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An Overview of The Nervous System |
| Researched and Composed by Jacob Wilson |
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Bodybuilders are in essence, computerized freaks! In that they are built like machines, and run by a system that is in another realm of proficiency. The goal of this article is simple. Utilizing your knowledge of the vertebral column, I will relay to you an overview of the nervous system. When I am finished speaking, each athlete reading this will be able to exclaim the general innervation of every muscle group in their body! Central Nervous System Explained
By way of review, the Central Nervous System, commonly referred to as the CNS is a fancy way of saying inside of the spinal cord, and or the brain. As Dave Draper would say, there’s nothing to it. Except that messages can be relayed to and from your body, and processed at just about the speed of lighting, you can recall memories from 20 years past in the blink of an eye, and recruit millions of cells at a very thought. But, that’s another story… Note: In Order to understand this article, you must understand the vertebral column. To do so, click here In reality, we only have one nervous system. It is our main frame, or body’s computer system if you will, and everything is continuous with its neighbor. The main reason why we separate it into sections, is due to the fact that different aspects of this computer either: Or The CNS as I discussed is localized in the center of our body, but the peripheral nervous system which is continuous with its predecessor is located outside of the spinal cord and brain. Therefore the PNS is made up of nerves, which sprout off of the spinal cord, and brain, and travel the length (superiorly and inferiorly ) of the entire body. These nerves have two goals. The first is to carry senses such as taste, and touch toward the central nervous system. This is called somatic afferent. Somatic means general, and afferent means toward. If you touch the desk in front of you, a sensory neuron carries the message to your spinal cord, which then sends the message to your brain that you have made contact with the desk. One neuron exclaims the sense of touch, while another carried the sense of pressure, while still another carried the sense of proprioception in your hand. You have at the side of your brain, what looks like a huge wrinkle, that runs the about the length of the brain. If you touch the side of your head, about midway, and run finger the length of the skull you will be in the area that I am talking about. It’s called the post central gyrus. Gyri appear as wrinkles, that increase the surface area of your brain. Anyway, this gyrus has your entire body mapped out. It’s very cool when you think about it. Say I want to flex my biceps muscles. In my cerebrum( the conscious aspect of my brain ) where the gyrus is located I simply think, or give the command to flex my guns. At that very moment, a neuron( explained shortly ) carries the signal out to my spinal cord, and nerves off my cervical region then relay the message to my biceps brachii which then flex at the elbow joint. This is called somatic efferent innervation. Again somatic meaning general, while efferent is deemed as a message being carried away from the nervous system. The third function is to carry a message that is not in your control away from the nervous system. This is, as discussed last month, the autonomic nervous system. Your heart, organs, smooth muscle, blood vessels and glands are controlled automatically. Therefore this is called visceral efferent. Which is to say away from the body and to an organ( visceral ) What is a Neuron? Briefly, it is a cell who’s specialty is conducting electrical signals. It is composed of a body, and an axon which looks like a long tail or extension. In essence, the cell body receives a message and carries it along its axon to the destination it is intended to travel to. It is similar to the cord in your wall. Imagine the plug that inserts into the wall, as being the cell body, then imagine the extension of that plug which carries the electricity to your computer, to be the axon of a cell neuron. Nervous tissue is an incredible conductor, and we all know the efficiency, and speed at which electricity can run. A neuron can carry a message from my spinal cord, to my foot at unfathomable speeds! And on one other note. Once fixed in place, a neuron does not move. It does not travel at all. If its body lies inside of the spinal cord, then it will always stay inside of the spinal cord. And its axon will always travel and end in the same spot on the body. It’s the electrical signal that travels along the axon that moves. Where are Neurons Located? The cell bodies are located in the CNS or immediately outside of it. There are three types of neurons. Multi-polar, unipolar, and bi-polar. Currently, we are only interested in Multi-polar neurons. These are neurons with many extensions( like the picture seen above ) to carry out complicated functions.
