Welcome to the lab everyone. Today we're going to talk about and show you muscles that only males have. And this is because they are associated with the testes or testicles. Now I can make the argument that these muscles are also indirectly important to females due to reproduction because these muscles are about creating a wonderfully comfortable environment for the testes. And this is important because happy testes means happy sperm which again is important from a reproduction standpoint. And so we'll talk about what these muscles are, their functions, and if you can consciously control them, and what that would actually look like. Plus, as a wonderful bonus, we're going to show you how to do a test that causes one of these muscles to reflexively contract. It's definitely going to be a fun one that we are, of course, only doing in the name of science. So, let's jump into this anatomical awesomeness. [Music] First, let's start with the basics. Where exactly are the testes located? Now, I know for most this might seem like a very obvious answer, but for anatomical accuracy and for anyone that does not come equipped with such structures, it's worth a quick review. And we're about to take a look at a real human testicle on a cadaavver dissection. So, consider this your heads up. Here on the cadaavver, you're looking at the right side of the groin. And you can also see the right upper portion of the scrotum, that pouch of skin that houses the testes, which sits posterior and inferior or behind and below the penis. And here I'm going to remove the right testice. You can see that right testice or testicle here with this C-shaped structure surrounding it called the epidmus. But you can also see this cordlike structure called the spermatic cord, which is going to be important in our story in just a minute. But some structures that are found within the spiratic cord are veins, arteries, nerves, and even this really cool tube that you can see here called the vas deference. Sometimes referred to as the ductus deference. And this is the tube that transports sperm cells from the testes to the prostate gland and is also the tube that gets snipped during the male birth control procedure called a vasectomy. Now, what's fascinating is how the scrotum's position changes throughout the day. Sometimes it hangs lower, sometimes it's pulled up tighter, and that's no accident. But to figure out why this occurs, we need to rewind to development in the womb. Back when you were developing in the uterus, what I often like to refer to as the cocoon of love, the gonads, which become ovaries and females or testes and males, start developing up near the kidneys. As development progresses, they descend downwards and eventually they get to this level of the anterior superior iliac spine, which are these bony landmarks that you can see on Jeffrey the skeleton here. In females, the ovaries are like, "We're good. We'll stay put in the pelvis." Which, for fun, here's what a real ovary looks like. But in males, under the influence of testosterone, the testes get a little more adventurous. They actually push through the abdominal wall in a natural herniation and travel through a canal called the inguinal canal. Now, you've probably seen a diagonal line on both sides of individuals that are very lean with defined abs. Sometimes people refer to them as the Vline or sometimes other more risque terms, but there's a ligament that contributes to those lines called the inguinal ligament. And the inguinal canal is just above that inguinal ligament. But the testes run through this inguinal canal and as they pass through they drag veins, arteries, nerves and even some muscle fibers which these muscle fibers will be important in just a minute. But these structures like the veins, arteries and nerves and muscle fibers form the spermatic cord that we learned about earlier. But if there is a problem with this developmental process, it can lead to a condition called cryptor orchidism. Crypt means hidden. Orchid refers to testy. So, a hidden testicle, which most people refer to as an undescended testicle. And if an unescended testicle is left untreated, it can actually increase the risk of testicular cancer, cause infertility issues, and even increase the risk of a testicular torsion, which is when the spermatic cord twists. And take it from some of my patients that I've had in the ER, testicular torsions don't feel right. Meaning, it hurts more than Gamora reuniting with Peter Quill. I thought I lost you. [Music] touch. But coming back to what is supposed to happen, the descent of the testes into the scrotum is key because sperm production thrives at a temperature 2 to 4° C or about 3 to 7° Fahrenheit below core body temperature. And this is why the testes hang outside the body to stay cooler. And those muscles that I alluded to earlier are kind of like the thermostats for optimal sperm production. Now, there are two muscles that we are going to look at and one of them you might be able to control voluntarily. Plus, we're also going to show you quite the exciting reflex test that you can try on one of these muscles at your convenience. But the first muscle is called the cremaster muscle. And cremaster comes from a Greek word meaning to suspend or to hang, which is a pretty fitting name if you ask me. And if you look at the spiratic cord on the cadaavver dissection again, you may be able to see some fine looking fibers embedded in that spiratic cord. And these fibers are contributing to the cremaster muscle. And we may also be able to see some fibers embedded a little bit lower down like right through there. And what's really fascinating about this muscle is its origin story. Remember the descent of the testes. As the testes moved through that inguinal canal, they pulled muscle fibers with them. Specifically, they pulled muscle fibers from the internal oblique muscle. And those fibers from the internal oblique just became the cremaster muscle. And what this muscle does when it contracts is it elevates or pulls the testes closer to the body. Now, when I first learned about this muscle, my professor was teaching hundreds of students in a big lecture hall. And while he's presenting, he's like, "Everyone, this is the cremaster muscle, and it elevates the testes." When I was a little kid, we used to call this the muscle that bounced our balls. And the whole lecture hall erupts in laughter because my professor didn't make jokes of that nature very often. But then he follows it up with, "And remember everyone, this was derived from the internal oblique muscle, which is a skeletal muscle under voluntary control. So I could be contracting this cremaster muscle right now and you wouldn't even know it." And how many of you guys watching this video right now just tried to contract your cremaster muscle? If so, you better be admitting it in the comments below. But the reason for this muscle is for those frigid days. When the testes get too cold, it contracts, pulling the testes closer to the body for warmth. And when it's warm, it relaxes, letting them hang lower to cool off. And even though it can be contracted voluntarily, most of the time it reflexively contracts in response to those temperature changes. But the cremaster muscle isn't working alone. It has a partner in crime called the dartose muscle. The dartose muscle is a layer of smooth muscle right under the scrotal skin and embedded in the subcutaneous layer. And here we're showing you the left side of the scrotum. Here's the epidermis and dermis. So that skin has not been removed. But down here we've removed those two layers to expose that subcutaneous layer where that dartose muscle would be embedded in this tissue. But unlike skeletal muscle, smooth muscle, which the dartose muscle is made out of, is involuntary. So no direct control here. Although jumping into cold water would trigger it indirectly because this muscle also responds to temperature changes. But instead of elevating the whole testicle during contraction, the dartose muscle causes the scrotal skin to become tight, thereby reducing heat loss. And when temperatures become elevated again, the muscle will relax, loosening the skin of the scrotum. But as promised, there is a test that you can use to test the cremaster muscle called the cremaster reflex. Now, this test does have clinical value and I've actually used it on male patients with testicular pain to check for issues like a testicular torsion that I mentioned earlier because with a testicular torsion, this reflex is often absent. And so, this can contribute to the diagnosis of such a condition. But here's how the test works. One would gently stroke the skin of the inner thigh from the upper portion down towards the groin crease. And you could do it on either side. Just a gentle p gentle pass of the skin in this direction, if you will. And what this does is it sends a signal through the nerves in the area causing the cremaster muscle to reflexively contract which would pull the testice up slightly on the same side that you performed the test. Now the funny thing about this is that when I was again a college student and when we first learned about this test from our anatomy professor the next day before class there was a lot of whispering going on between the male students with most of them saying things like hey did you try it? Did you try it? And what the conclusion was is that the reflex definitely works. So if you do have access to a scrotum and testes, you could definitely perform this test for science.