L11 Hypothalamus 2025 PDF

The Hypothalamus Chapter 18 in Young et al. Introduction Basic Hypothalamic and Pituitary Structure and Function The Hypothalamus Hypothalamic Nuclei and their Functions...

The Hypothalamus Chapter 18 in Young et al. Introduction Basic Hypothalamic and Pituitary Structure and Function The Hypothalamus Hypothalamic Nuclei and their Functions Afferent and Efferent Hypothalamic Pathways Circumventricular Organs Required Reading Assignments Young, Young and Tolbert, 3rd ed., 2015 Chapter 18, pages 236-241, Appendix D, pages 426-427. Haines, 10th ed, 2019 Chapter 8, pages 288-293 2  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 3  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 4  Basic Functions of the Hypothalamus Homeostatic control of hunger, thirst, sexual desire, sleep-wake cycles, etc. Endocrine control Autonomic control Limbic mechanism involved in olfaction, memories and emotions. The Four Fs Basic Functions of the Hypothalamus and Pituitary (Young, Young and Tolbert – pages 236-241; Haines pages 288-293) The Basic Functions of the hypothalamus include 1) homeostatic control of drives such as hunger, thirst, sexual desire, and sleep; 2) control of the endocrine system; 3) control of the autonomic nervous system; and 4) involvement with limbic functions such as olfaction, memories and emotions. In other words, the hypothalamus controls ‘the four Fs’ (fighting, fleeing, feeding, and mating). See also Young, Young and Tolbert, Table 18-1, page 240, in your assigned textbook. 5  Medial View of the Hypothalamus and Pituitary Blumenfeld, Neuroanatomy through Clinical Cases, 1rst ed., 2002, page 739. The hypothalamus is part of the diencephalon and is named for its location underneath the thalamus. Dorsally, the hypothalamus is separated from the thalamus by the hypothalamic sulcus. The hypothalamus also forms the inferior walls and floor of the third ventricle. The third ventricle runs up through the center of the hypothalamus in a dorsal-ventral direction. See also Young, Young and Tolbert figure 18-1, page 237, in your assigned textbook. 6  Inferior View of the Hypothalamus With Pituitary Removed Blumenfeld, Neuroanatomy through Clinical Cases, 1rst ed., 2002, page 739. From an inferior view, the tuber cinereum and the mammillary bodies of the hypothalamus can be seen posterior to the optic chiasma. The infundibulum of the the hypothalamus arises from the tuber cinerum to become the pituitary stalk. The anterior portion of the infundibulum is called the median eminence (the final common pathway) which slightly protrudes ventrally. 7  Basic Functions of the Pituitary Posterior Pituitary (neurohypophysis) Release of ADH Release of OXY Intermediate Pituitary Anterior Pituitary (adenohypophysis) Synthesis and Release of GH, PRL, TSH, ACTH, LH, FSH, and MSH The basic functions of the pituitary include 1) release of antediuretic hormone (ADH) and oxytocin (OXY) from the posterior pituitary (AKA neurohypophysis or pars neuralis); and 2) synthesis and release of anterior pituitary hormones (growth hormone, prolactin, thyroid stimulating hormone, adrenocorticotropin hormone, melanocyte stimulating hormone, luteinizing hormone and follicle stimulating hormone). Alternative names for the anterior pituitary include adenohypophysis and pars distalis. The pituitary is suspended from the hypothalamus by the pituitary stalk and is securely seated within a depression of the sphenoid bone called the pituitary fossa. Anterior to the fossa is the anterior clinoid process and posterior to the fossa is the posterior clinoid process. Together, these processes along with the intervening fossa form the sella turcica (Turkish saddle). The posterior pituitary is continuous with the hypothalamus via the infundibulum. The anterior pituitary attaches to the infundibular stalk by way of the pars tuberalis. The thin intermediate pituitary (aka pars intermedia) is sandwiched between the anterior and posterior pituitary. JOKE Question: Why is it said that you pay through the nose for a hypophysectomy? Answer: Surgeons can get to the pituitary by way of the sphenoid sinus, located just beneath the sella turcica. The sphenoid sinus, in turn, can be accessed through the nose. This is called the transphenoidal surgical approach. 