Neurology Fundamentals
What is "neurology"?
Neurology is a field of medicine concerned with how the brain works, how nerves and muscles work and the diseases that affect them, in brief. Neurology focuses on the central nervous system, which includes the eye, the brain and the spinal cord; and neurology also focuses on the peripheral nervous system (nerves) and also on muscles. So neurology looks at the diseases and the effects on those things. For the most part, neurologists are interested in cognitive and behavioral changes, mostly as they relate to a disease of the brain rather than in terms of the environment. Neurologists think that most psychiatric diseases are probably of an organic nature, like bipolar disease, schizophrenia, etcetera. So they study the brain. Neurologists study how the brain works and so forth, and their branch of medicine is called neurology.
What is a "neuron"?
A neuron has the following parts to it: a nucleus and ribosomes which make proteins. That's where the RNA is. The DNA speaks to the RNA and there is a message that's sent, and proteins are made. So all those are in the cell body, in their own little cell bodies. Now, it has processes which are called dendrites, which are short processes, and they may have a hundred of them in a big neuron. That's the receiving end of the neuron. So a dendrite might have connections with fifty other neurons, and it's all going to be with connections to that dendrite. And then it has a part that goes to other neurons or to other structures. That's the axon. So there is the cell body with it's dendrites, which is the receiving part of the neuron, and it has an axon. It only has one axon. It has many dendrites. That one axons is going to go somewhere. Now if it is a motor neuron, it's going to go out to the muscle. If it is in the brain, it may go to other neurons, or it may go to the basal ganglia, or it may go to the medulla oblongata, or it may go elsewhere, but basically it is going to carry that neuron's message somewhere. Now, the axon has the neurotransmitter in it. It's made in the cell body, but it's going to carry it to wherever it wants to go. The dendrite is receiving. The axon is also going to have what we call the action potential. It's going to propogate an electrical signal. It is the axon that has myelin in it. Dendrites don't have any myelin. So the axon can be covered with an insulator so it can move faster, essentially, and there are axons that don't have myelin. They move slower. So there are different types of axons. Quite clearly, the axon is the nerve.
What is a "neurotransmitter"?
Neurotransmitter is a chemical made by the neuron which comes down into the nerve and is released to make whatever it's in contact with activate. If the neurotransmitter is going to make the muscle contract, it would come out of the motor neuron, the motor neuron would make that transmitter. It would send it down the nerve, and it would be released by what we call vessicales. There is a cleft between what we call the pre-synaptic which is the motor neuron, in this case, and the post-synaptic, which would be the muscle. The muscle now has a receptor for that neurotransmitter. So serretonin, for instance, is a neurotransmitter and dopamine is a neurotransmitter. But what they are is chemicals made by a neuron to speak to wherever they are making contact. They release it and it makes the other cell activate. Whether it be muscle or another neuron. Sometimes it's a hormone, sometimes its a kidney, sometimes it's a blood vessel. So whatever it's making contact with, it will do it.
What is a "nerve"?
Well, a nerve is something that goes to an organ or a tissue that makes up sensory motor function. It carries fibers from some place to the spinal cord or the brain, or it carries them from the brain and the spinal cord to (another place). So, for instance, your hearing nerve, your auditory nerve, is coming from your inner ear, and that goes into the nervous system to give you sound. It goes to areas in the brain that are equivalent to interpret this. That's a peripheral nerve. Your smell is a peripheral nerve; your taste is a peripheral nerve. All of those are fibers that are going to go directly into the brain. So, the eye movements are a peripheral nerve as well, so if you want to look to the right, you want to look to the left, you want to look up, you want to look down, those are contracting muscles, but the peripheral nerves are what makes the muscles contract.
What is the "central nervous system"?
Well, there is the brain. There is actually the brain, and the offshoot of the brain is actually the eye. The eye is an out-pocketing of the brain. So, it's really classified as the central nervous system. It's the same tissue as the brain. There's also the spinal cord, which has the input from the periphery that goes up to the brain, and it has the the impulses from the brain that go down into the periphery.
What is a person's "brain"?
