UNSW Embryology

Neural System Development - Ventricular System

© Dr Mark Hill (2008)

Acknowledgements

Introduction

The ventricular system develops from the single cavity formed from the hollow neural tube. This fluid-filled space is separated from the amnion following fusion of the neural tube and closure of neuropores. At different regions sites within the wall (floor of lateral ventricle and roof of the third and fourth ventricles) differentiate to form choroid plexus a modified vascular structure which will produce Cerebrospinal fluid (CSF) (More? Cerebrospinal Fluid).

Chorid plexus in the developing human brain (Stage 22)

In development and the space within the spinal cord (central canal) and the brain (ventricles) was derived from the same space within the neural tube. In the adult these 2 spaces remain connected containing the same CSF.

Early in development the cavity within the neural tube (which will form the ventricular space) is filled with amniotic fluid. As the brain and spinal cord grow, this fluid filled space makes up the majority of the nervous system (by volume). Upon closure of the neuropores and development of the embryonic vasculature, this fluid is then synthesized by the choroid plexus, a specialized vascular epithelium. In mammals, the choroid plexuses develop at four sites in the roof of the neural tube shortly after its closure, in the order forth (IV, lateral, and third (III) ventricles.

Choroid Plexus in lateral ventricle (Week 10 fetus)

The choroid plexuses form one region of the blood-brain barrier that regulates the brain's internal environment.

Normal CSF contains high amounts of salts, sugars and lipids and low amounts of protein (0.3-0.7 microg/microL), though there appears to be 60+ proteins as identified by 2D gel. Presence of some protein in the CSF can be indicative of disruption of or incomplete blood/brain barrier.

Page Links: Introduction | Some Recent Findings | Development Overview | Stage 22 Embryo | CSF Synthesis | Alpha-fetoprotein | Adult CSF Normal Values | CSF Circulation | CSF Abnormalities | References | Glossary | Terms

Other Pages: Cerebrospinal Fluid | CSF Production

Some Recent Findings

Heep A, Bartmann P, Stoffel-Wagner B, Bos A, Hoving E, Brouwer O, Teelken A, Schaller C, Sival D. Cerebrospinal fluid obstruction and malabsorption in human neonatal hydrocephaly. Childs Nerv Syst. 2006 Oct;22(10):1249-55.

"In neonatal posthaemorrhagic high-pressure hydrocephalus (HC), high concentrations of malabsorption-related biomarkers contrast with lower concentrations in spina bifida and non-haemorrhagic triventricular HC. During the early development of high pressure HC in spina bifida neonates, CSF biomarkers strongly indicate that CSF obstruction contributes more to the development of HC than malabsorption."

Patelska-Banaszewska M, Wozniak W. The subarachnoid space develops early in the human embryonic period. Folia Morphol (Warsz). 2005 Aug;64(3):212-6.

Development Overview

Ventricles and Central Canal

Stage 11 - appearance of the optic ventricle. The neural groove/tube space is initially filled with amniotic fluid.

Stage 12 - closure of the caudal neuropore, onset of the ventricular system and separates the ependymal from the amniotic fluid

Stage 13 - cavity of the telencephalon medium is visible

Stage 14 - cerebral hemispheres and lateral ventricles begin, rhomboid fossa becomes apparent.

Stage 15 - medial and lateral ventricular eminences cause indentations in the lateral ventricle

Stage 16 - hypothalamic sulcus is evident

Stages 17-18 - interventricular foramina are becoming relatively smaller, and cellular accumulations indicate the future choroid villi of the fourth and lateral ventricles

Stage 18 - areae membranaceae rostralis and caudalis are visible in the roof of the fourth ventricle, and the paraphysis is appearing.

Stage 19 - choroid villi are visible in the fourth ventricle, and a mesencephalic evagination (blindsack) is visible

Stage 20 - choroid villi are visible in the lateral ventricle

Stage 21 - olfactory ventricle is visible

Stages 21-23 - lateral ventricle has become C-shaped (anterior and inferior horns visible). Recesses develop in the third ventricle (optic, infundibular, pineal).

Fetal Period - posterior horn of the lateral ventricle, choroid plexus of the third ventricle, suprapineal recess, interthalamic adhesion, aqueduct, and apertures in the roof of the fourth ventricle.

(Data from: O'Rahilly R, Müller F., 1990)

Choroid Plexus Development

Epithelium from the neural tube epithelium.

