Hypothalamus

The hypothalamus is a small, vital section of the brain located just below the thalamus; it is in charge of numerous important bodily functions. The hypothalamus is shaped like a cone and ends in the pituitary stalk, a part of the pituitary gland. It forms the major portion of the ventral region of diencephalons, and oversees autonomic and metabolic processes. The hypothalamus is the connection between the nervous system and the endocrine system, creating this link by producing and secreting neurohormones that in turn stimulate the anterior pituitary gland to secrete hormones. The hypothalamus is central in the regulation of body temperature, hunger, thirst, and in the management of emotions and sexual activity.

The hypothalamus situated on both sides of the third ventricle, below the thalamus. In the hypothalamus there is a paraventricular nucleus, which contain large neurons that send axons to the posterior pituitary. The periventricular zone possess cells that send axons to the median eminence (a section of the lower hypothalamus), which then carry to the anterior pituitary, released factors. The basalis nucleus is involved in sleep and restlessness. The hypothalamus also has a fornix, which begins in the hippocampus and ends in the mammillary bodies.

The hypothalamus's main function is that of homeostasis. In order for the hypothalamus to successfully fulfill this task, it must receive inputs about the body's "state," and it must be able to create changes in the body that will correct anything that might be misaligned. The hypothalamus receives inputs from the nucleus of the solitary tract, which provides it with information about gut distension and blood pressure. The reticular formation tell the hypothalamus about the body's skin temperature. Inputs received from the retina go to the suprachiasmatic nucleus, a small nucleus in the hypothalamus, which help regulate circadian rhythms. The circumventricular organs, which contain no blood-brain barrier, monitors substances in the blood, and which can sense toxins in blood, and through the hypothalamus, induce vomiting. The limbic and olfactory systems (the amygdala, the hippocampus, and the olfactory cortex) help control eating and reproduction through the hypothalamus. The thermoreceptors and the osmoreceptors in the hypothalamus are receptors that help monitor temperature and ionic balance. The hypothalamus can control every endocrine gland in the body. The hypothalamus can alter blood pressure, body temperature, metabolism, and adrenaline levels. There are two outputs that the hypothalamus uses when it becomes aware of a problem. One of the outputs it uses is sending neural signals to the autonomic system. The hypothalamus sends signals to the medulla, where the parasympathetic vagal nuclei and cell groups that descend to the spinal cord are located, which help drive the autonomic system. When the hypothalamus gains admittance to these systems, it is able to control functions such as digestion, heart rate, sweating, and vasoconstriction (when blood vessels narrow, and consequently reduce the flow of blood or create high blood pressure). The other input the hypothalamus uses is sending endocrine signals, chemical signals sent through the blood stream, to the pituitary. Large cells from the hypothalamus send axons to the posterior pituitary, which in turn releases oxytocin and vasopressin into the bloodstream. More axons are also sent by smaller cells to the base of the pituitary. There the axons discharge releasing factors into the pituitary's capillary system. This enables the pituitary to release at least six different hormones.

The hypothalamus is composed of intertwined neurons (or nerve cells), and various forms of neurosecretion go hand in hand with hypothalamic function. Neurotransmission is one form of neurosecretion were one neuron communicates with another in a synapse. This type of neurosecretion is an electrical impulse where one cell emits a chemical substance, called a neurotransmitter, into the synaptic space.

Important neurotransmitters which include: epinephrine, norephinephrine, serotonin, acetylcholine, and more recently neuropeptides. Neuropeptides function as both neurotransmitters and as neuromodulators, in which they act as stimulators of neurotransmission. The release of neurotransmittors