8  Mid-Sagittal View of the Pituitary Gland !"#$%"CD()#$%"*$+ I(-(++.+CL01$-.+ T%;.%8$R.*")CI(-(++ L01$-COP$"+#" D.R()CO$%().# 4")+ D.R()"*$+ T%;.%8$R.*")C91"*< 4")+ S$+1"*$+ S$"0P)":#" 9(**" I(+$8."*C!.#(% 9(**" 4")+ D.)-$-" T%1()#(8$" 4")+ %(.)"*$+ O")*+=%>C!"##$%&'EF*+%,"#-*%E*.E/012P*4*5P>C?1PC(8@CCA4":(C?BCa Within the pituitary fossa, the pituitary is surrounded by dura mater. The dura covering the superior portion of the pituitary is called the diaphragma sella and the pituitary stalk (infundibular stalk and the pars tuberalis) pass through the diaphragma sella via a small hole. 9  The hypothalamus is divided into lateral, medial and periventricular areas. The medial and lateral areas are separated by fibers (i.e. fornix) running from the hippocampus to the mammillary bodies. The lateral hypothalamic area includes the lateral hypothalamic nucleus, several other small nuclei and the Medial Forebrain Bundle (which runs rostrocaudally). The Medial Forebrain Bundle (MFB) is a collection of nerve fibers (both afferent and efferent) that run to and from the hypothalamus and other brain regions. The medial hypothalamic area also includes many nuclei. The thin periventricular area or periaqueductal gray is most medially and lines the wall of the 3rd ventricle. Hypothalamic Areas and Nuclei (Young, Young and Tolbert – pages 236-241; 426- 427; Haines pages 288-293) The hypothalamus can be divided into lateral, medial and periventricular areas. The medial and lateral areas are separated by fibers running from the hippocampus to the mammillary bodies. 10  Periventricular Area Third Ventricle Anterior Commissure Lateral Area (with MFB) Medial Area Blumenfeld, Neuroanatomy Anterior View through Clinical Cases, 1rst ed., of the 2002, page 741. Hypothalamus The lateral hypothalamic area includes the lateral hypothalamic nucleus, several other small nuclei and the Medial Forebrain Bundle (which runs rostrocaudally). The Medial Forebrain Bundle (MFB) is a collection of nerve fibers (both afferent and efferent) that run to and from the hypothalamus and other brain regions. The medial hypothalamic area also includes many nuclei which we will discuss shortly. The thin periventricular area or periaqueductal gray is located most medially and lines the wall and floor of the 3rd ventricle and is continuous through to the 4th ventricle. 11  The hypothalamus can also be divided into four coronal regions. From anterior to posterior these regions are the ………. 1) Preoptic area 2) Anterior (supraoptic) region 3) Middle (tuberal) region 4) Posterior (mammillary) region The hypothalamus can also be divided into four coronal regions. 12  Important Hypothalamic Nuclei Posterior Anterior Blumenfeld, Neuroanatomy Medial View through Clinical Cases, 1rst of the ed., 2002, page 740. Hypothalamus From anterior to posterior these regions are the 1) Preoptic (chiasmatic) area, 2) Anterior (supraoptic) region, 3) Middle (tuberal) region and 4) Posterior (mammillary) region. 13  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 14 Nuclei of the Preoptic Area 1) Lateral Preoptic Nucleus (and MFB) 2) Medial Preoptic Nucleus These are the rostral extensions of the Lateral and Medial Hypothalamic areas. The preoptic nuclei are derived embryologically from the telencephalon, the rest of the hypothalamus is derived from the diencephalon. However, the preoptic nuclei are functionally part of the hypothalamus. 15  Preoptic Area Blumenfeld, Neuroanatomy through Clinical Cases, 1rst ed., Anterior View 2002, page 741. Nuclei of the Preoptic Area The nuclei of the preoptic area include the lateral and medial preoptic nuclei. These nuclei are the rostral extensions of the lateral and medial hypothalamic areas. The preoptic nuclei are derived embryologically from the telencephalon while the rest of the hypothalamus is derived from the diencephalon. However, the preoptic nuclei are functionally part of the hypothalamus. 