September 2019 – Page 4 – Intro Psych Blog (F19)

Neurotransmitters and their effect on the brain: Dopamine and Parkinson’s Disease

What are Neurotransmitters?

It’s a well-known fact that neurotransmitters have a profound impact on the brain. But how exactly do they work? Neurotransmitters are chemical substances released in vesicles at the end of a nerve fiber (at the terminal branches of an axon) with the arrival of a nerve impulse. They diffuse across the gap between two neurons, also called the synaptic gap or cleft, and are received by receptors on the receiving neuron (at the dendrite), which transfers the impulse from one nerve to another. The image below shows this process in greater detail.

Image 1: Neurotransmitters and the Synaptic Cleft

It helps to think of neurotransmitters and receptors like a lock and key mechanism: receptors act like locks, accepting some neurotransmitters and rejecting others that don’t “fit”. Neurotransmitters are the “key” that fits into its designated receptors. After a receptor accepts a neurotransmitter, it begins a chain reaction of events that locally charges the cell membrane, sending a signal along the length of the neuron and on to the next.

Dopamine and Parkinson’s Disease

Now that we have a basic understanding of how neurotransmitters work, we can discuss what effects a neurotransmitter imbalance would have on the brain. The neurotransmitter dopamine has pathways involved with Parkinson’s disease. Parkinson’s is considered a degenerative disorder and begins when cells in the part of the brain known as the substantia nigra begin to die. These nerve cells are responsible for dopamine production and relay messages that control body movement. In some people, these dopamine-producing nerve cells begin to die. When approximately 80% of dopamine is lost, symptoms such as tremors, slow movement, stiffness and loss of balance occurs in the body.

Parkinson’s is the second most common age-related disease after Alzheimer’s disease. It is estimated that 7-10 million people worldwide suffer from Parkinson’s, including my grandmother. As I’ve visited her frequently over the years, I’ve watched her symptoms manifest in several ways. She walks slowly and with a shuffling gait and relies on her walker to get around the house. Her hands often tremble even when she is not cold or scared and sometimes, she stutters in her speech. These are all classic symptoms of Parkinson’s as they all relate to a loss of motor function. This is likely because of the lack of dopamine in her brain. Her body movement is interrupted because the cells in the substantia nigra are unable to send nerve impulses as frequently between the spinal cord and the brain due to the lack of dopamine.

Image 2: Dopamine levels in a normal and a Parkinson’s affected neuron

Treating Parkinson’s Disease

While the initial cause of cell death in the brain remains unknown, scientists have been using their knowledge of dopamine and its pathways to create drugs that mimic how dopamine is supposed to work in the brain. My grandmother has recently begun using one of these drugs, which are also known as Dopamine-receptor agonists, to treat her symptoms. Like dopamine, they fit into the receptors that receive dopamine and are able to complete the neural pathway the leads to smooth body movement. The diagram below shows how dopamine agonists mimic the effects of dopamine.

Image 3: How dopamine-agonists mimic dopamine in the brain

While agonist drugs can help ease the symptoms of diseases like Parkinson’s, it is our hope that researches will soon be able to identify the source of this degenerative disease. One thing is certain: we must never underestimate the importance of neurotransmitters and their effect on our body and mind.

Links:

https://www.lexico.com/en/definition/neurotransmitter

https://mayfieldclinic.com/pe-pd.htm

https://parkinsonsnewstoday.com/parkinsons-disease-statistics/

Image 1: https://www.verywellmind.com/the-chemistry-of-depression-1065137

Image 2: https://www.atrainceu.com/course-module/1874200-080_antiparkinson-strategies-module-03

Image 3: https://parkinsonsdisease.net/medications/

Brain’s Plasticity

We learned in class about brain’s plasticity–Brain is sculpted by our genes but also by our experience, some type of injury or illness can modify our brain. Our brain is inborn, and in the past, some psychologists believe the brain can not be altered. But later on, scientists did some research and found that brain has the ability to modify itself due to injury or illness. By modifying, it’s referring to the brain’s ability to modify its own functions in certain areas or its physical structures.

