It’s no secret that nerves play a role in pain. Unfortunately, most people don’t fully understand how nerves work. Moreover, most people (including some professionals!) don’t understand that it’s not only nerves that play a role in pain but the entire central nervous system that is involved. (This is especially true when we’re talking about chronic pain, which is most commonly defined by pain that persists for over 6 months.) Even further, it’s important to understand that you can’t have pain without having the entire body getting involved! This includes the autonomic nervous system, the hypothalamic-pituitary-adrenal system, as well as the endocrine system. Though that may be seem obvious that the entire body is linked into this process, the intricacies of this fact are very complex and, honestly, not completely understand by anyone. Fortunately, this is a “hot topic” in the research world, with new data coming out all the time.
Why Pain Matters
This topic is one that I’m incredibly interested in…and, honestly, very personally invested in. (If you haven’t read my story, you can find it here.) As a result, pain, especially chronic pain, is something I hope to discuss at length in this blog. And I know that I’m not the only one interested. In fact, it is estimated that roughly 100 million Americans have a chronic pain problem at any given time. Compare that to the estimated 25.8 million Americans with diabetes, and you can gain an appreciation for how big this problem is! Even scarier is the fact that it is estimated that Americans spend close to $600 billion dollars annually on chronic pain treatment and management. Yup, that’s billion with a B.
So, with all that in mind. I thought it would be extremely high-yield and important to discuss the basics on how nerves, neurons, and the central nervous system work. (This is going to be a simplified version, of course.) All other blog posts on pain will be based on the foundation established here but we’ll build and expand on the details…so don’t worry if you don’t get it all on the first pass.
In order to get to the good stuff, we have to first talk about some anatomy. Most basically, let’s first address the difference between a nerve and a neuron. Luckily, most people have heard about nerves (after all, what would our families get on if it isn’t a nerve?!) so understanding neurons is pretty simple. Neurons are simply smaller units that makes up a nerve. The neurons are bundled in clusters, separated by ligamentous (aka: connective) tissue to make up an individual nerve.
Onward with our anatomy lesson! The parts of the neuron can be simplified into 5 parts (see illustration below):
- The Nucleus: This is where the “reproductive machinery” (the DNA) of the neuron resides. You can basically think of this as the “brain” of the cell, in that it responds to external influences and regulates the production of various proteins, enzymes, etc. Most importantly for our discussion, the nucleus creates the messengers that that help transmit messages to neighboring neurons.
- The Cell Body: this is where the rest of the cell’s machinery lives, including the parts that signal with and transport the products of the nucleus.
- Axon: This is the part of the neuron that helps speedily transmit the “message” that the neuron has received (more on this below).
- Axon Terminal: This is the part of the cell that stores “messengers” that were produced in the nucleus. This allows for the even speedier messaging. provided the message that is supposed to be transmitted hasn’t changed. (We’ll talk a lot more about this later.)
- Synapse: The “messengers” get released into the synapse (the space in between 2 neurons) so that the message can be then transmitted down the line to other neurons.
We’re bringin’ ‘er home, folks! So stick with me.
The last part of the neuron that you have to understand is how the parts allow for signaling to happen. Neurons have receptors all over the surface of the cell (but you can just imagine them on the side that has the nucleus, see picture below). These receptors are shaped to accept certain messages that are coming into the neuron…you can basically think of the messages (or messengers) as “keys” and the receptors as “locks”.
Once the messangers act on the receptors, it causes a cascade of actions that directly effect the nucleus. (Basically, the parts of the cell body run to the nucleus and tell it everything that’s happening.) The nucleus deciphers these incoming messages and comes up with a response. This cellular “response” is transmitted down the axon and causes the release of various other messengers that then go on to act on the receptors of the neighboring neuron.
Phew! That seems like a lot. But basically, neurons function to pass messages to and from the brain. The way they work, in the simplified sense, is like knocking down dominos…once you get one going, it’ll keep triggering all the others in the line.
Neurons In The Body
So now that you know you know generally how the neuron works, we can look at the neuron in the context of the whole body. (Simplified, of course. Don’t go running out on me.) This stuff is best explained by way of an example.
Imagine for a moment that you’ve stubbed your toe (gah!). What feels like instantaneous pain to you is actually a very long and intricate sequence of events that happens inside your body.
Lets start at step #1 on our neuron-man illustration above. When you hit your toe against a hard object, the nerves in your toe get the message first.
This message travels through the length of the neuron and transmits that message to the second neuron that starts in your spine (step #2).
That neuron that relays that message to the brain (step #3). (Like I said, dominos.)
Now, step #4 is something we’ll talk about at length later, but basically, your brain is going to figure out what to do what that message. (For example, your brain is going to process running your toe into your living room coffee table differently than if you’ve stubbed your toe while picking a burning car off a baby. The brain is an amazing thing.)
Step #5 will be for the brain to send an outgoing message to a neuron that travels down to your spine.
There, it will relay the brain’s message to the neuron that goes down to the big toe (step #6), and your toe will finally get the message (step #7). More than likely, the message will be “Watch where you’re going, Butterbreath.” but as we’ll see later, it all depends on the brain’s priorities and habits.
Well folks, you’ve just completed half a course in neuroanatomy. Next, we’ll cover how the brain controls this entire messaging system.