Medical brain notes 24

  Preliminary Review of the Internal Structure of the Brainstem          The following description is confined to those features of internal structure that can be seen with the naked eye.         The main features of the internal structure of the brainstem are most easily reviewed by examining transverse sections at various levels. These are illustrated in Figs. 6.4 to 6.8. The levels represented in these figures are indicated in Fig. 6.2.   The Medulla          A section at the level of the pyramidal decussation (Fig. 6.4) shows some similarity to sections through the spinal cord. The central canal  is surrounded by  central grey matter . The  ventralgrey columns  are present, but are separated from the central grey matter by  decussating pyramidal fibres . The region behind the central grey matter is occupied by the  fasciculus grac...

  SUBDIVISIONS OF NEURAL TUBE        We have seen earlier that even before the neural tube has completely closed, it is divisible into an enlarged cranial part and a caudal tubular part. The enlarged cranial part forms the brain. The caudal tubular part forms the spinal cord: it is at first short, but gradually gains in length as the embryo grows. The cavity of the developing brain soon shows three dilatations (Fig. 6.11B). Cranio-caudally, these are the  prosencephalon ,  mesencephalon , and  rhombencephalon . The prosencephalon becomes subdivided into the telencephalon  and the  diencephalon  (Fig. 6.11C). The telencephalon consists of right and left  telencephalic vesicles . The rhombencephalon also becomes subdivided into a cranial part, the  metencephalon , and a caudal part, the  myelencephalon . The parts of the brain that are developed from each of these divisions of the neural tube are shown in Fig....