The Eustachian tube, also known as the auditory tube or pharyngotympanic tube, is a tube that connects the nasopharynx to the middle ear. This is part of the middle ear. In adults, the Eustachian tube is about 35 mm (1.4 inches) long and 3 mm (0.12 inches) in diameter. It is named after the sixteenth-century Italian anatomist Bartolomeo Eustaki.
In humans and other land animals, the middle ear (like the ear canal) is usually filled with air. However, unlike the open ear canal, the air in the middle ear is not in direct contact with the atmosphere outside the body. The middle ear tube provides a connection from the middle ear chamber to the back of the nasopharynx.
Normally the Eustachian tube is closed, but it opens with both swallowing and positive pressure. When an airplane takes off, the ambient air pressure rises from higher (on the ground) to lower (in the sky). Airin the middle ear expands as the aircraft gains altitude and pushes into the back of the nose and mouth. On the way down, the volume of air in the middle ear decreases. Thus, a small vacuum is created. Active opening of the Eustachian tube is required to equalize pressure between the middle ear and the surrounding atmosphere as the aircraft descends. The diver also experiences this change in pressure, but at a faster rate. Active opening of the middle ear auditory tube provides pressure equalization.
Composition
The Eustachian tube extends from the anterior wall of the middle ear to the side wall of the nasopharynx. This happens approximately at the level of the inferior nasal concha. It consists of a bone part and a cartilage part.
Bone
The bone part closest to the middle ear (1/3) is made of bone and has a length of about 12 mm. It begins in the anterior wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at an angle between the squamous and temporal parts of the temporal bone. The limb represents a jagged edge that serves to attach the cartilaginous part.
Cartilage part
The cartilaginous part of the Eustachian tube is about 24 mm long and is formed by a triangular plate of elastic fibrocartigal, the top of which is attached to the edge of the medial end of the bony part of the tube. Its base lies directly under the mucous membrane of the nasal part of the pharynx, where the middle ear auditory tube provides the formation of an elevation - torus tubarius orpillows - behind the pharyngeal opening of the auditory tube.
The upper edge of the cartilage is twisted by itself, bent laterally to look like a hook in cross section; thus a furrow or furrow is formed which is open below and on the side. This part of the canal is terminated by a fibrous membrane. The cartilage lies in a groove between the malignant part of the temporal bone and the greater wing of the sphenoid bone; this groove ends opposite the middle of the medial pterygoid plate.
The cartilaginous and bony portions of the tube are not in the same plane, with the first downward slope slightly greater than the second. The diameter of the tube throughout the body is not uniform. It is most in the opening for the pharynx, least of all - at the junction of the bone and cartilage parts. It is enlarged again towards the tympanic cavity. The narrowest part of the tube is called the isthmus.
The mucous membrane of the tube is continuous in front with the nasal part of the pharynx, and behind - with the cavity of the tympanic cavity. The auditory tube of the middle ear provides a covering of ciliated pseudostratified columnar epithelium. It is thin in the bone part, while in the cartilaginous part it contains many mucous glands and, near the pharyngeal opening, a significant amount of adenoid tissue, which Gerlach called the tubal tonsil.
Muscles
There are four muscles associated with the function of the Eustachian tube:
- Levator veli palatini (innervated by the vagus nerve).
- Salpingopharyngeus (innervated by the vagus nerve).
- Tensor tympanic membrane(innervated by the mandibular nerve CN V).
- Tensor of the great palatini (innervated by the mandibular nerve CN V).
The middle ear tube ensures that the membrane opens during swallowing by contracting the tensor veli palatini and the levator veli palatini, the muscles of the soft palate.
Development
The Eustachian tube originates from the ventral portion of the first pharyngeal pouch and the second endodermal pouch, which forms a tubular depression during embryogenesis. The distal tubular groove gives rise to the tympanic cavity, and the proximal tubular structure becomes the Eustachian tube. Thus, the middle ear canal provides vibration and helps transform sound waves.
Functions
Pressure equalization. Under normal circumstances, the human Eustachian tube is closed, but it can open to let in a small amount of air and prevent injury by equalizing pressure between the middle ear and the atmosphere. The pressure drop causes temporary conductive hearing loss due to reduced movement of the tympanic membrane and ear ossicles. Various ear cleaning techniques, such as yawning, swallowing, or chewing gum, can be used to deliberately open the tube and equalize pressure. When this happens, people hear a soft crackle. This is an event familiar to aircraft passengers, scuba divers or drivers in mountainous regions.
Pressure equalization aids include a special balloon applied to the nose that inflates with positive air pressure. Some people learn to voluntarily “flick” their ears, either together or individually, by performing a pressure equalization procedure by opening their Eustachian tubes when there is a change in pressure, such as going up/down in an airplane, driving in mountains, going up/down an elevator, etc. e.
Some may even deliberately keep their Eustachian tubes open for a short period and even increase or decrease air pressure in the middle ear. In fact, the "click" can be heard by bringing the ear to the other while performing the click sound. This voluntary control may be first detected by yawning or swallowing, as well as by other means (see above). Those who develop this ability may find that it can be done consciously, without force, even if there is no pressure problem.
Drainage of mucus. Upper respiratory tract infections or allergies can cause the Eustachian tube or the membranes surrounding its opening to become swollen. They will retain fluid that harbors bacteria, causing ear infections because the middle ear canal drains mucus from the middle ear. Ear infections are more common in children because the tube is horizontal. It is shorter, which makes it easier for bacteria to enter, and also has a smaller diameter, which makes it difficult for fluid to move. In addition, children's developing immune systems and poor hygiene habitsmake them more prone to upper respiratory tract infections.
