Book - An Atlas of the Medulla and Midbrain 9

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Sabin FR. and Knower H. An atlas of the medulla and midbrain, a laboratory manual (1901) Baltimore: Friedenwald.

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This 1901 book by Florence Rena Sabin (1871 - 1953) and her collaborator presents one of the very earliest atlases of the human central nervous system, describing the midbrain and brainstem. This atlas was extremely useful for later researchers attempting to both understand the development and mapping of the midbrain and medulla. Florence Sabin later work was as a key historic researcher in early 1900's establishing our early understanding of both vascular and lymphatic development in the embryo. Modern Notes: Medulla | Mesencephalon | Florence Sabin Neural Links: ectoderm | neural | neural crest | ventricular | sensory | Stage 22 | gliogenesis | neural fetal | Medicine Lecture - Neural | Lecture - Ectoderm | Lecture - Neural Crest | Lab - Early Neural | neural abnormalities | folic acid | iodine deficiency | Fetal Alcohol Syndrome | neural postnatal | neural examination | Histology | Historic Neural | Category:Neural Neural Tube Development Neural Tube Primary Vesicles Secondary Vesicles Adult Structures week 3 week 4 week 5 adult neural plate neural groove neural tube Brain 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

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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)

Chapter IX. Formation Reticulaeis Alba et Geisea

Formatio Though the formatio reticularis is represented in the model for a ' the most part merely by a space, nevertheless certain of its relations can be made quite clear. In considering the three regions of the model, each is characterized, first, by a special form of the sensory or central fibre-mass, and second, by nuclei limited to the region. For example, the medulla oblongata has the vertical medial sheet and the olive; the pons has the horizontal sheet and the pontal nuclei, while the midbrain has the oblique-lateral sheet and the nucleus ruber and substantia nigra, which have, as has been said, a common bed of cells.

The position of the formatio reticularis has a definite relation to these main structures. It lies dorsal to the large nucleus of the region in every case. In the medulla oblongata it lies dorsal to the inferior olive and lateral to the vertical sheet; in the pons, it lies dorsal both to the pontal nuclei and to the pontal sheet, that is, the sheet forms a boundary between the pontal nuclei and the formatio reticularis. In the midbrain, the formatio reticularis lies dorsal to the nucleus ruber and the substantia nigra, but here the fibre-sheet is reversed in position as compared with the medulla oblongata, for it lies lateral rather than medial.

The reticular area of the medulla oblongata is best seen from the side (Plate v); the pontal and midbrain reticular areas from the dorsal aspect in Plate vn, and the midbrain area in Plate vm.

The intrinsic structures of the formatio reticularis are its long and short fibre-tracts and its cells, both the diffuse areas and the more or less definite nuclei.

The longitudinal section in Fig. 9 gives a comprehensive view of the entire formatio reticularis. It is bounded medially by the fasciculus longitudinalis medialis and the stratum profundum album; laterally by the nucleus funiculi gracilis and the nucleus funiculi cuneati, the corpus restiforme, the sensory cerebral nuclei and the lemniscus lateralis. In this section several points are to be noted: (1) the large number of longitudinal fibres, some of which seem to run the entire length of the formatio reticularis; (2) the comparatively even distribution of these fibres; (3) the large number of cells, and (4) the absence at this level of special groups or nuclei, for the whole area seems to be one continuous nucleus. This section may be taken as a type of the dorsal area of the formatio reticularis.

This level of the formatio reticularis is in contrast to a level farther ventral (Fig. 13). Here we have the longitudinal fibres and the cells again ; but the fibres run in fairly definite bundles and the cells form fairly definite nuclei. The first level was undifferentiated and showed fibres extending through the whole length of the medulla oblongata, pons and midbrain, while this level is distinctly differentiated and shows shorter tracts breaking up into nuclei. For example, distal to the radix 1ST. abducentis is the middle part of the medulla sheet, namely, its formatio reticularis Bundle; and proximal to the root of the E". abducens the fibrebundle turns lateral ward and splits into two parts, a medial and a lateral.

