- 1 Labeling developmental features from brain sections
Labeling developmental features from brain sections
This page will be used to discuss the anatomy of different structures identified in the developing chick embryo. Embryo MH008 was sectioned in the cryostat and the sections have either been photographed using a microscope or drawn by hand. The sections were stained using cresyl violet stain.
- This embryo was cut on an angle such that the structures on the right side of the embryo (lower half of embryo in diagrams) appear before their counterparts on the left side of the embryo. Hence in these diagrams the auditory vesicle first appears on the right side and then we see it beginning to develop on the left side.
Anatomical description of labeled structures
- The optic cup is adjacent to the diencephalon wall and is double-walled (see here.
- The eye originates in the wall of the diencephalon (Carlson, 1999).
- According to Carlson, 1999 the optic vesicles become the optic cup following induction of the lens.
- There is a SEM photogprah on pg 264 and a diagram on pg 263 in Carlson, 1999 which shows the distinctive continuous double layered morphology of the developing optic vesicle.
- According to these figures the inner thicker layer is the sensory layer and the outer thinner layer is the pigmented layer.
- (Note: how do you know that what you are seeing is the sensory and pigment layers? What histological criteria are you using? If I were to tell you that that was the auditory vesicle, what arguments would you use against that?--MF Kubke 18:30, 10 February 2011 (EST))
- The auditory vesicles are located on the dorsal side of the embryo lateral to the myelencephalon. The structures labeled as optic cups are located on the ventral side of the embryo.
- The optic cup has two layers which are continuous with each other. The outer layer of the cup (medialmost layer) is thinner and is the pigment layer. The innermost layer becomes thicker than the outer layer at the point of contact between the two layers. The inner layer remains about three times thicker than the outer layer and is the sensory layer. (Carlson, 1999 pg 263 fig. 12.1). The sensory layers has a striated pattern of fibres which is reflected in the staining where you can see parallel lines in the tissue radiating outwards from the cup. The inner layer is more congruently stained.
The structure labeled as the optic cup cannot be the optic cup since the primary optic vesicle forms as an outgrowth of the diencephalon (Carlson, 1999). This structure is not continuous with the large cavity in the section (labeled as diencephalon), there is no optic stalk-like structure connecting the cavity to the strucute that can be seen.Also there does not appear to be a structure forming through invagination of the head ectoderm within the 'optic cup' i.e. the structure does not appear to contain the lens. The section does not include the lens however the lens is smaller than the cup and so in some sections you will see only the cup and not the lens as well.
- After looking at the sections caudal and rostral to this one you can see a circular single-walled structure appear in the centre of the double layered 'optic cup' (suspected as the lens).
- One of my drawings includes a stalk-like structure attached between the 'optic cup' and the 'diencephalon' but I will need to relook at the slides to see if I can more definitively locate the stalk.
- The auditory vesicles are located lateral to and nearby the notochord. These structures are on the opposite side of the embryo to the notochord.
- The auditory vesicles are single layered whilst the optic cups are double layered. The structures labeled as optic cups are clearly double layered.
- I looked at our atlas and according to Hamburger and Hamilton (1951) a stage 19 chick embryo has 37-40 somites. Looking at the O'RAHILLY (1963) paper describing the human embryo's optic vesicle I made the following inferences from human embryos at the 30+ somites and 5-7mm 'stages':
- The otic cup has developed into the otic vesicle.
- The remains of the otic stalk have most likely wont be seen in sections.
- It has become enclosed by its basement membrane if the stalk is not present.
- The otic vesicle has a single membrane coverings as opposed to the optic vesicle which has the lens and surrounding membrane.
- The vesicle appears circular in sections (From Plate 2).
- The optic vesicle appears in sections as a cavity with few nuclei and cell remnants visible, fewer than the optic vesicle.
- The otic vesicle can be found in sections at the level of the mylencephalon (http://www.uoguelph.ca/zoology/devobio/72hrchck/72ck1.htm)
- The rhombencephalon is identifiable by its thin roof attached to the edge of the thickened alar plate (Brodal, 1998).
- The infundibulum appears as a groove in the floor of the diencephalon (see here.
- In the brain stem the neural tube produces a large ventral thickening and a smaller more dorsal thickening on each side of the neural tube, called the basal and alar plates respectively (Brodal, 1998).
The diencephalon is recognizable by the prominent lateral optic vesicles extending from its walls (Carlson, 1999). So a cross section through the diencephalon should show symmetrical optic vesicles on either side.
- (Note: I dont see what you call the optic vesicles as being attached to the diencephalon on this image --MF Kubke 18:30, 10 February 2011 (EST))
- The optic cups are not attached to the diencephalon in all sections through the optic cups. The optic stalk is thinner than the optic cups and so there will be sections where they appear as separate structures.
- Due to the cephalic and cervical flexures the developing brain doubles back on itself and in certain cross sections you wll be able to see the brain appear twice in the section.
- The dorsal side of the mylencephalon is thin compared to the walls of the diencephalon, telencephalon, metencephalon and mesencephalon. Within the structure labeled as myelencephalon you can see the dorsal wall is thinned. See here for diagram.
The cavities of the cranial end of the neural tube are continuous with each other and form the vesicles of the brain (Brodal, 1998). The most rostral ventricle is the 4th ventricle found at the level of the myelencephlon and metencephalon (Brodal, 1998). This becomes the 3rd ventricle at the level of the prosencephalon (Brodal, 1998). Connecting these two ventricles, at the level of the mesencephalon, is the cerebral aqueduct (Brodal, 1998).
- Please discuss the accuracy of my annotations, cheers. --Reuben Cutfield 21:12, 8 February 2011 (EST)
- Please provide references and the criteria you used to identify the structures --MF Kubke 22:32, 8 February 2011 (EST)
- This is a photograph of a section from MH008. I was looking through several books in the library and then a few websites to help. Fact is I found nothing that specifically had what I was looking for. One website (click here) had cross sections but in a different plane and I had to interpret the sections using the plane our embryo was cut with. I also looked at photos of embryos I had taken such as the one in MH007 to imagine what structures would be included in each section and what the exact plane of our cutting was. Another website I found useful was this one(
- (Note: Fixed the link)). Not sure what you are asking in terms of criteria. I was just comparing the morphology of different structures to those in diagrams whilst thinking about the angle we cut at. I think it will be easier to complete the labeling of all my section once I have confirmation that I am seeing what I think I am seeing and have a few structures labeled in concrete. Thanks.--Reuben Cutfield 01:59, 9 February 2011 (EST)
- Both links you provide link to the same webpage. What I mean by criterion is on what basis are you deciding what each structure you identify. When you say that you compare the morphology, you need to be more specific. For example, why are you deciding that what you have labelled as the optic cup is the optic cup? What other structure could it be, how would you differentiate between those, is the morphology you see consistent with what you would expect for the age of the embryo you are looking at, etc.
- Bruce Carlson (1999). Human Embryology and Developmental Biology, 2nd Edition, Mosby Inc, Missouri.
- RONAN O'RAHILLY, The Early Development of the Otic Vesicle in Staged Human Embryos, J. Embryol. exp. Morph., Vol. 11, Part 4,pp. 741-755, December 1963, From the Department of Anatomy, St. Louis University School of Medicine,and the Department of Embryology, Carnegie Institution of Washington, Printed in Great Britain
- Brodal (1998), The Central Nervous System: Structure and Function, 2nd Edition, Institute of Medical Sciences, University of Oslo, Oxford University Press, New York, 1998.