Neuroscience 101

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The Neuroscience of Pain
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Pain Rehab
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Family & Parenting

The Central Nervous System: Your Body’s Command Center

The central nervous system (CNS) is the command center of your entire body. Everything you do or feel is controlled by the CNS, from thinking about your day to walking to breathing.

The CNS is made of two main parts: the brain and the spinal cord.

The Brain

If the CNS is the command center of your body, the brain is the pilot that’s in control. The brain is the most complex organ in the body. To function properly, the brain has to be physically intact, communicate with the central nervous system and other parts of the body, send out clear and balanced chemical messages, and accurately read the chemical messages it receives.

One of the reasons that treating pain is so complicated is that the brain has few moving parts, so it is rare that we can see what is wrong when it doesn’t function properly. (The Egyptians thought the brain was so unimportant, they threw it out when they created mummies – it just looked like an inert lump of tissue.)

Much of what the brain does is transmit and receive information through chemical messages (neurotransmitters). It is difficult or impossible to measure neurotransmitters. How the neurotransmitters work depends on what other messages are being sent and what else your body is doing. Although we’re getting a better insight into how the brain functions through imaging like fMRI and CT scans, our knowledge is still very crude.

Still, a basic understanding of how the brain and nervous system works helps you understand how pain works, how pain treatment works, and how drugs used to treat pain and neurological disorders work.

Focusing on pain, the brain has three important areas: the cerebrum the cerebellum, and the brainstem.

  • Cerebrum: The cerebrum is the center for higher-level thinking, like conscious thoughts, memories, and your ability to solve problems.
  • Cerebellum: The cerebellum integrates information from the sensory systems and regulates muscles and voluntary movement. Because it coordinates your senses and muscles, it is the part of the brain that helps you balance.
  • Brainstem: The brainstem controls automatic functioning like heart rate and breathing and connects the brain to the spinal cord (backbone). It is also central to sensory processing – how you see, smell, hear, taste, and feel.

Everything you feel, think, or experience comes from processes happening in the brain.

The brain communicates with the rest of the body in two ways. The spinal cord (backbone) is packed with nerve cells (neurons) that carry information to all parts of the body. Chemicals (neurotransmitters) transmit information through neurons or move freely through the bloodstream.

The Spinal Cord

The spinal cord acts as the main physical communication system between your brain and your body. Running from the brainstem to the pelvis, the spinal cord’s insides use nerve cells to communicate between the CNS and the peripheral nervous system (PNS) – all the nerve cells that extend from the spinal cord. This communication between the body and brain lets your brain control your body and let’s the brain receive information from the body.

The Neuron: The Body’s Communication Network

Nerve cells, or neurons, are the physical (non-chemical) part of the body’s communication network. Most of the brain is made of neurons. Neurons also transmit information from the body to the brain and from the brain to the rest of the body. Most nerve cells are very well, although they can be quite long. However, working together, it is neurons that allow us to think, feel, and function. Many neurons are wrapped in a fatty covering called myelin, which helps them work more efficiently.

Neurons work together in networks. Neurons have three main parts: dendrites receive information, pass it through the cell body, and transmit it on through the axon.

When neurons ‘fire’, electrically charged chemicals (ions) move across the cell membrane. This is often triggered when the dendrite receives chemical information (neurotransmitters) from a nearby neuron. If the signal is strong enough, it is passed through the cell body and axon, which releases more neurotransmitters. These neurotransmitters go on to affect adjacent neurons.

This firing process is called an action potential. Neurons either fire or they don’t. The strength of a signal depends on how many neurons are firing together.

The likelihood that a neuron will fire depends on many things, including how recently it has fired and many other aspects of its near, chemical environment.

Have you ever walked into a room and been hit be a really bad smell? Then you stay in the room a little while and don’t notice it anymore? That’s because your sensory neurons have fired so often they’re exhausted and stop firing. The threshold to set off the action potential is very high. If you left for a few minutes and came back, the threshold would be lower and the neurons would start firing again.

