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Main article: Organ of Corti

Further information: Claudius cell and Deiters cells

Hensens' cells
Schematic anatomy of the Organ of Corti, the Hensen's cells form part of the outer hair cells.
Details
System	Supporting system
Anatomical terminology

Hensen’s cells are a layer of tall cells arranged in the Organ of Corti in the cochlea, which are part of the supporting cells lie on the outer hair cells (OHC) Their appearance are upper part wide with lower part narrow, column like cells. One significant morphologic feature of Hensen's cells is the lipid droplets, which are most noticeable at the third and forth turns of the cochlear, the lipid droplets are thought to have association with the auditory process because they are parallel to the innervation.

There are increased evidence which show that Hensen's cells are critical in many functions, they act as mediators of ion metabolism, the K+ spatial buffering pathway, the neuron innervation, and the purinergic receptors that found in the Hensen's cells are important in providing a suitable electrical and micro mechanical environment to support hair cells and to maintain homeostasis of the Organ of Corti.

Hensen’s cells are currently being investigated to be promising targets for gene therapy and regenerative medicine.

Hensen's cells are named after German anatomist and physiologist, Hensen Victor (1835-1924).

Location

Hensen's cells are one of the supporting cells found in the cochlea, and are located on the third row outer hair cells in the Organ of Corti.

Structure

The shape of Hensen's cells are various in different position of cochlea, they appear as a single layer of cells in the basal coil while appear as cuboidal form in the apical surface. They contain nuclei and microvilli but are limiting of plasma membrane, they are also lack of endoplasmic reticulum and have few mitochondria. In the apical surface, there are free enlarged poles found in the Hensen's cells, the cytoplasm of the cells is a little more dense in the apical surface than the cells in the basal coil. The enlarged poles in the cells which nearly fill the cytoplasm are lipid droplets, which are noticeable at the third and forth turns of the cochlea, the lipid droplets are thought to have relation with auditory process. The phagosomes found in the cells are another characteristic of the Hensen's cells, indicating that they have a function of phagocytosis.

There are gap junctions among supporting cells and also between supporting cells and hair cells, the gap junctions are made of connexins which are three times denser in the apex than the base. The gap junctions play an important role in regulating the concentration of intracellular K+ between the endolymph and the perilymph, maintaining pH homeostasis, and increasing movement of the ions between cells.

There are nerve fibres and terminals innervation in the Hensen's cells, these nerve fibers are chemical synapses which located on the supranuclear region of the outer hair , and are more common in the apical surface than the basal of the cochlea. The terminals, on the other hand, are more common in the basal of the cochlea, and contain mitochondria, Golgi apparatus and dense core vesicles. The innervation of the supporting cells were shown by the finding of synaptophysin-immunostained terminals in the guinea pigs and rats.

Function

There are increased evidence indicating that supporting cells serve many critical functions within the Organ of Corti, they may mediate the initiation of hearing activate during cochlea development. Hensen's cells are important in ion homeostasis regulation of both endolymph and perilymph, modulation of the hearing sensitivity, and prevention of the cochlea damage.The outer hair cells of the cochlea preprocess the signal by active movements, which can be elevated by electrical or chemical stimulation.

Ion metabolism

ATP can induce potassium current on Hensen's cells and also elevate the concentration of cytoplasmic calcium in both the inner and outer hair cells. Under negative potential condition, ATP is able to activate a biphasic current which increased the concentration of calcium in the Hensen's cells, following by a reversal potential which induced another current that was carried by chloride. When ATP induced an increase in cytoplasmic calcium, membrane becomes depolarized and the outer hair cells are contracted.

Purinergic receptors have been found in the cells of the Organ of Corti, which are able to mediate physiological and pathophysiological actions. There are various types of purinergic receptors, the most common expressed in the Hensen's cells is the P2 subtype. Another metabotropic P2Y receptor subtypes are also expressed in the cochlea, P2Y1, P2Y2, P2Y4, and P2Y6 are found in the Hensen's cells.

Cell regeneration

When the hair cells undergo apoptosis, the surrounding supporting cells would regenerate both new hair cells and supporting cells in vertebrates. however, studies found that humans and other mammals are unable to replace the damaged hair cells, the loss of hair cells could lead to permanent deafness. In addition to hair cell regeneration, supporting cells also act as mediators to hair cell survival. When under heat stress condition, the supporting cells could express heat shock protein 70 (HSP70) which is not up regulate in hair cells. Therefore, supporting cells could act as determinants of whether the hair cells be dead or alive. The supporting cells capacity to form new hair cells change at different time, it is most abundant in the embryonic Organ of Corti, and substantially decreased when maturing.