NASM Podcast: All About The Nervous System

National Academy of Sports Medicine
National Academy of Sports Medicine
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On this episode, NASM Master Instructor Rick Richey helps you better understand the nervous system. What about the central nervous system helps make you a better trainer? Let Rick map it all out for you.

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What you'll learn:

  • The roles of the central nervous system, peripheral nervous system, motor neurons and sensory neurons.

Certifications Mentioned:


You are listening to the NASM CPT Podcast with Rick Richey, the official podcast of the National Academy of Sports Medicine.

Welcome to the NASM CPT podcast. My name is Rick Richey and today I'm going to be talking about science. We're talking about more of the human movement science portion and specifically, about the nervous system.

Now, let me tell you what's going on and why we're doing it. In the beginning, I didn't have any guest on the show, and they were informative podcast and then I ended up adding a few guests and then we just had guests on the show.

I get a lot of messages from people saying thank you so much you helped me pass the NASM CPT test, I was able to get my certification because of the podcast. And I was thinking about that, and I realized that they didn't pass the test because I had Allison Brager on talking about sleep, which is one of my favorite episodes of all time, they were able to pass the test because of the episodes that dealt with some of the content in the chapter that helped people better understand.

The Importance of Understanding the Nervous System as a new CPT

So, I want to talk about the nervous system. Not that the test is filled with questions about the nervous system, and you know my goal isn't to just give you a bunch of information just to help you with the test.

I want to give you a lot of information to help you be a better trainer. But that begs the question, what about knowing about the central nervous system and the peripheral nervous system, about motor neurons and sensory neurons.

What about knowing that stuff makes me a better trainer. And I think it's interesting because you could have a trainer that knows all that stuff and then they have clients do bench press. And then you have people who don't know anything about personal training and they still do bench press.

So where does that come from? Why am I a better trainer if I'm doing some of the same things that everybody else is doing that has zero education in this field? And let me just also say that when I first became a personal trainer, I was stunned.

I'm sure you were too when you open up the textbook because it had a lot of science in it. I thought man, I would be a great trainer.

I was a competitive athlete, I like to work out, I exercise regularly, I'm going to be a great trainer... and then I got a textbook. And I'm like what the what? I did not see that coming.

Well, here's what happens. Knowing a little bit more about the central nervous system, and the peripheral nervous system, and the integrated function of the human movement system, allows us not just to make better choices for our clients, but makes better choices for what our clients should not be doing, how to make application, how to queue.

How to understand when not to queue but just to develop their motor learning practice and help to control their degrees of freedom through the information we have.

Exercise Movements and the Nervous System in Context

So, when you think about the first time you ever did bench press, probably did it with just the bar, no weight on it, and you were probably strong enough to lift that bar, but it's also very confusing how that bar could be so light, and yet how impossible it seemed to try to control that bar as it shook and twisted like you're trying to drive on an icy road for the first time.

And we could even take that a step further, if you have ever done hands on a stability ball push up. I know a lot of people who do that are super strong, certainly, strong enough to do a pushup, but when you add the unstable surface, suddenly it's not a strength issue, it's a neuromuscular control issue.

You're strong enough to do a pushup, but you have to learn how to control that. That's part of the learning system, that's part of the coordination system, that is a reactive system to the environment that's around us.

And so that's why we do this. That is what we study, and that's why we learn it. We help to refine. This is where we get into understanding more about the human movement system, so I want to talk about the nervous system today.

Those of you who are studying this in your textbook, the nervous system is just a short portion, but you probably kind of read through and go, "man, I sure hope I don't need to know any of this information for the test because I don't know what this stuff is." I'm going to give you a highlight reel of what's going on, do with it what you will.

Alright, so the nervous system is kind of this giant organ throughout the body, and it has a lot of neurons in it and the neurons are a specialized cell in the body that help to coordinate signals to increase communication between different parts of the body.

The 2 Main Parts of The Nervous System

So, we've got 2 main portions of the nervous system: there's the CNS and PNS. The CNS, central nervous system, is comprised of two things, the brain and the spinal cord. That's it.

The brain and the spinal cord. Those are: the brain, sometimes known as the command center, and the spinal cord as the transmitter.

So, it allows information from the brain to go through the spinal cord and then to branch out everywhere, but what it branches out into is the peripheral of the nervous system, the peripheral nervous system, so it's moving out to the periphery that contains the nerves, it contains the neurons that go into the body or that come from the body back into the CNS.

And so, we've got these functions of the nervous system. There's a sensory function, and that's being able to sense changes in the internal and external environment. You see me here, wiggling my fingers, it's the feeling, it's me, feeling and through feeling things I'm able to receive that information, take it up into my brain.

