There are two types of pathways. So we're going to start off talking about the differences between the two. As we can see that both of these systems, the top one showing autonomic, bottom one showing somatic, both of these systems are going to have a neuron with a cell body right here, start off either in the brain's gray matter or the spinal cord's gray matter.
So we can see in this one we have the cell body starting off in the spinal cords gray matter. You'll notice that the autonomic one is starting off closer to the middle of the gray matter, around the lateral gray horns, whereas the somatic is starting off in the anterior, our ventral gray horns. Both systems, as we can see, have that first neuron coming out. And in the autonomic system, we see that the first neuron coming out is going to be myelinated.
But that first neuron is going to stop and communicate with a second neuron. The second neuron, as you see, is unmyelinated. So in the autonomic pathway, we have two motor neurons in the pathway that lead to the effectors.
The effectors in the autonomic are going to be smooth muscle, glands, and cardiac muscle. In the somatic, we can see that we have that neuron coming out of the gray matter of the spinal cord. We can see that the neuron is also myelinated, but notice that in this pathway we only have one single neuron.
This neuron is going to go the entire length of the motor pathway until it reaches its... the effector, which in this case is skeletal muscle. Now, the somatic nervous system only has one motor neuron in the pathway. The autonomic has two motor neurons in the pathway. If you look at the autonomics picture, you'll see that that first motor neuron is releasing ACH.
If we look in somatic, this is the first and only motor neuron, and it releases ACH. So we can safely say that both somatic and autonomic release ACH. But if you look at the second motor neuron, the unmyelinated one that goes to the effectors in the autonomic system, you'll see that this second neuron releases ACH as acetylcholine RNE, which is norepinephrine. So that's another difference. The autonomic has two motor neurons in the pathway.
The somatic has one motor neuron in its pathway. The autonomic... is going to release ACHRNE, whereas the somatic is only going to release ACH. Autonomic goes to smooth muscle, cardiac muscle, and glands as the effectors.
The somatic only goes to skeletal muscles. So those are some major differences between the two systems. So just to reiterate it, this, it looks a little bit overwhelming, but it's really not that bad to follow. So this is showing you how both pathways are going to go through a portion of the spinal cord.
So remember that we have our sensory receptors. They're going to detect the stimulus. They're going to send the signal input down the sensory neurons into the back of the spinal cord. Once in the spinal cord, integration is going to occur in the gray matter. Use an interneuron or it doesn't have to use an interneuron.
So that can happen. Once integration occurs, we are going to send the signal either to a somatic pathway or an autonomic pathway. If we send it the somatic pathway, it's going to come out the anterior great horn directly to the skeletal muscle.
So this is the motor output down the red neuron to the skeletal muscle. Notice it's only one neuron leaving the front of the spinal cord. What type of neurotransmitter will be released in the somatic nervous system? Now, say this is going to cardiac smooth our muscle. integration with the gray model then you can see the first Which is the first one you have?
The first one you have. The first one you have. What does the first one you have? What? What does that second motor neuron release?
He said A-C-H-R-N-E. You are correct. So what this picture does is it just depicts the possible pathways that can occur in communicating with the systems. So one last time to go over the somatic pathway. Sensory information comes in.
It is integrated within the gray matter of the brain or spinal cord, and then motor information goes out. The motor information is going to come out the front of the spinal cord in the anterior gray horn. It's going to come down one single myelinated motor neuron to the effector, which is the muscle. Somatic always releases ACH. to the skeletal muscle.
So the somatic pathway of the motor neuron. And in this picture what you can see is that here we have that motor neuron coming out of the brain and here we have the motor neuron coming out of the spinal cord. As long as it's coming out of gray matter in the brain or spinal cord, that one motor neuron is going to travel the length to the skeletal muscle it integrates. Neurotransmitter does the single motor neuron release to the throat muscle.
You said ACH, you are correct. Now remember the autonomic is a little different. The autonomic pathway, we're going to have sensory input, integration within the spinal cord or brain's gray matter, and then the pathway is going to have two motor neurons. So what we see here is we see The first motor neuron coming out of the brain, here's another first motor neuron coming out of the spinal cord.
