue. The direct cause of Alzheimer’s is still unknown. There is evidence that genetic mutations could be responsible for this disease. Ultimately, it is likely that it is a combination of genetics, environmental factors, lifestyle choices, and age that lead to the onset of Alzheimer’s.
Huntington’s is a genetically inherited disease characterized by the degeneration of neurons. Unlike Alzheimer’s, it is more likely to have visible signs and symptoms earlier in people’s lives. Specifically around 30 or 40 years of age. This disease is caused by genetic mutations in the HTT gene, and is inherited in an autosomal dominant pattern. Most of the time, this means one parent will have this condition, and the other parent will not. Therefore, there is a 50 percent chance that their children will inherit the condition. Symptoms vary person to person, but are related to the disturbance of motor and cognitive functions. Similarly to Alzheimer’s, there is no current cure; however, treatments and medications are available to help alleviate or improve symptoms.
With millions of people affected by neurodegenerative diseases worldwide, and the continual scientific advancements in this field happening everyday, we will hopefully decipher the unknowns of the brain leading to cures and treatments to these fatal diseases.
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