Neuro: 4.2 - Hypothalamus

Front 1

What part of the embryological brain is the hypothalamus derived from?

Back 1

Diencephalon

Front 2

What is the primarily function of the hypothalamus?

Back 2

Maintenance of homeostasis

Front 3

What three systems is the hypothalamus related to?

Back 3

1. ANS
2. Endocrine system
3. Limbic system

Front 4

What structures are the hypothalamus anatomically related to?

Back 4

- Forms inferior portion of 3rd ventricle
- Underneath the thalamus (separated by shallow groove named the Hypothalamic Sulcus)
- Limited anteriorly by optic chiasm
- Limited posteriorly by mammillary bodies
- Infundibulum - stalk to pituitary

Front 5

What is the Infundibulum? Contents?

Back 5

- Stalk of the hypophysis (pituitary gland)
- Contains hypophyseal portal vessels (to the adenohypophysis - ant. pituitary)
- Contains several important tracts connecting the hypothalamus and the posterior part of the pituitary (neurohypophysis - post. pituitary)

Front 6

Which part of the hypophysis (pituitary) is connected by neural tracts?

Back 6

Neurohypophysis - Posterior Pituitary

Front 7

Which part of the hypophysis (pituitary) is connected by portal vessels?

Back 7

Adenohypophysis (anterior pituitary)

Front 8

What flows to the anterior pituitary (adenohypophysis) via the portal vessels? How?

Back 8

Various classes of (largely peptidergic) hypthalamic neurons release regulatory factors

Front 9

What is the Tuber Cinereum?

Back 9

"Gray Protuberance" - bulge located between the optic chiasm and mammillary bodies

Front 10

What are the Mammillary Bodies?

Back 10

- Paired structures
- Functionally a part of the limbic system (i.e., Papez circuit)

Front 11

How does blood supply the hypothalamus?

Back 11

Small branches from the Circle of Willis surrounding the ventral surface

Front 12

Why is the blood supply to the hypothalamus important (besides for nutrients/waste)?

Back 12

Key component of responsiveness of specific hypothalamic neuronal populations to the negative feedback actions of circulating hormones (e.g., adrenal and gonadal steroids)

Front 13

How is the Hypothalamus divided?

Back 13

- Lateral Zone
- Medial Zone
- Periventricular Zone

Front 14

What separates the different zones of the hypothalamus?

Back 14

- Lateral and Medial Zones separated by Fornix (ventrally) and Mammilothalamic Tract (dorsally)
- No distinct division between thin Periventricular Zone and Medial Zone

Front 15

What are the components of the Lateral Zone of the Hypothalamus?

Back 15

- Loosely arranged neuronal cell groups
- Traversed by fibers of Medial Forebrain Bundle
- Three major nuclei

Front 16

What are the three major nuclei of the Lateral Zone of the Hypothalamus?

Back 16

1. Lateral Preoptic Nucleus
2. Lateral Hypothalamic Area (Nucleus)
3. Lateral Tuberal (Tuberomammillary) Nucleus

Front 17

Which are the characteristics / roles of the three major nuclei of the Lateral Zone of the Hypothalamus?

Back 17

1. Lateral Preoptic Nucleus - anterior portion, telencephalic developmentally (involved in initiating sleep)
2. Lateral Hypothalamic Area (Nucleus) - induces eating when stimulated; ablation causes anorexia and starvation
3. Lateral Tuberal (Tuberomammillary) Nucleus - ventrolateral surface of medial zone - neurons release histamine to forebrain; involved in attention and arousal, inhibited during sleep

Front 18

Which nuclei of the hypothalamus is involved in inducing eating when stimulated? Lesion?

Back 18

- Lateral Hypothalamic Area (Nucleus) - part of lateral zone
- Ablation causes anorexia and starvation

Front 19

Which nuclei of the hypothalamus is involved in attention and arousal when stimulated? Inhibition?

Back 19

- Lateral Tuberal (Tuberomammillary) Nucleus
- Inhibition during sleep
- Releases Histamine

Front 20

What regions are a part of the Medial Zone of the Hypothalamus?

Back 20

- Preoptic Region (blue)
- Anterior (Supraoptic) Region (red)
- Middle (Tuberal) Region (orange)
- Posterior (Mammillary) Region (green)

Front 21

Which nuclei is found in the Preoptic Region of the Medial Zone of the Hypothalamus? Function?

