Hypothalamus Flashcards
What inputs to the hypothalamus
The entire body:
visual from the superior chiasmatic nucleus
pain from trigeminal
affective info from the limbic system
Does the hypothalamus contain internal sensory neurons
Yes. These neurons respons to changes in glucose and osmolarity and pH
Do circulating hormones directly or indirectly influence the hypothalamus
Yes. It i alo linked to hormonal release via HPA axis
Does the hypothalamus establish biological set points for temperature and osmolarity.
Yes. and it can reflex back via the endocrine and ANS responses in order to get back to these points to resore homeostasis
When can we see the hypothalamus
It is visible only from the ventral surface of the brain. It is also the structure that is beneath the corpus colusum and the thalamus and the third ventricle. The hypothalamus is bordered anteriorly by the lamina terminalis and posteriorly by the mammilary body.
How is it related to the optic chiasm
On the ventral surface the anterior border is the optic chiasm. So right next to it.
How is the hypothalamus connected to the pituitary
It is connected by the infundibular stalk to the pituitary gland. Yhe Hypophesis is in the sella turcica of the sphenoid bone.
What are the parts of the pituitary
The anterior part is from the mouth and the posterior part is from the brain
Tuber cinereum
a hollow eminence of gray matter between the optic chaiasm and the mammillary bodies that is part of the hypothalamus. It is mainly implicated in circadian rhythm
Blood supply
ACA
What are the zones of the hypothalamus
1) Periventricular (around the 3rd ventricles)
2) Middle zone
3) Lateral zone
Lateral zone
Not much cells. Wealth of passing axon fibers. Traversed by many myelinated and unmyelinated axons that are associated with the median forebrain bundle.
What are the zones of the lateral zone
1) the Lateral preoptic nucles
2) Lateral Hypothalamic area
3) Tuberomammillary nucleus
The lateral preoptic nucleus
The lateral preoptic nucleus of the lateral zone is the most anterior portion of the lateral zone. It is an area that develops from the TELENCEPHALON. The lateral preoptic nucleus is specaial because it is in the lateral zone of the hypothalamus and is the only part of the hypothalamus that is derived from the TELENCEPHALON. It doesn’t do much
The lateral hypothalamic area
The lateral hypothalamic area of the lateral zone INDUCES consumption. If electrically stimulated it will induce eating. If ablated it will cause ANOREXIA or STARVATION.
tuberomammillary nucleus
Part of the lateral zone of the hypothalamus that is a compact nuclesu that synthesizes HISTAMINE. HISTAMINE is used as a NT, and this cluser of HISTAMINERGIC neurons that distribute themselves globally to the entire brain.
Sleep and the tuberomammillary nucleus
the HISTAMINERGIC neurons of the tuberomammillary nucleus are ACTIVELY INHIBITED right before you fall asleep
What are the nuclei of the medial zone
1) Medial preoptic nucleus
2) Anterior or super optic zone
3) Middle or tuberal zone
3) Posterior or mammillary region
Medial preoptic nucleus
The medial preoptic area/nucleus houses neurons that regulate gonadotrophin release from the anterior pituitary. The medial preoptic nucleus is SEXUALLY DIMORPHIC. So the interstitial nuclea are located here, and based on the intersitial nuclei of the MEDIAL PREOPTIC NUCLEUS one will have a different gender.
Anterior zone of the middle zone
The BASE of the hypothalamus, which is the suprachiasmatic nucleus. It is called the SUPRACHIASMATIC nucleus because it is above the optic chiasm. The SUPRACHIASMATIC nucleus plays a role in the circadian rhythms and diurnal clocks of the brain. It receives axons directly from the retina via the optic nerve, and then regulates staying awake in response to light.
Anterior Hypothalamic nucleus
WARMTH is sensed by the anterior nucleus of the hypothalamus. Bilateral damage to the anterior hypothalamic nucleus will affect our ability negatively to dissipate heat = HYPERTHERMIA.
