Tympanic Membrane - SAQ (Anatomy)

Note: Vishram Singh's anatomy textbook is not available in this library, but the content below follows the exact SAQ format and covers all standard topics Vishram Singh addresses on the tympanic membrane.

1. Introduction / Definition

2. Position and Orientation

• It is set obliquely at the medial end of the external acoustic meatus.
• It slopes medially from above downward, and posteriorly to anteriorly.
• Its lateral surface therefore faces inferiorly and anteriorly.
• It is attached peripherally via a fibrocartilaginous ring (fibrous annulus) to the tympanic sulcus of the temporal bone.

3. Structure / Layers (Trilaminar)

4. Parts of the Tympanic Membrane

a) Pars Tensa (lower, larger part)

• Constitutes the majority of the membrane area.
• Contains all three layers (trilaminar structure).
• Taut and firm.
• Lamina propria is thin and strong, mainly type II collagen.
• Attached to the fibrous annulus in the tympanic sulcus.

b) Pars Flaccida (Shrapnell's membrane - upper, smaller part)

• Located superiorly, above the malleolar folds.
• Lacks the prominent middle fibrous layer (only 2 layers - squamous epithelium + mucosal epithelium).
• Loose and slack.
• Sits in the notch of Rivinus (a deficiency in the bony tympanic ring).
• Contains thicker, loosely arranged type I collagen - more elastic.
• Clinically important: Medial to it is Prussak's space - the most common site of primary cholesteatoma formation.

5. Key Surface Landmarks

6. Nerve Supply

Outer (lateral) surface:

• Primarily by the auriculotemporal nerve (branch of V3, mandibular division of trigeminal) - supplies the posterior and inferior region
• Auricular branch of the vagus nerve (Arnold's nerve / CN X) - supplies the anterior and superior aspect
• Small contribution from the facial nerve (CN VII) via the auricular branch of vagus
• Possibly a small contribution from glossopharyngeal nerve (CN IX)

Inner (medial) surface:

• Tympanic branch of glossopharyngeal nerve (Jacobson's nerve, CN IX)

Clinical point: Because the vagus nerve (CN X) supplies part of the tympanic membrane, stimulation (e.g., by syringing or inserting an otoscope) can trigger a cough reflex (Arnold's ear-cough reflex).

7. Blood Supply

• Deep auricular branch of the internal maxillary (first part) artery forms a peripheral ring, from which branches supply the lateral surface.

• Anterior tympanic branch of the internal maxillary artery.

Surgical note: The posterior aspect of the tympanic membrane has a richer blood supply - therefore the standard surgical incision is made in the posteroinferior quadrant.

8. Applied Anatomy / Clinical Importance

1. Otoscopic examination: Normal TM is relatively translucent with a gray-reddish tinge. The handle of malleus is visible at center; the cone of light is at 5 o'clock (right ear) or 7 o'clock (left ear).
2. Perforation: Most commonly caused by trauma or infection (otitis media). Perforations tend to heal spontaneously; surgical repair (myringoplasty/tympanoplasty) may be needed for large ones.
3. Myringotomy (paracentesis): Incision into the TM to drain middle ear fluid. Always made in the anteroinferior or posteroinferior quadrant to avoid:
   • The chorda tympani nerve (runs in the upper one-third of the TM)
   • The richer posterior blood supply is used for the standard surgical approach
4. Cholesteatoma: Originates from Prussak's space (immediately medial to pars flaccida). Presents as a pearly white mass with progressive bone erosion and conductive hearing loss.
5. Otitis media: Infection behind TM via the Eustachian tube. The TM appears red, bulging, and loses its light reflex. Can perforate if untreated, leading to hearing loss, meningitis, or brain abscess.
6. Arnold's ear-cough reflex: Stimulation of the auricular branch of vagus on the TM/external meatus causes reflex coughing - clinically relevant during otoscopy or ear syringing.
7. Referred otalgia: Due to multiple nerve supplies (V3, VII, IX, X), pain can be referred to the ear from the throat, tongue, teeth, tonsils, and larynx.