Apical half turn of cochlea

The apical turn of the cochlea refers to the most distal portion of the cochlear spiral, located furthest from the oval window and stapes, and is anatomically and functionally specialized for the detection of low-frequency sounds. In humans, the cochlea typically makes about 2.5 to 3 turns, with the apical turn comprising the final segment of this spiral, beginning after approximately 450 degrees of rotation and extending to the helicotrema at the apex.

This region is characterized by a wider and more flexible basilar membrane, distinct cytoarchitecture, and unique innervation patterns, including a relatively high density of unmyelinated efferent and type II afferent fibers.

The apical turn is responsible for encoding frequencies below approximately 1 kHz, and its tonotopic organization is compressed compared to the basal and middle turns, with a large portion of the organ of Corti mapped to a compact segment of the spiral ganglion in the modiolus.