Back 21

- Medial Preoptic Nucleus (blue)
- Neurons regulate gonadotropin secretion from the adenohypophysis
- Also contains interstitial nuclei of anterior hypothalamus (INAH1-4), one of which is sexually dimorphic (INAH3) and regulated by testosterone

Front 22

What are the nuclei in the Anterior (Supraoptic) Region of the Medial Zone of the Hypothalamus? Functions?

Back 22

- Suprachiasmatic Nucleus - immediately dorsal to optic chiasm, receives input from retina; involved in circadian rhythm
- Anterior Hypothalamic Area (Nucleus) - temperature regulation, senses warmth and excess heat; also stimulatory drive of PNS
- Paraventricular Nucleus - release neuropeptides AVP (water conservation), Oxytocin (milk letdown/release), and CRH (stress responsiveness); also projects to intermediolateral cell column of spinal cord (T1-L2 - SNS)
- Supraoptic Nucleus - synthesizes AVP and Oxytocin - projects to neurohypophysis to release into gen. circulation
(RED)

Front 23

Which nucleus in the hypothalamus regulates gonadotropin secretion from the adenohypophysis and is developmentally regulated by testosterone?

Back 23

Medial preoptic nucleus of the Preoptic region in the Medial zone of the hypothalamus
(RED)

Front 24

Which nucleus in the hypothalamus receives input from the retina and is important for circadian rhythm?

Back 24

Suprachiasmatic Nucleus - Anterior (Supraoptic) Region of Medial Zone of Hypothalamus
(RED)

Front 25

Which nucleus in the hypothalamus regulates temperature by sensing heat? Lesions?

Back 25

- Anterior Hypothalamic Area (Nucleus) in Anterior (supraoptic) region of Medial Zone of Hypothalamus
- Also concerned with stimulatory drive for PNS
- Lesions cause hyperthermia
(RED)

Front 26

Which nucleus in the hypothalamus regulates AVP, Oxytocin, and CRH release?

Back 26

- Paraventricular Nucleus of the Anterior (Supraoptic Region) of the Medial Zone of the Hypothalamus
- Also projects to intermediolateral cell column of spinal cord (T1-L2), to excite sympathetic preganglionic neurons
(RED)

Front 27

Which nucleus in the hypothalamus releases AVP and Oxytocin to the Neurohypophysis where it can enter the general circulation?

Back 27

Supraoptic Nucleus of the Anterior (Supraoptic) Region of the Medial Zone of the Hypothalamus
(RED)

Front 28

What are the nuclei of the Middle (Tuberal) Region of the Medial Zone of the Hypothalamus? Functions?

Back 28

- Dorsomedial Nucleus - aggressive behavior, BP regulation
- Ventromedial Nucleus - inhibits urge to eat (satiety center)
- Arcuate Nucleus - controls release of adenohypophyseal hormones via hypothalamic-releasing (and inhibiting) factors; involved in feeding behavior
(ORANGE)

Front 29

Which nucleus of the hypothalamus mediates aggressive and savage behavior as well as BP regulation?

Back 29

Dorsomedial Nucleus of the Middle (Tuberal) Region of the Medial Zone of the Hypothalamus
(ORANGE)

Front 30

Which nucleus of the hypothalamus inhibits the urge to eat ("satiety center")? Lesion?

Back 30

- Ventromedial Nucleus of the Middle (Tuberal) Region of the Medial Zone of the Hypothalamus
- Lesion causes hyperphagia (over-eating)
(ORANGE)

Front 31

Which nucleus of the hypothalamus controls the release of various adenohypophyseal hormones via hypothalamic releasing and inhibiting factors, also involved in feeding behavior?

Back 31

Ventromedial Nucleus of the Middle (tuberal) region of the Medial Zone of the Hypothalamus
(ORANGE)

Front 32

What are the nuclei of the Posterior (Mammillary) Region of the Medial Zone of the Hypothalamus? Functions?

Back 32

- Posterior Nucleus - thermoregulation by sensing cold
- Mammillary Nucleus - part of limbic system, input from hippocampus via fornix; projects to anterior nucleus of thalamus; also conveys sensory info to midbrain tegmentum
(GREEN)

Front 33

Which nucleus of the hypothalamus is involved in thermoregulation by sensing cold and initiating heat conservation? What happens if there is a lesion?

Back 33

- Posterior Nucleus of Posterior (Mammillary) Region of the Medial Zone of the Hypothalamus
- Poikilothermia - inability to thermoregulate if bilateral lesion
(GREEN)

Front 34

Which nucleus of the hypothalamus is part of the limbic system and receives input from hippocampus and projects to anterior nucleus of thalamus; as well as sending sensory info to midbrain tegmentum? Lesions?

