Posterior Longitudinal Fasciculus
The posterior longitudinal fasciculus (Schütz’s bundle) contains ascending and descending fiber systems that connect the hypothalamus with various nuclei of the brain stem and provide connections between the visceroefferent parasym-pathetic nuclei. A large portion of the fibers are peptidergic (somatostatin, among others). They originate or terminate, respec-tively, in the septum, the oral hypothalamus, the gray tubercle (B13), and the mamillarybodies (B14). They aggregate in the mid-brain below the ependyma of the aqueduct and form the longitudinal fasciculus, which runs beneath the ependyma on the floor of the fourth ven-tricle to the lower portion of the medulla oblongata.
Fibers branch off to the superior colliculi (B15) and to the parasympathetic nuclei, namely, the Edinger – Westphal nucleus (ac-cessory nucleus of oculomotor nerve) (B16), the superior (B17) and inferior (B18) sali-vatory nuclei, and the posterior vagus nu-cleus (B19). Other fibers terminate in thecranial nerve nuclei, namely, in the motornucleus of the trigeminal nerve (B20), the fa-cial nucleus (B21), and the hypoglossal nu-cleus (B22). Fibers are also exchanged withthe nuclei of the reticular formation.
The posterior longitudinal fascicle receives olfactory impulses via the lateroposteriortegmental nucleus (habenular nucleus – in-terpeduncular nucleus – lateroposterior tegmental nucleus).
Long ascending pathways.Fibers, probablytaste fibers, ascend from the solitary nucleus (B23) to the hypothalamus. The fibers of serotoninergic neurons can be traced by fluorescence microscopy from the posteriorraphe nucleus (B24) into the region of theseptum.
The posterior longitudinal fasciculus re-ceives hypothalamic, olfactory, and gustatory impulses that are relayed to the motor and sensory nuclei of the brain stem (reflex movement of the tongue, secretion of saliva).
A25 Subthalamic nucleus.