Neurodegeneration

Jakub – Year 12 Student

Editor’s Note: Year 12 student Jakub writes here for the GSAL Science Magazine on the serious issue of neurodegeneration, the progressive decline in the structure and function of neurons in the human body. Neurodegeneration lies behind serious incurable diseases such as Alzheimer’s, Parkinson’s and Creutzfeldt-Jakob. CPD

[Featured image: Human brain. (Pxhere: Public Domain)]

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It’s not hard to miss the many calamities facing the world today: global warming, COVID-19 or widespread hunger. However, something that many people disregard is something that is even more daunting than the latter, affecting roughly 1 in 10 of us and has the potential to destroy humanity from within: neurodegeneration.

Neurodegeneration is the progressive decline in the structure and function of neurons, leading to their eventual death. This causes diseases such as ill-famed Alzheimer’s, Parkinson’s and Creutzfeldt-Jakob. These diseases are unfortunately incurable, meaning that the condition becomes worse over time. But why?

Neurons are the most important means of communication in the human nervous system, making up both the central nervous system (CNS), which consists of the brain and spinal cord, as well as the peripheral nervous system (PNS) – the nerves and ganglia outside the brain and spinal cord.

They communicate with each other using electrical impulses, sending signals to produce a response to particular stimuli. There are several different types of neurons:

• Sensory neurons – detect stimuli and send impulses to the CNS;
• Motor neurons – facilitate the transition of impulses from the CNS to effectors (e.g. muscles);
• Relay neurons– allow sensory and motor neurons to communicate, being located in the brain and spinal cord.

This type of cell, unlike others, isn’t able to regenerate, thus any damage is irreversible. The inability to efficiently respond to stimuli leads to problems with mental function and impairs movement.

What causes neurodegeneration?

For such a relatively widespread condition, it would seem that the basis is well documented. Yet, there is large uncertainty regarding the underlying causes of most neurodegenerative diseases. It is clear that some cases are caused by genetic mutations, however, the majority are completely random – these are sporadic cases. So, the general causes of this seemingly random change are not well known. The only certain aspect is that they all contain a build-up of toxic proteins, which eventually results in neuronal decline.

The effects of neurodegeneration?

The deterioration of neurons has serious implications on daily life and cognitive functions.

There are many forms that this takes, including Parkinson’s, motor neuron disease and Alzheimer’s:

Alzheimer’s Disease 

This condition is a form of dementia, an umbrella term used to refer to various symptoms of cognitive deterioration, an example being forgetfulness. ^[2]

It is caused by the build-up of toxic proteins: Beta-amyloid and Tau. These are suspected to contribute to the pathophysiology of Alzheimer’s disease. Beta-amyloid is chemically adhesive and builds up into plaques, which stop vital communication within cells.

The Tau proteins normally aid cell transport. However, Alzheimer’s means they twist forming neurofibrillary tangles. These prevent transport and cells, deprived of nutrients, die.

Both of the latter are spread throughout the brain, mostly in the cortex. As the disease progresses, more of these appear in the brain. Leading to an eventual deterioration of more neurons. This process becomes inevitable and is a slow death. It can take many years; the rate varies between people. Some people survive up to 15 years, yet the average life expectancy after diagnosis is a mere 7 years. ^[3]

Parkinson’s Disease

Unlike Alzheimer’s, Parkinson’s is a movement disorder. This arises when another toxic protein, α-synuclein contributes to the death of a specific neuron class – namely dopaminergic neurons. These are dopamine suppliers to the brain. This facilities communication, which is responsible for movement control. Therefore as this is disrupted, so is the brain’s ability to control movement. ^[3]

Motor Neuron Disease (MND)

Similarly to Parkinson’s, this is a progressive movement disorder caused by the decline of motor neurons, predominantly resulting in the wasting of the muscles. Unlike these other diseases, motor neuron diseases can affect both children and adults equally. Still to this day many of the diseases seem to have unknown causes, and in many ways, are still a mystery. We know that some forms are genetic, others may be caused by an over-accumulation of oxygen free radicals in the brain, whose normal removal is impaired, causing the damage of motor neurons. As for the symptoms, they can be first exhibited at birth or can develop slowly as life progresses. Like the earlier examples, most of these cases worsen over time; whilst some, like ALS, are a definite death sentence, others are not. ^[2]

Therefore, as we can see, a slight deterioration of the brain may have profound consequences on our daily lives.

Why is this such a challenge in the modern world?

The human population is growing at an astonishing rate – by the time you have read this there will have been another 500 people born. All of these 7 billion humans will one day be over 60, which is in the risk group^[4].  In developed countries, life expectancy is high with an average of 79.3 for OECD countries^[4]. By 2050 all major countries, except Africa, will have over a quarter of their respective population over the age of 60^[4]. The fact that people are living longer, means that more and more people will develop these age-related diseases, as such degradation is a natural side effect of living. This will put a strain on social institutions and the economy, with less young people contributing to the pension system, will mean we will need to devise new institutions. The preliminary concern, however, it the impact on healthcare systems, which will have to devote more money to research and palliative care. So with a lower economic output and higher healthcare strain, countries must devise new health care strategies, which raises the questions: whether the already-strained NHS can last? And for how long can free healthcare be sustained?

Jakub 761303

References

[1] Hines, T., 2018. Brain Anatomy, Anatomy Of The Human Brain. [online] Mayfieldclinic.com. Available at: <http://www.mayfieldclinic.com/pe-anatbrain.htm> [Accessed 3 June 2020].

[2] NHS, 2020. Motor Neurone Disease (MND). [online] Nhsinform.scot. Available at: <https://www.nhsinform.scot/illnesses-and-conditions/brain-nerves-and-spinal-cord/motor-neurone-disease-mnd> [Accessed 3 June 2020].

[3] NIH, 2020. Parkinson’s Disease. [online] National Institute on Aging. Available at: <https://www.nia.nih.gov/health/parkinsons-disease#:~:text=Parkinson’s%20Disease,have%20difficulty%20walking%20and%20talking.> [Accessed 3 June 2020].

[4] Studer, L., Tabar, V., Dhindsa, J. and McCall, A., 2017. Neurodegeneration – Latest Research And News | Nature. [online] Nature.com. Available at: <https://www.nature.com/subjects/neurodegeneration#:~:text=Neurodegeneration%20refers%20to%20the%20progressive,Alzheimer’s%20disease%20and%20Parkinson’s%20disease.> [Accessed 2 June 2020].

[5] Yolanda Smith, B., 2019. Alzheimer’S Tangles And Plaques: What’S The Difference?. [online] News-Medical.net. Available at: <https://www.news-medical.net/health/Alzheimers-tangles-and-plaques-whats-the-difference.aspx> [Accessed 1 June 2020].