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
Spiral ganglion cells are strung along the bony core of the cochlea, and are part of the central nervous system. These spiral ganglion cells are bipolar first-order neurons of the auditory pathway of the brain. Their dendrites make synaptic contact with the base of hair cells, and their axons are bundled together to form the auditory portion of the VIII Cranial Nerve. In humans, the central axons number about 35,000 on each the left and right side. The acoustic information sent by this cranial nerve is very focused.