TM

Ear Anatomy and Function

Overview of the Ear Anatomy

  • The ear can be divided into three main sections:
    • External Ear: Comprises the pinna (auricle) and the auditory canal (external acoustic meatus).
    • Middle Ear: Contains the tympanic membrane (eardrum), eustachian tube (auditory tube), and three tiny bones (ossicles).
    • Inner Ear: Includes the cochlea, semicircular canals, and vestibule.

External Ear

  • Auricle (Pinna):
    • The outer structure of the ear that collects sound waves.
    • Funnels sound waves into the auditory canal.
  • Auditory Canal (External Acoustic Meatus):
    • Functions to further direct sound waves toward the tympanic membrane.
  • Tympanic Membrane (Eardrum):
    • Inner boundary of the external ear.
    • Vibrates with incoming sound waves, marking the transition to the middle ear.

Middle Ear

  • Tympanic Cavity:
    • Extends from the tympanic membrane to the oval window.
  • Ossicles:
    • Malleus (Hammer): Attached to the tympanic membrane.
    • Incus (Anvil): Positioned between the malleus and stapes.
    • Stapes (Stirrup): Fits into the oval window of the inner ear.
    • All three bones are small enough to fit on the head of a penny.
    • Function: Vibrations from sound waves hitting the tympanic membrane cause these bones to tap on the oval window, transmitting sound to the inner ear.
  • Eustachian Tube (Auditory Tube):
    • Connects the middle ear with the nasopharynx.
    • Balances air pressure in the ear; can also allow infections from the throat to the middle ear.
    • Shorter in children, making them more prone to middle ear infections.

Inner Ear

  • Labyrinth:
    • Comprises intricate interconnected tubes and chambers.
  • Cochlea:
    • Shell-shaped structure responsible for converting sound vibrations into nerve impulses for hearing.
    • Contains hair cells in the spinal organ of the cochlea which are sensitive to sound vibrations.
  • Semicircular Canals:
    • Responsible for dynamic equilibrium (balance during movement).
    • Fluid movement inside these canals, along with small rocks called otoliths, helps maintain balance.
  • Vestibule:
    • Critical for static equilibrium (balance when still).
  • Vestibulocochlear Nerve (Cranial Nerve VIII):
    • Contains two parts:
    • Cochlear: For hearing.
    • Vestibular: For balance.

Summary of Functions

  • Sound waves travel through the outer ear, vibrating the tympanic membrane.
  • This vibration is transferred through the ossicles to the oval window, leading to inner ear functions.
  • The cochlea processes sound, while the semicircular canals and vestibule manage balance.
  • The overall mechanism of hearing and balance relies on the coordinated action of these parts in response to sound waves and body movement.

Important Points to Remember

  • External Ear: Pinna, Auditory Canal, Tympanic Membrane
  • Middle Ear: Tympanic Cavity, Ossicles (Malleus, Incus, Stapes), Eustachian Tube
  • Inner Ear: Labyrinth (Cochlea, Semicircular Canals, Vestibule), Vestibulocochlear Nerve
  • Balance and hearing are distinct but interconnected functions facilitated by the ear's anatomy.