 Hi everybody, Dr. O here and this is where we're going to talk about the descending motor pathways in the spinal cord. So I don't make a huge deal out of this, but I do want to make sure you're familiar with these terms. I want to start with what's called a motor homunculus. A homunculus is a functional mapping of the primary motor cortex, which would be the pre-central driver of your frontal lobe. And you can see here it's a funny looking human because the larger the structure, the more nervous input it receives. So as you can see the hand and fingers are really big, the mouth is really big, the tongue is really big because there's a lot of the nervous system is used to control those areas. Notice that how small the trunk is, because it doesn't take as much motor innovation to control those areas, even though they're physically larger. So that's a motor homunculus. Here we see the descending pathways. So just general rule of thumb with your descending pathways, look, they should either start with the term cortico, meaning they start in the cerebral cortex or most of them will end in spinal, which means they're going from the cortex to the spinal cord. It's a reminder that they're descending tracks, they're descending pathways. The two most important ones by far are the two corticospinal tracks. So they start in the motor cortex and they control your body by traveling down to the spinal cord. We have the anterior corticospinal tract, which is about 15% of them. And this one travels down the same side of the spinal cord. Then you have the lateral corticospinal tract, which is 85% of the corticospinal nerves. And they actually are going to cross to the other side before traveling down the spinal cord. So I can show you that here. So notice in the end, they both do cross over though. The lateral corticospinal tract is, is decasating there or crossing in the pyramids. The anterior corticospinal tract travels down the spinal cord, but then crosses over. So remember, the right side of the brain controls the left side of the body. Left side of the brain controls the right side of the body. So those are your two corticospinal tracks by far the most important. This one's not on here. The cortical bulbar tract is the other part of this motor control system or your somatic nervous system. It sends information from the primary motor cortex to the face, head and neck. So it helps control the movement of the face, head and neck. That's called the cortical bulbar tracks next. And these are not near as important. And I just want to make sure you're familiar with the terms in case you hear them. Then next, we have the reticulo spinal tracks. And there's two different groups, both medial and lateral, so they can be further broken down. These are going to be subconscious control of reflex activity. But these can be broken down even further into the vestibulospinal tract, tectospinal tract and rubrospinal tract. So the two that are considered the medial are vestibulospinal tract with the vestibule. So it receives information from your inner ear and it helps regulate balance and postural muscle tone. That's the vestibulospinal tract. You see there, tectospinal tract. This is going to receive information from visual, but also auditory information, like light movement sounds. These kind of things is going to send information to the tectospinal tract and it's going to be responsible for the subconscious regulation of eye, head, neck and upper limb position. So if I hear something, I'm going to look towards the sound like that. If I see something moving, I'll track it. That's the tectospinal tracks that do those. The last group is rubrospinal tract, which rubro means red from the red nucleus. This is going to be subconscious regulation of upper limb muscle tone and movement. So those are going to be all the descending pathways. The corticospinal tract are the only ones that I really expect you to know much about, but those are all your descending motor pathways as well as the functional map of where this information is coming from. The motor homunculus. I hope this helps. Have a wonderful day. Be blessed.