[MUSIC] So it, it's very minimum. The ability to, to empty your bladder, depends on two muscles. It depends on the detrusar muscle or the bladder muscle, and it depends on this external urethral sphincter. So the bladder muscle is a smooth muscle. It gets its innervation from parasympathetic, neurons in the sacral cord. And so that is involuntary, and then the external urethral sphincter is a voluntary muscle and it is always closed for well over 99% of your life, well over 99% of everyday. Your external urethral sphincter is closed because, you spend over 99% of your life in urine storage. But every once in a while, when you want to void urine, this has to relax and the relaxation of this is controlled voluntarily. And it's controlled voluntarily by a place in the Pons. So the place that controls voiding, is about right there. It's in the, it's in the dorsal pons. What normally happens is that there is a sufficient volume in the bladder, and that elicits a voluntary decision to void which allows the parasympathetic motor neurons to be engaged, and also relaxes voluntarily, this external urethral sphincter. Now, anyone who has a dog or a cat, or anyone who well, everyone [LAUGH] is well aware I think that, not just dogs and cats. But, people and, and most animals have a particular posture that, that they adopt when they urinate. And so, voiding is so much more than these two muscles. It includes an entire posture and in fact, the movies use this to great effect. They'll show a posture and you know right away without actually seeing somebody you know that they're voiding. What is the trigger for this? Well, the trigger is not volume but pressure. And so, so here's pressure in the bladder and there are sensory neurons that detect this pressure. And here is the volume, and if this were just a balloon and it were a regular balloon, what you would see is that as the volume went up the pressure goes up. That's not what happens in the bladder. So, what happens in the bladder is that you can add volume, add volume, add volume, add volume. No increase in pressure and then all of a sudden, there's an increase in pressure, okay? So why? Because we have a sympathetic and a parasympathetic, innervation of this muscle which changes the elasticity of the muscle, all right. So it changes how much it will expand and if it's going to expand a lot, then it takes a lot of volume before you're going to feel any pressure. If it's really tight, it doesn't take very much volume. So this is under normal circumstances, a person doesn't feel their bladder at all until they get an urge maybe somewhere around here and it becomes intolerable somewhere around here. So they've got a space of time in which to find an appropriate place to, to void. Now there are there are situations that will make this come over here. So if you are really nervous, what you'll find is that you have the urge to void and you may actually go and see that there is almost nothing in your bladder. So that's a, that's a signal coming from your brain that's changing the structure of the bladder, so that there is that there is more sensitivity to a lower volume. And on the other end of things, we know that we're very good at keeping this pressure very low during sleep, and that enables us to, to sleep as we filter waste through our kidneys and it goes into our bladder. It doesn't wake us up and make us void several times a night. And so, this is one example of pushing this towards a higher volume and nervousness is an example of pushing this towards a lower volume. Okay, so in the next segment we'll look at what goes wrong, what can go wrong with the control of of, of, urinary voiding. [MUSIC]