16  Preoptic Area of the Hypothalamus 1) Lateral Preoptic Nucleus (and MFB) Erection in males 2) Medial Preoptic Nucleus Urinary Bladder Contraction Decreased Heart Rate Decreased Blood Pressure Erection in males The medial preoptic nucleus has been shown to be involved in contraction of the urinary bladder, decreased heart rate, decreased blood pressure and erections in males. The lateral preoptic nucleus may also be involved with erections in males. 17 Nuclei of the Anterior (Supraoptic) Region 1) Lateral Hypothalamic Nucleus (and MFB) 2) Supraoptic Nucleus Magnocellular 3) Anterior Hypothalamic Nucleus 4) Paraventricular Nucleus Parvocellular Magnocellular 5) Suprachiasmatic Nucleus 18  Anterior (Supraoptic) Region Blumenfeld, Neuroanatomy through Clinical Anterior View Cases, 1rst ed., 2002, page 741. Nuclei of the Anterior (Supraoptic) Region The nuclei of the anterior (supraoptic) region include the 1) lateral hypothalamic nucleus, 2) supraoptic nucleus which is made up of magnocellular neurons, 3) anterior hypothalamic nucleus, 4) paraventricular nucleus which is made up of parvocellular and magnocellular neurons and 5) suprachiasmatic nucleus. The anterior region of hypothalamus, along with the preoptic region, regulates most of the parasympathomimetic activity. 19  Anterior (Supraoptic ) Region of the Hypothalamus 1) Lateral Hypothalic Nucleus (and MFB) Thirst and Hunger (Orexogenic area) 2) Supraoptic Nucleus Release of ADH, OXY 3) Anterior Hypothalamic Nucleus Thermoregulation – Heat Dissipation (Panting & Sweating) 4) Paraventricular Nucleus Release of OXY, ADH, CRH, TRH 5) Suprachiasmatic Nucleus Circadian Rhythms of hormone release, feeding, body temperature, etc. The lateral hypothalamic nucleus is the orexogenic area of the hypothalamus and is involved with thirst and hunger. The supraoptic nucleus is responsible for the secretion of ADH from the magnocellular neurons, while the paraventricular nucleus is responsible for the secretion of oxytocin from magnocellular neurons, and ADH, corticotrophin releasing hormone (CRH) and thyrotropin releasing hormone (TRH) from parvocellular nurons. The anterior hypothalamic nucleus is an important area involved with thermoregulation; more specifically Heat dissipation through sweating and panting. The suprachiasmatic nucleus has long been considered the biological clock which entrains circadian (or other) rhythms of hormone release, feeding, sleep, body temperature etc. (Note: axons of the magnocellular neurons make up the supraopticohypophseal tract, while axons of the parvocellular neurons make up the tuberal hypophyseal tract.) 20 Nuclei of the Middle (Tuberal ) Region 1) Lateral Hypothalamic Nucleus (and MFB) 2) Dorsal Medial Nucleus 3) Ventral Medial Nucleus 4) Periventricular Nucleus 5) Arcuate Nucleus (and Median Eminence) 21  Middle (Tuberal) Region Blumenfeld, Neuroanatomy through Clinical Cases, 1rst ed., 2002, page 741. Anterior View Nuclei of the Middle (Tuberal Region) The nuclei of the middle region include the 1) lateral hypothalamic nucleus, 2) dorsal medial nucleus, 3) ventral medial nucleus, 4) periventricular nucleus and 5) arcuate nucleus which makes up the major portion of the median eminence. 