The cochlear nuclei are structures in the brainstem where nerves from the spiral-shaped cochlea pass through. They serve as a gateway between the inner ear and the rest of the brain, allowing nerve impulses and sound information to be processed and transmitted to the brain’s major auditory centers. Divided into both the ventral and dorsal cochlear nucleus, they form a crucial section of the auditory pathway, and are also divided up into anterior and posterior sections. Both are located alongside the rear section of the brainstem, opposite from a motor nerve tract called the inferior peduncle.
Nerve fibers in the nuclei are organized into a complex system of spiral ganglion cells, which detect low frequency sounds, and axions from hair cells in the cochlea, which detect high frequency sounds. The cochlear nuclei have three major nerve projections that spread into the brain via the brain stem through the medulla. One is known as the ventral acoustic stria and passes through a brain structure known as the superior olivary complex. The dorsal acoustic stria, another projection, also traverses the medulla, along with the intermediate acoustic stria. These then pass through the pons, a brain structure that links both hemispheres, and into the nucleus of the lateral lemniscus.
All of the nerve fiber projections from the cochlear nuclei end in the inferior collicus, from which other projections spread out to the major auditory processing centers in the brain. Many of the nerve cells also pass through the core of the cochlea and end as hair cells that pick up each sound from the ears. There are also various other types of cells within the cochlear nuclei. Bushy cells, which feature small branches that create the appearance of bushes, and in the anterior ventral cochlear nucleus. They are primarily responsible for transmitting timing information between the main auditory nerve and other auditory processing areas.
Star-shaped cells called stellate cells fire electrical pulses at regular rates when a noise is detected. The rate of activity is determined by how strong the auditory input is, while octopus cells, located in the posterial ventral cochlear nucleus, respond to frequency. They fire at the beginning of any change in frequency, and are also important in transmitting information on the timing of sounds. These are also the highest-precision nerve cells of the brain in terms of temporal detection. Together, the cochlear nuclei and the rest of the auditory system process sound from the outside world along with its location, frequency, and timing.
