- But I’m going to warn you - guys, take a deep breath,
I’m about to pull the testis out of the scrotal sac... Here we go!
Welcome to the Anatomy Lab everyone. In today's video, we're going to be going over and showing
muscles that only men have and that's because these muscles are associated with the testes or
the testicles. So then we have to ask ourselves: how much control do men have over these muscles
and how does this influence the efficiency of our sperm manufacturing plants? And as a bonus,
if you have access to a scrotum and testes, we're going to give you a little
test that you can try at home to test these muscles... A very scientific test, that is.
So, with all the maturity we can muster,
let's do this in the name of science and reproduction of our species.
[Intro]
So, whenever we teach about a new anatomical structure, we usually start by
talking about its location. I didn't initially think we needed to go over that because - let's
be honest, most people know where the testes are. However for the sake of consistency
and for those who do not come equipped with such structures, I think it's reasonable for a review
of the location. We're about to look at it on a cadaver though, so you have been warned.
So, take a look at this dissection here - you're looking at the right side of the scrotum or the
scrotal sac which houses the testes inside this pouch of skin that you're seeing here.
Now, one other cool thing about this is you can see this cord coming down here
called the Spermatic Cord. More on that in a few minutes. That Spermatic Cord
is attached to the testus (singular for testes) inside the scrotal tissue.
We also say that the scrotum is attached to the root of the penis here
and it's posterior and inferior to that structure - or in other words, behind and below. But how
far below are we talking here? As you can see here, there's the bottom part of the scrotum
and men tend to be acutely aware that that distance varies from time to time
throughout the day, and that is a function of these muscles we're about to talk about.
But to fully appreciate these muscles and their function, we have to understand where they
came from. So when you were inside mom in that little cocoon of love that we call the Uterus,
the Gonads (ovaries if you're female, testes if you're male)
develop up by the kidneys. And as you continue to develop, they descend downward.
They descend down to about this point inside and it's just medial to this bony landmark on Jeffrey
called the Anterior Superior Iliac Spine (you can see why a lot of people like to abbreviate it as
the A-S-I-S), but to show you the equivalent on the cadaver, it'd be about right here.
The ovaries are like "We're good, we're going to stay in here". The testes, under the wonderful
influence of testosterone, apparently get a little bit more adventurous and herniate out through the
abdominal body wall and they run through a canal called the "Inguinal Canal" (Inguinal
just means groin), and you can see these cords that have developed from that herniation - a
natural herniation, and when they're pushed into the skin, we call that skin the Scrotum.
Now, just a cool little FYI - this is an unnatural herniation which you
can look at our hernia video if you want to take a look at that.
But one other thing about the development of those muscles - have you ever been to the gym
and worked out these muscles on the sides of your abdomen called the Obliques? Specifically one I
want to talk about called the Internal Oblique and I’m going to show you a different dissection here.
This is an abdominal dissection and here is the side of the abdominal body wall muscles.
Here's the External Oblique here, but if I reflect that away, you can see the Internal Oblique here.
Now, what in the world does the Internal Oblique have to do with testicular muscle development?
Well, funny you should ask because it's awesome... When the testes are going through that
canal that I mentioned down through here, you can get this idea that they're pulling things
with them. They're pulling arteries and veins with them for the blood supply for themselves,
also pulling nerves with them as they're developing for sensation and controlling
the muscles we're going to talk about. And as the testes pass by the margin of the Internal Oblique,
they pull some of the Internal Oblique muscle fibers with them. They steal some
of the fibers - and that is the development of the muscle that we call the Cremaster muscle.
I know, it's a little bit of an interesting name, your minds are probably wondering.
However, Cremaster just simply means "To hang" which if you ask me
is a pretty good name based on the anatomy we're talking about here.
So, obviously we need to look at this Cremaster muscle, but I’m going to warn you - guys,
take a deep breath, I’m about to pull the testis out of the scrotal sac. Here we go!
So, if you guys see right here, I’m going to pull the testicle out of the scrotal sac
here and this is the testis here. But we want to talk about this Spermatic
cord - remember that whole developmental story I mentioned, you're gonna have to look closely
because some of these fibers are really fine and hard to see if you don't look.
