3 - Hypothalamus Flashcards
What is the hypothalamus a division of? What is it’s primary function?
It’s a dividion of the diencephalon and it functions in the maintenance of homeostasis.
The hypothalamus is functionally related to what three major systems?
- ANS
- Endocrine system
- Limbic system
Where is the hypothalamus located? What structures are found near it?
It forms the walls and floor of the inferior portion of the third ventricle.
Anteriorly is the optic chiasm and lamina terminalis and posteriorly is the mammillary bodies.
It’s medial and lateral borders are the third ventricle and optic tract, respectively.
How did the hypothalamus get its named?
It’s named for its location below the thalamus from which its separated by a shallow groove called the hypothalamic sulcus.
Describe the blood supply to the hypothalamus? What purpose does this serve?
It’s extremely vascularized; blood supply comes from small branches of vessels forming the circle of willis which surround its ventral surface.
This is a key component of the responsiveness of hypothalamis neuronal populations to the negative feedback actions of circulating hormones (adrenal and gonadal steroids).
What areas/zones are the hypothalamus divided into?
Periventricular, medial, and lateral zones.
The medial and lateral zones are separated by the fornix (ventrally).
What is the lateral zone of the hypothalamus composed of? What three nuclei are in the lateral zone?
Comprised of loosely arranged neuronal cell groups, and is traversed by fibers of the medial forbrain bundle.
Contains three nuclei:
- Lateral preoptic nucleus
- Lateral hypothalamic area
- Tuberomammillary (lateral tuberal) nucleus
What is the lateral preoptic nucleus of the lateral zone derived from?
It’s derived from the telencephalon developmentally.
It’s the anterior portion of the lateral zone.
What is the function of the lateral hypothalamic area of the lateral zone of the hypothalamus?
Induces eating when stimulation; ablation causes anorexie and starvation.
This area is also know to contain nts such as melanin-concentrating hormone and orexins that increase foodinate.
What is the function of the tuberomammillary (lateral tuberal) nucleus?
Contrains large neurons that release histamine via axonal projections to widespread portions of the forebrain. Thought to play an important role in attention and arousal. Inhibited during sleep.
Where is the tuberomammillary (lateral tuberal) nucleus located?
It’s part of the lateral zone and located at the ventrolateral surface at the level of the tuberal and mammillary levels of the medial zone.
What are the divisions of the medial zone of the hypothalamus?
Four anatomically distinct antero-posterior regions:
- Preoptic
- Anterior (supraoptic)
- Middle (tuberal)
- Posterior (mammillary)
What is the function of the preoptic region of the medial zone? What is it derived from?
Derived from the telencephalon.
Regulates gonadotropic secretion from the anterior pituitary.
Also contains interstitial nuclei of the anterior hypothalamus (INAH1-4) which is sexually dimorphic (bigger in men; regulated developmentally by testosterone.)
What are the four regions of the anterior region of the medial zone of the hypothalamus?
- Suprachiasmatic nucleus
- Anterior hypothalamus nucleus
- Paraventricular nucleus
- Supraoptic nucleus
What is the function of the suprachiastmatic nucleus in the anterior region of the medial zone? Where is it located?
Plays a critical role in control of circadian rhythm.
Compact nucleus located immediately dorsal to the optic chiasm; recieves input directly from the retina.
What is the funciton of the anterior hypothalamic nucleus of the anterior region of the medial zone? What do lesions here cause? Where is it located?
Temp regulation: contains neurons that sense warmth and initiate responses to dissipate heat. Bilateral lesions cause hyperthermia. Also does stimulatory drive of the parasympathetic division of the ANS.
Located between the suprachiasmatic and paraventricular nuclei.
What is the function of the paraventricular nucleus of the anterior region of the medial zone?
Neurons that make and release arginine vasopressin, oxytocin, and corticotropin-releasing hormone (CRH)
Other neurons project to the lateral cell column of the spinal cord to excite sympathetic preganglionic neurons and project to the brainstem.
What is the function of the supraoptic nucleus of the anterior region of the medial zone?
Contains neurons that make AVP and oxytocin,
Similar to neurons in the paraventricular nucleus that contain AVP and ocytocin, these cells project to the neurohypophysis to release these into circulation.
What are the three nuclei of the middle region of the medial zone?
- Dorsomedial nucleus
- Ventromedial nucleus
- Arcuate nucleus
What is the function of the dorsomedial nucleus of the middle region of the medial zone?
Involved in BP regulation.
When stimulated in animals, aggression and savage behaviour resulted.
What is the function of the ventromedial nucleus of the middle region of the medial zone?
Inhibits urge to eat when stimulated. Neurons within this nucleu play a role in relaying ingestion-related signals to the brainstem.
(opposite function from the lateral hypothalamic nuclei)
What is the function of the arcuate nucleus of the middle region of the medial zone?
Controls the release of adenohypophyseal hormones.
Neurons here make hypothalamic-releaseing factors and play a role in feeding behavior.
Where is the arcuate nucleus of the middle region of the medial zone located?
Ventrally in the tuber cinereum and has projections to the median eminence and portal vasculature.
What nuclei are located in the posterior region of the medial zone?