This is just to demonstrate that they can come from either the brain or the spinal cord. That first motor neuron comes out. It's going to communicate in this hole here.
This one has another type of effector, which are going to be specialized cells. So the autonomic motor pathway has two motor neurons, but there's a little bit more to it that we haven't talked about. So we can see the brain and spinal cord, and what we see is we have the first motor neurons exiting the brain and spinal cord.
These motor neurons are actually known as preganglionic neurons. So the first motor neurons in the autonomic pathway are known as preganglionic neurons. Those preganglionic neurons are going to communicate with a second motor neuron.
Where they communicate is in a spot called a ganglia. Ganglia are just groups of cell bodies clustered together. So what happens is we have lots of cell bodies in this area.
because we have lots of motor neurons that are in here. That first motor neuron, the preganglionic neuron, is going to communicate with this second motor neuron in the ganglia. We call the second motor neuron postganglionic neurons. So this right here is your postganglionic neuron, and so is this one, your postganglionic neuron.
Where the pre-and postganglionic neurons communicate is called the ganglia. These second neurons, the postganglionic neurons, are going to travel to the effectors. And as we can see, the effectors are going to be the same as that previous effector, smooth, glands, cardiac, and then specialized cells.
Now, if you can remember, what does that first motor neuron, the preganglionic neuron, always release? If you said ACH, you're correct. That. Preganglion neuron leaves the brain or spinal cord, travels to the second motor neuron, and where they communicate is called the ganglia.
In the ganglia, that second motor neuron is going to leave, and it's going to go to the effectors. That second motor neuron is going to release. If you said ACH or NE, you are correct.
It's going to depend on the system. So this is just another picture, just to give you a demonstration. We can see that we have our first motor neuron exiting the spinal cord.
Notice it's exiting around the lateral gray line. Where it exits, it's myelinated. So the preganglionic neuron is myelinated. It meets that postganglionic neuron, which is unmyelinated, in a ganglia. That postganglionic neuron is going to go to the effectors, smooth muscle, cardiac glands.
That first motor neuron releases what? If you said ACH, you're correct. But the second motor neuron doesn't have to release just ACH, it can release ACHRNE. Now, we've been saying that in the autonomic pathway, there are always two motor neurons. So if we look at this picture, this is just a little preview to the bulk of this chapter.
In this picture, we're talking about the sympathetic system, and in this bottom picture, we're talking about the parasympathetic system. What we see in both of these systems is we have our preganglionic neuron and our postganglionic neuron. So we have two motor neurons.
Both of these motor neurons are meeting at the ganglia. So these two systems are supporting the statement that we have two motor neurons in the pathway, but there's always an exception. So there is an exception to the rule when there's only one motor neuron in the pathway for the autonomic nervous system. And that's going to be very specific for the organ we go to.
This is when we go to the adrenal gland. So if we look at this picture, you'll notice that we still have our first motor neuron exiting the spinal cord, but we only have one. That first motor neuron is going to stop at the adrenal gland. specifically in the center of it, which is called the medulla.
But you'll notice that that first motor neuron is still releasing ACH. So what happens is the ACH goes to specialized cells that are called chromophane cells. I'm not worried if you know that.
But these chromophane cells are going to act like the second motor neuron. They are not a motor neuron, but they are taken... So the exception to the rule for two neurons in the motor pathway for the autonomic system is when the first motor neuron, the preganglion neuron, goes to the adrenal medulla gland. So here's just a quick chart to kind of sum up what we've talked about. Where is that first motor neuron located?
It can be in the gray matter of the brain or the spinal cord. In the somatic system, we have one motor neurons in the pathway. Autonomically, we have two, but remember we have that one exception. What was the exception? The exception, if you said when it went to the medulla, the adrenal medulla, you're correct.
The somatic only releases ACH, but the autonomic can release ACH or NE. So the rules, the first one always releases ACH, the second one can release ACHRNE. In somatic, the effectors are always skeletal muscle.
In the autonomic, it can be cardiac, cerebral glands. So the somatic is voluntary, contact-controlled. Autonomic is involuntary. The somatic will always cause excitatory effects on the skeletal muscles. So we'll always cause a contraction.
In the autonomic, it can be excitatory or it can be inhibitory. So we can cause something to slow down.