But you can see through this transparent tissue there's some muscle fibers there.
If I turn it over, you can see some darker fibers here and here and even flaring on to the testicle.
That is the Cremaster muscle. And what's interesting about this - if you guys have
ever taken an anatomy class, there's different types of muscle tissues; Skeletal muscle tissue,
Smooth muscle tissue, Cardiac muscle tissue - in general, we say - skeletal muscle tissue
is under Voluntary Control whereas smooth muscle tissue is Involuntary.
But if skeletal muscle tissue is under Voluntary Control
and this Cremaster muscle was pulling skeletal muscle fibers from the internal oblique,
that would mean there is some control over this muscle.
Now, when I first learned about this muscle, my professor said to us "This is the muscle that we
said bounced our balls when we were kids". You could imagine people got a laugh out of that in
a lecture hall of 400 people and then he would follow up and say "And it's a skeletal muscle.
So I could be doing it right now and you wouldn't even know it".
Now you may be wondering, did we just develop this muscle so
men could walk around just bouncing their testicles for fun? And the answer is 'no'. Yes,
it is a skeletal muscle that has voluntary control, but there's a few skeletal muscles
that are actually more controlled automatically or reflexively, the diaphragm for example
is one of those. Yes, you can control the diaphragm by holding your breath.
The majority of the time, it's just controlled automatically for you. Same with this muscle - it
responds more reflexively kind of automatically based on temperature. When it's cooler,
the muscle contracts and pulls the testes closer to the body, when it's colder, it relaxes and the
testes descend further away and there's a reason for that and that's for sperm cell production.
You see, sperm cell production is more ideal at a body temperature, or I should say,
a temperature that's about two to three degrees celsius, so three to five degrees fahrenheit
lower than body temperature. That is the whole reason for the testes herniating out of the body.
But there's still one other muscle that we need to talk about.
So, the next muscle men have no control over because it's a smooth muscle.
I guess you could argue men have a little bit of indirect control over it because I guess you could
jump into a cold body of water and really engage it in that way but
no voluntary control like we saw with the Cremaster muscle.
So this dissection is on the other side of the scrotum. We dissected a little differently here
and you can see a window that we cut into here. So, we've removed the epidermal tissue and some
of the dermis to reveal the Dartos muscle. And the Dartos muscle again, is that smooth muscle.
This muscle is responsible for the wrinkly nature of the scrotal sac and again, works in
conjunction with the Cremaster muscle when it's colder - contracts the scrotal skin, premaster
contracts around the testes and both pull up closer to the body when it's warmer, relaxation.
And so, these muscles again help with ideal sperm production by regulating the temperature
of the testes. And don't worry, we did not forget,
we still have to tell you about that test or that reflex that you can try.
So, like I mentioned, there is a test you can do on these muscles or in other words,
a reflex called the Cremasteric Reflex and this has a clinical correlation or clinical relevance.
I've done this on male patients when they've come in with testicular pain or testicular issues. For
example, if that spermatic cord twists on itself, which you guys saw on the cadaver,
that can compress the nerve and this reflex won't work properly.
So, how do you do the test, though? What you do is stroke the inside of the thigh skin or that
crease of the thigh, just stroke through there or stroke through there and it'll send a reflex arc
back through a nerve to that Cremasteric muscle and you should see, after you stroke the inside
skin there, that muscle contract around the testicle, and it should come up a little bit.
What's interesting and funny about that, when we first learned about this with my - when I was in
school, you could hear the guys, there was this buzz around the room the next day of like "Hey,
did you try it? Did you try it? Did you try it?" so, if you have access to a scrotum or a testis,
you have permission to do this test in the name of science and reproduction.
Thanks for watching everyone. Hopefully you learned some new
information about the male reproductive structures. We're gonna have some future
male reproductive structures that go further and further down the line
for reproducing the species. Hopefully you had some fun learning, but in all seriousness,
we always like to say thank you to those who've donated their bodies to science, not just in our
lab but just throughout the world. It's an amazing gift. There's no better way to learn anatomy and
our students who come through this lab benefit and obviously our viewers get the benefit as well.
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it really helps to support us to continue to make these videos, so thank you for all the support
that you guys have given us so far, and until next time, stay safe and reproduce responsibly.