Ear Lab

Overview of the Ear Structure and Function

• The ear can be divided into three main sections: external, middle, and inner ear.

External Ear

• External Auditory Canal:

  • Funnels sound toward the middle ear.

  • Collects sound waves which travel through air.

Middle Ear

• Tympanic Membrane (Eardrum):

  • Transmits vibrations caused by sound waves.

  • Acts like the head of a drum, moving in response to sound.

• Ossicles:

  • Three tiny bones: Malleus, Incus, and Stapes.

  • Transmit vibrations from the tympanic membrane to the oval window in the inner ear.

  • Sequence of transmission: Tympanic membrane → Malleus → Incus → Stapes → Oval Window.

• Oval Window:

  • Thin membrane covering the entry into the cochlea.

  • Transmits vibrations to the cochlea, crucial for sound detection.

Inner Ear

• Cochlea:

  • A liquid-filled tube that detects sound.

  • Contains structures that facilitate the detection process.

  • The detection mechanisms will be covered in detail in lectures and histology slides.

• Eustachian Tube (Pharyngotympanic Tube):

  • Connects the pharynx (throat) to the tympanic cavity in the middle ear.

  • Equalizes pressure across the tympanic membrane, which can change due to altitude (e.g., during plane descent).

  • Actions like swallowing, yawning, or chewing gum help keep this tube open, allowing air into the tympanic cavity.

Equilibrium

• Vestibule:

  • Part of the inner ear involved in maintaining balance.

  • Two types of equilibrium:

    • Static Equilibrium:

      • Detects linear movements (accelerating, braking in a vehicle, tilting head).

      • Structures within the vestibule help detect these changes.

    • Dynamic Equilibrium:

      • Helps detect rotational movements (e.g., spinning, cartwheeling).

      • Involves the semicircular canals with structures called Cristae Ampullaris located in the ampulla that respond to fluid movement within these canals.

Cochlear Structures

• Spiral Organ (Organ of Corti):

  • Located within the cochlea and is responsible for sound detection.

  • Contains hair cells that are sensitive to sound vibrations.

Sound Amplification

• The middle ear plays a critical role in amplifying sound before it reaches the cochlea.

• The ossicles leverage mechanical properties to increase the force of sound waves, ensuring that vibrations are strong enough to be detected by the cochlea.

Hearing Tests

• Weber Test:

  • Used to check for unilateral hearing loss.

  • A tuning fork is placed on the skull; a louder sound indicates potential conductive hearing loss in that ear.

• Rinne Test:

  • Assesses the function of the middle ear.

  • Evaluates if sound is heard better through air (normal function) or bone (indicating possible conductive deafness).

Types of Hearing Loss

• Conductive Deafness:

  • Results from anything obstructing sound waves from reaching the cochlea (e.g., fluid in middle ear, ossicle issues).

• Sensory Neural Deafness:

  • Occurs when sound waves reach the cochlea but cannot be processed due to neural pathway issues (e.g., damage to hair cells, auditory nerve).