These two longitudinal fibre-bundles can be traced from the region just proximal to the E". abducens through the pons and into the midbrain; the fibres pass directly through the brachium conjunctivum. The more centrally placed of these longitudinal fibres run to the border of the central gray masses and there end abruptly, while the more lateral fibres end indefinitely in a great cell area in the midbrain, namely, the nucleus lateralis superior of Flechsig. The fibres from the decussatio tegmenti dorsalis of Meynert turn spinalward and pass through the formatio reticularis of the pons. They cannot be separated as a distinct bundle.

The formatio reticularis area of the entire section is one large nucleus; nevertheless five fairly distinct groups of cells can be differentiated within it. The first of these is the nucleus centralis inferior, which lies in the medulla sheet distal to the radix N". abducentis (Plate vi, Fig. 35). The second, the nucleus reticularis tegmenti, lies between the formatio reticularis fibres just proximal to the E". abducens (Plate vm, Fig. 40). The third, the nucleus centralis superior medialis, lies between the two medial fibrebundles in the proximal part of the pons (Plate vm, Fig. 42). In Plate vin the curve of the formatio reticularis bundle corresponds to this nucleus. The fourth nucleus is the nucleus centralis superior lateralis, which lies at the same level as the third but farther lateral. It occupies the hollow of the brachium conjunctivum (Plate vm, Fig. 42). The fifth is the nucleus lateralis superior, or formatio reticularis grisea of the midbrain (Plate vm).

As has been said, besides these fibre-bundles and nuclei, the section in Fig. 13 shows a diffuse formatio reticularis area extending throughout the section and lying lateral from the tracts just considered. This lateral area is in contrast to the lateral area of the more dorsal level. The longitudinal fibres are almost entirely wanting, their place being taken by transverse fibres or internal arcuates. These fibres are so delicate that they show better in transverse section (cf. Fig. 30). Beside the definite arcuate bunbles from the dorsal funiculi of the cord and the decussating fibres of the brachium conjunctivum, the entire area from the proximal limit of the fasciculus cuneatus to the level of the motor root of the ~N. trigeminus shows numbers of delicate arcuate fibres cut in cross-section. This area corresponds in extent to that of the tractus spinalis IN", trigemini, and doubtless many of these fibres come from its nucleus.

It will make the formatio reticularis more interesting to compare with two sections, one taken dorsal to the level of the formatio reticularis and the other ventral. In the first place Fig. 6 lies dorsal to the formatio reticularis. This might be called the level of the dorsal cerebral nuclei or the level of the central gray matter and its differentiated nuclei. The longitudinal fibres of the formatio reticularis have disappeared, and the following nuclei of the cerebral nerves are visible, the !N". glossopharyngeus, 1ST. vagus, E". acusticus, "N. facialis and "N. trigeminus. Moreover, the central area of the section is a mass of cells around the central canal. The ventral level, on the other hand, as seen in Fig. 20, is the level of the main regional nuclei, the olive, the pontal nuclei, the substantia nigra and nucleus ruber. At this level there are no nuclei of cerebral nerves nor fibres of the formatio reticularis. It is, in fact, a non-medullated area in which the motor fibres, that are soon to characterize this level (i. e., pyramidal tract), can just be seen, as lines of brown stain on the sections.

In the reticular area of the medulla are two longitudinal tracts, first, the descending bundle from Deiters' nucleus to the spinal cord (Plate v), and second, the tract described as extending from Burdach's nucleus up to the region of the nucleus ambiguus (Plate vii, Fig. 12) (Tr. fr. Nu. D. and F. c. to F. r.).

