Lec 50 Hypothalamus Flashcards
What are the functions of the hypothalamus?
regulates body temp; hunger, thirst, metabolism; emotional states; circadian rhythms; sleep/wake; reproductive functions
What are the 3 main output functions of the hypothalamus?
- direct control of pituitary
- regulation of autonomic nervous system
- reciprocal connections to regions of brain, spinal cord including limbic system
Where is the hypothalamus locaed?
- midline bilaterally symmetric around 3rd ventricle just ventral to the thalamus and dorsal to the optic chiasm
What is the mnemonic for hypothalamus function from first aid?
hypothalamus wears TAN HATS
Thirst and water balance
Adenohypophysis control [anterior pituitary]
Neurohypophysis releases hormones produced in hypo
Hunger
Autonomic regulation
Temp regulation
Sexual urges
What are the two inputs to the hypothalamus not covered by the blood brain barrier?
OVLT = organum vasculosum of lamina terminalis – senses changes in osmolaterity
area posterma - responds to emetics
Where is ADH made?
hypothalamus supraoptic nucleus
Where is oxytocin made?
hypothalamus paraventricular nucleus
What is the function of the preoptic area and anterior hypothalamus?
thermoregulatoin
fluid and electrolytebalance
sexual behavior
sleep [ventrolateral preoptic area]
What is the function of the arcuate nucleus [infundibulum]?
feeding, body weight [site of major feeding peptides NPY, AgRP, a-MSH]
release DA to AP –> inhibit prolactin secretion
site of GHRF –> secrete GHRH to promote GR release from pituitary
What is the function of the suprachiasmatic nucleus?
circadian rhythm –> you need SLEEP to be CHARISMATIC [chiasmatic]
What is the function of ventromedial nucleus?
satiety [decrease feeding, drinking, body weight]
“if you zap the ventromedial nucleus you grow ventrally and medially”
What is the function of the posterior thalamus vs anterior?
anterior = A/C = cooling and parasympath
posterior = heating and sympathetic
What happens if ventromedial area of hypothalamus destroyed [ie craniophayngioma]?
have hyperphagia
What is effect of leptin on ventromedial hypothalamus?
leptin stimulates ventromedial area
What is function of dorsomedial nucleus of hypothalamus?
decrease feeding, drinking, body weight [satiety]
What is function of lateral hypothalamus?
increase feeding, body weight= hunger
“if you zap your lateral nucleus, you shrink laterally”
site of orexin = regulates sleep-wakefulness
What happens if lateral area of hypothalamus is destroyed?
anorexia, failure to thrive [infants]?
What is function of leptin on lateral hypothalamus?
leptin inhibits lateral area
What are the two types of cells in paraventricular hypothalamus? their function?
magnocellular = make oxytocin, vasopression [ADH] and project directly to PP
parvocellular = make releasing factors [CRH, TRH, GnRH] that influence the AP
What is function of tuberomammillary area of hypothalamus?
synthesizes histamine
What is the function of the supraoptic nucleus of hypothalamus?
magnocellular neurons that make ADH and project directly to posterior pituitary = main site of ADH synthesis
What is function of mammillary nuclei?
limbic structure, regulates memory [especially olfactory]
receives input from hippocampus via fornix
What is the basal nucleus of meynert?
kind of part of the hypothalamus
sends cholinergic projections to hippocampus
promotes learning, memory
Which neurons in paraventricular nucleus of hypothalamus act via pituitary portal system?
parvocellular neurons send axons to base of hypothalamus to release their peptide transmitters into capillary sinus that forms the pituitary portal system, provides blood to AP where releasing factors act on endocrine cells there to stimulate release of all AP major hormones
What is the path of hypothalamic-pituitary-adrenal [HPA] axis?
parvocellular nerves in hypo paraventricular nucleus secrete CRF [corticotropin releasing F] –> via pituitary portal system –> anterior pituitary corticotrophs –> release corticotropin that goes through circulation to adrenal cortex –> adrenal cortex releases glucocorticoids
–> glucocorticoids feedback and inhibit AP and paraventricular nucleus from secreting CRF/C
What is the best measure of hypothyroidism?
high TSH in blood –> when person does not have enough T3/T4 there will be loss of negative feedback inhibition
What are 2 important inputs to the hypothalamus that coordinate its control over bodily functions?
nucleus of solitary tract and reticular formation
what is path by whcih SCN entrains circadian rhythm to light-dark cycles? How does light turn this on and off?
- SCN receives innervation from optic nerve [directly + indirectly via thalamus]
- SCN innervates SCG [superior cervical sympathetic ganglion] which then innervates pineal
- sympathetic [NE] activation of pineal gland causes release of melatonin
Light = turns of superior cervical ganglion –> melatonin only released during dark [true whether animal diurnal or nocturnal]
SCN entrains rest of body by regulation neuroendocrine and pre-autonomic neurons via PVN and SON
What is the molecular basis of “molecular clock”?
- Clock and Bmal form dimers –> control expression of gene Period–> Period inhibits function of Clock:Bmal thus suppressing its own synthesis; meanwhile period has stead rate of degradation
- causes cycle of Period/Clock expression every 24 hr [when Period = high; clock = low]
this functions autonomously in absence of SCN entrainment
What is orexin? where is it made?
made in lateral hypothalamus
- promotes wakefulness, arousal, motivation
Where does orexin project?
- to histamine neurons in tuberomammillary nuc
- to NE neurons in locus ceruleus
- to 5HT neurons in dorsal raphe
- to DA neurons in VTA
- ACh neurons in pontine tegmentum
What is role of orexin in narcolepsy?
orexin knockout mice have narcolepsy-like syndromes
What is the most important sleep-promoting nucleus?
ventrolateral preoptic area [VLPO]
what is function of ventrolateral preoptic area?
- uses GABA NT and becomes active in onset of sleep
- inhibits tuberomammillary histamine nurons and lateral hypothalamus orexin neurons
- loss of orexin quiets ARAS [ascending reticular activating system]
- quiet thalamocortical circuits allows large syndchronized EEG waves characteristic of sleep
What is mech of onset of NREM sleep
- VLPO DOPA neurons inhibits tuberomammillary histamine nurons and lateral hypothalamus orexin neurons
- loss of orexin quiets ARAS [ascending reticular activating system]
- quiet thalamocortical circuits allows large syndchronized EEG waves characteristic of sleep
What is mech of onset of REM sleep?
- 5HT/NE “Rem-Off” cells stop firing
- triggers activation of specific PPT/LDT “Rem-on” cells that activate thalamic neurons resulting in more wake-like EEG
Where do general anesthetics act on sleep path?
activate VLPO
Where do H1 antagonists for insomnia at?
on TMN [tuberomammillary nucleus]
Where do older antidepressants disrupt sleep [especially REM] path?
affect rem-on/rem-off cells
how do you treat narcolepsy?
amphetamine
What is role of adenosine in sleep?
accumulates in VLPO as a function of duration of wakefulness, declines during periods of sleep
