Anterior cochlear nucleus

At a glance

English

Anterior cochlear nucleus

Latin (TA2)

Nucleus cochlearis anterior

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the anterior cochlear nucleus

The anterior, or ventral, cochlear nucleus is one of the two cochlear nuclei found on each side of the brainstem; the other is the dorsal (posterior) cochlear nucleus. Together they form the cochlear nuclear complex, which lies on the dorsolateral surface of the brainstem where the pons meets the medulla. The anterior nucleus sits ventrolateral to the inferior cerebellar peduncle, and the dorsal nucleus curves over it and over the peduncle, forming a bulge called the acoustic tubercle. The anterior nucleus is unlayered, unlike its dorsal partner.

All sound information reaches the brain through these nuclei. The cochlear nerve, part of the vestibulocochlear (eighth cranial) nerve, carries the axons of spiral ganglion cells from the cochlea of the same side. Each fibre enters at the nerve root in the anterior nucleus and divides, one branch running forwards into the anteroventral part and the other backwards through the posteroventral part and on into the dorsal nucleus. The root therefore divides the anterior nucleus into anteroventral and posteroventral parts. The fibres are laid out in order of the pitch they carry, so the frequency map of the cochlea, with low tones in one region and high tones in another, is repeated in the nucleus.

Several kinds of output neuron each pick out a different feature of the sound and start parallel pathways. Bushy cells, mostly in the anteroventral part, receive very large endings of nerve fibres (the endbulbs of Held) and pass on the exact timing of the signal to the superior olivary complex, which compares the two ears to locate sounds. Stellate (chopper) cells fire steady trains of impulses that encode the strength of sound at each frequency and so the spectrum of complex sounds such as speech. Octopus cells in the posteroventral part respond to the onset of a sound with great precision. Their axons leave mostly in the trapezoid body to the superior olives of both sides and to the lateral lemniscus, which leads to the inferior colliculus.

Damage here or to the cochlear nerve causes hearing loss on the same side, since every sound fibre ends here before any crossing. A vestibular schwannoma at the cerebellopontine angle may compress the nerve. Where both cochlear nerves are lost, an auditory brainstem implant on the nucleus can restore some hearing.

Function and supply

Function

Receives all fibres of the cochlear nerve from the same ear, preserves their frequency map and extracts timing, intensity and onset information, sending it to the superior olivary complexes and the lateral lemniscus for sound localisation and analysis.

Blood supply

Supplied by the anterior inferior cerebellar artery, with branches from the posterior inferior cerebellar and vertebral arteries.