modiolus

Modiolus refers to two distinct anatomical structures in human anatomy, depending on the context: the central axis of the cochlea in the inner ear, and a fibromuscular node at the corner of the mouth.

In the cochlea, the modiolus is the central bony pillar around which the cochlear spiral is wound. It forms the core of the osseous labyrinth and runs along the cochlear axis. The modiolus houses the spiral ganglion cells and the nerve fibers that constitute the cochlear portion of the vestibulocochlear nerve (cranial nerve VIII). It is perforated by openings that allow passage of vessels and nerve fibers through the tract called the canal of the modiolus. The structure provides the base for the cochlear ducts and contributes to the organization of sensory neural elements essential for hearing. Its architecture can influence cochlear implant placement and overall cochlear mechanics.

The other use of the term describes a fibromuscular node at the corner of the mouth, where multiple muscles converge. The modiolus at the oral commissure acts as an anchor point for the orbicularis oris, buccinator, risorius, zygomaticus major and minor, levator anguli oris, and depressor anguli oris. This modiolus contributes to lip movement, oral sphincter function, and facial expression. Clinically, it is relevant to procedures in facial reanimation, cosmetic surgery, and considerations of dental occlusion and speech.