Hello, everybody. We're back here talking about male reproductive system and mechanisms underlying that reproductive system. We've spent time talking about kind of general anatomy, general physiology. We've talked about the hormonal mechanisms kind of associated with some of this, and especially in the development of sperm. And in the last mini-lecture, we were actually talking about the process of erection and the physiology around that.
Well, we need to move over now. If we have an erection, we need to understand ejaculation and the physiology behind that. So it's time to move and talk a little bit about this physiology.
All right? Well, let's see here. Let me get my slides ready to go. I'm actually, just to let you all know, I'm actually looking at my hotel room.
I'm actually off at a conference and it's a beautiful day where I'm at. I understand back home that it's raining like crazy, but it's beautiful where I'm at. And it sounds really weird, but I'm here talking about reproductive mechanisms in my hotel room, trying to get you guys to understand. Well, let's finally get on with this, okay? If you remember from previous lectures, in talking about the erection process, we said it relied on a couple of different sensory components.
Mainly tactile sensation, and that tactile sensation usually is touch associated with the reproductive organs, but it could also be neural mechanisms coming from psychological aspects of our forebrain sending off signals to the spinal cord saying, we're observing a process that you should be ready for reproduction. We could spend a whole semester talking about what actually sets that off. But just to let you know, that is a possibility.
In talking about sensation, and we'll try to make it as simple as possible here, we're going to talk about tactile, mainly tactile sensation, touch. So this tactile sensation anywhere around, usually, the reproductive organs, that sensation, that information will be sent over to, mainly, the pudendal nerve and sacral nerve. but you're going to send that information directly over to the spinal cord. So now, this is specifically sensory information, specifically sensory information.
That information will synapse in particular nuclei within the spinal cord. Now that information, it could be sent up to the forebrain by way of particular pathways, mainly going to the hypothalamus, mainly going to the hypothalamus, which sits at the base of the brain. That hypothalamus is also a major control area for all autonomic functions. All autonomic functions. That means parasympathetic and sympathetic.
Now, hypothalamus has connections to everybody. So it can send that information to cortex. It could send it back down the spinal cord. It could literally set off parasympathetic mechanisms on its own. On its own.
With that in mind, the information that the spinal cord is sending to the hypothalamus, it is also sending it over to other groups of nuclei that will initiate the parasympathetic mechanism for erection. Do you remember that, folks? That parasympathetic mechanism coming over, inhibiting the smooth muscle contraction at the base of the penis, allowing... those vessels at the base of the penis to be able to dilate and allow blood flow into the penis itself, into the erectile tissue, which as it engorges with blood will cut off blood flow back towards that area.
So that means it's going to close off the veins themselves, which means all that fluid gets trapped in the penis. We get an erection. We get an erection.
Now, this is only part of this whole sexual response here. We need to figure out, okay, what's the next step? And that next step, sorry, that next step is how do we actually get ejaculation? Ejaculation, folks, actually requires sympathetic mechanisms.
Sympathetic mechanisms. Now, I'm hoping you see some things here. For you, for the male to have an erection, they have to be in a parasympathetic mode.
So what does that mean, folks? What does that mean? Think about that for yourself. That means, for the most part, the male needs to be in a relaxed.
or close to baseline type of activity around the body. This is why some males, if they're too excited moving into the sexual act, they don't get an erection. Why?
Because the sympathetic system has taken over and you can't get an erection. You need to have the parasympathetic component first, setting up the process, setting up the erection. Once that has happened, once that has happened.
If sensation continues at some point, and this is variable for every individual, every male individual, that sensation will stimulate enough of the sympathetic components that they will start to override the parasympathetic. And this will lead to ejaculation. This will lead to ejaculation. How does that kind of work?
Let's see. Let's look at this next slide. So, with sympathetic stimulation, with sympathetic stimulation, after erection, that sympathetic stimulation will set off contraction of smooth muscle.
That means contraction of the smooth muscle, yes, at those same arteries that are sitting behind the penis. So ejaculation has to happen very, very quickly. Once that happens, or once... Smooth muscle contraction takes place there at those vessels.
It's also taking place in glandular tissue. So the smooth muscle that is surrounding particular glands that are part of the reproductive organs in males. So you'll hear us talk about the prostate gland. You'll hear us talk about the seminal vesicles.
You'll hear us talk about the vulvo-urethral glands. You'll hear me... bring that up in a subsequent lecture. But that glandular tissue will start to contract, squeezing the materials out of those glands into the urethra and allowing sperm to follow along with it. Now, I forgot one major glandular component or what's not necessarily considered a glandular component.
Do you remember I was talking about the epididymis at the back? of the testes, this sympathetic stimulation will also cause contraction of the epididymis. Once it causes contraction of the epididymis, that's going to force all the sperm cells that are being stored in the epididymis to start moving through the vas deferens.
Once that contraction occurs, we get peristaltic waves in the vas deferens that are moving those sperm cells or helping to move those sperm cells over towards the urethra. And as those sperm cells move over towards the urethra, we'll get the glandular tissues adding materials, adding materials that will help support those sperm cells. This is what makes up semen.
Now remember, contraction of smooth muscles, contraction of the glandular tissue, and I'm bringing up one more time, vasoconstriction, vasoconstriction. The blood vessels at the base of the penis are going to start contracting. So think about what that means.
In this image, if we look over on the left here, we have the development of an erection, and we've gone through that already in a previous lecture. Here we have what's called the plateau phase. That plateau phase is when, as I mentioned just a few minutes ago, sympathetic stimulation has gotten to a particular point where it will start to send information over to. the epididymis to the prostate gland, the vulval urethral gland, and the seminal vesicles, which sit here at the back of the bladder.
All of those, along with the peristaltic waves that are going to be occurring in the vas deferens, will help move sperm down over towards the urethra. Now, these glandular components here, the vulva urethral gland, the prostate gland, the seminal vesicles, and a couple of others in this area, actually start secreting materials into the urethra before the sperm gets there. That's where we have these secretions that usually occur right at the beginning, right before ejaculation actually occurs.
Everybody got that? As orgasm happens, and that orgasm is the culmination of that sympathetic activity, and all of these glandular mechanisms, and that includes the epididymis, contracting fully. Spasms or peristaltic waves in the vas deferens again, everything moving semen through that urethra as fast as possible, as fast as possible. And now we have ejaculation. We have ejaculation.
Remember that last point I had in the last slide. We are also causing contraction, vasoconstriction, of the blood vessels that are bringing blood into the penis. That constriction is going to mean that pretty soon the erection goes away because no more blood flow coming in. Blood flow in the penis will start to seep out by way of that dorsal vein and as more and more seeps out, less and less pressure is on it. It's able to empty the rest of it.
And at this point, we have relaxation. Relaxation of the penis. Okay? Everybody got that? Now, back to our original kind of flow chart here.
We talked about sensation, setting up communication back towards the spinal cord. Spinal cord sending that information to multiple spots, the forebrain, and... to mechanisms within the spinal cord to help set up parasympathetic mechanisms, which will then help set up sympathetic mechanisms for ejaculation and emission, leading us to the final stage of all of this. Oops, sorry, wrong way. The resolution.
This is what physiologists like to call ejaculation for the most part, or I should say orgasm. Resolution. It's almost as if we had a problem and we were trying to resolve it. Well, we did. We have ejaculation.
We have movement of sperm over to wherever we're looking to move it towards, and hopefully procreation at that point. All right. We will continue in our next mini lecture actually talking about the glandular tissue and all the components associated with that. We'll talk to you then, folks.