Okay, well, let's now look in a little bit more particular detail at different nuclei of the hypothalamus, and I want to give you a sense of what is the diversity of function that is attributable to different nuclei in this collection. that we call the hypothalamus. Now, I don't intend for you to know all of this detail, I really don't. I give some of this to you in the tutorial notes, mainly as a way for you to just spend a few minutes thinking together with me, about the hypothalamus and the diversity of systems that it impacts. there is one however that I want to highlight for you, because we're going to come back to this in a later session. Okay, I mentioned one can look at the hypothalamus in different axes, from front to back, from anterior to posterior, from medial to lateral. What I want to do is just highlight a few nuclei that catch my attention at least, going from the medial to lateral axis of the hypothalamus. And let's begin right along the walls of the third ventricle. There's a very interesting pair of nuclei that we find right along the wall of the third ventricle and just inferior to it. these nuclei are found in what we might call the Periventricular zone, right around the ventricle. There is a nucleus called the periventricular nucleus and there is another one called the arcuate nucleus and these nuclei are intimately related to the production of hormones in the anterior part of the pituitary gland. This is the part that we call the adenohypophysis. So the anterior pituitary receives hormones that are produced by cells that sit in this periventricular region of the medial hypothalamus. And those hormones enter the portal circulation where they are then Transported via this blood supply to the anterior part of the pituitary. These hormones, we call them releasing factors, then have an impact on the neuro secretory cells of the anterior pituitary, and these cells then produce a hormone that enters the general circulation. And can impact physiology throughout the entire body, so right along the medial border of the hypothalamus is where we find those neurons that govern the output of the anterior part of the pituitary. Well, moving on just a bit more lateral in the color code here these would be these darker so, solid shaded regions in here. we have a variety of interesting nuclei that do all kinds of different functions. Let me just highlight a few of them. There is a set of nuclei called the paraventricular nucleus and the supraoptic nucleus. So here's the supraoptic nucleus, it's called supraoptic because it sits just above the optic chiasm. And in a slightly more dorsal position is this paraventricular nucleus. these nuclei are, are two of many that we find in this more medial zone of the hypothalamus. I mentioned the paraventricular supraoptic nuclei because these are the nuclei that have the neurons that grow their axons through the infundibulum, that is, the stalk of the pituitary, and release hormones directly into the general circulation in the neurohypophysis or the posterior part of the pituitary gland. Okay? So the periventricular zone is where we find our neurons that are engaging the anterior part of the pituitary. And then in this more medial zone, that's where we find the super optic and paraventricular nucleus that are releasing hormones into the posterior pituitary. Well there are other neurons in this para-ventricular nucleus in particular, that are not releasing hormones in the pituitary rather they are growing axons and descend into the brain stem, and even into the spinal cord. And these para-ventricular neurons that grow these long axons are involved in coordinating the output of pre-ganglionic neurons in the parasympathetic and in the sympathetic divisions of our visceral motor outflow. So the paraventricular nucleus is a very important structure in regulating various dimensions of our behavioral response. Okay, I'd like to highlight a few more nuclei here in this medial zone. generally speaking, this medial and lateral preoptic area here. And I'll, I'll guess I'll highlight the medial preoptic region. this is a, a really fascinating part of the interior hypothalamus. This is a part of the hypothalamus that is involved in various aspects of coordinating reproduction. And sexual behavior. So this is a part of the hypothalamus that we think is especially involved in defining our sexuality, and motivating sexual activities, and here there are circuits that are coordinating various aspects of mating behavior, and in women various dimensions of pregnancy, and postpartum behavior. So, this preoptic area has connections with important parts of our limbic forebrain, that are involved with emotion, as you might expect our emotions are important sources of input to circuits that are mediating sexual behavior and sexual activities. This medial pre-optic area is also involved in governing the release of urine in the process of micturition. We'll have more to say about that in the final part of this tutorial. But just keep that in mind. The medial preoptic area is also involved in governing bladder function. Other structures in this medial zone worth mentioning include the suprachiasmatic nucleus. So this is a small nucleus that sits just above the chiasm here, just a little bit. Medial and anterior to where I highlighted the super optic nucleus. So this is the suprachiasmatic nucleus. Hopefully, that's easy to remember. And I do want you to remember this nucleus, because this is a nucleus we'll come back to when we talk about the regulation of sleep. The suprachiasmatic nucleus is the master clock of the human body. This is the place where we have neurons that generate a circadian rhythm, that is, a rhythm that runs roughly 24 hours, not precisely 24 hours, we'll mention that in a later tutorial, but it allows us to establish a daily rhythm For behavior, for the release of hormones that can affect our body's physiology and our behavior. so very important part of the hypothalamus, and it's that part that I mentioned when we discussed the visual pathways that receives input from the special set of photosensitive ganglia cells in the retina. So by this connection with the retina, this suprachiasmatic nucleus can be entrained to our natural cycles of light and, and darkness, of daytime and nighttime. There's another set of medial zone nuclei that I would mention. the dorsal medial nucleus. and also the ventral medial nucleus. These two nuclei seem to be involved in some other dimensions of reproductive behavior. And even parenting behavior. At least based on animal studies one might expect that. these nuclei seem to contain circuits that are involved in the feeding system. helping to motivate the consumption of food. As well as mediating signals that are related to satiety. so very important networks here for motivating the ingestions of foods and possible also particular appetites for things like salts. Or particular food substances that we might happen to be in deficit of. There are other circuits here that are also involved with