Intradural microanatomy of the nerve roots S1–S5 at their origin from the conus medullaris

Object The conus medullaris and the nerve roots from S-1 to S-5 regulate bladder function as well as movement and sensation of the lower extremities. This most caudal region of the spinal cord has not been studied in great detail anatomically despite its important regulatory role. The goal of this analysis is to characterize the normal intradural microanatomy of the sacral nerve roots at their origin from the conus medullaris. Methods The thecal sacs from 20 cadavers were fixated in formaldehyde and dissected under the operative microscope. Results More than 50 rootlets originated from the conus medullaris over a distance of < 3 cm. The rootlets were loosely organized into bundles by the arachnoid membrane with decreasing diameters. These diameters were 1.7 mm (ventral)/2.4 mm (dorsal) at S-1, and 0.17 mm (ventral)/0.4 mm (dorsal) at S-5. The roots were separated by neither the dentate ligament nor interradicular gaps. The number of rootlets decreased in the rostrocaudal direction with 2 ventral and 5 dorsal rootlets at S-1, but only 1 ventral (inconsistently found) and 2 dorsal rootlets at S-5. Typically, 1 nerve anastomosis was present between adjacent dorsal roots from S-1 to S-4. Nerve anastomoses between ventral roots or rootlets of the same root were less frequent. The dorsal segment of origin (linea radicularis) decreased in length from 7.2 mm at S-1 to 4.8 mm at S-5. Conclusions The current study provides anatomical details and specific morphometric data of the intradural contents at the level of the conus medullaris. This information is valuable for intraoperative orientation, endoscopic navigation, and possible intradural nerve stimulation.

An anatomical study of the abdominal muscular, nervous and respiratory systems of the praying mantid, Hierodula membranacea (Burmeister)

The musculature of a typical (fourth) abdominal segment of the praying mantid, Hierodula membranacea (Burmeister), consists of 15 pairs of muscles, which can be divided into three groups: tergals, sternals and laterals. The tergals and sternals are arranged in two broad, flat layers: the internal longitudinal layer and the external longitudinal oblique layer. The laterals are a diverse group but can be divided broadly into ‘vertical segmentals’ (the cylindrical tergosternal muscles and the broad, flat tergosternal muscle) and ‘oblique intersegmentals’ (the narrow, flat tergosternal muscles and the pleurotergal muscle). There are four abdominal ganglia, the first three of which give rise to a pair of lateral nerves, which bifurcate after a short distance to form an anterior and a posterior branch, and an unpaired median nerve, which divides to form a pair of transverse nerves. A description is given of the innervation fields of the nerves in the fourth abdominal segment. Several peripheral nerve anastomoses are described and labelled with the aid of ‘symbolic landmark’ and ‘nominal’ systems of nomenclature. Three peripheral neurons are also described. There are ten pairs of spiracles located laterally on the body segments: two pairs of external thoracic spiracles and eight pairs of internal abdominal spiracles. Lateral longitudinal trunks, tergal and sternal longitudinal and transverse trunks and visceral trunks serve to interlink the spiracles.