Hypothalamus neuroanatomy

Added: 2026-05-15

[00:00:02]Everybody should know a little bit more about the hypothalamus. Well, unless you're a hypothalamus expert already, in which case, well, why are you here? But, um, the hypothalamus, it's a part of the brain that is literally central and also figuratively central to a lot of our behaviors, a lot of automatic things that we do and our bodies do. So, let's have a look at the anatomy of the hypothalamus. We'll see where it is. is we'll look at structures nearby so we get a better understanding of where it is. We'll talk about its inputs. We'll talk about its outputs. We won't talk about the nuclei in detail.

[00:00:38]We'll mention a couple of them. But in doing all that, we will be able to talk about its function. And maybe you'll see better how it works and remember all the things that it does maybe.

[00:00:52][music] Okay, where are we? We are here. So there's a little depression here. This is a midsagittal section of the head, right? There's a little depression there which in life is filled with cerebral spinal fluid. So this is the space of the third ventricle. There is a left hypothalamus and a right hypothalamus. So they're in the wall of the third ventricle here.

[00:01:23]The hypothalamus is called the hypothalamus because it is below the phalamus. The phalamus is this structure here. Kind of an egg-shaped structure.

[00:01:32]Again, there's a left one and a right one. I live in Wales, so it's rugby ball-shaped. So, we have this rugby ball-shaped structure here. Again, forming part of the wall of the third ventricle. And that's the phalamus. So, the phalamus is again a very deep central part of the brain. The phalamus is like the gateway to the cerebral cortex. it um everything going to the cerebral cortex never say everything in biology um goes through the phalamus and the phalamus has circuits deciding whether that should go to the cerebral cortex or not right now but we're not talking about the phalamus but there's the phalamus uh there's the hypothalamus now this here well this is the brain stem uh so we have medulla oblongata and the pawns and then here's the midbrain so the midbrain we can see the cerebral acid product running through. So the hypothalamus is superior to the midbrain. The midbrain in 3D is kind of it's kind of doing that. It's a it's it's sending tracts from the spinal cord and the brain stem up to the cerebral cortex and back down again. So midbrain, phalamus, hypothalamus.

[00:02:40]Um this is the pituitary gland. So the pituitary gland is sat in the sppheninoid bone here. So the hypothalamus is sat um superior to posterior to the pituitary gland. The pituitary gland is an endocrine organ that is releasing hormones that regulate or affect other tissues and organs in the body. So it's a it's kind of a central regulator and we'll see that it's controlled by the hypothalamus.

[00:03:08]um this little bit here. Well, here we've got the two optic nerves coming from either eye and they're crossing over at the optic cayazm. So, the optic kayazm is adjacent to the hypothalamus.

[00:03:21]Up here we have the anterior commissure.

[00:03:25]The anterior commissure is a bundle of white matter tracts. So, mileelinated axons of neurons linking the left and right sides of the cerebral cortex. So linking the left and right um temporal loes. And then we have this here. This is the forex. The forex again white matter tracts which are connecting to the hippocampus which are outside the plane of section. The hippocampus being largely associated with memory and learning and particularly spatial memory and and that sort of thing. So the forex is very important in making new memories uh in learning recalling information and that sort of thing right. Um what else have we got? Oh yeah, if we look very carefully under here we can see a little lump. That's a mamillary body.

[00:04:19]Millary body. Well essentially that's also connecting to the hippocampus and through some of these other tracks that we've been talking about here. So the the millary body, the fornix, the hippocampus, we're talking limbic system stuff. So the hypothalamus is is closely slow associated with limbic structures, with the cerebral cortex and with the brain stem and stuff coming up the brain stem from the spinal cord. I have another brain here. This is a lovely detailed model. I don't think students take it apart very much, which means the brain isn't as uh uh mucky, as worn as some other brains.

[00:04:58]But under here, if we look at this from the 3D perspective, so there's the medulla oblongata, there's the pawns, and there's the brain stem in there. So remember what we just saw there, the hypothalamus is just superior to the midbrain. So there's the midbrain, hypothalamus is just superior to that.

[00:05:16]And look, there are the two optic nerves and that's where they're crossing. So there's the optic kayazm. So the hypothalamus is also superior to that. A little bit posterior to that is adjacent to that. Right? All those little lumps we see under there, those are the millary bodies. So the hypothalamus is superior to that. Right? So we can imagine where the hypothalamus is internally relative to these external structures that we can see here. And we can again pull this brain in two and see the hypothalamus on both sides. Let's pick this side. So again, there's the midbrain, there's the um there's the optic cayazm, there's the hypothalamus in the wall of the third ventricle, there's the phalamus, there's the forex, etc., etc., etc. Well, there's a nice brain that one. Okay.

