EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
148. The Brainstem: Myelencephalon (fifth Vesicle) – Alar Sensory and Roof Plates
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- The myelencephalon
- THE ALAR SENSORY PLATES contain the sensory relay nuclei which, like the basal plate, are divided into 3 groups
- The most lateral is the somatic afferent group: receives impulses from the ear and surface of the head via the staticoacoustic (VIII) and bulbospinal part of the trigeminal (V) nerves
- The intermediate is the special visceral afferent group: receives impulses from the taste buds of the tongue and from the palate, oropharynx, and epiglottis
- These neurons later form the nucleus of the solitary tract
- The medial is the general visceral afferent group: represented by the dorsal sensory nucleus of the vagus (X) nerve with its neurons receiving interoceptive information from the heart and gastrointestinal tract
- In addition to the sensory relay nuclei, other cells of the alar plate migrate downward to be ventrolateral to the basal plate and form a part of the olivary nuclear complex
- THE ROOF PLATE, CHOROID PLEXUS, AND THE FORAMINA OF LUSCHKA AND MAGENDIE
- The roof plate of the myelencephalon consists of a single layer of ependymal cells which is later covered by vascular mesenchyme, the pia mater. Together they make up the tela choroidea
- As a result of active proliferation of vascular mesenchyme, the tela choroidea forms a series of saclike invaginations that project into the underlying ventricular cavity in the region of the pontine flexure, forming the choroid plexus. The latter are tuftlike invaginations that produce the cerebrospinal fluid of the central nervous system
- At about month 4, areas of the roof plate of the rhombencephalon thin out, bulge outward, and finally disappear. The apertures formed are the 2 lateral foramina of Luschka and a median foramen of Magendie which allow the cerebrospinal fluid to move freely between the ventricles and the surrounding subarachnoid space