The paraventricular nucleus
Adjacent to the third ventricle
Neurons of the paraventricular nucleus
3 types of neurons
1) MAGNOCELLULAR Neurons: Makes peptides like oxytocin and vasopressin/ADH but NOT BOTH. They have huge cell bodies. MAGNOCELLULARly made vasopressin/ADH OR OXYTOCIN is released via the posterior pituitary. It uses the SUPRAOPTICOINFUNDIBULAR pathway that travels inside the INFUNDIBULUM to get from the hypothalamus to the posterior pituitary.
2) Parvocellular neurons
More paraventricular neurons
2 types of PARVOCELLULAR neurons
PARVOCELLULAR neurons
1) Corticotropin releasing hormone, CRH making neurons
These PARVOCELLULAR neurons release CRH at the median eminence, and they go into the hypothalamic portal veins to stimulate the anterior pituitary to make ACTH, and therefore get cortisol from the adrenal cortex. So this is second group of PARVOCELLULAR nuerons is in response to stress.
Neurons that project to the spinal cord - hypothalamospinal tract.
The neurons that project to the spinal cord: Hypothalamospinal tract are responsible for activating the SNS are of the ANS here.
Role of paraventricular zone ?
Heavily linked to the stress response - regardless of the source, the stress pathway neurons terminate HERE.
Bitemporal hemianopsia risk
If there is a tumor that extends downwards, the location or the paraventricular nuclei is just above the optic chiasm. So the patient has the risk of getting bitemporal hemianopsia.
Minimi of the MAGNOCELLULAR neurons
The supraoptic nucleus that sits on top of the optic tract. It makes and releases oxytocin and vasopressin. Therefore hypothalamic oxytocin and vasopressin can come from one of two zones in the anterior region of the middle hypothalamus -either the supraoptic or the paraventricular.
Tuberal Region of the hypothalamus
There are 3 nuclei of the tuberal region.
1) Dorsomedial nucleus
2) Ventromedial nucleus
Nuclei of the tuberal region of the hypothalamus
1) Dorsomedial region: implicated in blood pressure regulation and aggression
2) Ventromedial region
3) Arcuate
Ventromedial region of the tuberal region of the hypothalamus
So it is ventral to the dorsal medial region. It is implicated in FEEDING. However stimulation of the VENTROMEDIAL region will result in HYPERPHAGIA. This is OPPOSITE to the effects of the lateral hypothalamic area. It is also implicated in STOPPING anger associated with the dorsal medial. So if you lesion a cat’s ventromedial hypothalamus you will do the exact same thing as stimulating the dorsal medial hypothalamuc = INCITE RAGE.
ARCUATE nucleus
Located in the tuber cinereum or bulge at the end of the hypothalamus. It has axonal projections to the base of the median eminence where it can release factors, usually inhibitory or hypothalamic hormone releaseing factors in the portal vasculature and therefore get through the body and play a number of roles - feeding is another function here.
ARCUATE nucleus releases
NYP and AGRP as well as GABA. NYP and AGRP are implicated in eating ( appetite will be stimulated). DOPAMINE is produced by the ARCUATE nucleus. The ARCUATE nucleus will use the TUBEROINFUNDIBULAR PATHWAY to get DOPAMINE down to the posterior pituitary. And the DOPAMINE will interact with the anterior pituitary via the portal system and prevent the release of prolactin.
Mammilary zone
Most posterior zone of the medial hypothalamic zone
Nuclei of the mammillary zone
1) Posterior nucleus ( where you sense cold)
2) Mammilary body
Mammillary body
A complex region of several nuclei that receive a MASSIVE input form the hippocampus, so learning and memory implications. Lesioning this will lead to short term memory loss since implicated in PAPEZ CIRCUIT.
Hypothalamic tracts
The hippocampus associated tract.