I’ve read a story about a man named Ben, who got into a car accident with a truck (Morgans, 2019). He was sent to the hospital immediately, and then he was put in a coma for a week. When he woke up from the coma, he found that no one could understand him but a Chinese nurse. Surprisingly, he was speaking fluent Chinese to his families when he only learned really basic Chinese in high school. He didn’t realize he was speaking Chinese and was frustrated since people can’t understand him. Luckily, he didn’t forget how to speak English and he was able to communicate with people in English a few hours later. His parents were worried about him, so they asked a neurologist to do a brain check for him. And the neurologist told them due to the car accident, his brain is modified, the left hemisphere is damaged and the right hemisphere now is taking the responsibility of managing language. And according to past experiments and research, English speakers use more of their left hemisphere when Chinese speakers use both hemispheres. And because his left hemisphere is resting, the right brain is managing language, his old Mandarin memory becomes more accessible and his Mandarin becomes more natural than English.

This story showed us the brain’s plasticity–its ability to modify its function due to injury or illness. Because of the car accident, Ben’s brain’s left side was damaged, which drives the brain to modify its old functions on that side and makes the right side to take over it. And this is why Ben becomes more fluent in Chinese than English.

Reference:

Morgans, Julian. “Meet the Guy Who Woke From a Coma Speaking Another Language.” Vice, 28 June 2019, www.vice.com/en_uk/article/3k3w8w/ben-mcmahon-woke-car-accident-coma-speaking-chinese-mandarin-language.

The Sympathetic Nervous System

Within the nervous system is the autonomic nervous system, which then contains the sympathetic and parasympathetic nervous systems. These two systems are involuntarily, meaning our body does not have control over what it is performing. The sympathetic nervous system is known as “fight-or-flight”, while parasympathetic is known as “rest and digest”. Even though they are different, these systems still work hand in hand with one another to help control the way our body works. Sympathetic is almost like an alarm clock, as it arouses the body and stimulates the nerves to start working. On the other hand, parasympathetic helps calm the body down, as it brings the body back to its normal state. The sympathetic division is not responsible for physically helping you fight or run, but rather prepares your body for the events it is about to encounter. Meanwhile, the parasympathetic division focuses on influencing our response to the situation so our body can ease back to its usual ways.

When triggered, the sympathetic nervous system carries out certain functions to prepare the body to make a decision within that moment. The symptoms normally experienced in a “fight-or-flight” situation are dilated pupils, accelerated heart rate, rapid breathing, and sweating. With these symptoms, it helps one to see and process information more clearly, transfer more blood to your muscles, and helps fight off whatever it is encountered.

Sympathetic and parasympathetic nervous system 3d medical illustration on white background
A “fight-or-flight” moment can be experienced in several different ways by anyone. A time in which I experienced a “fight-or-flight” moment was when I was on vacation in the Bahamas in 2018. My family rented out a yacht for the day to sail through Rose Island for fun excursions, such as snorkeling, tubing, jet skiing, and much more. Though something the cabin members always make their guests do is jump off of the highest level of their boat. My brother and I decided to jump together, and off we went from the third level of the boat. After landing in the water, my brother and I noticed a black/grey figure swimming towards us, realizing it was a Stingray. I immediately felt a rush of adrenaline, my heart rate became rapid, my breathing became intense, my body sweating, and I swam as fast as I could back to the boat. Now having an understanding of “fight-or-flight mode”, I realize that in that moment my body was experiencing all the sympathetic symptoms. My only intention was to swim away as fast as I possibly could from the Stingray, therefore showing the use of the “flight” mode to help reach myself to safety.

Once I got back on the boat my body then went through the effects of the parasympathetic system. My heart rate began to slow down, my breathing was not as intense, my pupils constricted, and my body went back to its normal state. I believe my experience demonstrates one of the purposes of the sympathetic nervous system because it describes a memory of when I was in a stressful situation and had to react in a timely manner by using the “flight-or-fight” method. Experiencing the sympathetic nervous system may not always be enjoyable, but with this system it helps our bodies respond to demanding situations and is essentially responsible for controlling what we do in the moment.

Image result for fight or flight