[00:06:12]What does it do?

[00:06:15]You know, when maybe you've been studying for a while and you decide to stand up and go into a different room or maybe even go to a cafe to get a drink because you're thirsty. That's your hypothalamus.

[00:06:31]This is this is part of the um how much are we in control?

[00:06:37]you know, um, that's the hypothalamus.

[00:06:39]You know, when you sat in a cold lecture theater and you decide to put your coat on and zip it up, that's your hypothalamus. It's not you, it's your hypothalamus.

[00:06:49]You know, when you get home, so you've been studying all day, maybe you get home and you know dinner's going to be ready in an hour, but you still raid the cupboard for chocolates and snacks.

[00:06:58]That's your hypothalamus. So the hypothalamus is driving behavior as a result of sensory inputs and nuclei and circuits within the hypothalamus. So it's very much a central homeostatic um structure. So it's it's regulating fluid in your body through thirst and the kidneys. It's um I it's regulating hunger and appetite. It's regulating sexual behavior. It's uh regulating um emotional responses.

[00:07:34]Um it's regulating the pituitary gland and the hormones that the pituitary gland sends out to affect other tissues and organs. It's regulating your temperature both by encouraging you to put a coat on because you're cold and also by regulating blood flow throughout the body so that more blood flows to your skin when you're hot so you lose heat, less blood flows to your skin when you're cold so you lose less heat. Um, switching on your sweat glands to lose heat, that sort of thing. So, it regulates your temperature. It regulates your circadian rhythms. I've talked about circadian rhythms and the pineal gland and intrinsically sensitive retinal photo ganglen cells.

[00:08:13]Intrinsically photosensitive retinal ganglen cells. There we go. Um so it regulates the circadian rhythms, your sleep wake cycles of your body. Um it's clearly tightly integrated with the autonomic nervous system. If you have been looking to see where sympathetic and parasympathetic motor outputs come from, you need to look at the hypothalamus. So what are the inputs to the hypothalamus then? Well, there are lots of cortical inputs, lots of inputs from the cortex. There are lots of inputs from the lbic system, from the amygdala, through the forex, from the retina. I was talking about circadian rhythm. So light is important in resetting circadian rhythms. Um and then you have uh sematic and visceral sensory inputs which are coming from the spinal cord and from the brain stem. We've got a whole bunch of autonomic reflexes in there. Um so spinal and brain stem track sensory tracks are putting inputs into the hypothalamus.

[00:09:21]On top of that, the hypothalamus has got sensors inside it. It has temperature sensors inside the hypothalamus. So, neurons specially adapted to measure central temperature. When we talk about core temperature, the core, this is this is pretty cool, right? So, temperature sensors, glucose sensors. So, there are neurons that are monitoring the blood glucose in the hypothalamus.

[00:09:51]um and osmolality. So the water salt concentration is being monitored by specialized neuron rece neurons in the uh in the hypothalamus. And then there are receptors on cells in here for various hormones. So we have a lot of negative and positive feedback loops through the hypothalamus and often through the pituitary to other tissues.

[00:10:14]So there are sensors within the hypothalamus itself. So it has external inputs and then it has its own monitors inside the hypothalamus. What about outputs then? The outputs from the hypothalamus often match the inputs. So there are lots of outputs from the hypothalamus to many cerebral cortex locations. There are outputs to the lbic system through the forex to the hippocampus and what have you. There are outputs down to the brain stem down the spinal cord. Um if you think that the hypothalamus is involved in regulating the amount of fluid in the body and blood pressure and temperature as I mentioned then the hypothalamus is using the sympathetic nervous system um to control the diameter of blood vessels throughout the body so that a you're managing blood pressure levels appropriately, you're also sending the blood that you've got to the parts of the body that need it right now. If you're digesting food, blood goes to the GI tract. If you're not digesting food, blood does not go to the GI tract. If you're exercising, blood goes to your muscles and so on.

[00:11:31]So, the hypothalamus is linked to the sympathetic nervous system and has that outflow. The hypothalamus also links to the the parasympathetic nervous system.

[00:11:40]So it links to the the motor nuclei of the vagus nerve for example and sends parasympathetic outputs to part of the body. Um it also has a very physical link to the pituitary gland. The infundibulum links the hypothalamus with the pituitary gland. So another output well there are two outputs. There's an output from the hypothalamus to the pituitary in which there are neurons in the hypothalamus that send axons into the posterior pituitary which release hormones into the posterior pituitary.