22  Middle (Tuberal) Region of the Hypothalamus 1) Lateral Hypothalamic Nucleus (and MFB) Thirst and Hunger (Orexogenic area) 2) Dorsal Medial Nucleus GI Motility 3) Ventral Medial Nucleus Satiety Center (anorexogenic center) Control of Aggressive Behavior 4) Periventricular Nucleus Fear and Escape Behavior, Release of GHIH (Somatostatin) from anterior periventricular 5) Arcuate Nucleus Reproductive Functions, Release of GnRH (also in preoptic area), GHRH, Dopamine (PIF) The lateral hypothalamic area is continuous with the anterior region and is still the orexogenic area. The dorsal medial nucleus is involved with regulation of GI motility. The ventral medial nucleus is the anorexogenic area and is considered to be the satiety center in the brain. The activities of the lateral and and ventral medial hypothalamic nuclei are involved in maintaining a normal set point for body weight. The ventral medial nucleus has also been associated with aggressive behavior. The periventricular nucleus is involved with fear and escape behavior and secretion of growth hormone inhibiting hormone (GHIH, aka somatostatin). The arcuate nucleus is known to have reproductive functions and is responsible for the secretion of gonadotropin releasing hormone (GnRH). GnRH has also been shown to be secreted from the preoptic area. In addition to GnRH, the arcuate nucleus also secretes growth hormone releasing hormone (GHRH) and dopamine which is the prolactin inhibiting factor. The middle region of the hypothalamus regulates much of the endocrine activity. See also Young, Young and Tolbert figure 18-2, page 237, in your assigned textbook. 23 Nuclei of the Posterior (Mammillary ) Region 1) Lateral Hypothalamic Nucleus (and MFB) 2) Mammillary Nuclei Lateral Intermediate Medial 3) Posterior Hypothalamic Nucleus 24  Posterior (Mammillary) Region Blumenfeld, Neuroanatomy through Clinical Cases, 1rst ed., 2002, page 741. Anterior View The Nuclei of the Posterior (Mammillary) Region The nuclei of the posterior region include the 1) lateral hypothalamic nucleus, 2) mammillary nuclei (lateral, intermediate and medial) and 3) posterior hypothalamic nucleus. The posterior region of hypothalamus regulates most of the sympathomimetic activity. 25  Posterior (Mammillary) Region of the Hypothalamus 1) Lateral Hypothalamic Nucleus (and MFB) Thirst and Hunger (Orexogenic area) 2) Mammillary Nucleus Role in memory as part of limbic system (Part of hypothalamus on anatomical grounds and play very little role in autonomic and endocrine function) 3) Posterior Nucleus Thermoregulation – Heat Conservation The lateral hypothalamic area is continuous with the anterior region is still the orexogenic area. The mammillary nuclei are actually part of the limbic system and play a role in memory. On anatomical grounds, the mamillary nuclei are considered to be part of the hypothalamus but play a limited role in actual hypothalamic function. The posterior hypothalamic nucleus is the counterpart of the anterior hypothalamic nuceus. It too is involved in thermoregulation and is responsible for heat conservation. The activities of the posterior and anterior hypothalamic nuclei are involved in maintaining a normal set point for body temperature. 26  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 27  Major Pathways to and from the Hypothalamus 1) Medial Forebrain Bundle (MFB) 2) Fornix (FX) 3) Dorsal Longitudinal Fasiculus (DLF) 4) Mammillothalamic Tract (MTT) 5) Stria Terminalis (ST) and the Ventral amygdalofugal pathway (VAFP) 6) Supraopticohypophyseal Tract (SOHT) 7) Tuberohypophyseal Tract (THT) 8) Retinohypothalamic Tract (RHT) The Major Pathways to and From the Hypothalamus (Young, Young and Tolbert – pages 236-241; Haines pages 288-293) The hypothalamus communicates with other regions of the brain through tracts or pathways that are either bidirectional or unidirectional. Most notably, these other brain regions include the limbic areas, the autonomic centers of the brain stem, the thalamus, the pituitary, and the retina. The pathways you are responsible for include the following. 28 Major Pathways to and from the Hypothalamus 1) Medial Forebrain Bundle (MFB) Runs through the Lateral hypothalamic area. Consists of afferent and efferent fibers that extend from the basal forebrain (amygdala, and striatum) to the brain stem (reticular formation, locus ceruleus, dorsal raphe and ventral tegmental areas). These fibers have been implicated in appetite control, sleep, olfaction, depression, pleasure and autonomic regulation. 