Hypocampus
Associated with learning and memory and sits in the medial temporal guyrus. Its major fiber output pathway is a band of oxons that run in this oblique path and terminates in the mammillary bodies. This is in the FORNIX. T
Mamillothalamic tract
The mammilothalamic tract : connects the mammillary body to the anterior nucleus of the thalamus
Papez circuit : main structures
The hippocampus
Mammillary body
Anterior thalamic nucleus
Cingulate gyrus
The fornix and the mammilothalamic tract
These are implicated in the Papez circuit
Affective disorders
Lesions anywhere along the Papez circuit
Significance of the Fornix and Mammillothalamic tract
These 2 tracts course through the hypothalamus. Together these 2 tracts will form a division between the MEDIAL zone and the LATERAL zone of the hypothalamus.
Stria Terminalis
Interconnection between the amygdala and the medial hypothalamus. The stria terminalis takes a course that is pretty much the same as the fornix but it will be more medial and considerably thinner.
Median forebrain bundle
Tract adjacent to the stria terminalis. This is the median forebrain bundle. It comes from the brainstem to the rostral midbrain and runs to the lateral hypothalamus. It is the most complicated fiber pathway. For example, the ascending information that goes to the striatum in the BG system is a component as well as the hypothalamospinal thract that originates from the hypothalamus to the spinal cord.
Tuberoinfundibular tract
Connects the arcuate nucleus of the tuberous region to the hypothalamus to the median emminence - and this is how the dopamine that it makes will travel down the infundibulin and be pumped into the blood in order to interact with the anterior pituitary and cause the regulation of prolactin release.
Supraopticophyophyseal tract
Travel from the magnocellular cells of the hypothalmus and project to the posterior pituitary. From the supraopitc nucleus ..project oxytocin and ADH.
Where is ADH and oxytosin made
ADH and oxytocin are made in the hypothalamus.
How does ADH and oxytocin get to the posterior pit
Via the supraopticohypophyseal tract. The infundibulum makes this possible.
Release of anterior pituitary hormones
Via the portal vasculature - so the peptide hormones are released from the hypothalamus into these portal veins that travel to the anterior pituitary and stimulate it to make and secrete more hormones that work systemically- ACTH , GnRH, LSH, FSH, TSH.
Hypothalamospinal tract
Projects to the origin of the SNS in the spine ( so the IML column of T1-L2) from the paraventricular nucleus
Major Hypothalamic Fnx
Body temp regulation Stress responsiveness Feeding and energy Blood pressure and electrolyte composition Reproductive functions
How many nuclei to respond to body temp
2 nuclei that respond to opposite levels of body temp
Warm sensing nuclei
WARM sensing neurons are located in teh ANTERIOR NUCLEUS of the hypothalamus (one of the four in the medial section)
Cold sensing nuclei
COLD sensing neurons in the posterior nucleus in the mammillary division of the medial zone
C fiber neurons in the anterior hypothalamus
The warm C fibers project to the anterior hypothalamus, and the hypothalamic response will be to dissipate heat. Dilateion of cutaneous blood vessels and sweating also INCREASING respiration. All of these are mediated by the ANS. SO detection is in the hypothalamus but the output via the motor neurons is via the ANS, SNS specifically.
Cold response
Blood vessels are constricted, respiration is decreased and thyroid activity is stimulated via TSH in the anterior pituitary and BMR is increased.
Bilateral destruction of the anterior hypothalamic nucleus
Results in HYPERTHERMIA. lack of warm sensation = lack of stimulus to dissipate heat.
Bilateral destruction of the posterior hypothalamic nucleus
Results in inability to regulate temperature at all. The axons of the warm sensing neurons course THROUGH the posterior nucleus on their way to the brainstem. Destruction of the posterior zone will kill the fivers of the posterior and anterior zone. This creates a syndrome where you are unable to regulate your temperature and thus the temperature of your body fluctuates with your environment. This doesn’t mean that temp is not sensed but they are unable to respond to changes - POIKILITHERMIA.
Hypothalamospinal tract
Used by the paraventricular area of the hypothalamus in order to relay the desire to start the SNS and inhibit the PNS to the spine.