And then there's an integrative function that integrator function takes what I feel, takes the environment, is it hot, or is it cold? Am I stepping in sand? Did I get to what I thought was the bottom step and there is one more step.

Your body has to respond to that, and it's got to take that and integrate what you're sensing and then analyze it. It's got to interpret it, and then it's got to create its best decision-making properties.

In order to create a muscular or a motor response. Motor, like locomotion, is movement, and that responds to the sensory information. For instance, think about a muscle that stretch too far when you stretch a muscle, you are sensing that muscle being stretched, and maybe it goes too far.

And then you integrate that information. You realize that's too far. Let's make it stop. And then there's muscle contraction that says I don't want you to go any farther. Don't go any farther.

That's why when we do stretching with people, if we do partner assisted stretching, we can stretch somebody to the point that they hurt, which doesn't help them at all, doesn't help them to relax.

It gets them no additional flexibility benefit an if it does anything, it makes them never want to stretch again, so you stretching them, makes them tighter in the long run because they think it's supposed to hurt. And people don't like being hurt.


All right, well there's another sensory concept here called proprioception. And proprioception is your body's ability to sense the relative position of the adjacent body parts in the body. So think about this, what you can do is just stand upright, and you're going to take, let's say your right arm, and I want you lift your right arm out in front of you in the sagittal plane, elbow stays straight, just lift the arm up in front of you, and you're going into shoulder flexion.

Perfect and now close your eyes, and lift the other arm up and try to align it with your right arm. So, is your left arm aligned with the right arm? Open your eyes.

What? How did that happen? That's proprioception. I'm able to sense what's going on in one part of my body, and I can sense what's going on the other side of it, and through my proprioception I was able to align them.

That's a very remedial example, but is an example because we use proprioceptive abilities to help us with our balance, and our coordination, and our posture, and to interact with the surroundings and let's say walking on the boardwalk and then I step into the sand, I feel the changes in what's going on, and I'm able to respond.

Sensory integrated create a different motor response, so my movement changes that's appropriate for the environment. Think about barefoot training. Just exercising in bare feet changes your experience with the environment and that's why there's such a big push towards barefoot training in the last several years.

And it's because your feet can sense the environment and react and support you and we don't use those mechanisms in our feet because we put braces on our feet, known as shoes, from basically the time that were born.

So, we want to be able to get more feedback from our system, and also just knowing that if this is our posture, we have a protracted shoulder girdle, internal rotation at the shoulders, maybe a forward head, increased kyphotic curve, and Racic our spine, but that's life, that's how we live.

Then that's our proprioception. Our proprioception says okay, this is, this is our current experience. And so, when we go out of that positioning it feels weird, it can feel strange, but we need to prime our proprioception and then we need to teach and learn in a different way what a neutral position feels like, and that happens with exercises as well.

Poor Position = Poor Technique

If we're in poor position when we exercise or poor technique, then we may do those techniques because we think that's what we're supposed to do. We may do those techniques because we're not thinking about what we're doing, and we get a lot of spinal flexion in the lumbar spine, but our proprioception needs to be able to notice that and adjust for that, particularly when lifting heavier weights.

I'm not talking about the curls where you roll your spine up, I'm really just talking about in general form in order to protect the disc in your back and support your spine with particularly heavy weight.

All right, now we're going to move on into the anatomy of the nervous system. So, let's talk about the neuron for a moment.

Now, the neuron is what's called the functional unit of the nervous system, and there are bazillions of these things that make up our nervous system, and it allows us to communicate with what's going on inside of us, with what's going on outside of us, receive information, interpret it, and then provide a feedback mechanism.

So, when we look at this, there are some electrical signals that take place, there are chemical signals that take place, but let's talk about the nerve body in general, or the nerve cell in general. There is a nerve body, right?

So, there's the cell body and that contains the nucleus of the cell. There are dendrites on the nerve body, and they reach out all over and think about it, because there's so many of them, they're reaching out and they're trying to understand what's going on in the environment.

They're feelers for what's going on, these dendrites, and I think it's kind of cool. The dendrites have been shown these things that gather information from other structures. They send it back, transmit it back to the neuron, it's getting this information.

Brain Derived Neurotrophic Factor

And there's been proof that shown that exercise increases the number of dendrites that reach out of the cell body of a neuron, and they've even said Doctor John Ratey's book called 'Spark', they took a something called BDNF, Brain Derived Neurotrophic Factor.

