“Walking is man’s best medicine”

This is one of the famous sayings attributed to Hippocrates, the Ancient Greek physician, born around 460 BC and widely regarded as the father of Medicine. It still holds true in the modern day and age, as countless studies have shown the health benefits of aerobic exercise such as brisk walking, on the human body, also benefitting the brain. Some scientists now say that the biggest enemy to brain function specifically, is a sedentary lifestyle!

Once the aerobic exercise increases the heart rate, usually when it is vigorous enough to break into a sweat, the increased blood flow to the brain brings an additional influx of substances that are crucial for brain functioning, such as oxygen, water, hormones and nutrients. This has positive effects on brain function on multiple fronts, ranging from the cellular level to higher functions such as behaviour.

The effects of exercise on the blood supply to the brain:

The brain’s blood vessels have a unique security system that allows oxygen, hormones, and essential nutrients to enter the brain, while refusing entry to toxins and other unwanted substances such as bacteria. All blood vessels are lined with endothelial cells, but in the brain these cells are wedged tightly together to form a nearly impermeable barrier between the brain and bloodstream. This is aptly called the blood-brain barrier.

While small compounds easily cross the blood-brain barrier, larger molecules, such as glucose or insulin, are ferried across by transporter proteins in the blood vessel walls. The cells inside and on either side of the blood-brain barrier constantly sends messages about which molecules are needed by the brain and should be allowed through. For example, when the nerve cells in a particular area of the brain are working hard, they signal the blood vessels to dilate in order to allow energy-powering nutrients such as oxygen and glucose to quickly travel to the area where they are needed.

Nutrients such as glucose, amino acids, ketone bodies, various vitamins and minerals cross the blood-brain barrier to nourish the brain and keep it functioning. Nutrients also promote the activities of the chemical messengers in the brain, called neurotransmitters.

Any exercise that is good for the heart is also good for the brain, as aerobic exercise increases the heart rate, resulting in an increased supply of oxyen and nutrients to the brain, as well as increased capillary density. Not only is exercise beneficial for the optimal functioning of the brain, but the quality of the nutrients being fed to the brain is equally important. Hippocrates has millennia ago already realized the importance of good nutrition and is quoted as saying:

“Let food be thy medicine and medicine be thy food”

The effects of exercise on white matter and grey matter:

While the brain is the most complex item known to man, its workings can be compared to a computer, where the grey matter (consisting mostly of nerve cells, called neurons) can be compared to the processing component of the computer, while the white matter can be compared to the wiring that connects all the components and transmits all signals. Neurons in the brain are linked and communicate with other neurons through trillions of connections. White matter carries nerve signals between the gray matter in different areas of the brain and via the central nervous system to the rest of the body.

White matter consists of glial cells and the nerve fibers (called axons) that connect the more than 100 billion nerve cells in the brain and is called white matter due to the colour of the insulating sheath (called myelin) that covers the axons. The myelin is made up of a type of fat that is white in colour. White matter makes up about half of the brain and grey matter the other half, with the vascular network making up the rest.

Studies have linked exercise to improvement in the microstructures of white matter, resulting in improved integrity of the white matter and a decreased risk of cognitive decline and dementia. Being physically active may help to delay and arguably prevent the onset of cognitive decline and disease that is associated with aging.

The hippocampus is a part of the brain that was found to respond strongly to aerobic exercise and can even show an increase in size as people get fitter. The hippocampus is part of the limbic system (the region that regulates emotions) and is responsible for the processing of long term memory, being involved in both the forming and retrieval of memory.

A recent (2019) international research project at both the Queensland Brain Institute (Queensland University, Australia) and the Dresden University of Technology has discovered the underlying mechanism that improves brain function after exercise, and came up with very interesting findings in a study conducted with mice. When exercising, the stem cells in the hippocampus (center of memory and learning) divide and turn into new neurons, leading to improvements in memory function. This study tried to determine how these stem cells are triggered to start dividing and form new neurons after exercise.

