Cerebrum development human embryo (week 8, Stage 22)
- Understand early neural development.
- Understand the formation of the brain; grey and white matter from the neural tube.
- Understand the formation of spinal cord.
- Understand the role of migration of neurons during neural development.
2014 Lecture 19 PDF
- Detailed structure of the adult nervous system is provided in other Anatomy courses.
- History - Santiago Ramón y Cajal
|Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved May 15, 2021, from https://embryology.med.unsw.edu.au
|Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2011). The developing human: clinically oriented embryology (9th ed.). Philadelphia: Saunders.
||The following chapter links only work with a UNSW connection.
|Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. & Francis-West, P.H. (2009). Larsen's human embryology (4th ed.). New York; Edinburgh: Churchill Livingstone.
||The following chapter links only work with a UNSW connection.
Early Brain Structure
- rostral neural tube forms 3 primary brain vesicles (week 4)
- 3 primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)
Rapid growth folds the neural tube forming 3 brain flexures
- cephalic flexure - pushes mesencephalon upwards
- cervical flexure - between brain stem and spinal cord
- pontine flexure - generates 4th ventricle
From the 3 primary vesicles developing to form 5 secondary vesicles
- prosencephalon- telencephalon (endbrain, forms cerebral hemispheres), diencephalon (betweenbrain, forms optic outgrowth)
- rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)
Carnegie stage 13 Embryo showing neural tube and brain flexures.
Neural Tube Development
||Rhinencephalon, Amygdala, hippocampus, cerebrum (cortex), hypothalamus, pituitary | Basal Ganglia, lateral ventricles
||epithalamus, thalamus, Subthalamus, pineal, posterior commissure, pretectum, third ventricle
||tectum, Cerebral peduncle, cerebral aqueduct, pons
||medulla oblongata, isthmus
|spinal cord, pyramidal decussation, central canal
Historic figure showing the parts derived from the walls of the fore-brain. (After Wilhelm His (1831-1904))
- Hindbrain - Rhombomeres represent the crania-caudal segmentation of the neural tube at the levee lot the hindbrain.
- Historic - Identified morphologically as identifiable regions.
- Modern - Represent the different expression levels of Hox genes and levels of neural crest migration.
|Historic image of embryonic rhombomeres
||Hindbrain neural crest migration
Hox-proteins crania-caudal expression (species comparison)
- Ventricular Germinal Zone (VGZ) - mitosis at the ventricular luminal surface, produces early-generated macroneurons
- Subventricular Zone (SVZ) - mitosis away from the ventricular surface, produces later-generated microneurons and glia
|Human Embryo developing head cross section (Week 8, Stage 22)
||Detail of developing cortex (shown in blue box)
- Neural progenitor cells migrate from the ventricular layer along radial glia.
- Cortex layers develops inside (first) outside (last)
- Glial progenitor cells develop later from the same ventricular stem cells.
- Similar processes to those described for brain.
- Remember notochord ventral patterning by SHH and dorsal ectoderm (dorsalisation).
- Identify the different regions within the neural tube (floor plate, basal plate, alar plate, roof plate)
|Half of a transverse section of the spinal cord
|Human embryo of 18.5 mm (7.5 weeks).
||Human embryo of 24 mm (8.5 weeks).
||Human fetus of about 3 months.
|Wilhelm His (1831-1904)
Human Embryo (week 8, Stage 22) ventricular system
- 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)
- choroid plexus is a modified vascular structure which will produce Cerebrospinal fluid (CSF)
Human Fetus (week 10) showing choroid plexus and early ventricular system
(FYI - you do not need to know detailed stage development)
|Human Ventricular Development Timeline
- 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).
Data from O'Rahilly R, Müller F., 1990
Historic diagram showing the relationship of the Cranial Nerves to the Primitive Segments of the Head.
Timeline of events in Human Neural Development
|During the fetal period there is ongoing growth in size, weight and surface area of the brain and spinal cord. Microscopically there is ongoing: cell migration, extension of processes, cell death and glial cell development.
Cortical maturation (sulcation and gyration) and vascularization of the lateral surface of the brain starts with the insular cortex (insula, insulary cortex or insular lobe) region during the fetal period. This cerebral cortex region in the adult brain lies deep within the lateral sulcus between the temporal lobe and the parietal lobe.
- sulcation - The process of brain growth in the second to third trimester which forms sulci, grooves or folds visible on fetal brain surface as gyri grow (gyration). Abnormalities of these processes can lead to a smooth brain (lissencephaly).
- gyration - The development of surface folds on the brain (singular, gyrus)
Insular Gyral and Sulcal Development
- 13-17 gestational weeks - appearance of the first sulcus
- 18-19 gestational weeks - development of the periinsular sulci
- 20-22 gestational weeks - central sulci and opercularization of the insula
- 24-26 gestational weeks - covering of the posterior insula
- 27-28 gestational weeks - closure of the laeteral sulcus (Sylvian fissure or lateral fissure)
- Between 29-41 weeks volumes of: total brain, cerebral gray matter, unmyelinated white matter, myelinated, and cerebrospinal fluid (from MRI)
- grey matter- mainly neuronal cell bodies; white matter- mainly neural processes and glia.
- total brain tissue volume increased linearly over this period at a rate of 22 ml/week.
- Total grey matter also showed a linear increase in relative intracranial volume of approximately 1.4% or 15 ml/week.
- The rapid increase in total grey matter is mainly due to a fourfold increase in cortical grey matter.
- Quantification of extracerebral and intraventricular CSF was found to change only minimally.
(Text - modified from )
Neural development will continue after birth with substantial glial development, growth, death and reorganization occuring during the postnatally.
|Human brain at three months (median sagittal section)
||Human brain at four months (inferior surface)
||Human brain at five months (outer surface)
- Links: Neural System - Fetal | Neuroscience - Regional specification of the developing brain
Thyroid System and Neural Development
Timeline of human thyroid system and brain development from conception to birth. (Estimation of neurogenesis adapted from Bayer et al.)
- Links: Endocrine - Thyroid Development
- ↑ <pubmed>2285038</pubmed>
- ↑ <pubmed>17962979</pubmed>
- ↑ <pubmed>9485064</pubmed>
- ↑ <pubmed>12060827</pubmed>
- ↑ <pubmed>8361683</pubmed>
|Historic Disclaimer - information about historic embryology pages
| Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers)
|Text-Book of Embryology - 1921
|Bailey, F.R. and Miller, A.M. (1921). Text-Book of Embryology. New York: William Wood and Co.
The nervous system
Fig. 358 A two-neurone reflex arc in a Vertebrate
} Gray, Henry. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1918.
|Anatomy of the Human Bod - 1918
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