- Anatomical References: anterior/rostral, midsagital/coronal/horizontal
- Axon is different from dendrites in that axon's diameter is the same throughout.
- Myelin is the white matter. Outerlayer in spine and inner layer (surrounded by cortex) in brain.
Tract: a collection of nerve fibers with a common origin and destination. ex: corticospinal/pyramidal tract, hypothalamo-hypophyseal tract.
Formation of neural tube.
- Differentiation of brain area:
--Forebrain: Telecephalic vesicles (cerebral cortext), diencephalon (hypothalamus), optic vesicles,
- Ventricular system: lateral (2), third, and fourth ventricles. They also receive neuropeptides and transmitters. Most endocrine cells sit on ventricles.
- cerebral cortex: prominent in primates and humans.
- Corpus callosum: at base of cortext, biggest tract, connect two hemisphere
- biencephalia : sit under 2 hemispheres, sensory travels through here, plays a regulatory role.
- pons and medullla: pacemaker.
- There's a groove that marks the edge of hypothalamus and thalamus.
- major structures in forebrain at the thalamus-telecephalon junction :
--lateral ventricles, thalamus, third ventricle, hypothalamus, basal forebrain, temporal lobe, lateral/Sylvian fissure, insula, frontal lobe.
1.3Anatomical organization of neuroendocrine hypothalamus¶
- Important neuropeptides:
--hypothalamic releasing factors: CRH, GHRH, gnRH, Somatostatin, TRH
--Mostly regulate anterior pituitary.
--CRH and GHRH: have to do with sleep cycle.
--Neurohypophyseal peptides: oxytocin, vasopressin
Those neuropeptides are produced in hypothalamus. they might also have function in the brain as neuromodulators.
Hypothalamus is connected to major effector areas of the brain, such as limbic (emotional behaviours), lower brainstem, spinal cord, thalamus, and connection with neocortex via limbic system.
Outputs of hypothalamus:
--humoral: to pituitary. steroids, peptide hormones,
--neural outputs: to limbic, thalamus, and brain stem.
--inputs: from all kinds of places.
in hypothalamus: Parvo hypothalamic neurons (10micrometer, small cell) and magnocellular neurons (24micrometer, very big)
2Nuclear groups and zones of "hypothalamus"¶
Rostral to caudal: preoptic, anterior, tuberal, mammillary.
Preoptic: regulation of hormonal and neural activities of sexual and reproductive behaviors.
- Anterior and tuberal: classical endocrine activities and sometimes act with parts of preoptic. Has big nuclei, connected to limbic system and thereby regulate aggressive and repetitive behaviors.
- Mammillary : chiefly limbic system itself, connected to hippocampus.
Medial to lateral: Periventircular, medial, lateral:
Periventricular zone :
--majority of neuroendocrine nuclei, predominantly intrahypothalamic connections
--almost all neural endocrine nuclei reside here. Contain macrocellular, oxyoxin, vasopressin, axons to media eminence, mmagnocellular neurons, parvo neurons (with their axons extend to pituitary).
- Medial zone: lare nuclei involved in initiation of motivated behaviors such as aggressive or appetitive behaviors. extensive connections throughout the brain, many sensory inputs (usually via limbic: amygdala, hippocampus) and through brainstem nuclei relaying visceral info (such as nucleus of solitary tract).
- Lateral zone: functional importance is hard to study because it's traversed by medial forebrain bundle. Has to do with general arousal (lack of orexins/hypocretins lead to narccolepsy).
- ependyma: lining of ventricles (in this case, on third), where neuroendocrine neurons sit.
- preoptic area: at the level of optic chiasm
- anterior thalamic, dorsalmedial, and ventormedial nuclei: medial to preoptic, rich onnection to hypothalamus, lymbic system, and brainstem in regulation in repetitive behaviors (food intake, sexual behaviours, etc).
2.3Between Preoptic and Anterior¶
- anterior hypothalamus: optic chiams is ending, has optic track, has suprachiasm nucleus(SCh) which regulates circadian rhythm.
-reduced production in hypocretin (a neuropeptide in lateral hypothalamus) leads to narcrolepcy.
- Paraventricular nucleus (PVN): butterfly shape nucleus on top of third ventricle. has magnocellular neurons on the lateral and pavocellular neurons more medial.
- Periventricular nucleus (PeA): lining on the third ventricle.
