Anatomy of the Ear

Introduction

• The ear is a complex and fascinating organ.
• Contains the three smallest bones in the body.
• Converts vibrations into recognizable sounds.
• Has an organ to aid balance by recognizing head position.

Main Components of the Ear

1. External Ear

• Auricle (Pinna): Captures sound and transmits inward. Resembles a satellite dish.
  • Helix: Outermost curved surface.
  • Antihelix: Runs parallel to the helix, splits into superior and inferior crura.
  • Concha: Shallow depression before the ear canal, directs vibrations.
  • Tragus: Small cartilaginous projection near the concha.
• External Acoustic Meatus: Hollow tunnel running horizontally, slightly S-shaped.
  • Outer third walled by cartilage, inner two-thirds by the temporal bone.

2. Tympanic Membrane (Eardrum)

• Divides external and middle ear.
• Covered by a thin layer of skin; mostly translucent.
• Allows visibility of the malleus (middle ear bone) through it.
• Parts: pars tensa (below lateral process of malleus) and pars flaccida (above).
• Anchored by a fibrocartilaginous ring.
• Internal surface crossed by the cauda tympani branch of the facial nerve.

3. Middle Ear

• Located within the tympanic bone.
• Tympanic Cavity: Main cavity for bone vibration.
• Epitympanic Recess: Upper cavity; communicates with mastoid air cells.
• 3 Bones (Auditory Ossicles):
  • Malleus: Handle contacts tympanic membrane, connected to incus.
  • Incus: Connects malleus to stapes.
  • Stapes: Stirrup-shaped; contacts oval window of vestibule.
• Eustachian Tube: Balances air pressure between middle ear and outside world.
• Muscles:
  • Tensor Tympani: Connects eustachian tube to malleus; innervated by mandibular nerve.
  • Stapedius: Connects to stapes; innervated by facial nerve.
  • Acoustic reflex contracts these muscles to protect the inner ear from loud noises.

4. Inner Ear

• Cochlea: Converts vibrations to sound signals.
  • Spiral-shaped, wraps around the modiolus bone.
  • Communicates with the middle ear via the round window.
• Vestibule: Middle portion of bony labyrinth; contacts stapes.
• Semicircular Canals: Responsible for sense of balance.
  • C-shaped, positioned at 90 degrees to each other.
  • Fluid flow determines head movement direction.
  • Base contains the ampulla.
• Vestibulocochlear Nerve: Enters via internal acoustic meatus; splits into cochlear and vestibular nerves.
• Facial Nerve: Passes through the inner ear without innervating.

Conclusion

• Overview of external, middle, and inner ear components.
• Stay tuned for detailed tutorials on the inner ear and other cranial nerves.