It was fitting that the present series began with a discussion of Alfonso Corti, as most of the Cochlear Explorers in this series are named for the discoverers of the anatomical structures of his famous Organ of Corti. So far, we have discussed Corti and Friedrich Matthias Caludius. Hearing International’s next explorer is Christian Andreas Viktor Hensen.

Recall that in the 19th century it was rather common to name anatomical structures after the person who first discovered/described them, such as “the cells that Hensen described.” As we start each of these descriptions, it necessary to point out that eponyms were a convenient method to describe structures, since the original authors, such as Hensen, often did not understand the role or the precise structure of the cells they were describing and, therefore, could not propose precise anatomical names. Additionally, naming the cells when a more precise assessment of their structure and function probably made the cochlear anatomy less confusing.

Cells of Hensen

Cells of Hensen are located in the organ of Corti and are defined as one of the supporting columnar cells for the hair cells. They are located in an area delimited by the phalangeal processes of the third row of supporting cells between the outer hair cells and the cells of Claudius. They form a layer of tall cells, arranged in several rows and rest on the basilar membrane (see drawings above).

There are, however, some recent findings by Caye-Thomasen et al (2005) that these cells may express erythropoietin receptors. The expression of erythropoietin by local spiral neurons suggests the existence of paracrine regulatory circuits. The cells have also been shown to express cyclooxygenase-2. This expression is altered by sound exposure (Heinrich et al, 2006) and may indicate that the cytoprotective function of products is generated by this enzyme in hearing and in cellular stress situations like intense noise exposure. It has been further suggested that Hensen’s cells may play a regulatory role in ion and water balance of cochlear fluids through the expression of purinoceptors and Ca (2+) activated chloride channels (Sugasawa et al, 1996). Zhang et al (2002) have reported that the cells express heregulin and thus may play an important role in cell proliferation and survival in the cochlea and vestibular system for cells expressing erbB receptors.

Hensen’s cells have been shown to retain the capacity to differentiate into either tectal cells, which differentiate into outer hair cells, or into undertectal cells , which differentiate into supporting Deiters’ cells (Malgrange et al, 2002). Currrent research notwithstanding, the cells of Hensen have been known for more than 100 years and investigations on their function(s) are still waiting for an answer as to their specific function..

Viktor Hensen – Cochlear Explorer

Christian Andreas Victor Hensen (1835-1924) was born February 10, 1835, in the German city of Schleswig. His father, Hans Hensen, was director of the school of
deaf and dumb at Schleswig and his mother, Henriette, was the daughter of the court physician Carl Saudicani. From the two marriages of his father, Victor Hensen had eight sisters and six brothers. In 1845, Victor Hensen graduated from the school of the Cathedral of Schleswig and then the grammar school at Glückstadt in Holstein in 1854. He studied medicine at the Universities of Würzburg, Berlin and Kiel and passed the final examination in 1858, sustaining the Doctorate Thesis in 1859 with a paper on epilepsy and urinary secretions. That same year he qualified as a Lecturer in Anatomy and Physiology.

After the doctorate and qualification, he worked at the University of Kiel, initially as prosector. In1864 he was appointed successor to Peter Ludwig Panum as associate professor of Physiology and Director of the Physiology Laboratory at Kiel. In 1868, he became full professor of physiology in 1871 and worked until 1911. It appears that Hensen was at the University of Kiel at the same time that Friedrich Claudius was the Director of the Zoological Museum there, but there are no records of collaboration on cochlear research. While not really part of our discussion of his cochlear research, Hensen led five marine biological expeditions during his four decades of research. In 1870 he married Andrea Katarina Friederika Seestern-Pauly, and they had two sons and two daughters. From 1878, he was the director of the Institute of Physiology of Kiel. He was Dean of the Faculty of Medicine for several years and Rector of the University of Kiel many times.Victor

ce33 Hensen was an active member of the Leopoldine Academy and corresponding member of the Prussian and Bavarian academies of Science. Hensen worked mainly in physiology and marine biology. In physiology, he preferred the histophysiological method and, using it, settled essential questions regarding the basic conditions for hearing and sight. In 1863, he investigated the decapod hearing organ and the morphology of the human cochlea, describing what are now called Hensen’s supporting cells and Hensen’s duct (in the vestibular system). He identified the fibers of the basal membrane in the cochlea as resonant corpuscles capable of vibrating. He wrote lengthy summaries on the physiology of hearing (1880, 1902) and on propagation (1881). He also proved that these fibers, rather than decreasing, increase in length from base to tip of the cochlea. Hensen also investigated the organ of hearing in the forelegs of grasshoppers and also in the fishes (1904).