It will be noted in both of the sections (Figs. 9 and 13) that the formatio reticularis region does not reach either the proximal or the distal limit of the section; that is to say, the formatio reticularis of the model region is not connected with the cord, nor yet with the hypothalamic region at so dorsal a level. This is due to the cervical and the midbrain curves. The model shows this point well. A cross-section of the spinal cord, showing its reticular area is to be seen in Plate v. The fibres of this area must curve over the dorsal surface of the olive to enter the formatio reticularis area of the medulla oblongata. On the other hand, the proximal connection shows best in Plate vm, where the transition is made just over the dorsal capsule of the nucleus ruber. It is not necessary to say that it is impossible to limit exactly the dorsal capsule from the formatio reticularis; indeed, Forel says that the formatio reticularis enters into the formation of the capsule of the nucleus ruber. Fig. 16 shows these relations clearly, for at either end of the section is to be seen an area of formatio reticularis.

Beside the large diffuse cell-masses of the formatio reticularis and the more definite cell-groups connected with the longitudinal tracts, there are scattered in the formatio reticularis certain definite little masses of cells. They are situated on either side of the brachium conjuiictivum sheet in its ventral course from the cerebellum to the decussation (Plates in and iv).

CONCLUSION.

GENERAL SUMMARY.

It will now be possible, I think, to reduce the model to simple summary of terms, even though it may seem to be complex. As viewed from the side, the model consists, in general, of two levels a ventral J and a dorsal. The ventral level is characterized, first, by a remarkable absence of medullated fibres at this stage of development, and second, by the presence of large definite nuclei. These nuclei characterize the regions they occupy; the olive of the medulla,

Comparison the pontal nuclei, the nucleus ruber and substantia nigra in the withcSS! midbrain. This is the level and these the structures by which the medulla oblongata, pons and midbrain differ from the cord. The absence of medullated fibres speaks for the later development of these structures. This level is eventually occupied by the brachium pontis and the pyramidal tract, the fibres of which have long been laid down at this period. 1

The pyramidal tract, which develops in this level, lies wholly on the surface of this region, save where it plunges through the pontal nuclei. It lies far from the dorsal area, which represents the more developed part of the model and has no form relation to it save that the decussation makes a slight impression on the trough for the ventral horn; that is to say, the pyramidal tract has no influence in moulding the shape of other structures; it rather adjusts itself to structures already formed. In this it is in contrast to the sensory tract, which is so closely related in form to adjacent structures. This illustrates well the point which His has made, that the difference in time development determines the relative positions of structure. 2

Continuation The dorsal half of the model, on the other hand, corresponds structures, rather to the spinal cord. The easy transition of the cord into the dorsal part of the model is clear in the view of the lateral surface of the model. This level, with all its complexity, is in reality simple. It consists (1) of long tracts on the way to the cortex, (2) of long tracts to the cerebellum, namely, the brachium conjunctivum and corpus restiforme; (3) of the cerebral nuclei, their root-bundles and paths; (4) the association areas or formatio reticularis alba and grisea.

The central fibre mass is a structural unit in the form of three sheets, the medulla, pontal and midbrain, which contain the medial and lateral lemniscus, or the main sensory path toward the cortex. It contains also certain shorter tracts, the fasciculus longitudinalis medialis, the lemniscus superior and unnamed formatio reticularis fibres. Of the tracts to the cerebellum, the corpus restiforme lies on the lateral surface of the medulla oblongata, while the brachium conjunctivum, being related to the nucleus ruber, lies within the pons and midbrain.

1 Flechsig. Die Leitungsbahnen im Geblrn und Kiickenmark des Menschen, Leipzig, 1876, S. 192.

2 Die Neuroblasten und deren Entstehung im embryonalen Mark, Abhandl. d. math.-phys. Cl. d. k. sachs. Gesellsch. d. Wissensch., Bd. xv, Leipzig, 1889, S. 292.