Mesenchyma from the meninges.

Enzymes required for CSF production are Na+/K+ ATPase and carbonic anhydrase.

Subarachnoid Space Development

Stage 14 (33 days) - initially as irregular spaces on the ventral surface of the spinal cord.

Stage 18 (44 days) - dura mater is formed and spaces surround the circumference of the spinal cord, which coalesce and contain many blood vessels.

(Data from: Patelska-Banaszewska M, Wozniak W., 2005)

There are also several good research articles and reviews from the 1980's and 1990's on CSF development.

Reviews:

Catala M. Embryonic and fetal development of structures associated with the cerebro-spinal fluid in man and other species. Part I: The ventricular system, meninges and choroid plexuses. Arch Anat Cytol Pathol. 1998;46(3):153-69.

Osaka K, Handa H, Matsumoto S, Yasuda M Development of the cerebrospinal fluid pathway in the normal and abnormal human embryos. Childs Brain. 1980;6(1):26-38.

Articles:

O'Rahilly R, Muller F. Ventricular system and choroid plexuses of the human brain during the embryonic period proper. Am J Anat. 1990 Dec;189(4):285-302.

Osaka K, Handa H, Matsumoto S, Yasuda M Development of the cerebrospinal fluid pathway in the normal and abnormal human embryos. Childs Brain. 1980;6(1):26-38.

Stage 22 Embryo

Head Stage 22- blue box (lower right) shown in image below

Chorid plexus in the Stage 22 Human Brain

Chorid plexus

See also: A section of Stage 22 human head, and a high power image of choroid plexus from this same section.

 

CSF Synthesis

Two key enzymes are required to produce CSF they are the Na+/K+ ATPase and carbonic anhydrase.

Other known chorid plexus enzymes include: alkaline and acid phosphatases, magnesium-dependent ATPase, glucose-6-phosphatase, thiamine pyrophosphatase, adenylate cyclase, oxidoreductase, esterases, hydrolases, cathepsin D, and glutathion S-transferase. (More? Catala M., 1998)

"The epithelial cells of the choroid plexus secrete cerebrospinal fluid (CSF), by a process that involves the movement of Na(+), Cl(-) and HCO(3)(-) from the blood to the ventricles of the brain. This creates the osmotic gradient, which drives the secretion of H(2)O. The unidirectional movement of the ions is achieved due to the polarity of the epithelium, i.e., the ion transport proteins in the blood-facing (basolateral) are different to those in the ventricular (apical) membranes."

(text from: Speake T, Whitwell C, Kajita H, Majid A, Brown PD. Mechanisms of CSF secretion by the choroid plexus. Microsc Res Tech. 2001 Jan 1;52(1):49-59. Review.)

CSF Reabsorption

Arachnoid Granulation (image: Gray's Anatomy)

CSF drainage (absorption or reabsorption) into the venous system is through arachnoid granulations.

CSF in the subarachnoid space extends into the arachnoid granulations, which then project through the dura into the superior sagittal sinus.

See also note in CSF Circulation section, point 3.

Alpha-Fetoprotein (AFP)

"AFP is produced by both the yolk sack and fetal liver. At around 12 weeks of gestation, the yolk sack degenerates and the fetal liver becomes the main site of AFP synthesis. Concentration of this protein in the fetus is very high (1-10 mg/ml), but it decreases abruptly soon after the birth (by the end of second month postpartum, only a trace amount of AFP can be detected), and it is almost completely substituted by serum albumin. It has been also established that variation in the AFP content during pregnancy can be of use for the detection of fetal abnormalities, including Down's syndrome and open neural tube, defects, such as spina bifida."

(text from:GillespieJR, Uversky VN. Structure and function of alpha-fetoprotein: a biophysical overview. Biochim Biophys Acta. 2000 Jul 14;1480(1-2):41-56.)