water balance and thermo-regulation. Well lastly I would highlight this more lateral part of the hypothalamus indicated by this stippled region here. So there are nuclei out here more laterally that are involved in really a variety of functions that pertain to attention and arousal. Now these aren't the only neurons in the brain that are important for those kinds of functions. But these parts of the hypothalamus seem to have broad connections, especially with the cerebral cortex. And they seem to be in a position to modulate the way the cortex responds to other kinds of inputs. So in that sense, the lateral hypothalamus seems to have role to play in modulating levels of vigilance in the brain. in a manner might be similar to signals that are motivated by the amygdala, as well as some of the biogenic amine systems in the brain stem. Well, as I said when we got into this slide there are way too many details that are beyond the scope of this course to expect you to take in, in this brief tutorial. rather what I want you to do is at least remember this important suprachiasmatic nucleus, cause we're going to come back to that. But even more so, I hope you get just an impression that there are a variety of physiological functions that can be absolutely central to motivated human behavior that are coordinated at the level of the hypothalamus. Well, now that you've had a bit of a sense of some of the functions associated with nuclei of the hypothalamus. I want to conclude this session by talking about a particular clinical condition called Horner syndrome. Now Horner syndrome is relatively common, we might see it in a variety of patients for different reasons, and it is a presentation of signs and symptoms that are typically associated with the face. Now Horner's syndrome could be bilateral but it more commonly is unilateral and its characterized by a set of signs that can be best appreciated clinically by focusing on the region of the eyes. So what we find most significantly is miosis, which is a constriction of the pupil. Now what you're looking for when you examine the diameters of the pupils is not so much an absolute size but an asymmetry. In the case of Horner's Syndrome what we see is the effected iris has a smaller pupil than the normal iris. Well it might be somewhat difficult to appreciate what is normal, but I think you can see that the dimension of the pupil is smaller in this patient's right eye compared to the left eye. So this is miosis. It's evidence of an abnormal constriction of the pupillary muscle. Well, in addition to the constriction of the pupil, we also see a drooping of the eyelid associated with Horner's syndrome. So this might be a subtle sign But, it's one that you should look for nevertheless. And, one might also get the impression that the eyeball itself, the globe, is somewhat sunken into the orbit. There are some other signs and symptoms associated with Horner's syndrome that may be a little more difficult to appreciate clinically. But perhaps to suit patient interview you can Confirm their presence or absence. one sign you may be able to detect if you were to put your fingertips on the, on the cheeks of your patient. You may discover that the side with the constricted pupil actually feels a little bit warmer to the touch than the opposite side. Now, if you were to ask the patient about their sweat response to hot environments or to exercise you may discover that the side with the smaller pupil doesn't actually seem to sweat as much as the opposite side of the face. Well, can you think of what all of these signs might have in common? Do you remember what's responsible for the dilation of the pupil? What about the ability to keep our eyelids open throughout the day? And what system supplies innervation to the sweat glands? Or what do you think an increase in the temperature of the skin might tell you. About the tone of the vasculature that's supplying these cutaneous structures of the face. Well, hopefully, I'm leading you along the path that allows you to understand that what all of these systems have in common, is sympathetic control. Well, Horner's Syndrome can result from an interruption in the pathway that links the hypothalamus up here in the ventral and anterior part of the diencephalon with our ganglionic neurons. Which, with respect to the governance of these structures in the face Are localized to the superior part of that sympathetic trunk. Specifically, the pupillary dilator muscle is supplied by ganglionic neurons that sit in the superior cervical ganglion and grow an axon through the carotid plexus to reach the orbit where there's innervation of this dilator muscle of the iris. So, just given the broad distribution of this system from hypothalamus to face or to iris, you could imagine that, one could have a legion or some other kind of disease process that would affect this pathway, either within the nervous system or outside of the nervous system, and produce Horner's Syndrome. And indeed, one might have, damage to the neck, that's outside of the nervous system that potentially could impact, the, superior aspect of the sympathetic trunk and produce a Horner's syndrome. Or one might have damage within the nervous system itself. So for example, if there were a stroke in the lateral tegmentum of the brain stem. Here is a representation of the medulla. we potentially could have a Horner syndrome in conjunction with signs and symptoms that would help you localize the lesion to this particular level. In addition, one might have an injury to the cervical spinal cord, or perhaps even to the thoracic spinal cord, that might impact the ability of the hypothalamus and the brain stem to interact with the intermediolateral cell column, or one might have damage to that cell column itself and produce Horner's syndrome. So, of course, one can have an injury to the neck and have some kind of a, of a isolated Horner's syndrome, at least isolated with respect to other neurological signs and symptoms. But whenever we have the image within the CNS itself, we're likely to have a Horner's syndrome together with other neurological signs and symptoms. That, you'll piece together as a means of localizing the injury. Well, I would suggest that we conclude this, segment of our tutorial, focusing on the hypothalamus, with a couple of study questions. So I'll invite you to think through those study questions, and then we'll, finish up on the visceral motor system and indeed all of unit 4. By using one physiological system as a way of demonstrating how visceral motor control is integrated with sensory signals, and coordinated with somatic motor control, to govern behavior. And the example I'm going to choose is called micturition, or otherwise the voiding of our bladder, urination. Well, I know I've had just a little bit just too much coffee this morning. So, before I talk to about voiding the bladder. Well, I think I need to do it myself. Let's take a short bathroom break and when we come back Let's talk about how the nervous system governs maturation.
