Back and central nervous system
Aida Lai in Essential Concepts in Anatomy and Pathology for Undergraduate Revision, 2018
Spinal cord– developed from alar lamina and basal lamina separated by sulcus limitans– continuous with medulla oblongata– has cervical and lumbar enlargements– denticulate ligament connects pia mater to dura mater– ends at lower border of L1 as conus medullaris → continuous with a single layer of pia mater that attaches to first coccygeal vertebra (filum terminale)– subarachnoid space distal to conus medullaris = lumbar cistern– central canal contains CSF– H-shaped grey matter with ant. and post. horns joined centrally by grey commissure– lat. grey column present in thoracic and lumbar region (gives off preganglionic sympathetic fibres)
Comparative Anatomy of Medullary Vagal Nerve Nuclei
Sue Ritter, Robert C. Ritter, Charles D. Barnes in Neuroanatomy and Physiology of Abdominal Vagal Afferents, 2020
Comparative neuroanatomists at the turn of the century (e.g., as described by Herrick17 or Ariens Kappers, et al.3) discerned that the brainstem in virtually any vertebrate could be divided into four major longitudinal columns according to the nerve components terminating or originating therein (see Table 1, Figure 1). These four longitudinal subdivisions were also described as being related to the embryogenesis of the neural tube in that the function of each cell column is related to its place of origin along the ventricular surface of the neural tube. The neural tube is grossly divisible into an alar plate, lying dorsal to the sulcus limitans, and a basal plate situated ventral to this sulcus. Cell groups originating from the alar plate serve sensory functions while neurons generated from the basal plate serve motor functions (Figure 1). Somatic functions are performed by neurons generated at the dorsolateral and ventromedial portions of each half of the neural tube; visceral functions are carried out by neurons generated closest to the sulcus limitans. Since the vagus nerve contains components involved in three (somatic sensory, visceral sensory, visceral motor) of these four principal functions, vagal nerve nuclei are located in three of the four main zones. A confounding factor in this scheme is that in most vertebrates, although neurons are generated at the ventricular surface, the maturing neuroblasts migrate outward to collect into nuclei lying some distance from the ventricular surface. Thus the four longitudinal columns do not always maintain sharp boundaries.
Microsurgical techniques for achieving gross total resection of ependymomas of the fourth ventricle
Published in Acta Chirurgica Belgica, 2020
The prominences, contours, and curves of the fourth ventricular floor provide several useful landmarks delineating surface and deep structural anatomy [48,52]. The floor is diamond shaped and formed by the dorsal surfaces of the metencephalon and myelencephalon. Midline and paramedian sulci, ridges, and impressions in the fourth ventricular floor provide a series of natural landmarks corresponding with underlying pontomedullary zones. The immediately parasagittal median eminence is interposed between the median sulcus and the bilaterally flanking sulci limitans, with respect to which the vestibular area is laterally located, overlies the abducens nucleus and ascending portion of the facial nerve genual fibers. These axons originate ventromedial with respect to the abducens nucleus and course medioposteriorly across the ventral surface of the abducens nucleus then lateroanteriorly around its dorsal surface in the fourth ventricular floor immediately above the pontomedullary junction. Impressions of the sulci limitans form dimples comprised of the metencephalic superior fovea (marking the location of the motor trigeminal nucleus) and the myelencephalic inferior fovea, medial to which are the fibers comprising the hypoglossal rootlets. An area exhibiting bluish gray hue reflecting intraneuronal lipofuscin pigment may be found at the rostral sulcus limitans and effectively marks the location of the locus coeruleus. A series of V-shaped impressions near the caudal end of the median sulcus are comprised rostrocaudally of the hypoglossal trigone, vagal trigone, and area postrema [48,52]. A dark triangular shaped area interposed between the hypoglossal trigone medially and the vestibular area laterally, termed the triangular area by Rhoton [48] and ala cinerea by other authors, specifically corresponds with, and overlies, the myelencephalic extent of the nucleus tractus solitarius and the dorsal motor nucleus of the vagus and is crossed caudally by the funiculus separans. The ala cinerea may thus be found between the hypoglossal trigone, corresponding with the hypoglossal motor nuclei, adjacent paired neuronal clusters located in the dorsal medulla, and the vagal trigone, corresponding with the nucleus tractus solitarii and dorsal motor nuclei of the vagus. The area postrema is a bilaterally paired circumventricular organ lacking a blood brain barrier located immediately caudal to the vagal trigone, flanked by the funiculus separans bilaterally, and bridged caudomedially by the interfunicular commissure. The caudal contoured edge of the interfunicular commissure and rostral contoured edge of the ligula represent the medullary attachment of the tectoria membrana and may be conceptualized to delineate the obex. Vasopressin and angiotensin acting upon the area postrema effectively desensitize the baroreflex mechanism and permit sharp rises of the arterial pressure and heart rate occurring in the setting of the defense reaction. The laterally oriented acoustic striae overlie the course of the dorsal pontocerebellar fibers and provide a natural landmark readily orienting the astute neurosurgeon to the beauty and elegance of the microsurgical ventricular anatomy.
Related Knowledge Centers
- Fourth Ventricle
- Rhomboid Fossa
- Cranial Nerves