Adult CSF Normal Values (Lumbar CSF)

Opening pressure: 50–200 mm H2O CSF

Color: Colorless

Turbidity: Crystal clear

Mononuclear cells: less than 5 / mm3

Polymorphonuclear leukocytes: 0

Total protein: 22–38 mg/dl Range 9–58 mg/dl (mean ± 2.0 SD)

Glucose: 60–80% of blood glucose

(Data from: Clinical Methods, 3rd ed, Table 74.1)

CSF Circulation

Greitz D. Cerebrospinal fluid circulation and associated intracranial dynamics. A radiologic investigation using MR imaging and radionuclide cisternography. Acta Radiol Suppl. 1993;386:1-23. (modified text below from this reference abstract)

1. CSF-circulation is propelled by a pulsating flow, which causes an effective mixing. Flow is produced by the alternating pressure gradient, which is a consequence of the systolic expansion of the intracranial arteries causing expulsion of CSF into the compliant and contractable spinal subarachnoid space.
2. No bulk flow is necessary to explain the transport of tracers in the subarachnoid space.
3. Main absorption of the CSF is not through the Pacchionian granulations (arachnoid granulations), but a major part of the CSF transportation to the blood-stream is likely to occur via the paravascular and extracellular spaces of the central nervous system. (MH- Note this statement conflicts with previous CSF Reabsorption in literature)
4. The intracranial dynamics may be regarded as the result of an interplay between the demands for space by the four components of the intracranial content (arterial blood, brain volume, venous blood and CSF). Interaction has a time offset within the cerebral hemispheres in a fronto-occipital direction during the cardiac cycle (the fronto-occipital "volume wave").
5. Outflow from the cranial cavity to the cervical subarachnoid space (SAS) is dependent in size and timing on the intracranial arterial expansion during systole.

CSF Abnormalities

Hydrocephalus

Hydrocephalus is the result of an imbalance between the rate at which the CSF is being formed and the rate at which the CSF is passing through the arachnoidal villi back into the blood (hydrocephalus rate is a function of the degree of imbalance in these two).

very small imbalance exhibit subtle, if any, symptoms.

large imbalances will have rapidly evolving symptoms of unmistakable import.

Obstructive Hydrocephalus

Obstruction of the CSF pathways within the interior of the brain or at the tentorial notch (the opening in the tentorium cerebelli fold of dura mater for the brainstem).

Tentorium cerebelli, viewed from above (image: Gray's Anatomy)

Communication Hydrocephalus

Inability of the CSF to pass through the arachnoidal villi to get back into the blood stream. This can result when the arachnoidal villi become inflamed by infection or blood with the inflammatory process blocking the microscopic pores through which the CSF must pass from the subarachoidal space into the blood.

Congenital Hydrocephalus

Present at birth and can be due to blockage at the aqueduct (aqueductal stenosis), congenital anomalies such as an Chiari malformation or Dandy-Walker malformation (malformations at the base of the brain resulting in obstruction of outflow of CSF from the brain's interior) or it can be due to an inflammatory process when premature birth has resulted in bleeding within the brain.

Acquired Hydrocephalus - arises later in postnatal life.

(text modified from: CSF Production and Hydrocephalus Institute for Neurology and Neurosurgery at the Beth Israel Nedical Center New York)

Hydrocephalus - treated by endoscopic third vetriculostomy (ETV) surgery.

Neoplasms

Represents about 0.4 - 0.6% of all intracranial, 2 - 3% of pediatric neoplasms.

Plexus papillomas outnumber choroid plexus carcinomas (by a ratio of 5:1). Choroid plexus carcinomas 80% arise in children.

Plexus tumors are most common in the lateral (80% of lateral ventricle tumors in children) and fourth ventricles (evenly distributed all age groups). (More? text modified from: Rickert )

References

Links: Journals | Online Textbooks | Search Textbooks | PubMed | Search PubMed | Glossary

Journals

Cerebrospinal Fluid Research ISSN: 17438454 Papers on all aspects of cerebrospinal fluid in health and disease.

Online Textbooks

Clinical Methods Third Edition Walker, H.K.; Hall, W.D.; Hurst, J.W.; editors Stoneham (MA): Butterworth Publishers; c1990 Cerebrospinal Fluid

Neuroscience Purves, Dale; Augustine, George.J.; Fitzpatrick, David; Katz, Lawrence.C.; LaMantia, Anthony-Samuel.; McNamara, James.O.; Williams, S. Mark, editors. Sunderland (MA): Sinauer Associates, Inc. c2001. The Ventricular System

Basic Neurochemistry, Molecular, Cellular, and Medical Aspects 6th ed. Siegal, George J.; Agranoff, Bernard W.; Albers, R. Wayne; Fisher, Stephen K.; Uhler, Michael D., editors. Philadelphia: Lippincott, Williams & Wilkins; c1999.ale; Augustine, George.J.; Fitzpatrick, David; Katz, Lawrence.C.; LaMantia, Anthony-Samuel.; McNamara, James.O.; Williams, S. Mark, editors. Sunderland (MA): Sinauer Associates, Inc. c2001. Blood—Cerebrospinal Fluid Barrier

PubMed

Reviews

Beni-Adani L, Biani N, Ben-Sirah L, Constantini S. The occurrence of obstructive vs absorptive hydrocephalus in newborns and infants: relevance to treatment choices. Childs Nerv Syst. 2006 Dec;22(12):1543-63.