- supraoptic nucleus zone (SON):
--in lateral zone of hypothalamus (very lateral),
--born right next to optic chiasm and retinoid axons
--part of PVN that's exclusively magnocellular, but gets separated from PVN during development by growth of hypothalamic neurons and optic track.
--with magnocellular of PVN: endocrine system that decide either to make oxytoxin or vasopressin.
--together with PVN, largest nucleus.
- Arcuate nucleus (Arc): sit right above median eminence (ME), complicated structure, many neuroendocrine neurons reside here, lateral part release GHRH.
- Median eminence (ME) : site where all neuroendocrine neurons that release hypophyseal hormones, major site of ant. pituitary regulation by releasing hypophyseal hormones.
- post. pituitary : originates from base of the diencephalon (neuroectoderm), has no neural cell body but only axon terminal. Basically part of the neural tissue.
- ant. pituitary: arises from Rathe's pouch (entoderm)
- Opiate peptides (b-endorphin, dynorphin, etc)
- Neurohypophyseal peptides (oxytocin, vasopressin/antidiuretic hormone) : made in hypothalamus and released in pituitary.
- Pituitary hormones (ACTH, b-endorphin, GH, prolactin, FSH, LH, TSH) : made in pituitary upon stimulation by signals from hypothalamus.
- three cell type staining: acidophilic cell, basophilic cell, chromophobic cell (doesn't stained).
- very nicely stained comparing to posterior lobe.
|Cell type||Secretion||target||Location in the lobe||Staining|
|Corticotrope||ACTH (upon stress)||Adrenal Cortex||Dorsal||chromophobic|
|gonadotrope||FSH and LH||gonads||ventral||basophilic|
- GH (growth hormone) : aka somatotropin, stimulate growth of bone and muscle, protein synthesis, and carbohydrate metabolism mediate by IGF-1 (insulin-like growth factor-1)
- ACTH (adrenocorticotropic hormone) : stimulate glucocorticoid (cortisol) secretion from adrenal cortex.
- TSH (thyroid-stimulating hormone): aka thyrotropin, stimulates T3 and T4 from thyroid gland.
- FSH (follicle-stimulating hormone): follicle growth and estragen secretion in females, sperm production and inhibin secretion in males.
- LH (luteinizing hormones) : stimulates ovulation, formation of the corpora lutea, progesterone secretion in females. androgens from leydig cells (in males).
- PRL : milk production and secretion.
- has many folds of ER. many secretory granules.
- large capillaries space
- light nucleus (chromatin unfolded)
- large pericapillary space.
- poorly developed in human.
- mostly basophilic
- produce B-endorphin and MSH (melanocyte stimulating hormone) --> skin darkening.
3.4Posterior lobe (lobus nervosus)¶
- Has many blood vessels
- formed by terminations of neurosecretory axons from hypothalamo-hypophyseal tract and fenetrated capillaries
--PVN: paraventricular neurosn producing vasopressin and oxytocin--> paraventricular hypophyseal tract.
--SON: supraoptic neurons producing vasopressin and oxytocin --> supraopti-hypophyseal tract.
- The neurosecretory axons are swelled and has varicosities, filled with neurosecretory granules: Herring bodies (could be stained by GOMORI)
- pituicytes: specialized glial cells, provide suppport and metabolic function for neuro-secretory axons.
contain those cells only: pituicytes and endothelial cells and pericytes of capillaires.
much denser than ant. pituitary.
- little capillaries space.
- Vasopressin (VP) : aka antidiuretic hormone, promotes water-readsorption in kidneys and elevate blood pressure.
- oxytocin : smooth muscle contraction
4Parvocellular system of neuroendocrine hypothalamus¶
- extend axons (unmyelinated) to median eminance
- control ant. pituitary by releasing hypophysiotropic hormones through hypophyseal portal veins.
- hypophysiotropic hormone: hormone that's present in ME.
|PVa||Anterior periventircular nucleus|
- DMN, PVN, VMN
- 41 aa , very lage
- diumal pattern of release
- stimulator of ACTH and b-endorphin
- DMN, VMN, PVN, ARC, PVa
- also neuromodulator in ANS
- ARC, FOA, ah
- increase release of FSH, LH
- increase GH
- inhibitor of prolactin release
- release of MSH
- POA, ah, DMN, VMN, Arc, PVa
- inhibit release of GH, TSH, PRL (act mostly as inhibitor of secretion)
- antagonist to GHRH, TRH
- widespread throughout the brain outside hypothalamus and periphery.