The scientists suspected that our blood composition changes while we exercise, so they investigated whether the post-exercise changes to the neurons are the result of changes in the blood. They found that a significant number of the changes that occur to blood after exercise were related to the platelets in the blood. (The cellular component of blood consists of red blood cells, white blood cells and platelets.) The platelets triggered the neural stem cells to multiply and develop into new neurons. Platelets were previously best known to play a role in the healing of wounds, as they cause blood to clot and skin cells to adhere together.

The study found that exercise activated a different response in the platelets than the usual wound healing response, indicating that platelets are far more complex in function than was previously known. The results of the study indicate that platelets have the ability to release different molecules, depending on the stimulus which has triggered the response. This discovery has opened up intriguing new research possibilities, such as whether the positive effect of platelets on neuron development can be harnessed to boost neuron development in both mice and humans.

A comprehensive review by the National Center for Biotechnology Information (USA) of major research projects on the effects of exercise on the brain, has concluded that the study of the effects of exercise on brain structure and cognition is still in its infancy. However, it is clear that aerobic activity was found to be a powerful modulator of brain plasticity, which refers to the brain’s ability to change and adapt as a result of experience.

The effects of exercise on mood and depression:

Research has shown that exercise boosts critical neurotransmitters and that people who exercise have better mental fitness and less depression. Neurotransmitters are chemical substances that facilitates the transmission of nerve impulses across synapses, the junctions (tiny gaps) between neurons, which do not directly touch each other. About 50 different neurotransmitters are known to scientists and substantially high or low levels can affect the balance and functioning of these neurotransmitters.

The following well-known neurotransmitters can affect mood through abnormal functioning, but are to known to be positively affected when levels increase during exercise:

Dopamine is a neurotransmitter that controls voluntary movements of the body and regulates the pleasurable emotions (the reward mechanism) of the brain.

Serotonin levels affects emotion, mood and anxiety. Low levels are associated with depression and suicidal thoughts. Many antidepressant drugs work on the levels of serotonin in the brain.

Gamma-aminobutyric acid (GABA) slows down the activities of neurons and by slowing down neurons when they get excited, plays an important role in controlling anxiety.

Endorphins can reduce pain and stress, and also promote calmness.

Epinephrine controls mental focus, attention and cognition.

Norepinephrine regulates mood as well as physical and mental arousal.

Melatonin controls the body’s sleep-wake cycle, but is also associated with controlling mood.

The wise man Hippocrates realized the importance of exercise on mood, even without the benefit of modern scientific knowledge, when he said:

“If you are in a bad mood go for a walk. If you are still in a bad mood, go for another walk”

Sources:

This is your brain on exercise. Published 26 February 2016. Neuroscience News & Reasearch, from Technology Networks. (www.technologynetworks.com)

Why is physical exercise so good for your brain? Published 22 September 2014. Psychology Today. (www.psychologytoday.com)

The effects of aerobic activity on brain structure. Published 23 March 2012. National Center for Biotechnology Information. National Library of Medicine. National Institutes of Health. (USA). (www.ncbi.nlm.nih.gov)

How does exercise help the brain? Published online. Livestrong. (www.livestrong.com)

Blood cells the missing link in post-exercise boost. Published 22 March 2019. Queensland Brain Institute. University of Queensland. Australia. (www.qbi.uq.edu.au)

The role of the blood-brain barrier. Published online and updated 18 May 2019. Verywellhealth. (www.verywellheath.com)

White matter in the brain. Published online and updated 2 July 2019. Verywellhealth. (www.verywellheath.com)

The blood-brain barrier. Published 2 July 2014. BrainFacts. (www.brainfacts.com) Nutrients that cross the blood-brain barrier. Published online. Livestrong. (www.livestrong.com)

All you need to know about neurotransmitters. Published 18 March 2018. Bodytomy. (Source of information about human anatomy and physiology.) (www.bodytomy.com)

Neurotransmitters. Published online. Encyclopedia of Mental Disorders. (www.minddisorders.com)

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