29  Major Pathways to and from the Hypothalamus Anterior Posterior Medial Forebrain Bundle (MFB) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Medial Forebrain Bundle: The MFB runs through the lateral hypothalamic area. It consists of afferent and efferent fibers that extend from the basal forebrain (amygdala, and striatum) to the brain stem (reticular formation, locus ceruleus, dorsal raphe and ventral tegmental areas). These fibers have been implicated in appetite control, olfaction, sleep, depression, pleasure and autonomic regulation. 30 Major Pathways to and from the Hypothalamus 2) Fornix (FX) Consists of afferent and efferent fibers that extend from the hippocampus to the mammillary bodies of the hypothalamus while connecting to various limbic structures. These fibers run between the lateral and medial hypothalamic areas and play a role in interpretation and expression of memories and emotions. 31  and Hippocampus 3D-View of the Fornix 32 3D-View of the Fornix 33  Major Pathways to and from the Hypothalamus Anterior Posterior Fornix(FX) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Fornix (FX): The FX consists of afferent and efferent fibers extending from the hippocampus to the mammillary bodies while connecting to various limbic structures. These fibers run between the lateral and medial hypothalamic areas and play a role in the interpretation and expression of memories and emotions. See also Young, Young and Tolbert figure 18-3, page 238, key 13, in your assigned textbook. 34 Major Pathways to and from the Hypothalamus 3) Dorsal Longitudinal Fasiculus (DLF) Consists of afferent and efferent fibers that extend from the periventricular nucleus of the hypothalamus to the periventricular and periaqueductal gray of the brain stem. These fibers play a role in autonomic regulation. 35  Major Pathways to and from the Hypothalamus Anterior Posterior Dorsal Longitudinal Fasiculus (DLF) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Dorsal Longitudinal Fasiculus (DLF): The DLF consists of afferent and efferent fibers extending from the periventricular nucleus of the hypothalamus to the dorsal regions of the brain stem. These fibers play a prominent role in autonomic regulation. 36 Major Pathways to and/or from the Hypothalamus 4) Mammillothalamic Tract (MTT) Consists of primarily efferent fibers that extend from the mammillary bodies of the hypothalamus to the anterior nucleus of the thalamus. These fibers are involved in relaying information to the limbic cortex in the cingulate gyrus (cerebral cortex). 37  Major Pathways to and from the Hypothalamus Anterior Posterior Mammillothalmic Tract (MTT) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Mammillothalamic Tract (MTT): The MTT consists of primarily efferent fibers that extend from the mammillary bodies to the anterior nucleus of the thalamus. These fibers are involved in relaying information to the limbic cortex in the cingulate gyrus. See also Young, Young and Tolbert figure 18-3, page 238, key 14, in your assigned textbook. 38 Major Pathways to and from the Hypothalamus 5) Stria Terminalis (ST) Consists of primarily afferent fibers to the hypothalamus from the amygdala. These fibers follow the caudate nucleus and are involved with limbic system function. Long path to the hypothalamus. Ventral amygdalofugal pathway (VAFP) Consists of primarily afferent fibers to the hypothalamus from the amygdala. Shortcut to the hypothalamus 39  Major Pathways to and from the Hypothalamus Posterior Anterior Stria Terminalis Tract Stria Terminalis (ST) Ventral Amygdalofugal Pathway Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst Ventral Amygdalofugal ed., 2003, page 271. Pathway (VAFP) Stria Terminalis (ST) and Ventral amygdalofugal pathway (VAFP): The stria terminalis consists of primarily afferent fibers to the hypothalamus from the amygdala. These fibers follow the caudate nucleus and are involved with limbic system function. This tract represents the long pathway to the hypothalamus. The ventral amygdalofugal pathway consists of primarily afferent fibers to the hypothalamus from the amygdala and represents the short pathway to the hypothalamus. 