Super nerdy word. Why we oftentimes just go BDNF, and that is produced when we exercise, and it helps to sprout dendrites. They take it on a Petri dish, drop BDNF on the cell, and the dendrites sprout almost immediately. It's pretty cool.

They call it miracle grow for the brain. So, it helps our brain, the dendrites in our brain, gather information better. It helps us think better.

So now we're going to get rid of the phrase dumb jock because we know that exercise, in fact, can make you smarter.

So, let's look at that and then move on to the next one. The dendrite attaches branches out from the cell body, but so does something called the Axon, and the Axon is, it's like a long tail, and it connects to other neurons.

So, the Axon is something that's going to connect to other neurons, and it provides communication from the brain, the spinal cord, to other parts of the body and back.

Afference 101

So, there are different types of classifications when it comes to nerves. There are sensory nerves, or sensory neurons, and there are motor neurons. Now the sensory neurons are also known as afferent, A-F-F-E-R-E-N-T-, afferent.

Motor is afferent, and I'm going to give you a little way to help you remember the difference between those, but a sensory neuron, it's going to receive information, things that we touch, things that we hear, light, and it's going to take that information, and it's going to provide that back to the spinal cord up to the brain.

And then the interneurons transmit nerve impulses from one neuron to the other. So, it goes, you know, nerve, nerve, nerve, nerve, and they all bounce it all the way, all the way, all the way. And then they go, the spinal cord up to the brain.

But now we have to make a decision what to do with that information. So, let's say the light is bright, then I'm going to send a signal back, doesn't have to have to go very far, going to send a signal back and say close your eyes.

So, there's a motor response, a movement response and movement response requires effort. That's where I connect effort and efferent neurons, E-F-F-E-R-E-N-T. So, motor neurons are effort, or efferent neurons. It's not just blinking, I don't think the effort that goes into closing my eyes, but any motor pattern that takes place.

So, I think of this kind of classic example of receiving information into our brains and making a decision is touching a hot object, you touch a hot object, you feel that, not yet, not yet.

I haven't felt it yet, or I haven't interpreted any of that yet and it gets to my brain and my brain decides that's hot. But now what?

Now I've taken that information, I've gathered it, interpreted it, I analyzed it, and making a decision because of it, and the decision says you need to move your hand.

So, then the motor neuron, all the way down, all right, so we're getting my inner neuron, inner, all the way, all the way, all the way, all the way, until it gets to the effector sites, and then the action takes place from me to effortly motor move my arm. So, it goes through those motor neurons.

I think it's kind of funny too if you think about a foul ball being hit in baseball, if you ever watch it, you can tell in slow motion that it takes a little bit of time for these impulses to take place.

You could have somebody intently watching a game, and they're behind home plate, and the pitcher throws the ball, the batter swings at it, they connect it, but it's a foul ball and it goes directly back to the cage behind them.

People are sitting behind that cage, or that fence, or that netting, and as the ball comes, they see it, and they know they haven't registered that it's dangerous yet, and as it gets closer to the fence, then you see them slowly, their eyes, open their face, twist, their head turns out of the way, and then they they retch their whole body into strange positions, and it hits the net.

But seeing that in slow motion is so delightful. One, because it's funny, and two, because you see the time it actually takes in order to register information. It doesn't happen like that, it just doesn't do that, so it's interesting to watch these things take place.

All right, so let's move on. The central and peripheral nervous systems. I used to say peripheral, peripheral?

I don't know. I just grew up saying that. That's not how it's said, it's peripheral, and we've got the peripheral nervous system, and, all right, that's going to take everything from the central nervous system to the rest of the body. There are 12 cranial nerves, 12 pairs. Or 12 cranial nerves, 31 pairs of spinal nerves, and there are two main functions.

One, they provide a connection to the nervous system and they activate effector sites, right? Effector sites, that's going to affect that and then I move. So those effector sites might be my muscles for motor function.

Secondly, the peripheral nerves are going to relay information from the effector sites back to the brain via sensory receptors. Then it's just like a closed loop, this constant update that takes place between the body, the environment, and the brain.

But we're going to break it down even farther. There are two subdivisions of the peripheral nervous system. There's somatic and autonomic.

Now, somatic is SOMA, think of a SOMA is the body. Then there are this portion of the system controls the voluntary movement, right? So that's my muscular system, those things that are voluntary skeletal muscle, but the autonomic nervous system is working in a really interesting way, is that these are the involuntary things that take place in our body that we don't, thank goodness, have to think about which is my heart beating, glad I don't have to think about keeping that up, breathing, even though we can breathe voluntarily, digestive system, the endocrine system, the hormonal responses that take place in our body, the autonomic nervous system.

