Anatomy of the Ear

Introduction

• The ear is complex but fascinating.
• Contains the three smallest bones in the body.
• Converts vibrations into recognizable sounds.
• Aids in balance via specialized organs.

Main Components

1. External Ear
2. Middle Ear
3. Inner Ear

External Ear

• Oracle/Pinner: The visible part of the ear designed to capture sound.
  • Helix: Curved outer surface.
  • Anti-Helix: Runs parallel to the helix; splits into superior and inferior crus.
  • Concha: Shallow depression that directs sound waves inward.
  • Tragus: Small projection near concha.
• External Acoustic Meatus: Hollow tunnel leading into the head.
  • Outer third: surrounded by cartilage.
  • Inner two-thirds: surrounded by temporal bone.
  • Ends at the tympanic membrane.
• Tympanic Membrane (Eardrum):
  • First part to vibrate with sound waves.
  • Covered by thin skin, mostly translucent.
  • Visible structures: malleus (lateral process, handle, umbo).
  • Divided into pars tensor (below malleus) and pars flacida (above malleus).
  • Anchored by a fibrocartilaginous ring.
  • Crossed by the chorda tympani branch of the facial nerve.

Middle Ear

• Tympanic Cavity: Hollow space allowing free vibration of bones.
  • Main part: Tympanic cavity.
  • Upper part: Epitympanic recess (communicates with mastoid air cells via superior mastoid antrum).
• Auditory Ossicles: Three tiny bones transmitting vibrations.
  • Malleus: Handle (contacts tympanic membrane), anterior process, neck, head (articulates with incus).
  • Incus: Body, short and long process (articulates with stapes).
  • Stapes: Stirrup-shaped, has head (articulates with incus), footplate (joins oval window).
• Eustachian Tube: Connects middle ear with nasopharynx to equalize pressure.
• Tiny Muscles:
  • Tensor Tympani: From Eustachian tube to malleus; innervated by the mandibular nerve.
  • Stapedius: Connects to stapes; innervated by the facial nerve.
  • Both muscles protect the inner ear from loud noises via the acoustic reflex.

Inner Ear

• Key Structures: Cochlea (sound), vestibular apparatus (balance), and semicircular canals (balance).
• Divided into:
  • Bony Labyrinth: Main structures.
  • Membranous Labyrinth: Series of ducts containing endolymph fluid.
• Cochlea: Converts vibrations into sound signals.
  • Spiral-shaped; attaches to the modiolus bone.
  • Communicates with middle ear via the round window.
• Vestibule: Middle portion in contact with stapes bone (oval window).
• Semicircular Canals: Three c-shaped projections responsible for balance.
  • Contain fluid that moves to determine head direction and body position.
  • Each base has an ampulla.
• Vestibulocochlear Nerve: Enters through internal acoustic meatus and splits into cochlear and vestibular nerves.
  • Facial Nerve: Passes through but has no innervation.

Conclusion

• Overview of the external, middle, and inner ear.
• Future tutorials will cover details of the inner ear and cranial nerves.