40 Major Pathways to and from the Hypothalamus 6) Supraopticohypophyseal Tract (SOHT) Consists of efferent fibers that extend from the supraoptic and paraventricular nuclei of the hypothalamus to the neurohypophysis. ADH and OXY are released into the circulation from these neurons and act as hormones on a variety of tissues. 41  Major Pathways to and from the Hypothalamus Anterior Posterior Supraoptico- hypophyseal Tract (SOHT) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Supraopticohypophyseal Tract (SOHT): The SOHT (AKA hypothalamic hypophyseal tract) consists of efferent fibers that extend from the magnocellular neurons of the supraoptic and paraventricular nuclei to the neurohypophysis. ADH and OXY are released into the circulation from these neurons and act as hormones on a variety of tissues. See also Young, Young and Tolbert figure 18-3, page 238, key 11, in your assigned textbook. 42  Major Pathways to and from the Hypothalamus 7) Tuberohypophyseal Tract (THT) Consists of efferent fibers that extend from the periventricular , arcuate, medial preoptic and the paraventricuar nuclei of the hypothalamus to the median eminence of the hypothalamus (The Final Common Pathway). Releasing hormones and Inhibiting hormones are released from these axon terminals into the hypophyseal portal system. These hormones ultimately control the synthesis and release anterior pituitary hormones. 43  Major Pathways to and from the Hypothalamus Anterior Posterior Tuberohypophyseal Tract (THT) Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Tuberohypophyseal Tract (THT): The THT consists of efferent fibers extending from the periventricular , arcuate, medial preoptic and paraventricuar nuclei to the median eminence of the hypothalamus (The Final Common Pathway). Releasing hormones and inhibiting hormones are released from these axon terminals into the hypophyseal portal system. These releasing and inhibiting hormones ultimately control the synthesis and release anterior pituitary hormones. See also Young, Young and Tolbert figure 18-3, page 238, key 12, in your assigned textbook. 44 Major Pathways to and from the Hypothalamus 8) Retinohypothalamic Tract (RHT) Consists of afferent fibers that extend from the retina to suprachiasmatic nucleus of the hypothalamus. These fibers relay information regarding light conditions in the external environment. 45  Major Pathways to and from the Hypothalamus !"#$%C Anterior Posterior '() Retinohypothalamic Tract (RHT) Retinohypothalamic Tract Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 269. Retinohypothalamic Tract (RHT): The RHT consists of afferent fibers extending from the retina to the suprachiasmatic nucleus. These fibers relay information to the hypothalamus regarding light conditions in the external environment. 46  Modified and Redrawn form Summary of Felten and Jozefowics, General Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, Hypothalamic Cortex page 274. Connections MFB ST, VAFP Midbrain, Lateral Brain Stem & Limbic System FX MFB Hypothalamus Autonomic structures Thalamus & Medial Brain Stem & MTT DLF Cerebral Cortex Hypothalamus Autonomic structures DLF RH THT T Retina Anterior Pituitary Periventricular Hypothalamus Posterior Pituitary SOHT A summary of the major hypothalamic connections. 47  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 48  Circumventricular Organs Circumventricular organs are “Windows on the Brain” because these areas are equipped with a fenestrated vasculature rather than a continuous vasculature. As a result, the Blood-Brain-Barrier in these areas are nonexistent or weak at best. This means that the hypothalamus can be targeted by various humoral factors. 