Oi S, Di Rocco C. Proposal of "evolution theory in cerebrospinal fluid dynamics" and minor pathway hydrocephalus in developing immature brain. Childs Nerv Syst. 2006 Jul;22(7):662-9.

<Catala M. Embryonic and fetal development of structures associated with the cerebro-spinal fluid in man and other species. Part I: The ventricular system, meninges and choroid plexuses. Arch Anat Cytol Pathol. 1998;46(3):153-69.

Osaka K, Handa H, Matsumoto S, Yasuda M Development of the cerebrospinal fluid pathway in the normal and abnormal human embryos. Childs Brain. 1980;6(1):26-38.

Articles

Killer HE, Jaggi GP, Flammer J, Miller NR, Huber AR, Mironov A. Cerebrospinal fluid dynamics between the intracranial and the subarachnoid space of the optic nerve. Is it always bidirectional? Brain. 2007 Feb;130(Pt 2):514-20.

Killer HE, Jaggi GP, Flammer J, Miller NR, Huber AR. The optic nerve: a new window into cerebrospinal fluid composition? Brain. 2006 Apr;129(Pt 4):1027-30.

Heep A, Bartmann P, Stoffel-Wagner B, Bos A, Hoving E, Brouwer O, Teelken A, Schaller C, Sival D. Cerebrospinal fluid obstruction and malabsorption in human neonatal hydrocephaly. Childs Nerv Syst. 2006 Oct;22(10):1249-55.

Patelska-Banaszewska M, Wozniak W. The subarachnoid space develops early in the human embryonic period. Folia Morphol (Warsz). 2005 Aug;64(3):212-6.

Dziegielewska KM, Ek J, Habgood MD, Saunders NR. Development of the choroid plexus. Microsc Res Tech. 2001 Jan 1;52(1):5-20.

Speake T, Whitwell C, Kajita H, Majid A, Brown PD. Mechanisms of CSF secretion by the choroid plexus. Microsc Res Tech. 2001 Jan 1;52(1):49-59.

Rickert CH, Paulus W. Tumors of the choroid plexus. Microsc Res Tech. 2001 Jan 1;52(1):104-11.

Guermazi A, De Kerviler E, Zagdanski AM, Frija J. Diagnostic imaging of choroid plexus disease. Clin Radiol. 2000 Jul;55(7):503-16.

Segal MB. The choroid plexuses and the barriers between the blood and the cerebrospinal fluid. Cell Mol Neurobiol. 2000 Apr;20(2):183-96.

Weisgerber C, Husmann M, Frosch M, Rheinheimer C, Peuckert W, Gorgen I, Bitter-Suermann D. Embryonic neural cell adhesion molecule in cerebrospinal fluid of younger children: age-dependent decrease during the first year. J Neurochem. 1990 Dec;55(6):2063-71.

O'Rahilly R, Muller F. Ventricular system and choroid plexuses of the human brain during the embryonic period proper. Am J Anat. 1990 Dec;189(4):285-302.

Osaka K, Handa H, Matsumoto S, Yasuda M Development of the cerebrospinal fluid pathway in the normal and abnormal human embryos. Childs Brain. 1980;6(1):26-38.

