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The Hypothalamus and the Limbic System CAN'T FOLLOW JOHN CIRIELLO?!? These are notes made from a recording of the lecture. They include HINTS about potential EXAM QUESTIONS!

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Western University
Physiology 1021
John Ciriello

Physiology The Hypothalamus and the Limbic System Functions of the Posterior Pituitary - Involved in the release of two hormones: Oxytocin and Vasopressin (Anti-Diarrhetic hormone) - Posterior Pituitary is actually part of the brain. Is made up of the axon terminals neurons found in two parts of the Hypothalamus; the Paraventicular nucleus and Supraoptic nucleus - Paraventicular nucleus and Supraoptic nucleus contain neurons which produce Vasopressin and Oxytocin - These hormones are carried down the axon where it is released directly into the blood stream at the posterior pertuitary Oxytocin - Very important in a lactating body (critical for milk let down) - The pathway for Oxytocin is very unique - This does not exist in males and does not always exist in females - When a mechanical stimuli is applied to the nipple and afferent neuron which through pathways through the spinal chord to the thalamus, which gets relayed to the Hypothalamus, then gets relayed to the Paraventicular and Supraoptic nucleus. - Once there that stimulus activates Oxytocin producing neurons - As soon as those neurons are activated they produce more oxytocin - And as it produces more Oxytocin it is carried down via the axons into the posterior Pituitary where it is released into the blood stream and through the blood stream works at the breast. - This causes contraction of Myoepithelial cells which allows for milk let down * This is and example of a Neural-Endocrine Reflex (see image above) Unique Properties of Oxytocin - Once suckling of the breast is induced the first time we see a rise in Oxytocin production. The second time the level of Oxytocin rises even higher. - Once Oxytocin is released into the blood stream, the Oxytocin comes back and works on Oxytocin producing neurons. Therefore the next time the same stimulus is applied, the number of action potentials rises. For the same stim more AP. More Oxytocin = more milk let down OR if you are about to give birth Oxytocin neurons also respond to inter- uterine pressure (contractions). More Oxytocin = Stronger Contractions - Two main stimuli for Oxytocin are Suckling of the Breast and Inter-Uterine Pressure Vasopressin - There are three Stimuli which affect the release of Vesopressin; Plasma Osmolality, Blood Loss, Low Blood Pressure - Plasma Osmolality increases when you ingest salt. This causes us to want to drink more is order to get back to homeostatic levels of plasma osmolality. - When Plasma Osmolality increases it activates a section of the brain called Circumventricular organs. - These organs allow sodium to have access to neurons - Normally there is a blood brain barrier which would prevent sodium from accessing such neurons, but at the Circumventricular organs we have what is called a leaky BBB (certain things can get through the BBB and come in contact with neurons) - The sodium activates those neurons at the Circumventricular organs - These neurons then project to the Hypothalamus, and then on to the Paraventicular nucleus and Supraoptic nucleus - These nuclei produce Vesopressin - Vesopressin then acts at the kidney so that we reabsorb more solution (don’t pee as much) - This maintains blood volume and dilutes the sodium - It also activates pathways in the brain that are involved with drinking - Blood Loss - decreased blood volume activates receptors found within the heart - One way to increase blood volume is to stop urinating - Vesopressin acts on the kidneys to cause fluid reabsorption - Low blood volume activates these neurons in the Paraventicular and Supraoptic nucleus which produces Vesopressin, which causes the release of Vesopressin by the Posterior Pituitary - The consequence of low blood volume is low blood pressure - Low Blood Pressure - This low blood pressure activates mechanoreceptors found within the blood vessels - This also signals the release of Vesopressin - Vesopressin constricts the blood vessels in order to maintain homeostatic blood pressure How do we control how much food we take in? Negative feedback system - amount of Glucose or Fat is read by the hypothalamus which tells us to eat more or not - There is a direct relationship between how much Adipose/ Fat tissue and the amount of Leptin (hormone released by the fat tissue) in the circulation. More fat tissue more Leptin - Leptin exerts a dual effect in the Hypoth
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