1) Organum Vascularum of the Laminar Terminalis (OVLT) – Neuroendocrine Functions 2) Subfornical Organ – Water Balance 3) Area Postrema (paired) - Chemical Trigger Zone 4) Median Eminence – Release of RH and IH 5) Neurohypophysis – Release of ADH and OXY 6) Pineal Gland – Release of Melatonin The Circumventricular Organs (Young, Young and Tolbert, pages 238-239) The circumventricular organs have been referred to as the ‘Windows on the Brain’ because these areas are equipped with a fenestrated vasculature rather than a continuous vasculature. As a result, the Blood-Brain-Barrier in these areas is nonexistent or weak at best. This means that the hypothalamus can be targeted by various humoral factors circulating in blood by way of the organum vascularum of the laminar terminalis, median eminence, and posterior pituitary (see next slide). 49  Circumventricular Organs Posterior Anterior Felten and Jozefowics, Netter’s Atlas of Human Neuroscience, 1rst ed., 2003, page 277. The organum vascularum of the laminar terminalis (OVLT) appears to be involved in neuroendocrine functions. The subfornical Organ is involved with water balance. The area postrema (the only paired circumventricular organ) is considered the chemical trigger zone and is involved in the central emetic response. The median eminence is the location where the hypothalamic releasing and inhibiting hormones are secreted into the hypophyseal portal circulation. The neurohypophysis is the site of ADH and OXY secretion. The pineal gland synthesizes and secretes melatonin. 50  OBJECTIVES 1. recall the general anatomy and physiology of the hypothalamus and pituitary. 2. recall the location and function of the major hypothalamic nuclei. 3. recall the location and function of the major afferent and efferent neuronal pathways that connect to and from the hypothalamus. 4. recall the location and function of the circumferential ventricular organs. 5. determine the physiological consequences of a lesion to a specific hypothalamic area (i.e., nuclei, pathways, or circumventricular organs). 51 Hypothalamic Area Nuclei Major Functions Preoptic Lateral Preoptic Nucleus erection? Medial Preoptic Nuclues contraction of bladder; decreased heart rate and blood pressure; erection; release of GnRH Anterior (Supraoptic) Lateral Hypothalamic Nucleus Hunger and Thirst (Orexogenic Center) Supraoptic Nucleus Release of ADH (water balance) Anterior Hypothalamic Nucleus Temperature Regulation (Heat Dissipation) Paraventricular Nucleus Release of Oxy (uterine contractions and milk ejection);Release of ADH, CRH and TRH Suprachiasmatic Nuclues Biological Clock; Entrainment of Biological Rhythms Anterior region of hypothalamus regulates most of the parasympathomimetic activity. Middle (Tuberal) Lateral Hypothalamic Nucleus Hunger and Thirst (Orexogenic Center) Dorsal Medial Nucleus GI Motility Ventral Medial Nucleus Satiety Center (Anorexogenic Center); Aggressive Behavior Periventricular Nucleus Fear and Escape behavior; Release of GHIH (somatostatin) Arcuate Nucleus Reproductive Functions; release of GnRH, GHRH, dopamine Posterior Lateral Hypothalamic Nucleus Hunger and Thirst (Orexogenic Center) (Mammillary) Mammillary Nuclei Limbic Mechanisms Involved in Memory Posterior Hypothalamic Nucleus Temperature Regulation (Heat Conservation); Arousal Posterior region of hypothalamus regulates most of the sympathomimetic activity. 52  Afferent (A) or Hypothalamic Pathway Efferent (E) Major Functions Medial Forebrain Bundle A and E Fibers from Basal Forebrain to Hypothalamus to Brain Stem; Appetite Control, Sleep, Olfaction, Depression, Pleasure, and Autonomic Regulation Fornix A and E Fibers from Hippocampus to Mammillary Bodies: Limbic Mechanisms Involved in Memory Dorsal Longitudinal Fasiculus A and E Fibers from Periventricular Nucleus of Hypothalamus to Periventricular Area of Brain Stem; Control of Autonomic Regulation Mammilothalamic Tract a and E Fibers from Mamillary Bodies to Thalamus; Limbic Mechanisms Stria Terminalis A and e Fibers from Amygdala to the Hypothalamus (long path); Limbic Mechanisms Ventral Amygdalofugal Pathway A and e Fibers from Amygdala to the Hypothalamus (short path); Limbic Mechanisms Supraopticohypophyseal Tract E Fibers from