Back 34

- Mammillary Nucleus of the Posterior (Mammillary) region of the Medial Zone of the Hypothalamus
- Lesions cause memory disturbances due to extensive interconnectivity with the hippocampus

Front 35

What are the nuclei of the Periventricular Zone? Functions?

Back 35

Periventricular Nucleus - layer of cells lines the wall of the 3rd ventricle at supraoptic and tuberal levels

Front 36

The hypothalamus is extensively interconnected with what portions of the neuraxis?

Back 36

- Basal forebrain regions that are components of the limbic system
- Brainstem regions that serve as part of the ANS

Front 37

What are the major fiber tracts of the Hypothalamus?

Back 37

- Fornix
- Mammillothalamic Tract
- Stria Terminalis
- Medial Forebrain Bundle
- Supraopticohypophyseal Tract
- Tuberoinfundibular Tract
- Hypothalamospinal Tract

Front 38

What happens in the Fornix?

Back 38

- Mammillary bodies of the Hypothalamus receive a large axonal projection from the Hippocampus
- Also contains axons that serve as inputs to the hippocampus from multiple brain regions

Front 39

What happens in the Mammillothalamic Tract?

Back 39

- Projects from the Mammillary Bodies (nuclei) to the Anterior Nucleus of the Thalamus
- Key component of the Papez Circuit

Front 40

What happens in the Stria Terminalis?

Back 40

Proinent pathway interconnecting the amygdaloid complex (e.g., amygdala) and the medial zone of the hypothalamus

Front 41

What happens in the Papez Circuit?

Back 41

- Fornix connects Hippocampus to Mammillary Body
- Mammillothalamic Tract connects Mammillary Body to Anterior Thalamic Nuclei
- Superior Thalamic Radiation connects that to the Cingulate Gyrus
- Cingulum connects CG back to Hippocampus

Front 42

What happens in the Medial Forebrain Bundle?

Back 42

- Most complex fiber pathway in CNS w/ >50 distinct constituent parts/pathways
- Extends through entire Lateral Hypothalamic Zone, interconnecting regions from the septal nuclei (rostrally) to the brainstem (caudally)

Front 43

What happens in the Supraopticohypophyseal Tract?

Back 43

Conducts fibers from the Supraoptic and Paraventricular Nuclei to the Neurohypophysis

Front 44

What happens in the Tuberoinfundibular Tract?

Back 44

Conducts fibers from the Arcuate Nucleus to the Hypophyseal Portal System at the Median Eminence of the Infundibulum

Front 45

What happens in the Hypothalamospinal Tract?

Back 45

Contains descending axons that regulate the spinal cord preganglionic neurons of both sympathetic and parasympaethtic divisions of the ANS; originates from the Paraventricular Nucleus

Front 46

What are the major functions of the Hypothalamus?

Back 46

- Body temperature regulation
- Stress responsiveness
- Feeding and energy metabolism
- BP and electrolyte composition
- Reproductive functions

Front 47

What are the fundamental capacities of the hypothalamus?

Back 47

1. Hypothalamus can access sensory information from virtually the entire body
2. Hypothalamus is thought to establish biological set points for temperature, blood osmolality, glucose, Na+, and levels of hormones
3. Deviation from set point is detected, the hypothalamus responds by adjusting autonomic, endocrine, and behavioral responses to restore homeostasis

Front 48

Which areas of the Hypothalamus are involved in Thermoregulation? How?

Back 48

- Anterior and Posterior Hypothalamic Nuclei
- Anterior senses warmth and triggers heat dissipation (sweating, vascular dilation, increased respiration) and by activating PNS
- Inflam. cytokines and pyrogens act on anterior hypothalamus to alter body temp set point causing fever
- Posterior senses cold, triggering heat conservation via sympathetic outflow (shivering, stop sweating, vascular constriction, increased thyroid to increase metabolic rate
- Both influenced by limbic forebrain and connected to brainstem and spinal cord
- Also behavioral responses (change environment, put on / take off clothes)

Front 49

What happens if there are lesions to the areas of the Hypothalamus regulating Thermoregulation?

Back 49

- Bilateral lesions to Ant. Hypothalamic Nuclei causes hyperthermia due to loss of warm-sensitive neurons
- Bilateral lesions to Post. Hypothalamic Nuclei causes inability to thermoregulate (poikilohermia) due to loss of cold-sensitive neurons and descending projections of warm-sensitive neurons

Front 50

How does the Hypothalamus play a role in stress responsiveness?