One part of the brain is not the same as another part. We tend to think of the frontal lobes, which is the front of the brain, as being involved with behaviour and emotion. It's not exclusively the only area that's involved in that but that's primarily what it's about. It also has input into the autonomic nervous system. So, if you stimulate the bottom of the frontal lobes you can influence heart rate, things of that sort, and breathing, and so forth. That's a very important. A little further back from the frontal lobes are the motor strips. The motor strips are very oriented to a particular area. That area might have the legs and the bladder function. Then, you'll find that along the motor strip, each area has a specific series of neurons. So, if I stimulate one, the area that has the largest motor neurons is the thumb; the thumb is where there's the largest number of what we call pyramidal neurons; the thumb is big in humans. Now, you go on a little further back into the next hemisphere, which is the parietal lobe; the parietal lobe is a sensory organ. Now, the motor area, the frontal lobe, also has an area in it for speech. However, it's motor speech; how you say words, how you form words, etcetera, etcetera. Now, if you go into the parietal lobe you have the same thing but in a sensory way. So, if I stimulate your foot, there's an area of the brain that gets stimulated. As I go up your anatomy, wherever there's an area of sensory input and there's something coming, it eventually gets sent to the parietal lobe. It's also where the speech is; where the speech is sensory. In other words, if I talk to you and you don't understand what I'm talking about but you can still speak, that would be the parietal lobe. So, that's what we call the Wernicke's Area; that's the cognitive communicative area for input. If you don't understand what is being said to you, then that's in the parietal lobe. Frontal lobe is the speech area, so speech is both a motor function and an input function; you have to have both. The temporal lobes are where there's also a considerable amount of emotion, it makes up part of the limbic system, and it's also where the memory is; where the memory is critical for learning, etcetera, etcetera. The occipital area is visual, and obviously that's very important, the visual area. The hearing parts are also in the temporal lobe. So, temporal lobe has hearing, it has some speech components, and it has memory. The occipital lobe has visual, and it's not just seeing, but also interpreting, visual memory and all these other things.
What is the "peripheral nervous system" and its functions?
Once the spinal chord nerves leave the spinal chord, they go to the arms and the legs. They innervate the muscles, they innervate the skin. They innervate the GI tract. They have innervation of the heart, and all the internal organs. So that's the autonomic nervous system, because you don't have to think about it. So there is this central nervous system, which then gives input to the peripheral nervous system, muscle, etcetera, and then there are autonomic nerves that go to all your vital organs, visceral organs. And obviously your skin has input, because it sends messages back. So you touch something, and your peripheral nervous system allows you to know that, because you're not looking at it so you're brain can't tell you that. You don't have to look at it to know it. So your peripheral nervous system has to send it back into the spinal chord and then up to the brain for interpretation.
What are the "somatic" and the "autonomic" parts of the peripheral nervous system?
The somatic would mean the muscles of your hands and arms and so forth. The sensory input from your periphery from your skin: How do you know where your feet are, etc.? And there's the autonomic, which basically is going from the brain to all of these visceral organs. The reason it's called autonomic is because it can be influenced by emotion, it can be influenced by what the brain does, but it works all the time. So, otherwise your heart would not continue to beat? And your GI tract would not continue to digest? It opens and closes blood vessels, depending on what the circumstances are, and in doing that it also controls blood pressure.
What is the "spinal cord"?
The spinal cord has neurons in it that are like weigh stations. Some of the impulses that come in make a connection, and then go up into the brain and make different connections in the regions of the brain. Those that go out, come down and make connections in the spinal cord, they're tracks. So there's gray matter which is where the neurons are that are weigh stations, and then there's the white matter surronding it, which is the tracks. The tracks are eather going up or coming down, depending on where the impulses started. For instance, if I want to write something I pick up my pencil. The motor neurons are getting commands from my cortex to pick up that pencil. The actual contraction of the muscles and the relaxation of other muscles so that you can make a pinch movement, that requires regulation of the motor neurons. The actual writing however requires the motor neurons but it needs direction from the brain. So the impulses are coming down, hitting the motor neurons, and telling us that information. We have to feel the pencil as well. So there are impulses coming from the finger tips going into the spinal cord and then up to the brain as well. So you need the motor movement, but you need the sensory input to tell you that you have a pencil in your hand.
