Tympanic Membrane Anatomy - Head and neck Anatomy medical animations / USMLE Step 1
Tympanic Membrane: Structure and Function
Overview of the Tympanic Membrane
- The tympanic membrane, or eardrum, is a thin, semi-transparent membrane that separates the external ear from the middle ear. It measures approximately 0.1 mm in thickness and 8 to 10 mm in diameter, positioned at an acute angle of about 55 degrees.
Subdivisions of the Tympanic Membrane
- The tympanic membrane consists of two main parts:
- Pars Tensa: This thicker portion forms most of the membrane and has a fibrocartilaginous rim called the annulus tympanicus.
- Pars Flaccida (Shrapnell's Membrane): A small triangular area above the lateral process of the malleus that is thinner and appears pink.
Structural Characteristics
- The tympanic membrane has two surfaces:
- Lateral Surface: Concave towards the external ear, directed downwards, forwards, and laterally.
- Medial Surface: Convex and bulges into the middle ear; its maximum convexity is known as the umbo.
Layers of the Tympanic Membrane
- The structure comprises three layers:
- Outer Cuticular Layer: Lined by hairless keratinized squamous epithelium.
- Intermediate Fibers Layer: Contains outer radiating fibers from the handle of malleus and inner circular fibers more prevalent at the periphery.
- Inner Mucosal Layer: Lined by ciliated columnar epithelium.
Blood Supply and Innervation
- Blood supply includes:
- Outer surface supplied by deep auricular artery (maxillary artery).
- Inner surface supplied by anterior tympanic artery (maxillary artery) and posterior auricular artery (stylo-mastoid artery).
- Nerve supply involves:
- Anterior half innervated by auriculotemporal nerve.
- Posterior half innervated by vagus nerve's auricular branch.
- Medial surface innervated by glossopharyngeal nerve via tympanic plexus.
Development and Clinical Correlation
Developmental Origins
- The tympanic membrane develops from ectodermal cleft tissue combined with mesoderm. Its three layers correspond to their embryonic origins:
- Cuticular layer from ectoderm,
- Intermediate layer from mesoderm,
- Mucous layer from endoderm.
Clinical Examination Techniques
- Otoscopic examination provides insights into middle ear conditions through observation of color, curvature, lesions, and malleus position.
Key Observations During Inspection
- A cone of light reflects in the anterior inferior quadrant during illumination due to concavity at umbo attachment point.
- Structures visible include:
- Handle of malleus as a yellow streak,
- Lateral process as a white prominence,
- Long processes of incus appearing as white streaks parallel to malleus handle.
Quadrant Division for Clinical Assessment
- Clinically, four quadrants are defined using imaginary lines through umbo for detailed assessment during otoscopic examination.
Pathological Considerations
Perforation Causes and Treatments