Lecture on the Anatomy of the External and Middle Ear

Introduction

• Focus on the external and middle ear.
• Importance: foundational to understanding auditory and vestibular pathways.

External Ear Anatomy

• Auricle/Pinna
  • Structure: Elastic cartilage, covered by stratified squamous epithelium.
  • Function: Flexibility and elasticity.
  • Other location of elastic cartilage: Epiglottis.
• External Acoustic Meatus
  • Bony canal lined with stratified squamous epithelium.
  • Contains ceruminous glands (modified apocrine glands) producing cerumen (earwax).
  • Function of cerumen: Deters insects.

Tympanic Membrane

• Separates external and middle ear.
• Structure:
  • Pars Tensa: Dense irregular connective tissue.
  • Pars Flaccida: Loose areolar connective tissue.
• Importance: Vulnerable to punctures, affecting middle ear pressure.

Middle Ear Anatomy

• Ossicles: Tiny bones in the middle ear.
  • Malleus (hammer), Incus (anvil), Stapes (stirrups).
  • Function: Transmit sound vibrations to the oval window, leading to fluid movement in the cochlea.
• Tensor Tympani Muscle
  • Innervated by the mandibular branch (V3) of trigeminal nerve.
  • Function: Pulls malleus to dampen sound vibrations.
• Stapedius Muscle
  • Innervated by the facial nerve.
  • Function: Controls movement of stapes to dampen sound vibrations.

Nerve Supply and Canals

• Facial Canal
  • Contains the facial nerve (cranial nerve 7).
  • Branches to stapedius muscle and forms the chorda tympani.
  • Chorda Tympani: Provides taste to anterior two-thirds of the tongue and salivation via submandibular ganglion.
• Tympanic Plexus
  • Formed by parasympathetic fibers of the glossopharyngeal nerve and sympathetic fibers.
  • Function: Innervates the middle ear.

Important Features and Functions

• Pharyngeal Tympanic Tube (Eustachian Tube)
  • Function: Equalizes pressure between the middle ear and the atmosphere.
• Mastoid Sinus
  • Can provide air to the middle ear.
  • Risk of mastoiditis affecting cranial nerves.
• Tegmen Tympani
  • Forms the roof of the middle ear cavity.
  • Thin bone, risk of infection spread to cranial cavity.

Additional Muscles

• Tensor Veli Palatini
  • Innervated by trigeminal nerve, affects soft palate tension.
• Salpingo Pharyngeus
  • Innervated by vagus nerve, helps equalize ear pressure.

Summary

• Covered the anatomy and functions of the external and middle ear components.
• Important structures include the auricle, tympanic membrane, ossicles, and Eustachian tube.
• Discussed the nerve supply and significance of mastoid and tympanic structures.
• Highlighted potential complications like mastoiditis and the importance of protecting the ear’s structures.