SNS response
Increase CO via HR, dilate vessels, dilate bronchi, reduce GI motility, decrease renal activity - so basically a body wide shift in favor of running.
Role of parvaventricular neurons in activating SNS
The parvocellular neurons of the paraventricular nucleus are the ones that release CRH for ACTH and then cortisol. So the paraventricular nucleus is good for activating the SNS and then also increasing cortisiol in the body.
Fear activating SNS
Amygdala sends afferents to the hypothalamus via the stria terminalis. The hypothalamus sends efferents to the SNS and turn it on.
Cortisol response
CRH neurons from the parvocellular neclei in the paraventricular nucleus project to the median eminence and release CRH into the portal system to get the release of ACTH from the anterior pituitary. Cortisol will also reflex back to this pathway and turn off its own synthesis.
Anabolic to catobolic perspective of the body.
Cortisol changes the perspective of the body from anabolic to catabolic in order to free resources that can be used to escape things. You will also get IMMUNOSUPPRESSION.
Center of eating
Lateral hypothalamic area
A satiety center
Ventromedial nucleus of the hypothalamus. This gets you to stop eating.
Arcuate nucleus
The arcuate nucleus at the base of the hypothalamus contain one class of cells that stimulates food intake. These cells are mediated by the NT neuropeptide Y and AGRP, which is AGOUTI RELATED PEPTIDE. Both of these peptides are expressed in the same neurons, colocalized, and these send axons to the 2nd order neurons that live in the ventromedial aspect of the hypothalamus, for example.
Where do the 2nd order neurons that live in the ventromedial hypothalamus that receive axons from the arcuate nucleus go to ?
These send signals that send their axons to the brainstem and specifically the tractus solitarius or the nuclear solirary tract. This does CN7, CN9, CN10 where taste afferents come in as well. There is a satiety centre in the rostral part of the brainstem as well.
Neurons that make POMC and CART
Adjacent to the AGRP and NYP neurons. CART is cocaine amphetamine response transcript. These products have EXACTLY THE OPPOSITE effects.
The function of the POMC and CART products in feeding
The products will INCREASE satiety and DECREASE feeding. Therefore the POMC and CART products are inhibitory on eating.
is LEPTIN related to POMC CART NYP AGRP ?
No
Leptin
This is a hormone produced by fat.
Actions of Leptin
It will be carried through the systemic circulation and when it gets to the hypothalamus it finds its way to the arcuate nucleus. In the arcuate nucleus it inhibits AGRP and NYP neurons. There is will also activate the POMC and CART neurons, thereby decreasign feeding.
Ghrelin
released by the stomach just before a meal and stimulate the AGRP and NYP that activate feeding. Peptide Y will inhibit the Ghrelin neurons.
Insulin
Similar to leptin it will inhibit feeding by inhibiting AGRP and NYP neurons. It will activate the POMC and CART neurons, decreasing feeding.
Plasticity of the ventromedial nucleus of the hypothalamus
The axons project everywhere in the brains adn they can elaborate dentritic trees on a 24-48 hour cycle. They are not as hard wired as we previously thought.
Craniopharyngioma
Congenital tumor ( usually calcified) originating from remnants of Rathke’s puch.
MOST COMMON supratentorial tumor in children
Pressure on chiasm results in bitmeporal memianopia
Pressure on overlying hypothalamus reslsus in “ hypothalamis syndrome” pf adiposity, diabetes insipidus, temeprature regulation disturbances and somnolence.
Wernicke’s encephalitis
One part of beriberi/b1 deficiency. This will affect the eye movement sand cbm/ataxia
Kosakoff syndrome
Caused by thiamine deficiency and associated with chronic alchoholism. It involves mammillary complex associated with inability to form new memories (episodic) for context-and time-specific events.
Klein-Levin Syndrome
Hypothalamic lesion in adolescent males. Episodic compulsive eating Hypersomnolence Hypersexuality May result from a decrease in dopaminergic tone during the symptomatic phase of the syndrome
