Lab 14 Hypothalamus Flashcards
Hypothalamus Functions
- maintenance of internal homeostasis
- organization of emotional responses via groups of nuclei that affect autonomic, endocrine and emotional function
- nuclei located in different mediolateral zones and anterioposterior regions
Anterior Region (Nuclei)
- preoptic nuclei
- paraventricular
- supraoptic
- Suprachiasmatic
Middle Region (nuclei)
- arcuate
- ventromedial
- dorsomedial
Posterior region (nuclei)
- mammillary bodies
- posterior nuclei
- tuberomammillary nuclei
Mediolateral Zones
Medial zone: contains all of the nuclei we’ll study EXCEPT for the tuberomammillary nuclei
-also contains a tract: DLF (dorsal longitudinal fasciculus)
Lateral zone: contains tuberomammillary nuclei and a tract, the medial forebrain bundle (MFB)
Medial Forebrain Bundle (MFB)
-lateral Hypothalamus
- A major 2 way fiber system that is continuous with the brainstem reticular formation
- it’s fibers travel caudally in the midbrain PAG, then in the dorsolateral reticular formation of the pons and medulla, and some extend into the intermediate gray of the spinal cord
- it sends branches to visceral centers and visceral and somatic motor nuclei
- descending fibers called: Hypothalamospinal tract
NOTE: most brainstem fibers that ascend into the hypothalamic MFB (e.g. Axons from chemospecific brainstem nuclei) pass thru the brainstem reticular formation and PAG
Dorsal Longitudinal Fasciculus (DLF)
-medial Hypothalamus
-a mainly descending system that originates in the paraventricular nucleus and periventricular hypothalamic neurons, with axons that descend in the midbrain PAG and the pontine/medullary periventricular gray to terminate mainly in visceral centers and parasympathetic nuclei of the brainstem
Walls of the 3rd Ventricle
Lamina terminalis: anterior wall
Anterior Commissure: posterior to the lamina terminalis
Hypothalamic sulcus: groove in the wall of the third ventricle
Thalamus: superior to hypothalamic sulcus
Hypothalamus: inferior to hypothalamic sulcus
Mammillary Body: posterior bulge of the mammillary nucleus
Stalk of the Hypophysis (area in general)
Infundibulum: stalk of the hypophysis
Tuber cinereum: floor of hypothalamus around the infundibulum
Median Eminence: grossly=lower area of tuber cinereum that’s continuous with the infundibular stalk; functionally=contact zone between terminals of hypothalamic parvocellular secretory neurons and hypophysial portal capillaries (will be bright on MR with contrast enhancement because lack of BBB in hypophysial portal vessels)
Gross Regions of the Hypothalamus (landmarks)
Anterior (superior to the optic chiasm)
Middle (superior to the infundibular stalk and tuber cinereum)
Posterior (at and superior to mammillary bodies)
Uncus
-part of the primary olfactory cortex, located superficial to the amygdala
Preoptic Area (note general locations)
-a major receiving area for peripheral data, as well as integrating and distribution center
Preoptic Nuclei (preoptic area)
- receptors for detecting chemicals, hormones, and physical features of circulating blood and CSF
- warm and cold temperature receptors and circuits for heat-dissipation when body temperature rises above it’s preprogrammed level
- neuroendocrine cells that secrete GnRH into the median eminence to regulate gonadal hormone secretion by the anterior pituitary
Paraventricular Nucleus (preoptic area)
a large nucleus posterior to the preoptic nuclei which is a major center for output to of both neural and hormonal regulation of ANS including
- regulation of activity of the sympathetic nervous system via the medial forebrain bundle (MFB) and the parasympathetic nervous system via the dorsal longitudinal Fasciculus (DLF) - regulation of emotional responses that involve both visceral (ANS) and somatic actions (like shivering) via descending fibers in the MFB, DLF, reticular formation and intermediate gray of the spinal cord - hormone secretion into both the median eminence and the posterior hypophysis (oxytocin and vasopressin) -these output systems are organized primarily for stress responses to emotional states graded as "danger" in the amygdala and transmitted to the PVN via pathways including the VAFP
Supraoptic Nucleus (preoptic area)
- small nucleus above the optic tracts
- contains magnocellular neurosecretory cells that produce oxytocin and vasopressin (ADH) for release into permeable vessels of the posterior hypophysis
Suprachiasmatic Nucleus (preoptic area)
- a small nucleus above the optic chiasm that:
- contains a preprogrammed daily or circadian clock or oscillator
- receives direct fibers from the retina (retinohypothalamic tract) that adjust the SCN oscillator circuits to a 24-hour cycle based on ENV light
- sends output to other structures (including hypothalamic nuclei) that participate in activities that fluctuate within a 24 hour cycle
Middle Hypothalamus (gross location)
- area between the optic chiasm and the mammillary bodies (above the infundibulum)
- is separated by fornix into lateral and medial zones
- the medial zone contains arcuate, ventromedial and dorsomedial nuclei
Medial Forebrain Bundle (MFB)
- middle hypothalamus
- lateral region
- ascending fibers from brainstem Nuclei (chemospecific, parabrachial nucleus, nucleus solitarius) and the hypothalamus that reach other forebrain structures such as the emotional cortex, thalamus, and basal ganglia
