Hypothalamus-Polston Flashcards
What is the hypothalamus?
- it regulates the homeostatic responses that are endocrine
- the boss of the autonomic system
- it gets sensory input
What are the hypothalamic inputs?
????
Why is the hypothalamus able to detect????
it has circumventricular organs
OVLT forms the front wall of the 3rd ventricle
What are the basic hypothalamic functions?
-the main source of central control over homeostasis
descending PS/sympathetic tract comes from the hypothalamus (Horner’s syndrome)
regulates the anterior and posterior pituitary gland (master gland that regulates all the other endocrine glands)
regulates our physiological drives (thirst, body temp, sexual behaviors)
-intimately associated with the limbic system which is responsible for learning motivational state desire, reward
Where is it located?
at the very base of the brain; sits on both sides of the 3rd ventricle; sits directly below the thalamus but above the pituitary gland
external landmarks: sits under optic chiasm (rostrally); has two bumps on the posterior side (mammillary bodies); in the middle is the median eminence (pituitary stalk blobbed onto it)
internal landmarks: 3rd ventricle and lateral ventricle meet and on both side of the 3rd ventricle is the hypothalamus; large descending tract called fornix that tells hypothalamic neurons whats going on in the limbic system
sagittal view: 3rd ventricle is inferior to the corpus callosum and you can still see the median eminence
What are the division of the hypothalamus?
1) Anterior hypothalamus
2) Midlevel hypothalamus rostral: optic chiasm splits into optic tract
3) Midlevel hypothalamus caudal
- Arcuate and ventromedial nuclei: important for feeding behavior
4) Posterior hypothalamus
Anterior hypothalamus
OVLT is important in reproductive function; surrounding it are neurons that release GnRH; they are responsible for ovulation in women as they detect progesterone and estrogen levels
Medial preoptic area – Water balance, blood pressure
Sexually dimorphic nucleus of the preoptic nucleus (SDN-POA) – Male sexual behavior: brain sexual differentiation between male and female;
Midlevel hypothalamus rostral
Suprachiasmatic nucleus (SCN):
- light detecting nucleus
- above the optic chiasm
- regulates circadian rhythm
- Direct input from retina via retino-hypothalamic tract
- Per and tim genes identified in Drosophila as major players: period and time; respond to the light dark signals
- is basically on a 12 hour cycle
Regulates 24 h circadian rhythm (12-12)
- dark is when rat is not moving as much; white is
- if you lesion the SCN they have no circadian rhythm anymore (bottom pic)
Midlevel hypothalamus caudal
Lateral Cell Groups
- More of an ‘area’ than a ‘nucleus’
- Multiple neuronal phenotypes
- orexin neurons: deals with feeding (anorexia= no feeding drive); involved in sleep and wakefulness: area where the optic chiasm is starting to split out into the tracts
Supraoptic Nucleus (SON)
- Magnocellular neurons
- produces two cells that release oxytocin (OT) and vasopressin (VP) into the periphery via the posterior pituitary gland; are a product of the posterior pituitary gland
- OT stimulates smooth muscle contraction related to reproduction (uterus and mammary gland); where the receptors are present is specific to uterus and mammary gland
- VP regulates water balance and blood pressure; acts on the kidney and vasculature
Paraventricular Nucleus (PVN)-IMPORTANT
- also has magnocellular OT and VP neurons that release their product through the posterior pituitary gland
- make an arch shape structure need to get ot the median eminence to get to the pituitary gland
- Parvicellular OT and VP neurons – centrally projecting neurons implicated in mood disorders and social bonding.
- OT (“The Love Hormone”) is especially implicated in bonding. May be clinically useful in autism (lack of social bonding in this disorder)–> related to monogamy; OT does not cross the BBB so has to be administered nasally; may help autistic children connect with other people (bond)
-Other parvicellular neurons act as neuroendocrine releasing and inhibiting factors that regulate anterior pituitary hormones (this is how the hypothalamus regulates the pituitary gland which is the master of endocrine function)
Mediobasal Hypothalamus –
Ventromedial Nucleus
-which is stained for estrogen receptors; Primary regulator of female sexual behavior (in rodents)
Mediobasal Hypothalamus – Arcuate Nucleus
- arcuate encapsulated by a fiber capsule FROM the rest of the hypothalamus
- Has specialized cells called tanycytes, with end feet that can sample the CNS (kind of like a circumventricular organ but is not)
- Detection of nutrient-related solutes across the blood-brain-barrier (like glucose)
Regulates mael and female sexual behavior
snpoa (male)
–
Ventromedial Nucleus (female)
Posterior hypothalamus
Posterior nucleus
-is important for thermoregulation (make me sweat)
remember anterior nucleus responds to HIGH body temps
posterior responds to LOW body temps (make me shiver)
-mammillary bodies: major output from the hypothalamus to the limbic system
remember fornix is from limbic system to hypothalamus
This pathway is strongly implicated in adding emotional salience to hypothalamic functions.
What controls emotion and sex drive?
emotions limbic system
sex drive: hypothalamus
PPG/ APG
Posterior pituitary gland: axons are here; neurons that produce hormones released from posterior pituitary gland
Anterior pituitary gland: controlled by parvocellular neurons; don’t send all their axons down but they have????; release their products into the median eminence
Posterior pituitary gland
induces water retention
ADH=vasopressin
-induce labor in women
Anterior pituitary gland
Parvicellular neurons (mostly in the paraventricular nucleus) produce hypothalamic releasing and inhibiting factors are that are released into the median eminence and are then transported to the anterior pituitary through the pituitary portal vasculature
go into the bloodstream
