spiralganglion

The spiral ganglion is a cluster of sensory neuron cell bodies located within Rosenthal's canal in the modiolus of the cochlea. It forms the sensory component of the cochlear nerve, the cochlear division of the vestibulocochlear nerve (cranial nerve VIII), and it relays sound information from the hair cells to the brainstem.

Two main neuronal populations populate the spiral ganglion. Type I neurons are large, myelinated, and constitute the majority of afferent fibers; they innervate the inner hair cells. Type II neurons are smaller and unmyelinated, and they innervate outer hair cells. The peripheral processes of these neurons connect with hair cells in the organ of Corti, while their central processes join to form the cochlear nerve fibers that project to the brainstem.

Central projections from the spiral ganglion enter the brainstem via the internal auditory (acoustic) meatus and terminate primarily in the dorsal and ventral cochlear nuclei. The spiral ganglion maintains a tonotopic organization, with spatial position along the cochlea corresponding to different frequency representations in the central auditory pathways.

Developmentally, spiral ganglion neurons arise from precursors derived from the otic placode. They are essential for transducing mechanical vibrations into neural signals and for transmitting auditory information to higher auditory centers.

Clinically, degeneration or dysfunction of spiral ganglion neurons can contribute to sensorineural hearing loss. Cochlear implants, which electrically stimulate surviving spiral ganglion neurons, rely on the integrity of these cells for effective auditory perception.