10. Hypothalamus Flashcards
homeostasis:
define
- integrated physiological processes to maintain the internal environment of the body w/in narrow physiological range in response to changing environment
- based on theory of milieu interieur (constant internal environment)
key fxn of hypothalamus?
to maintain homeostasis, which means “similar position”
what allows the hypothalamus to maintain homeostasis?
broad circuitry of inputs/outputs of hypothalamus
- inputs: peripheral sensory information, cortex, limbic areas
- outputs: ANS and Pituitary
hypothalamus: general functions
Control:
- BP & electrolyte come
- body temp
- energy metabolism
- reproduction
- emergency responses to stress
what is found at the anterior-most aspect of the hypothalamus?
anterior commissure, lamina terminalis, and optic chiasm
what is found at the posterior-most aspect of the hypothalamus?
mamillary bodies
divisions of hypothalamus, from medial –> lateral
- medially: periventricular zone, and the arcuate nucleus
- then, ventromedial and dorsomedial nuclei
- the lateral zone incl. the supraoptic nucleus
hypothalamic nuclei to know, from ANTERIOR –> POSTERIOR
- preoptic
- suprachiasmatic
- paraventricular
- supraoptic
- arcuate
- mamillary
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important tracts and other structures to know for hypothalamus
- column of fornix (tract)
- anterior pituitary
- posterior pituitary
brief location of hypothalamus in relation to other structures
optic chiasm –> anterior portion
optic tract –> intermediate portion
mamillary bodies –> posterior portion
anterior division of hypothalamus:
nuclei and functions
In general: controls behaviors more aligned w/ rest/digest type fxns
- preoptic –> heat loss
- supraoptic & paraventricular –> water balance, milk ejection, uterine contraction
- suprachiasmatic –> circadian rhythm
Other fxns: thirst, sleep, parasympathomimetic
intermediate division of hypothalamus:
nuclei and functions
- tuberal and arcuate nuclei –> endocrine activity
Other fxns: satiety, feeding, emotions
posterior division of hypothalamus:
nuclei and functions
- mammilary nuclei –> consolidation of memory (pt of Papez circuit)
Other fxns: heat conservation, arousal, aggressive behavior, analgesia, sympathomimetic
match key function w/ corresponding hypothalamic nuclei:
heat loss
preoptic nuclei
(anterior division)
match key function w/ corresponding hypothalamic nuclei:
water balance, milk ejection, uterine contraction
supraoptic & paraventricular
(anterior division)
match key function w/ corresponding hypothalamic nuclei:
circadian rhythm
suprachiasmatic nuclei
(anterior division)
match key function w/ corresponding hypothalamic nuclei:
endocrine activity
arcuate and tuberal nuclei
(intermediate division)
match key function w/ corresponding hypothalamic nuclei:
consolidation of memory
mammillary nuclei
(posterior division) – part of broader circuitry in the Papez circuit
rhythms such as diurnal rhythms (sleep/wake cycle) and hormonal rhythms are controlled by which nucleli?
suprachiasmatic nucleus in anterior hypothalamus;
- receives visual inputs from the retina –> allows body to synchronize intrinsic pacemaker to the day/night cycle based on light
- *Synchronizing with wake/sleep cycle is the key function of circadian system
where do axons of the optic nerve terminate w/in the brain?
4 nuclei
- lateral geniculate nuclei (LGN) of thalamus
- superior colliculus of midbrain
- pretectum of midbrain
- suprachiasmatic nucleus of hypothalamus
functions of the 4 nuclei where the optic nerve terminates?
- LGN –> visual perception
- superior colliculus –> control of eye movements
- pretectum –> control of pupillary light reflex
- suprachiasmatic nucleus –> control of diurnal rhythms and hormonal changes
entrainment:
definition
occurs when rhythmic physiological or behavioral events match their period to that of an environmental oscillation
(caused by suprachiasmatic nucleus)
association of light and rhythms
- light –> synchronizes pacemaker-like activity in Suprachiasmatic Nucleus (SCN) –>
- outputs of SCN –> neural, hormonal, and behavioral outputs
leptin:
define
protein produced by fat cells;
if increase in # of fat cells –> more leptin
relationship of leptin & feeding
(inc. in fat cells) –> increase in leptin –> decrease in feeding
(inversely related)
what happens if mouse LACKS leptin gene
–> increase in feeding –> mouse becomes obese
fxn of arcuate nucleus
integrates multiple satiety and hunger signals
2 major arcuate projections and respective effects
-
paraventricular nucleus (PVN): effects on cellular metabolism via regulation of endocrine system and ANS
- (TSH and ACTH)
- lateral hypothalamic area (LHA): effects on feeding behaviors
thermoregulation pathway:
inputs to hypothalamus
- thermoreceptors in skin
- blood temp monitored by central thermoreceptors of hypothalamus
Either can detect inc or dec in body temperature
heat loss response (if body temp is inc)
triggered by hypothalamus
- vasodilation of surface blood capillaries –> to inc heat loss by radiation
- increased sweating
- relaxation of erector pili muscles –> hairs lie flat
- dec metabolic rate
- (and behavioral component, like taking off jacket if too hot)
heat conservation response (if body temp is dec)
triggered by hypothalamus
- vasoconstriction of surface blood capillaries –> reduce heat loss by radiation
- reduce sweating
- contract erector pili muscles – hairs pulled upright
- shivering
- increased metabolic rate
regulation of water intake:
2 types of thirst
- volumetric thirst <– from decreased blood volume (i.e. hemorrhage)
- osmometric thirst <– from dehydration/ hypertonicity (inc. in blood solutes)
outputs of hypothalamus from thirst:
PVN
- paraventricular nucleus (PVN) in hypothalamus –>
- increases antidiuretic hormone (ADH)/vasopressin
- inc water retention; and dec urine production –>
- returns fluid volume to homeostatic levels
outputs of hypothalamus from thirst:
lateral hypothalamic area (LHA) of hypothalamus
- lateral hypothalamic area (LHA) of hypothalamus –>
- directly stimulates thirst and drinking
(promote the sensation of thirst to encourage the behavior)
hypovolemic thirst:
inputs to hypothalamus
- KIDNEYS detect reduced blood flow –> inc renin –> inc angiotensin ii –> act on hypothalamus –> release ADH/vasopressin –> inc water retention/ dec urine production
- CARDIOVASCULAR SYSTEM detects reduced BP –> vasoconstriction to counteract blood loss –> hypothalamus –> (same final steps as other)
how is hypothalamus related to emotion?
- hypothalamus is connected to limbic system structures by the fornix
- hypothalamus mediates autonomic manifestations of emotion
