Vestibulocochlear Organ Overview
The external ear is just one component of a more complex system—the vestibulocochlear organ (organum vestibulocochleare). This organ is unique in that it combines two major sensory systems:
- The organ of hearing, which is functionally adapted to perceive various sound vibrations.
- The organ of balance, responsible for registering body position and movement in three-dimensional space.
Anatomically, the entire vestibulocochlear complex is traditionally divided into three major parts: the external, middle, and internal ear. The external ear serves as the initial link in this chain.
Auricle (*Auricula*)
The foundation of the auricle is a plate of elastic cartilage tightly covered by skin on the outside. This structure gives the auricle flexibility and the ability to maintain its shape.
Several key anatomical features are distinguished on the complex relief surface of the auricle:
- Helix — the outer folded margin.
- Antihelix — a ridge located parallel and medial to the helix.
- Tragus — a projection anterior to the external acoustic meatus.
- Antitragus — a tubercle located opposite the tragus.
- Scapha — a depression between the helix and antihelix.
- Concha (concha auriculae) — the central depression leading into the acoustic meatus.
The skin of the auricle is not uniform. It contains sebaceous and sweat glands, as well as hairs. Hair growth is especially prominent in the region where the auricle transitions into the external acoustic meatus.
External Acoustic Meatus (*Meatus acusticus externus*)
This canal functions as a connecting link between the auricle and the tympanic membrane. Its total length is approximately 3.5 cm. An important anatomical feature of the meatus is its S-shaped course, which is clinically significant during medical examinations.
The walls of the external acoustic meatus vary in structure and are divided into two parts:
- External part — cartilaginous (pars cartilaginea), which is a continuation of the auricular cartilage.
- Internal part — bony (pars ossea), located more deeply.
The meatus is lined internally with skin. This skin lining contains hair follicles and specific ceruminous glands (glandulae ceruminosae), which are modified sweat glands. The blind end of the external acoustic meatus is securely closed by the tympanic membrane.
Tympanic Membrane (*Membrana tympani*)
The tympanic membrane acts as the anatomical boundary strictly separating the external and middle ear. It does not lie vertically, but obliquely: its plane is tilted anteriorly and inferiorly.
Histological structure of the membrane includes three layers (from outside to inside):
- Outer cutaneous layer (stratum cutaneum).
- Middle fibrous layer (stratum fibrosum).
- Inner mucosal layer (stratum mucosum).
Anatomically, the membrane is divided into two unequal parts. The main and larger portion is the pars tensa. In the superior region lies the smaller pars flaccida.
On the inner side (facing the middle ear), the handle of the malleus—one of the auditory ossicles—is firmly attached to the tympanic membrane.