SUMMARY: GROUPING OF CEREBRAL NERVES, ETC. Ill

The cerebral nerves are divided into two groups, a medial and a Grouping of lateral. The motor nuclei are definite, compact masses, with the C( exception of the nucleus ~N. accessorii, which represents the transition from the type of the nuclei to the spinal cord. The motor nuclei correspond to the ventral-horn cells. They are related to f ormatio reticularis areas ; the median group to the fasciculus longitudinalis medialis, the lateral to the formatio reticularis alba. The root-fibres of the lateral group, with one exception, take an indirect course to the surface, showing that they have developed in an area of complex growth. The sensory nuclei all belong to the lateral group. They correspond, in the main, to the dorsal horn of the spinal cord, and thus occupy a dorsal level. They are diffuse and cover a wide area. All but two of them, namely, the nuclei of the !N". trigeminus and !N". cochleae, lie in the substantia centralis grisea. With the exception of the nuclei N. cochleae, they border the formatio reticularis. In general, they are characterized by long descending tracts accompanied by nuclei. The nerves of the special senses do not conform wholly to the general type, for the !N". vestibuli is peculiar in its relations to the cerebellum, and the "N. cochleae in its well-developed and complex central path.

The formatio reticularis consists of mixed cells and fibres. The Formatio dorsal level represents the longer association paths of the model, rt and its cells are diffuse. In the ventral level the fibres are grouped into shorter paths and then the cells form nuclei in connection with these short bundles.

The model brings out the fact that the region is divided into four levels, as has been shown by His from a study of earlier embryos. I wish to emphasize the large number of nerves represented by nuclei in the first layer, or the substantia centralis grisea. They are (1) all of the spinal nerves through the nuclei of the dorsal funiculi, (2) the nuclei of the four motor nerves of the median group, and (3) all of the sensory cerebral nuclei of the model except the nucleus of the !N". trigeminus and the N. cochleae. The second layer, that of the formatio reticularis, includes the remaining four motor nuclei of the cerebral nerves. That this position is not primary for these nuclei, but is rather the result of development, is suggested by courses of their fibres. The third layer includes the olive, pontal nuclei, substantia nigra and red nucleus, the fourth the pyramidal tract.

The question of the origin of these four layers is one of great interest. According to His, the motor nuclei, both of the median and lateral groups, come from the ground plate, while the sensory nuclei come from the medial part of the wing plates. 1 The third layer offers an attractive field for study.

Three of its nuclei, namely, the olive, the pontal nuclei and the red nucleus, are connected with the cerebellum. In the spinal cord the cells related to the cerebellum are in the nucleus dorsalis Clarkii which lies between the dorsal and ventral horns. The origin of the olive, according to His, is from the cells of the Rautenlippe, which forms the lateral part of the wing plate adjacent to the cells which form the sensory nuclei. This serves to open up the question of the origin and relations of this ventral nuclear layer. Have these nuclei a common origin, and what is the relation of the substantia nigra to the other three?

A part of this question is being studied in this laboratory. Problems along this line have been opened up by the work of His, and I can but believe that the application of the wax-plate method to the study of the development of the central nervous system has a promising future. With a series of models, the course of development may become a matter of sight and not a theory. Moreover, all those individual differences which may be misleading in any one model can be easily eliminated when each model is but one of a series.

1 His, W., Die Entwickehing des menschlichen EautenWms. Abhandl. d. math.-phys. Cl. d. k. sachs. Gesell. d. Wissensch., Leipz., 1891, S. 1-74.

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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)

An Atlas of the Medulla and Midbrain (1901): Chapter I. Introductory | Chapter II. The Long Tracts | Chapter III. The Columns Of The Spinal Cord | Chapter IV. Cerebellar Peduncles | Chapter V. The Cerebral Nerves And Their Nuclei | Chapter VI. The Cerebral Nerves And Their Nuclei (Continued). Lateral Group | Chapter VII. The Inferior And Accessory Olives | Chapter VIII. The Midbrain | Chapter IX. The Formatio Reticularis Alba And Grisea | General Summary of what Is shown In Reconstruction | References To Literature | Abbreviations | Description of Figures and Plates

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