- fibers that connect hypothalamic nuclei at different rostrocaudal levels
- descending fibers from forebrain emotion structures (emotion cortex, ventral Pallidum, amygdala, and hypothalamus) en route to structures of the brainstem and spinal cord
Arcuate Nucleus (middle hypothalamus)
- a nuclear sheet in the periventricular area immediately above the median eminence
- it’s a major location for parvocellular neurosecretory cells that produce hormones (e.g. GHRH, GnRH, TRH, POMC)
- these substances are released into the median eminence for transport to the anterior hypophysis
- this nucleus also contains receptors for many blood-borne tissue hormones such as lepton, produced in adipocytes
Ventromedial Nucleus (middle hypothalamus)
- located above the region of the arcuate nucleus
- involved in the regulation of food intake and may contain the set-point circuitry for linking food intake with the needs for energy metabolism
- it has receptors for peripherally generated substances like lepton, and receives neural input from the emotion telencephalon via the MFB and from brainstem visceral structures
Mammillary Nuclei (posterior hypothalamus)
- involved in declarative memory pathways
- receives fibers from the hippocampal formation via the postcommisural fibers for the fornix
- send fibers via the mammillothalamic tract to the anterior nucleus of the thalamus
Anterior Nucleus of the Thalamus
-termination site of the mammillothalamic fibers
Cingulate Gyrus
-termination site for many fibers that leave the anterior nucleus
Tuberomammillary Nuclei (posterior hypothalamus)
- are located in the lateral zone of the posterior hypothalamus
- they contain histaminergic neurons that communicate with brainstem chemospecific nuclei and they send fibers to widespread areas of cortex and other forebrain structures
- involved in arousal and sleep-wake cycle
Periaqueductal Gray (PAG)
-contains:
DLF (descending fibers from the hypothalamus that travel to brainstem parasympathetic nuclei)
Other descending hypothalamic fibers: that travel in or near the PAG to reach brainstem visceral centers, preganglionic sympathetics (T1-L2) and preganglionic parasympathetic neurons (S2-4) in the spinal cord
Ascending fibers: to the hypothalamus and forebrain emotion centers from the brainstem chemospecific nuclei and other lower centers
Descending Hypothalamic Fibers (medulla)
Send axons to:
Medullary visceral centers (solitary nucleus, ventrolateral medullary centers, emetic center)
Visceral motor nuclei in the spinal cord (intermediolateral horn and the sacral parasympathetic)
Somatic and brachial efferent motor nuclei for responses to emotion and homeostasis processing, such as shivering in the cold and the facial expressions of fear or anger
Note about the Salivatory Nucleus
-the reticular formation of the caudal pons/rostral medulla contain scattered cells that form the superior and inferior salivatory nuclei,m parasympathetic nuclei that send axons into:
Facial nerve: supply the lacrimal gland, mucous membranes of nasal and oral cavities, sublingual and submandibular salivary glands
Glossopharyngeal nerve: supply the parotid gland
IN THE CLINIC (Paths of the hypothalamus fibers)
Fibers from the hypothalamus and emotion centers descend on the same side through the brainstem reticular formation and the intermediate gray of the spinal cord and terminate on motor neurons that are ipsilateral to the source of stimulation. Thus, clinical signs like unilateral miosis, ptosis of the upper eyelids or facial vasodilation can be caused by a lesion in Hypothalamic descending fibers of the same side as they traverse the brainstem reticular formation or upper spinal cord
Taste Pathways
-taste receptors of the tongue and pharynx send input to the brainstem via afferent fibers of the facial, glossopharyngeal, and vagus nerves
Solitary tract: central processes of taste and visceral afferent fibers of CN VII, IX and X
solitary nucleus: neurons that receive the terminals of fibers in the solitary tract. This necleus can be subdivided into a rostral gustatory portion for processing taste and a lower portion for the processing of GVA data
Dorsal motor nucleus of the vagus nerve: in the periventricular zone, lateral to the hypoglossal nucleus
VLM: in the lateral reticular formation
Solitary Nucleus
-gustatory part send fibers thru the reticular formation for connections with interneurons that terminate in the:
VPM of the thalamus: for taste processing; send axons via the posterior limb of the internal capsule to reach primary taste cortex in the insular cortex and postcentral gyrus
Salivatory nuclei: of the medulla/pons for delivery of impulses via the facial and glossopharyngeal nerves for reflex activation of gland cells to increase production of saliva
Medullary digestive center: in the VLM, trigger central pattern generators that send synchronized signals to the dorsal motor nucleus of X, for rhythmic peristalsis and secretion of digestive glands
Olfactory Pathways
Olfactory bulb: a processing center for input from the olfactory nerve
Olfactory tract: fibers that bring olfactory information to processing centers in the forebrain
Medial olfactory stria: fibers from the olfactory tract to the septal area
Lateral olfactory stria: fibers from the olfactory tract to the uncus, amygdala, and hippocampus
Uncus: primary olfactory codrtexl; receives fibers from the lateral olfactory stria