[00:12:17]Those hormones are antidiuretic hormone also known as ADH and vasopressin and that encourages the kidneys to reabsorb water so you hold on to water and make less urine. And those neurons also secrete oxytocin into the posterior pituitary gland. Oxytocin causes the uterus to contract. It's involved in uh lactation and it's involved in social bonding as well. Whereas so those neurons run those are actual neurons secretary neurons that have their nuclei their neuron cell bodies in the hypothalamus and send axons into the posterior pituitary. You have secretary neurons in the hypothalamus that secrete hormones into a specialized capillary network in the hypothalamus that then transports those hormones into the anterior part of the pituitary gland and releases them to affect the cells cells that also produce hormones in the anterior part of the pituitary. This is the hypothesial portal system. So when you have um a portal system of blood vessels, you normally have an artery and a capillary bed and then a vein. This is where you have kind of instead of going from artery to vein, you go from tissue to tissue. So we have a hypothesial portal system. So there are two ways in which the hypothalamus is connected to the pituitary gland. So the hypothalamus is producing somatastatin uh corticotropic, corticotropin releasing hormone, gonadotropin releasing hormone, uh thyroropin releasing hormone, growth hormone releasing hormone. And those hormones are only passing this far to get to the pituitary gland. And then they cause the cells of the anterior part of the pituitary gland to either you know to release growth hormone um to release luteinizing hormone, follical stimulating hormone, uh thyroid stimulating hormone, um adrenoccortic trophic hormone, you know, um and those hormones then pass into the blood and affect the thyroid gland, the cortex of the adrenal gland, the gonads and what have you at a distance. So this is what we mean when we talk about hypo uh when we talk about um hypothalamic pituitary something else axis like ovarian axis um and then that loop um so those other cells we talked about inside the hypothalamus that are able to detect hormones are able to respond to the levels of those hormones circulating in the blood and complete the loop by reducing the amount of hormone produced in the hypothalamus so that you reduce the amount of hormone released by the pituitary gland. D see very central really important homeostatic mechanisms at play here.

[00:15:13]Now my final point um the hypothalamus really is um it's a region of the brain. So we have a number of structures down here called the dian sephflon. So the phalamus and the hypothalamus and some other bits form the dianphylon.

[00:15:35]Um but the hypothalamus this region of the brain this is a region of gray matter. It's a collection of of nuclei.

[00:15:43]Nuclei being themselves collections of neuron cell bodies of neurons usually doing similar jobs or forming circuits. Do you see what I mean? So, we talk about this as being the hypothalamus because we can point at it. As humans, we like giving things names. Look, there's the hypothalamus.

[00:16:01]If you look inside the hypothalamus, you see a number of different nuclei, all with different names that probably have slightly different jobs, but they're kind of related. So, that's an important idea. There are nuclei within the hypothalamus. I am not going to go into the detail of all the nuclei because that's not the aim of what I'm trying to do here. Um, but I will give you a couple of examples. We've talked before about the supraismatic nucleus and I said that we have the optic cayazm here.

[00:16:30]So the supraismatic nucleus is superior to the optic kayazm. The supraismatic nucleus is the part of the phalamus involved in uh managing circadian rhythms and the the wake sleep cycle in response to light. And it's oh that's interesting. And then we have something called say the par ventricular nucleus.

[00:16:53]So I said this is the third ventricle here. So the parventricular nucleus is leaning up against the ventricle para it's beside the ventricle. And then we have another nucleus that's actually well it's the supra uh supraoptic nucleus. We have the optic nerve coming in there before it becomes the optic kayazm. So the supra optic nucleus is kind of beside it's adjacent to the supraismatic nucleus and it's supra superior to the optic tract. Anyway the parentricular nucleus and the supraoptic nucleus for example those are the nuclei that are involved in sending the hormones down to the posterior pituitary gland. those that's where we find the the neurons that are making antidiuretic hormone and oxytocin blood supply to the hypothalamus. Well, look, I've taken the brain out. Um, there are the optic nerves coming in there. So, there's the optic cayazm. So, you know that the hypothalamus is right here and these blood vessels forming this circle of the circle of Willis. So the hypothalamus essentially receives a number of small branches from various branches various parts of the circle of Willis. We could say anterior cerebral artery some of the posterior communicating artery and possibly even the posterior cerebral arteries. But I think the hypothalamus is very central receives branches from the circle of Willis. Okay.

[00:18:25]Do you better understand the hypothalamus now in terms of its anatomy, where it is, what it's next to?

[00:18:33]Can you better visualize where it lies?

[00:18:35]Do you have a reasonable understanding of its functions? Or have I just made it all worse? Um, if you want to really trim it down, the hypothalamus does homeostasis, things like managing body temperature and hunger and thirst and what have you.

[00:18:52]But remember that it also then drives the behavior so that you do keep your temperature at the right level by putting a jacket on and um satiate your thirst by going to get a drink and so on and so on. You get it? Okay, speak to you next time. I hope it was useful anyway. It's quite a good bit of neuro anatomy. I like it.