A Study of Potentials Recorded From the Hypoglossal Nucleus

Abstract

The hypoglossal nucleus is located in the floor of the fourth ventricle and extends almost the entire length of the medulla. The nucleus maintains a paramedian position in close relationship to the medial longitudinal fasciculus. The rostral end of the nucleus is lateral, while more caudally, the relationship to the medial longitudinal fasciculus becomes dorso-lateral. The nucleus is ventral to the central canal in the medulla below the obex. Formerly, the nucleus was considered to be entirely composed of general somatic efferent cells, but in recent years the evidence indicates that it also has an afferent component. | Ramon y Cajal (*09) described the motoneurons of the cat as being very similar to those in the ventral horn of the spinal cord. He identified two main types of motoneurons in the hypoglossal nucleus. They were motoneurons with short dendrites and motoneurons with both short and long dendrites. The majority of the motoneurons have short dendrites which ramify in the nucleus, while the minority of cells have short dendrites which remain in the nucleus and long dendrites which extend beyond the boundary of the nucleus in a ventrolateral direction. Lorente de No' ('47) described the "marginal dendritic zone"; a dense dendritic plexus containing no cell bodies that forms the dorsal boundary of the nucleus. Boyd ('41) described the hypoglossal cells of the rabbit embryo as being similar to the ventral horn motoneurons.