Back 50

Neuroendocrine control of the release of stress hormones from adrenal cortex (e.g., glucocorticoids) as well as epinephrine and NE from adrenal medulla

Front 51

What sort of sympathetic changes are mediated by the hypothalamus in a stress response?

Back 51

- Diversion of blood from viscera to skin and muscles
- Increased cardiac output
- Pupillary dilation (CN III inhibited)
- Bronchodilation
- Decreased GI motility and renal activity
- Inhibition of PNS neurons in brainstem

Front 52

What controls the hypothalamus stress response?

Back 52

Afferent regulatory control by pre-frontal cortex, limbic forebrain, and brainstem

Front 53

Which components of the limbic system are interconnected with the hypothalamus response to stress?

Back 53

- Amygdala
- Hippocampus

Front 54

Which CNs are inhibited in the stress response by the hypothalamus?

Back 54

- CN III - pupil dilation
- CN VII - sublingual and submaxillary gland secretion inhibited
- CN IX - parotid gland secretion inhibited
- CN X - decreased HR and decreased intestinal motility

Front 55

Which hypothalamic nuclei are involved in feeding and energy metabolism?

Back 55

- Lateral Hypothalamic Area - induces eating
- Ventromedial Hypothalamic Nucleus - inhibits eating
- Arcuate Nucleus - involved in eating

Front 56

Which hormones are involved in feeding and energy metabolism?

Back 56

- Insulin
- Glucagon
- Leptin

Front 57

How is the Arcuate Nucleus of the Hypothalamus (middle/tuberal level) involved in feeding?

Back 57

- Two distinct sets of neurons have opposite effects
- First set co-expressess agouti-related peptide (AgRP) and neuropeptide Y (NPY) w/ local hypothalamic projections to signal increased feeding and decrease in metabolism
- Second set co-expresses pro-opiomelanocortin (POMC --> converted to α-melanocyte-stimulating hormone, α-MSH) and cocaine- and amphetamine-responsive transcript (CART) which signals decreased feeding and increased metabolism
- Integrated at Nucleus of the Solitary Tract (NST) = Satiety Center

Front 58

Which hormones modulate feeding in the short-term?

Back 58

- Ghrelin (released from stomach just prior to a meal)
- PPY (polypeptide Y - released from GI following a meal)
- Act on two sets of arcuate neurons (AgRP/NPY and POMC/CART) to stimulate or inhibit feeding

Front 59

Which hormones modulate feeding in the long-term?

Back 59

- Leptin - released by fat cells
- Signals a decrease in feeding
- Inhibits AgRP/NPY neurons (that usually signal increased eating and decreased metabolism)

Front 60

What are three clinical correlates regarding the hypothalamus?

Back 60

1. Craniopharyngioma
2. Hypothalamic Memory Disturbances
3. Klein-Levin Syndrome

Front 61

What is a Craniopharyngioma? Symptoms?

Back 61

- Congenital tumor (usually calcified) originating from remnants of Rathke's pouch
- Most common supratentorial tumor in children
- Pressure on chiasm results in bitemporal hemianopia
- Pressure on overlying hypothalamus results in "hypothalamic syndrome" of adiposity, diabetes insipidus, temp. regulation disturbances, and somnolence (sleepiness)

Front 62

What causes a Hypothalamic Memory Disturbance? Symptoms?

Back 62

- Posterior hypothalamic lesions involving the Mammillary complex
- Associated with inability to form new memories (episodic) for context- and time-specific events

Front 63

What is an example of a cause of Hypothalamic Memory Disturbances?

Back 63

Korsakoff Syndrome - caused by thiamine deficiency associated with chronic alcoholism (not eating enough food)

Front 64

What is Klein-Levin Syndrome?

Back 64

- Hypothalamic lesion in adolescent males (autoimmune?)
- Episodic compulsive eating
- Hypersomnolence - excessive daytime sleepiness
- Hypersexuality
- May result from a decrease in dopaminergic tone during the symptomatic phase of syndrome

Front 65

Which of the hypothalamic nuclei has groups of neurons that synthesize and release Oxytocin, AVP, and CRH?

Back 65

Paraventricular Nucleus

Front 66

Which fiber pathway is a major efferent of the hippocampal formation, and also divides the medial zone of the hypothalamus from the lateral zone?

Back 66

Fornix