Spiral ganglion

The spiral ganglion is the group of nerve cells that serve the sense of hearing by sending a representation of sound from the cochlea to the brain. The cell bodies of the spiral ganglion neurons are found in the spiral structure of the cochlea.

Development
The rudiment of the acoustic nerve appears about the end of the third week as a group of ganglion cells closely applied to the cephalic edge of the auditory vesicle. The ganglion gradually splits into two parts, the vestibular ganglion and the spiral ganglion. The proximal fibers of the spiral ganglion form the cochlear nerve.

Anatomy
Cells found in the spiral ganglion are strung along the bony core of the cochlea, and send projections into the central nervous system (CNS). These cells are bipolar first-order neurons of the auditory system. Their dendrites make synaptic contact with the base of hair cells, and their axons are bundled together to form the auditory portion of eighth cranial nerve. The number of neurons in the spiral ganglion is estimated to be about 35,000–50,000.