What are the different areas of the spinal cord, and what are their functions?
There are tracks that come from the brain. Those include the cortices, the basal ganglia, coordination areas in the cerebellum, the medulla oblongata; all of those are going down. The spinal cord gray matter has neurons that connect from the outside and they have neurons that connect from the inside. The sensory neurons are going to be in the posterior part of the cord, or the back of it, and the motor neurons are going to be in the ventral part, or the front of the cord. So, that's it, and it's regional. The cervical cord has the motor neurons for your upper extremities but also has fibres that have come from your lower extremities, because they're on their way up, and they're going from your brain to the lower extremities. The fibres in the cervical cord will be from both, but the motor neurons are going to be for your hands. The thorasic cord controls your intercostal; your muscles that are for breathing. Then the lumbar cord is basically for your lower extremities' motor neurons. You realise the your spinal cord stops at the end of your rib cage. After that there's no spinal cord, it's all the roots and the nerves, particularly the ones that have to go to the lower extremities. So, when you're born, your spinal cord comes all the way down to the end of the vertebral column. As you grow, the spinal cord doesn't grow but the bones grow and, therefore, the spinal cord gets lifted up. It stays the same size but now you're growing, so the bottom of that is now where the nerves are going. So, when you have a herniated disc, it's the root that gets compressed. If you have a fracture, it's the root that gets depressed. Whereas, if you have a fracture of your neck or a fracture of your thorasic spine, you do run the risk of compressing the spinal cord which is a considerably more difficult thing and winds up with paralysis.
What is "cerebrospinal fluid"?
Your brain and spinal cord are bathed in a fluid. In the brain, there are ventricles; just like the heart has ventricles, the brain has ventricles. The top of the spine, and the brain, and the spinal cord are surrounded by fluid. That fluid is to get rid of waste and also to bring nutrition. So, those are the two purposes of the spinal fluid. It has protein in it, it has a certain level of sugar in it, and has a number of other kinds of chemicals in it and so forth, but it is essentially a cushion, although it also has nutritional elements to it. Quite clearly, if you were to quickly stop your brain with a movement, theoretically there's some fluid cushioning to it, so it wouldn't so bad. Now obviously if you hit it too hard, it's not going to do much good, but spinal fluid is surrounding your brain, surrounding your spinal cord. When the spinal cord ends at around the end of the rib cage, the top of the lumbar spine, there's a sac there filled with spinal fluid, which is where we do our spinal tap. There's no spinal cord there, there are only the roots. So, God has given us a little space to find spinal fluid, right? Okay, now obviously, the younger the child, the smaller that space is, but as you grow up it becomes a space that's maybe three or four inches wide, and it's full of fluid.
How does pain work in the nervous system?
There are two elements to pain. One of them is the actual irritation of the pain fibre, and then there is the central nervous system perception of it. Acute pain is usually from a local irritation, and that's an easier thing to deal with. It responds to a whole host of narcotics and all kinds of other things. Chronic pain means that your pain has been conditioned, and even though the cause of it is no longer there, you still have pain. The best example of that, really, is phantom pain. Take an amputation of a leg; you say, "Gee, my foot is hurting me." You don't have a foot, but your brain doesn't know that. It's been conditioned. That usually does not respond to narcotics. So, it is the acute pain that you have to differentiate from a chronic pain. In one instance, the chronic pain really has to be dealt with in a different way than simply treating fibre. You have to know that there's not a continuing irritation. So for instance, if somebody has low back pain that goes on for six months, even though it's theoretically chronic pain, the cause of it is still there. This is not what we're talking about, but for instance, say you have a patient who has had something happen to them; they have pain, and they get better from that, but they still have the pain. The pathways are open, it's real pain; it's not imaginative, but the treatment becomes very much more difficult, and it is generally not something that we treat with narcotics.
