**Question:** The secondary tympanic membrane is present over

A. Eustachian tube
B. External auditory canal
C. Middle ear
D. Inner ear

**Correct Answer:** A. Eustachian tube

**Core Concept:** The secondary tympanic membrane, also known as the Eustachian tube tympanic membrane or tympanic membrane of the Eustachian tube, is a small, thin, and translucent membrane located within the Eustachian tube (ET) orthmosis. The Eustachian tube is a horizontally oriented tube that connects the middle ear to the nasopharynx, playing a crucial role in maintaining middle ear pressure balance and facilitating the equalization of air pressure in the middle ear.

**Why the Correct Answer is Right:** The secondary tympanic membrane is present in the Eustachian tube because it plays a vital role in the functioning of the Eustachian tube. This membrane acts as a passage for the transmission of vibrations from the middle ear to the nasopharynx, enabling communication between the middle ear and the nasopharynx. This ensures a proper functioning of the Eustachian tube, which aids in equalizing the pressure in the middle ear with the ambient pressure outside the body (pressure equalization), preventing middle ear infections (otitis media) and other complications associated with pressure imbalance.

**Why Each Wrong Option is Incorrect:**

A. **Eustachian tube** (Correct answer): Although option A is partially correct, the actual correct answer is the Eustachian tube tympanic membrane or orthmosis, as mentioned earlier.

B. **External auditory canal (EAC)**: The primary tympanic membrane, found in the EAC, is known as the EAC mucosa, not the secondary tympanic membrane. The EAC mucosa is responsible for sensing temperature and moisture but not for pressure equalization.

C. **Middle ear**: While the middle ear is an essential component of the eustachian tube system, the secondary tympanic membrane is specifically located within the Eustachian tube (option A), not the middle ear itself.

D. **Inner ear**: The inner ear is responsible for hearing and balance, not pressure equalization. The secondary tympanic membrane is situated within the Eustachian tube (option A), ensuring pressure balance.

**Clinical Pearl:** A thorough understanding of the location and function of the secondary tympanic membrane (Eustachian tube tympanic membrane or orthmosis) is crucial for recognizing complications related to the Eustachian tube, such as tubal dysfunction, which can lead to otitis media with effusion (OME) and other middle ear disorders. It is essential for physicians to be aware of the anatomy and physiology of the Eustachian tube system to diagnose and treat these conditions effectively.