Population and density of the bipolar ganglion cells in the cochlea of the harp seal ( Pagophilus groenlandicus Erxleben, 1777)

• Published in: Canadian Journal of Zoology
• Main Author: Ramprashad, F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1976
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Harp Seal; Pagophilus groenlandicus
• Online Access: http://dx.doi.org/10.1139/z76-222; http://www.nrcresearchpress.com/doi/pdf/10.1139/z76-222

The population and density of the bipolar ganglion cells were determined from serial horizontal sections and graphic reconstructions of the cochleas of five captive harp seals. The [Formula: see text]-turn spiral ganglion forms a continuous ring throughout its course except at the extreme basal end where it is narrowest. The nerve cell body is 25 μm long (16.1–38.8 μm) and 16 μm wide (10–24 μm). The average number of ganglion cells present was 57 185 (46 389 – 70 952), with a corrected total number of 52 000 ganglion cells. Two peaks are present in the density curve of the ganglion cells. The first was at 1–1.5 mm and the second at 20 mm, where 2620 cells/mm 2 and 2250 cells/mm 2 respectively are present.The ratio of total ganglion cells to total sensory hair cells was about 3:1. This ratio was not uniform throughout the length of the cochlea; it was 6:1 at 2–3 mm from the basal end and declined gradually to 3:1 at the apical end. The average total of ganglion cells in the harp seal exceeded the average value in humans, but did not exceed the values found in dolphins.