Search PubMed: term= cerebrospinal fluid development | choroid plexus development | brain ventricular development | fetal cerebrospinal fluid |

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Glossary

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Terms

• 3rd ventricle- ventricular cavity within the diencephalon.
• 4th ventricle- ventricular cavity within the rhombencephalon.
• accessory nerve-
• adenohypophysis- anterior pituitary= 3 parts pars distalis, pars intermedia, pars tuberalis
• alar plate- afferent, dorsal horns
• anlage- (Ger. ) primordium, structure or cells which will form a future structure.
• arachnoid- (G.) spider web-like
• basal ganglia-
• basal plate- efferent, ventral horns
• brachial plexus- mixed spinal nerves innervating the upper limb form a complex meshwork (crossing).
• brain- general term for the central nervous system formed from 3 primary vesicles.
• buccopharyngeal membrane- (=oral membrane) at cranial (mouth) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet. (see also cloacal membrane)
• cauda equina- (=horse's tail) caudal extension of the mature spinal cord.
• central canal- lumen, cavity of neural tube within the spinal cord. Space is continuous with ventricular system of the brain.
• cerebral aqueduct- ventricular cavity within the mesencephalon.
• cervical flexure- most caudal brain flexure (of 3) between spinal cord and rhompencephalon.
  • ( sc-^V^ )
• choroid plexus- specialized vascular plexus responsible for secreting ventricular fluid that with further additions becomes cerebrospinal fluid (CSF).
• cloacal membrane- at caudal (anal) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet forms the openings for GIT, urinary, reproductive tracts. (see also buccopharyngeal membrane)
• cortex-
• cortical plate- outer neural tube region which post-mitotic neuroblasts migrate too along radial glia to form adult cortical layers.
• cranial flexure- (=midbrain flexure) most cranial brain flexure (of 3) between mesencephalon and prosencephalon.
  • ( sc-^V^ )
• diencephalon- the caudal portion of forebrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). (cavity- 3rd ventricle) Forms the thalmus and other nuclei in the adult brain.
  • (sc-My-Met-Mes-Di-Tel)
• dorsal root ganglia- (=spinal ganglia) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
• dura mater-
• ectoderm- the germ layer which form the nervous system from the neural tube and neural crest.
• ependyma- epithelia of remnant cells after neurons and glia have been generated and left the ventricular zone
• floorplate- early forming thin region of neural tube closest to the notochord.
• ganglia- (pl. of ganglion) specialized neural cluster.
• glia- supporting, non-neuronal cells of the nervous system. Generated from neuroepithelial stem cells in ventricular zone of neural tube. Form astrocytes, oligodendrocytes.
• glossopharyngeal ganglion-
• grey matter- neural regions containing cell bodies (somas) of neurons. In the brain it is the outer layer, in the spinal cord it is inner layer. (see white matter)
• growth factor- usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway. The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg shh)
• hox- (=homeobox) family of transcription factors that bind DNA and activate gene expression. Expression of different Hox genes along neural tube defines rostral-caudal axis and segmental levels.
• intervertebral foramina-
• isthmus- (G. narrow passage)
• lamina terminalis- anterior region of brain where cranial neuropore closes.
• lumbar plexus- mixed spinal nerves innervating the lower limb form a complex meshwork (crossing).
• mantle layer- layer of cells generated by first neuroblasts migrating from the ventricular zone of the neural tube. Layers are rearranged during development of the brain and spinal cord.
  • (Ven-Man-Mar-CP)
• marginal zone- layer of processes from neuroblasts in mantle layer.
  • (Ven-Man-Mar-CP)
• mater- (L. mother)
• meninges- mesenchyme surrounding neural tube forms 3 layer (Dura-, pia-, arachnoid- mater) connective tissue sheath of nervous system.
  • (D-P-A-cns)
• mesencephalon- (=midbrain), the middle portion of the 3 primary vesicle brain (week 4).
  • (sc-R-M-P)
• metencephalon- the cranial portion of hindbrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). Forms the pons and cerebellum in the adult brain.
  • (sc-My-Met-Mes-Di-Tel)
• myelencephalon- the caudal portion of hindbrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). Forms the medulla in the adult brain.
  • (sc-My-Met-Mes-Di-Tel)
• neural tube- neural plate region of ectoderm pinched off to form hollow ectodermal tube above notochord in mesoderm.
• neural tube defect- (NTD) any developmental abnormality that affects neural tube development. Commonly failure of neural tube closure.
• neuroblast- undifferentiated neuron found in ventricular layer of neural tube.