Posterior nucleus and mammillary nucleus.
What is the function of the posterior nucleus of the posterior region of the medial zone? What occurs with a bilateral lesion here?
Thermoregulation: sense cold and initiate heat conservation and heat production. (opposite of the anterior hypothalamuc nucleus that senses warmth).
Bilateral lesion results in inability to thermoregulate - called poikilothermia.
What is the function of the mammillary nucleus of the posterior region of the medial zone? What results from damage here?
Functionally considered part of the limbic system: recieve major input from hippocampus via fornix.
Project to anterior nucleus of the thalamus and recieve sensory input from the midbrain tegmentum.
Damage results in memory disturbances due to connecitivity to the hippocampus.
What is located in the periventricular zone? Where is this located?
The pericentricular nucleus, a layer of cells lining the wall of the third ventricle mainly at the anterior and middle levels of the medial zone.
Consists of several small nuclei often considerd by some to be part of the medial zonel.
What are the major regulatory functions of the hypothalamus?
- Thermoregulation
- Stress responsiveness
- Feeding and energy metabolism
- BP and electrolyte composition
- Reproductive functions
How does the hypothalamus do thermoregulation?
Anterior hypothalamufc nucleus and portions of the medial preoptic area contain neurons sensitive to wamrth and trigger heat dissaption.
The posterior hypothalamuc nucleus contains neurons sensitive to cold that trigger heat conservation via sympathetic outflow.
The hypothalmic regions sensitive to heat and cold are under the influence of what?
The limbic forebrain, and are interconnected with brainstem and spinal cord regions that mediate the effects needed to change body temperature.
What results from bilateral destruction of the anterior hypothalamic area? What bout bilateral lesions of the posterior hypothalamuc nucles?
Anterior hypothalamic area: hyperthermia
Posterior hypothalamuc nucleus: inability to thermoregulate altogether doe to loss of both cold sensitive neurons and the descending projections of the warm-sensitive neurons which course through the region on the way to the brainstem.
How does the hypothalamus play a role in the stress response?
Coordinates the fight or flight response involved neuroendocrine control of release of stress hormones from the adrenal cortex (glucocorticoids) as well as epi and norepi from the adrenal medulla.
What role do sympathetic connections to the viscera have in the fight or flight response?
It initiates physiological changes to support an integrated fight or flight response, including diversion of blood from viscera to skin and muscles, increasedcardiac output, pupillary dilation, bronchodilation, and decreased GI motility and renal activity.
Parasympathetic neurons of the brainstem are inhibited.
The hypothalamus is under regulatory control by which regions? What is the purpose of this during a stress response?
Pre-frontal cortex, limbic forebrain, and brainstem.
It serves to integrate signaling from these areas, the input from which varies according to the nature of the stressor, and to make an appropriate set of responses involving outflow through autonomic, endocrine, and other systems.
What two regions are extensively interconnected with the hypothalamus and play a major role in the stress response?
The hippocampus and the amygdala.
Recent research suggests that neurons in the _______ _____ play a central role in feeding and satiety.
The arcuate nucleus.
What are the two distinct sets of neurons within the arcuate nucleus and what effect do they have on food intake?
- Agouti-related peptide (AgRP) and neuropeptide Y (NPY) have projections that signal increased feeding and a decrease in metabolism.
- a-opiomelanocortin (POMC) and cocain and amphetamine-responsive transcript (CART) synthesive and release and act upon secondary neurons which dignals decreased feeding and increased metabolism.
Signals from both sets of neurons in the arcuate nucles is integrated where?
The brainstem, specifically in the nucleus of the solitary tract (NTS) which appears to act as a satiety center.
When are ghrelin and polypeptide Y (PPY) released from the GI tract and what effect dfoes each have?
Ghrelin is released from the stomach just prior to a meal - activates AgRP/NPY to stimulate feeding
Polypeptide Y (PPY) is released from the GI tract immediately following a meal - activates aMSH/CART to inhibit feeding
What effect does insulin have on the arcuate nucleus?
It appeas to inhibit AgRP/NPY neurons and stimulate aMSH/CART neurons.
What is the effect of peptides hypocretin and melanin-concentrating hormone (MCH)? Where are they released from?
Released from neurons in the lateral hypothalamic area and induce feeding when released.
Release of what has been shown to decreased food intake?
Central oxytocin and CRH secretion in response to stress.
What is a craniopharyngioma? Who does it occur in and what are the symptoms?
Congenital tumor (usually calcified) most common supratentorial tumor in children.
Puts pressure on optic chiasm and causes bitemporal hemianopsia. Pressure on overlying hypothalamus causes hypothalamuc syndrome of adipositym DB insipidous, temp regulation disturbances, and somnolence.
What can cause hypothalamic memory disturbances?
Posterior hypothalamic lesions involving mammillary bodies.
Associated with inability to form new memories (episodic) for contextr and time specific events.
What is Klein-levin syndrome? What are the symptoms and who does it occur in?
Hypothalamic (autoimmune?) disorder primarily in adolescent males.
Hypersomnolence, episodic compulsive eating, hypersexuality, and associated with decrease in dopaminergic tone during symptomatic phase.
