Isthmus r0

Abstract

In this neuromere, the second trigeminal nucleus following the spinal one (see Chap. 3) develops, i.e., the principal sensory trigeminal nucleus. By contrast to the protopathic properties of the spinal nucleus of the trigeminal nerve this nucleus is the epicritic component of the trigeminal system providing sensibility to the skin of the face, the cranial mucosa of mouth, nasal cavities, teeth, and sinuses. This distribution pattern—alongside that of the spinal trigeminal nucleus—indicates the clinical disciplines that potentially deal with the epicritic properties of the trigeminal nerve like neurology, neurosurgery, ENT, neuroradiology but also dentistry. The principal sensory trigeminal nucleus gets input from three major branches, the ophthalmic, the maxillar and the mandibular nerves. In addition to the sensory function, branches of the trigeminal nucleus subserve the guidance of parasympathetic and sympathetic fibers to their target organs, for example, to the lacrimal gland and the minor salivary glands. The trigeminal nerve plays an important role in neurological examination and for neurological disorders as, for example, trigeminal neuralgia and trigeminal herpes zoster.

The interpeduncular nuclei are the target structure of the habenulo-interpeduncular tract (formerly Fasciculus retroflexus) from the epithalamic habenular nuclei, one of the largest cholinergic tracts of the brain. Data from animal studies point to a role in the regulation of several behavioral patterns.

Barrington’s nucleus—a derivative of rhombomere 2—is an important integration center for the regulation of the urinary bladder function.

The interpeduncular fossa, exit site of the oculomotor nerve, is an important anatomical and neuroradiological landmark. The close anatomical relationship between the oculomotor nerve and the vessels of the circle of Willis (see Chaps. 1 and 15) in the region of the interpeduncular fossa is the basis of aneurysm-related disturbances of the oculomotor nerve.