Vestibulocochlear organ overview
The external ear is only one of the components of a more complex system — the vestibulocochlear organ (organum vestibulocochleare). This organ is unique in that it combines two major analyzers at once:
- The organ of hearing, which is functionally adapted to perceive various sound vibrations.
- The organ of balance, responsible for registering body position and its movements in three-dimensional space.
Anatomically, the entire vestibulocochlear complex is traditionally divided into three major parts: the external, middle, and inner ear. The starting link in this chain is the external ear.
Auricle (Auricula)
The basis of the auricle is a plate of elastic cartilage, tightly covered with skin on the outside. This structure provides the auricle with elasticity and the ability to maintain its shape.
Several key anatomical structures are distinguished on the complex contoured surface of the auricle:
- Helix (helix) — the outer folded margin.
- Antihelix (antihelix) — a ridge located parallel and medial to the helix.
- Tragus (tragus) — a prominence anterior to the acoustic meatus.
- Antitragus (antitragus) — a tubercle lying opposite the tragus.
- Scapha (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 homogeneous. It contains sebaceous and sweat glands, as well as hair. Hair is especially prominent in the transition area from the auricle to the external acoustic meatus.
External acoustic meatus (Meatus acusticus externus)
This canal acts as a connecting link, joining the auricle directly to the tympanic membrane. Its total length is approximately 3.5 cm. An important anatomical feature of the meatus is its S-shape, which is of significant importance during a medical examination.
The walls of the external acoustic meatus are heterogeneous in structure and divided into two parts:
- External part — cartilaginous (pars cartilaginea), which is a continuation of the auricular cartilage.
- Internal part — osseous (pars ossea), located deeper.
The meatus is lined from the inside 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 tightly closed by the tympanic membrane.
Tympanic membrane (Membrana tympani)
The tympanic membrane acts as an anatomical boundary strictly separating the external and middle ear. It is not positioned 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 mucous layer (stratum mucosum).
Anatomically, two unequally sized parts are distinguished in the membrane. The main, larger one is the tensed part (pars tensa). In the upper region, there is a small flaccid part (pars flaccida).
From the inner side (from the middle ear side), the handle of the malleus — one of the auditory ossicles — is firmly attached to the tympanic membrane.
Briefly: answers to topical questions
What is the innervation of the skin of the auricle?
The skin of the auricle is supplied by branches of the cervical plexus and the vagus nerve.
- Greater auricular nerve (n. auricularis magnus, C₂–C₃) — supplies the skin of the auricle, as well as behind and below it.
- Auricular branch (from the vagus nerve) — supplies the skin of the posterior surface of the auricle.
What are the shape and dimensions of the external acoustic meatus?
The external acoustic meatus has an S-shaped course and appears as a longitudinally oriented oval in cross-section.
Its length ranges from 25 mm to 3.5 cm. The meatus consists of two parts:
- Cartilaginous part (pars cartilaginea) — makes up the lateral third.
- Osseous part (pars ossea) — makes up the medial two-thirds.
Which arteries supply blood to the external ear?
The blood supply to the external ear is provided by branches of the external carotid artery.
- Anterior auricular branches (rr. auriculares anteriores) — arise from the superficial temporal artery and head toward the auricle.
- Posterior auricular artery (a. auricularis posterior) — runs upward along the posterior margin of the auricle, supplying it and the mastoid region.
To remember the three layers of the tympanic membrane from outside to inside (cutaneous, fibrous, mucous), use the mnemonic — Skin-Fibrosis-Mucus.
Class and exam questions
What type of cartilage forms the framework of the auricle?
The framework of the auricle is formed by elastic cartilage covered with skin.
What parts are distinguished in the structure of the external acoustic meatus?
The walls of the acoustic meatus are divided into an outer cartilaginous part (pars cartilaginea) and an inner osseous part (pars ossea).
What are ceruminous glands and where are they located?
Ceruminous glands (glandulae ceruminosae) are modified sweat glands located in the skin lining the external acoustic meatus.
Which layers form the tympanic membrane?
The tympanic membrane consists of outer cutaneous, middle fibrous, and inner mucous layers.
What else to study on this topic
- Anatomy of the middle ear and auditory ossicles
- Structure of the organ of balance (vestibular apparatus)
- The inner ear and the mechanism of sound perception
- Age-related structural features of the tympanic membrane
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