The opposite can happen with chronic pain. The more you experience pain, the easier it is to set off the action potential and for the neurons to fire. In chronic pain, the neurons are on a hair-trigger and ready to fire.

Understanding action potentials is critical for understanding pain. Most pain medications work by altering action potentials. They change how neurotransmitters are sent or are received, changing how messages are spread through the neural net.

What Are Neurotransmitters?

Neurotransmitters are a category of chemicals that affect neurons. Some are made entirely in the brain, others are produced in other parts of the body. There are many types of neurotransmitters, but in the context of chronic pain, you hear a lot about serotonin, dopamine, and tyramine.

Neurotransmitters affect each other in very complex ways, making it difficult to discuss what each one does in isolation.

Serotonin

Serotonin is produced by and for nerve cells, primarily those in the stomach and central nervous system. It is made using the amino acid tryptophan, commonly found in nuts, cheese, and red meats.

Serotonin is one of the body’s primary mood stabilizers, helping with depression, anxiety, and nausea. Surprisingly, most of your serotonin is produced in the intestines. It plays a major part in digestion, causing muscle contractions in the intestines.

Imbalances in serotonin can be marked by issues with emotional regulation, nausea, sleep, bowel movements, blood clotting, and bone health.

For chronic pain, serotonin works with another neurotransmitter (norepinephrine) to decrease centrally sensitized pain (Marks and Shah et al, Serotonin-Norepinephrine Reuptake Inhibitors for Pain Control: Premise and Promise, Current Neuropharmacology 7(4) 331-6. 2009). Antidepressants may be prescribed in conjunction with pain killers for this reason, as serotonin-norepinephrine reuptake inhibitors (SNRIs) prevent the body from absorbing these too fast before their job is done. 

Serotonin levels are affected by exercise, meditation, diet, sleep, and light. One reason that lifestyle changes can help with pain is that they strongly affect serotonin levels.

Dopamine

Dopamine is produced in the brain and in the kidneys. Dopamine is often talked about as part of the brain’s “reward” system. However, it is more accurate to say dopamine is a motivator.

Dopamine has a number of effects within the body, especially in the context of the chronic pain experience. Because dopamine works with the parts of the brain that control movement, low levels of dopamine can contribute to pain sensations. This is especially true in chronic pain conditions that hinder movement, such as fibromyalgia. 

Because dopamine levels plays a part in disorders such as schizophrenia and ADHD, dopamine antagonist drugs that block receptors can help the brain use its available dopamine before it is broken down. These drugs can also help reduce nausea and nerve disorders, such as restless legs syndrome.

Tyramine

Tyramine is an amino acid. It is NOT a neurotransmitter. Lots of foods have tyramine in them. It occurs in soy beans, snow peas, and other broad beans (Italian or lima beans, for example). Aged foods like cheese, sauerkraut, vinegar, and soy sauce are naturally high in tyramine.

Most people have enzymes that break down tyramine so it never enters the bloodstream. However, many people with conditions like migraines have low levels of that enzyme – they are tyramine sensitive. When undigested tyramine enters the bloodstream and interferes with the way that neurons process serotonin. It also has a direct effect on the circulatory system.

References:

Butler, D. S., & Moseley, G. L. (2018). Explain Pain (2nd ed.). Adelaide, Australia: Noigroup Publications.

Vander, A. J., Sherman, J. H., & Luciano, D. S. (2001). Human Physiology: The Mechanisms of Body Function (6th ed.). Boston: McGraw-Hill. 

Zeltzer, L. K., & Schlank, C. B. (2005). Conquering Your Childs Chronic Pain: A Pediatricians Guide for Reclaiming a Normal Childhood. New York: Harper Resource. 

Theacpa.org. (n.d.). Retrieved June 3, 2019, from https://www.theacpa.org/conditions-treatments/conditions-a-z/