• neurohypophysis- (=posterior pituitary=pas nervosa)
• neuron- The cellur "unit" of the nervous system, transmitting signals between neurons and other cells. The post-mitotic cells generated from neuroepithelial stem cells (neuroblasts) in ventricular zone of neural tube.
• neuropore- opening at either end of neural tube: cranial=rostral=anterior, caudal=posterior. The cranial neuropore closes (day 25) approx. 2 days (human) before caudal.
• notochord- rod of cells lying in mesoderm layer ventral to the neural tube, induces neural tube and secretes sonic hedgehog which "ventralizes" the neural tube.
• olfactory bulb- (=cranial nerve I, CN I) bipolar neurons from nasal epithelium project axons through cribiform palate into olfactory bulb of the brain.
• optic cup-
• optic nerve- (=cranial nerve II, CN II) retinal ganglion neurons project from the retina as a tract into the brain (at the level of the diencephalon).
• otocyst- (=otic vesicle) sensory placode which sinks into mesoderm to form spherical vesicle (stage 13/14 embryo) that will form components of the inner ear.
• pars- (L. part of)
• pharyngeal arches- (=branchial arches, Gk. gill) form structures of the head. Six arches form but only 4 form any structures. Each arch has a pouch, membrane and cleft.
• pharynx- uppermost end of GIT, beginning at the buccopharyngeal membrane and at the level of the pharyngeal arches.
• pia mater-
• placode- specialized regions of ectoderm which form components of the sensory apparatus.
• pontine flexure- middle brain flexure (of 3) between cervical and cranial flexure in opposite direction, also generates thin roof of rhombencephalon and divides it into myelencephalon and metencephalon. ( sc-^V^ )
• prosencephalon- (=forebrain), the most cranial portion of the 3 primary vesicle brain (week 4).
  • (sc-R-M-P)
• Rathke's pouch- a portion of the roof of the pharynx pushes upward towards the floor of the brain forming the anterior pituirary (adenohypophysis, pars distalis, pars tuberalis pars intermedia). Where it meets a portion of the brain pushing downward forming the posterior pituitary (neurohypophysis, pars nervosa). Rathke's pouch eventually looses its connection with the pharynx.
  • [Martin Heinrich Rathke 1973-1860, embryologist and anatomist]
• rhombencephalon- (=hindbrain), the most caudal portion of the 3 primary vesicle brain (week 4).
  • (sc-R-M-P)
• roofplate- early forming thin region of neural tube closest to the overlying ectoderm.
• spinal cord- caudal end of neural tube that does not contribute to brain. Note: the process of secondary neuralation contributes the caudal end of the spinal cord.
• spinal ganglia- (=dorsal root ganglia, drg) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
• spinal nerve- mixed nerve (motor and sensory) arising as latera pairs at each vertebral segmental level.
• sonic hedgehog- (=shh) secreted growth factor that binds patched (ptc) receptor on cell membrane. SHH function is different for different tissues in the embryo. In the nervous system, it is secreted by the notochord, ventralizes the neural tube, inducing the floor plate and motor neurons.
• sulcus- (L. furrow) groove
• sulcus limitans- longitudinal lateral groove in neural tube approx. midway between roofplate and floorplate. Groove divides alar (dorsal) and basal (ventral) plate regions.
• sympathetic ganglia-
• telencephalon- the cranial portion of forebrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). (cavity- lateral ventricles and some of 3rd ventricle) Forms the cerebral hemispheres in the adult brain.
  • (sc-My-Met-Mes-Di-Tel)
• thalamus- (G. thalamos= bedchamber) cns nucleus, lateral to 3rd ventricle, paired (pl thalami).
• transcription factor- a factor (protein or protein with steroid) that binds to DNA to alter gene expression, usually to activate. (eg steroid hormone+receptor, Retinoic acid+Receptor, Hox, Pax, Lim, Nkx-2.2)
• trigeminal ganglion- (=cranial nerve V, CN V) first arch ganglion, very large and has 3 portions.
• vagal ganglion- (=cranial nerve X, CN X) fourth and sixth arch ganglion, innervates the viscera and heart.
• ventricles- the fluid-filled interconnected cavity system with the brain. Fluid (cerebrospinal fluid, CSF) is generated by the specialized vascular network, the choroid plexus. The ventricles are directly connected to the spinal canal (within the spinal cord).
• ventricular zone- Neuroepithelial cell layer of neural tube closest to lumen. Neuroepithelial cells generate neurons, glia and ependymal cells.
  • (Ven-Man-Mar-CP)
• vestibulocochlear nerve- (=cranial nerve VIII, CN VIII, also called statoacoustic)
• white matter- neural regions containing processes (axons) of neurons. In the brain it is the inner layer, in the spinal cord it is outer layer. (see grey matter)

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