Wednesday, January 11, 2012

Neuroanatomy

1Basics:¶

1.1Overview¶

• 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,
  --midbrain
  --hindbrain

1.2Brain Areas¶

• 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"¶

2.1Overview¶

• 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).

2.2Preoptic¶

• 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.

2.4Anterior¶

• 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.

2.5Tuberal¶

• 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.

3Pituitary Gland/Hypophysis¶

• 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)

3.1Biopeptides¶

• 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.

3.2Anterior lobe¶

• three cell type staining: acidophilic cell, basophilic cell, chromophobic cell (doesn't stained).
• very nicely stained comparing to posterior lobe.

3.2.1Cell type¶

3.2.2Hormones¶

• 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.

3.2.3Ultrastructure¶

• has many folds of ER. many secretory granules.
• large capillaries space
• light nucleus (chromatin unfolded)
• large pericapillary space.

3.3Intermediate lobe¶

• 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.

3.4.1Ultrastructure¶

• 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.

3.4.2Hormones¶

• 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.

CRH

• DMN, PVN, VMN
• 41 aa , very lage
• diumal pattern of release
• stimulator of ACTH and b-endorphin

TRH

• DMN, VMN, PVN, ARC, PVa
• also neuromodulator in ANS

GnRH

• ARC, FOA, ah
• pulsatile
• increase release of FSH, LH

GHRH

• 44aa
• increase GH

Dopamine

• inhibitor of prolactin release
• release of MSH

Somatostatin

• 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.