And then we're going to break that down even farther. There's a sympathetic nervous system and a parasympathetic nervous system.

The sympathetic nervous system is nervous system that's going to get us kind of prepared for activity if we're thinking about it in terms of, we think about this in terms of activities or athletics. We're trying to get amped up for the game. We're trying to get our sympathetic nervous system going through the roof. This is the fight or flight nervous system.

We also hear a lot about the sympathetic nervous system because of stress. So constant activation of the sympathetic nervous system can be stressful, and it can lead to chronic stress, and so one of the words that we've heard a lot in the past five years for sure especially, is recovery has started to kick into the mainstream of our population is focus on the parasympathetic nervous system.

And the parasympathetic nervous system is the rest and digest, the rest and recovery nervous system. And that's what we want to get people to do.

So, when people are stressed out, they tell people to focus on their breathing. Focus on your breathing, take a breath, calm down, and that's been proven to help with our parasympathetic nervous system to get us to calm down; Slows the heart rate, decreases adverse hormonal responses that keep that low level of stress constantly feeding our system.

Parasympathetic nervous system and sympathetic. Thinking about sympathetic and parasympathetic is very confusing, or they can get confused very easily.

So, I think sympathetic, if somebody is very sympathetic, then they are focused on their emotions, and we know heightened emotions, think about fight or flight, that's a heightened emotional state, that is a sympathetic state. That's what helps me at least know the difference between sympathetic and parasympathetic. And then parasympathetic is just the other one.

So, it is the rest and digest, it's the one keeping us cool. Alright.

So now let's talk about sensory receptors. And sensory receptors are the things that are receiving information from our environment, and so we've got four of them:

there's mechanoreceptors, nociceptors, chemoreceptors, and photoreceptors. So, when you think about all those things, photoreceptors. might be pretty easy to think about, those are going to be light vision.

Chemoreceptors are chemicals, and those chemicals could be smell and taste. Those are chemicals that we are tasting and smelling. And then nociceptors are pain receptors.

Nociceptors are pain receptors. And then we've got mechanoreceptors, and those respond to mechanical force, like touch and pressure.

So, I want to spend a little bit talking about some of the mechanoreceptors. There are three major ones. Two, we're going to talk about and spend some time on, and then we'll also mention another one.

So, the mechanoreceptors, what they do, you've got touch and pressure and stretching and even sound waves motion. They all transmit these sensory impulses. And so, we detect them in our mechanoreceptors, then we detect them through proprioception.

And mechanoreceptors are in muscles, they're found in tendons and ligaments and in joint capsules. And we're going to talk about muscle spindles, Golgi tendon organs, and then a special mention for joint receptors.

So, a muscle spindle, muscle spindle are spindly receptors in the body and mechanoreceptors that are within the fibers of the muscle, kind of in the in the muscles, not in the muscle fibers themselves, but they align next to it, and when you stretch a muscle, the muscle spindle stretches with that, and so those are going to be receptive to the change in length and how fast that length changes. Think about the muscle spindle, and spindle and stretch both start with an S, so muscle spindle is the stretchometer, it's measuring the amount of stretch, so how long, and it's measuring how fast you're being stretched.

Both of those, your body is going to react to, because if you're stretched too long your body is going to receive that information and say I don't like this. They're going to receive that stretch, and they're going to create a protective response, like tightening up. Or if your muscle stretches too fast, and it gets to a certain length too quickly, it's going to contract in order to protect it.

Well, that's where we get our integrative continuum here, where we look at what's called the stretch shortening cycle. And when we drop down into a squat, like a short squat, real quick, and then jump right back up, we're stretching. The muscle spindles received that stretch and they activate the muscles.

Well, if we consciously activate at the exact same time, we jump higher. But, if we drop down, and we wait for one Mississippi, two Mississippi, three Mississippi, four Miss... you get the point, and then we try to jump, we can't get up as high, because we no longer have the muscle spindle in that stretch reflex supporting our jump. So, the muscle spindles have a very important role in performance, not just protection.

Golgi Tendon Organ Explanation

And then we have the Golgi tendon organ. Golgi tendon organ is located somewhere, somewhere...not sure where ...but the Golgi tendon organ is located in the tendon and it is going to be sensitive to changes in tension and how much tension actually takes place and changes.

So, if there's a lot of tension in a muscle, the Golgi tendon organ may receive that information, it is the tension, tendon and tension go together, so, it is the tensionometer. It's measuring the amount of tension and it helps to protect us from too much tension that tends to take place within the body.

This is very important. They play a pivotal role, the GTO and the muscle spindle, in understanding flexibility training. That when we stretch a muscle, the muscle spindle gets stretched.

