Lecture - Neural Development: Difference between revisions
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# Understand the role of migration of neurons during neural development. | # Understand the role of migration of neurons during neural development. | ||
* Detailed structure of the adult nervous system is provided in other Anatomy courses. | |||
History - [[Embryology_History_-_Santiago_Ramón_y_Cajal|Santiago Ramón y Cajal]] | * History - [[Embryology_History_-_Santiago_Ramón_y_Cajal|Santiago Ramón y Cajal]] | ||
==Lecture Resources== | ==Lecture Resources== | ||
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Revision as of 10:52, 14 October 2014
Introduction
- 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.
- Detailed structure of the adult nervous system is provided in other Anatomy courses.
- History - Santiago Ramón y Cajal
Lecture Resources
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Early Brain Structure
Primary Vesicles
- rostral neural tube forms 3 primary brain vesicles (week 4)
- 3 primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)
Brain Flexures
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
Secondary Vesicles
From the 3 primary vesicles developing to form 5 secondary vesicles
- prosencephalon- telencephalon (endbrain, forms cerebral hemispheres), diencephalon (betweenbrain, forms optic outgrowth)
- mesencephalon
- rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)
Carnegie stage 13 Embryo showing neural tube and brain flexures.
Neural Tube | Primary Vesicles | Secondary Vesicles | Adult Structures |
---|---|---|---|
week 3 | week 4 | week 5 | adult |
prosencephalon (forebrain) | telencephalon | Rhinencephalon, Amygdala, hippocampus, cerebrum (cortex), hypothalamus, pituitary | Basal Ganglia, lateral ventricles | |
diencephalon | epithalamus, thalamus, Subthalamus, pineal, posterior commissure, pretectum, third ventricle | ||
mesencephalon (midbrain) | mesencephalon | tectum, Cerebral peduncle, cerebral aqueduct, pons | |
rhombencephalon (hindbrain) | metencephalon | cerebellum | |
myelencephalon | 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))
Rhombomeres
- 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)
Neural Layers
- 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
Brain
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.
Spinal Cord
Stage 13 | Stage 22 |
Half of a transverse section of the spinal cord | ||
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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) |
Ventricular Development
- 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)
(FYI - you do not need to know detailed stage development) 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[1]
Cranial Nerves
Historic diagram showing the relationship of the Cranial Nerves to the Primitive Segments of the Head.
Fetal Neural
Timeline of events in Human Neural Development
Human brain at three months (median sagittal section) | Human brain at four months (inferior surface) | Human brain at five months (outer surface) |
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)
(Data from[2])
- 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 [3])
Neural development will continue after birth with substantial glial development, growth, death and reorganization occuring during the postnatally.
Thyroid System and Neural Development
Timeline of human thyroid system and brain development from conception to birth.[4] (Estimation of neurogenesis adapted from Bayer et al.[5])
References
Movies
Mouse E11.5 microCT scan | Human Adult Brain |
Neural Sylvian Fissure |
Historic Embryology
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) |
- Contributions to Embryology Carnegie Institution No.59 Relative Weight and Volume of the Component Parts of the Brain of the Human Embryo at Different Stages of Development. Jenkins, G.B. (1921). pp5-54.
Images
Bailey, F.R. and Miller, A.M. (1921). Text-Book of Embryology. New York: William Wood and Co.
Gray, Henry. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1918.
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Cite this page: Hill, M.A. (2024, May 4) Embryology Lecture - Neural Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Neural_Development
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