Supraoptic and Paraventricular Nuclei to Posterior Pituitary; secretion of ADH and OXY Tuberohypophyseal Tract E Fibers from Arcuate, Periventricular, Paraventricular and Medial Preoptic Nuclei to Median Eminence; Secretion of Releasing Hormones or Inhibiting Hormones into Portal System Retinohypothalamic Tract A Fibers from Retina to Suprachiasmatic Nucleus; Relay Lighting Condition *Capital A or E indicates major *Lower Case a or e indicates minor Major Functions Circumferential Organ Organum Vascularum of the Laminar Terminalis Neuroendocrine Sensory Subfornical Organ Water Balance Sensory Area Postrema Chemical Trigger Zone; Central Emetic Response Sensory Median Eminence Release of Hypothalamic Releasing and Inhibiting Hormones into the Hypophyseal Portal System Secretory Neurohypophysis Release of ADH and OXY Secretory Pineal Gland Release of Melatonin Secretory 53  The Hypothalamus Chapter 18 in Young et al. Introduction Basic Hypothalamic and Pituitary Structure and Function The Hypothalamus Hypothalamic Nuclei and their Functions Afferent and Efferent Hypothalamic Pathways Circumventricular Organs 54 Chapter Review Questions: What are the anteroposterior subdivisions of the hypothalamus? 55 Chapter Review Questions: What are the anteroposterior subdivisions of the hypothalamus? Textbook Answer Anterior (Chiasmatic) Intermediate (Tuberal) Posterior (Mamillary) 56 Chapter Review Questions: What are the anteroposterior subdivisions of the hypothalamus? PDF Answer Preoptic Anterior (Supraoptic) Middle (Tuberal) Posterior (Mamillary) 57 Chapter Review Questions: What is the chief neural output of the hypothalamus? 58 Chapter Review Questions: What is the chief neural output of the hypothalamus? 1) Cerebral Cortex via the Thalmus MTT 2) Brainstem and Spinal Cord DLF and MFB 59 Chapter Review Questions: What is the Hypophyseal Portal System? 60 Chapter Review Questions: What is the Hypophyseal Portal System? Vascular connection between the tuberal region of the hypothalamus and the anterior pituitary in which releasing and/or inhibiting hormones are conveyed from hypothalamic neurons to trophic cells of the anterior pituitary. 61 Chapter Review Questions: Which parts of the hypothalamus are associated with….. temperature regulation? 62 Chapter Review Questions: Which parts of the hypothalamus are associated with….. temperature regulation? Heat Dissipation – preoptic & anterior hypothalamic nuclei Heat Conservation – posterior hypothalamic nucleus 63 Chapter Review Questions: Which parts of the hypothalamus are associated with….. parasympathomimetic activity? sympathomimetic activity? 64 Chapter Review Questions: Which parts of the hypothalamus are associated with….. parasympathomimetic activity? Preoptic and Anterior regions of the hypothalamus sympathomimetic activity? Posterior region of the hypothalamus 65 Chapter Review Questions: Which parts of the hypothalamus are associated with….. hypothalamic regulatory hormones? water balance? sleep-wake cycles? emotions? 66 Chapter Review Questions: Which parts of the hypothalamus are associated with….. hypothalamic regulatory hormones? Tuberal Region of the Hypothalamus water balance? sleep-wake cycles? emotions? 67 Chapter Review Questions: Which parts of the hypothalamus are associated with….. hypothalamic regulatory hormones? Tuberal Region of the Hypothalamus water balance? Anterior Region of the Hypothalamus sleep-wake cycles? emotions? 68 Chapter Review Questions: Which parts of the hypothalamus are associated with….. hypothalamic regulatory hormones? Tuberal Region of the Hypothalamus water balance? Anterior Region of the Hypothalamus sleep-wake cycles? Anterior Region of the Hypothalamus emotions? 69 Chapter Review Questions: Which parts of the hypothalamus are associated with….. hypothalamic regulatory hormones? Tuberal Region of the Hypothalamus water balance? Anterior Region of the Hypothalamus sleep-wake cycles? Anterior Region of the Hypothalamus emotions? Ventral Medial and Posterior Nuclei 70