It receives that information, sends it to our brain, sends it back, goes we stretched too far, stop. Stop, don't go any farther.

And we can go too far in a stretch. Go too far in a stretch, people don't like it. It hurts them. Then they say, "oh, I don't like stretching 'cause it hurts," it shouldn't, it shouldn't.

It should not be painful. And with trainers over stretching people, it's very dangerous, potential litigations can be there if any injury does take place, but the fact that you are also not helping them with their flexibility, and maybe making them less flexible because they're not going to want to choose to stretch overtime, because they think it's supposed to hurt. It's not. And you as a trainer need to know that.

So, we're going to take it to a resistance barrier, give the muscle spindle that stretch, and it says alright, it's going to tighten up a little bit.

That's the resistance barrier, when it tightens up a little bit more. And then we give the Golgi tendon organ about 30 seconds, about how long it takes. The Golgi tendon organ is measuring the tension, it's feeling out the environment.

"Are we safe?" "Are we not safe?" Yeah, it's not too bad. We can stop being so tense and it relaxes the muscle.

Once it does that, we can stretch a little bit farther into that flexibility range of motion until the muscle spindle feels that out and goes "that's enough."And then wait about 30 seconds or longer, maybe less for some people, but just hold it for 30 anyway.

Let the GTO get time to suss out the environment. Does it feel safe? Causes us to relax and we can continue stretching. That's how we increase our range of motion. That's how we perform corrective flexibility, through this static stretching process: muscle spindles and Golgi tendon organ.

There's also something called a joint receptor, and it's around the capsule of the joint, and it can have a reflexive inhibitory response.

So, let's say that I've got a joint, like my knee joint, and I've got the capsule around it, which is just the soft tissue that creates a vacuum within that joint, hold that right there, and then something happens. A twist happens.

Something not good, something not good happens to the knee and I don't actually need my brain in this particular moment because that's what a reflex is.

A reflex is going to take the afferent sensory information from the knee joint, and it's going to get to the spinal cord and the spinal cord receiving this information as a reflex realizes we don't have enough time to send this impulse to the brain, for the brain to figure it out, send it back to the spinal cord, and then out from the spinal cord, through efferent motor neurons, to make the decision to move out of that bad position.

So, we cut out the spinal cord to the brain and then bring it back to the spinal cord. A reflex goes directly to the spinal cord and makes a decision immediately.

So, when you've gone to the doctor and they take that little triangle mallet and they have you sit with your legs off the side of a table, and they tap you on the patellar tendon, just below, just inferior to, your Patella or your kneecap, and they give you that tap, and your leg juts forward.

That information never made it to your brain. That's a reflex and made it to the spinal cord and made that decision and sent it right back. So that's what a reflex is, and your joint receptors can take that information.

So, think about like if you've ever tweaked your knee, and your leg just gives out on you for a second, and then you look around and you kind of make believe like you tripped over something and you're like, "What was that? Y'all, better be careful around this area right over here."

But nothing happened, it was just a tweak in your knee, and you just gave out for a second. So that's what it's doing, it's trying to stop and create a safer environment in a split second.

COncluding Thoughts

So anyway, I hope you found that pretty helpful and then just helps us to understand more about how the human movement system works, how the nervous system works, and it works with the muscular system and with the skeletal system, and it allows us to understand how we're going to produce force and reduce force and dynamically stabilize force.

It's going to help us to be able to do that and the sagittal frontal transfers planes, in them, throughout them, in different dimensions, in different variations, at different speeds and tempos, in a safe manner and in a coordinated manner.

So I hope that helps. Thank you so much for listening. It was a little heady, this episode today, so if you made it to the end, I appreciate it. If ya'll have topics that you want to hear more about, feel free to reach out to me. You can hit me up on my email rick.richey@nasm.org or I'm most active on Instagram where you can reach me on a DM @dr.richey and I'm happy to entertain questions that you may have or topics you may want to hear about.

Thank you so much for tuning in, watching this, if you're watching it.

If you'd like to see this then feel free to go to the NASM Facebook page and they'll be loaded up and they'll be on the YouTube channel as well, and if you're listening to the podcast, thank you so much.

This has been the NASM CPT podcast.

The Author

National Academy of Sports Medicine

National Academy of Sports Medicine

Since 1987 the National Academy of Sports Medicine (NASM) has been the global leader in delivering evidence-based certifications and advanced specializations to health and fitness professionals. Our products and services are scientifically and clinically proven. They are revered and utilized by leading brands and programs around the world and have launched thousands of successful careers.


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