Inside of the spinal cord, at its center is a grayish looking substance. As you may have guessed, this is called gray matter! The gray matter is simply a collection of cell bodies inside the cns. The neurons have a grayish color to them, and there are several in there! Following this the axon( longest extension ) of the neuron leaves the CNS and becomes part of the PNS( once outside of the spinal cord, you have entered the pns, again this is a distinction by location ), in which it carries a message to the muscle its axon ends at or is near. There is one more thing I would like to discuss in regards to neurons. There is such a thing as inter-neurons. It’s simply a fancy term for nervous cells that do not leave the CNS. If one nerve begins in the spinal cord, it needs to be able to carry the message to the brain. Therefore you have nerves that originate in the brain and end in the spinal cord. A message is sent by the brain, via an inter-neuron, it then travels down its axon and dishes the message off to the SE neuron, which then sends the motor message to the muscle being worked. It’s that simple. Badda bing, badda boom! Think of it like a telephone wire carrying a voice signal. Quick Overview 1. A Neuron is a cell with a body, and an axon which looks like a tail. The Cell Body is where the message is received. The axon is where the message is conducted through. 2. The CNS = Central Nervous System and simply means that a cell is within either the spinal cord or brain. The PNS = Peripheral Nervous system, means a cell body or axon is outside of the spinal cord or brain What is a Spinal Nerve? I’d tell you, but you are getting on my nerves. I am full of unfunny jokes this month aren’t I? Anyway, the simple definition of a nerve is a collection of cell axons( which are extensions of cell bodies of neurons ) outside the cns. Coming off of the spinal cord are two roots. The first root comes off at the rear of the spinal cord, and the second comes off near the front. In anatomical terms, when dealing with nervous tissue, scientists like to use the term dorsally( to the rear ) and ventrally ( to the front ). Why? Because it sounds cooler. This is why the lats are called the latissimus " dorsi. " Getting back to the point, the cell bodies or gray matter inside the cns extend off via their axons and travel into the ventral root. These are the cell bodies of interest to us. Motor neurons always start in the CNS. The sensory or somatic afferent neurons begin in the actual dorsal root. Then they come together in one central cord called the spinal nerve. This spinal nerve then branches out again. The branches come out of the vertebral foramen. If you recall, a vertebral foramen is simply a hole created by one vertebra stacked on top of another vertebra. There are two branches formed. One again to the front( ventrally ) and one to the back ( dorsally ). These are called the ventral and dorsal rami. The word rami in latin means branch. Short Version of the Story That may seem a bit confusing, but I feel its important information. The nervous system is a complicated unit, and will be covered extensively in future issues. To break the point down simpler though I will leave you with this. A. Two vertebra placed on top of each other make up a hole called the vertebral foramen. B. A spinal nerve comes off the spinal cord and branches into two rami( which means branches ). The nerve is made up of a collection of cells called neurons. C. The Nerve then leaves and heads to an area that it controls motor actions( contracts muscles, both smooth and skeletal ) and also sensations such as touch. What Nerves Reside In the body and What Do They Innervate There are a total of 31 spinal nerves, and guess what? They correspond almost spot on with the vertebral column. The rule is this. When a nerve passes above a vertebra then it is named for the vertebra it passed above. This is correspondent to spinal nerves above the first thoracic vertebra. However, spinal nerves that pass inferior( below ) t-1, are named and numbered for the vertebra they pass inferior to. It looks like this ------ Spinal nerve t-1 The only problem we run into, is that there cannot be two t-1’s. So the nerve above t-1 is named c-8, even though there are only 7 cervical vertebrae. Ventral Primary Rami and Dorsal Primary Rami As stated, nerves branch off into rami( which means branch ). One branches off dorsally( to the rear ) and one does so ventrally ( to the front ). Here’s the trick. Dorsal primary rami, always only innervate the skin of the back, and the deep muscles of the back! That’s it! Therefore the spinal erectors you are using to keep your body erect are innervated by dorsal primary rami. You now know the general innervation of every single deep muscle of the back( to be covered in part V of the back anatomy series )! Therefore if I were to ask you, what is the erectors spinae innervated by, you would say: The erectors spinae is innervated by dorsal primary rami. Ventral Primary Rami innervate everything else, except the head and neck. These areas are innervated by cranial nerves. Cranial nerves, are nerves branching off from the brain. But we will not get into that today. However, if you smile, cranial nerve VII was what innervated the muscles to do so. Our concern is muscles involved in bodybuilding. Brachial Plexus – Spinal nerves C 1 – T1 combined, form a branch of the nervous system called the brachial Plexus. This plexus innervates the following muscles.All The muscles of the upper extremity including, all superficial muscles of the back, the entire arm and forearm and hand for that matter. The deltoids and everything else in between! Therefore If I asked you to name the general innervation of the biceps brachii, your answer would be:
You can literally exclaim the general innervation for every muscle in your body! That is amazing! The next article in reference to the nervous system, will get into greater detail, and discuss specific innervations. However, you now understand the following aspects of the nervous system: A. Neurons
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