Inner Ear Function and Structure Quiz

Inner Ear Function and Structure

• Transformations of energy in hearing: Acoustic energy is converted to mechanical energy, then hydraulic energy as it travels through the ear.
• The inner ear amplifies sound; however, only a fraction (1/1000) of air’s acoustic energy efficiently transmits to inner ear fluids, resulting in approximately 30 dB hearing loss.
• The tympanic membrane (eardrum) shows right or left orientation based on the cone of light: in the right ear, it is positioned at the 5 o’clock mark.

Tympanic Membrane and Cavities

• The umbo is the tip of the malleus located at the center of the tympanic membrane, which displays a small depression.
• Parts of the tympanic membrane: superior section above anterior and posterior malleolar folds lacks a fibrous layer and connects to the bony ring (notch of Rivinus).
• Anatomical divisions of the tympanic cavity include the epitympanum, mesotympanum, and hypotympanum.

Hypotympanum Borders

• Anterior: Internal carotid artery
• Posterior: Mastoid portion of facial nerve
• Superior: Dura of the middle cranial fossa
• Inferior: Bulb of the jugular vein
• Medial: Cochlea
• Lateral: Tympanic membrane and bony ear canal

Blood Supply to the Ear

• Blood circulation to the ear is provided by branches of the external carotid artery, including middle meningeal, ascending pharyngeal, maxillary, and stylomastoid arteries.

Development of the Inner Ear

• The inner ear begins development in the 4th week of gestation when the ectoderm thickens beside the hindbrain, forming the otic placode.
• The otic placode undergoes invagination, leading to the formation of the otic pit, which fuses to create the otic vesicle.

Structure and Function of the External Ear

• The pinna (auricle) leads to the external auditory canal, bordered by the temporalis muscle (superior), parotid gland (anterior/inferior), mastoids (posterior), and epitympanum (superomedial).
• Functions include sound collection, localization (using interaural time and amplitude differences), and serving as an acoustic antenna, amplifying sounds in the 2-4 kHz range by 10-15 dB.

Eustachian Tube Anatomy and Function

• Adults have a longer and more angulated (45 degrees) eustachian tube compared to children's shorter and wider version, making otitis media more common in young children.
• The eustachian tube’s lining consists of pseudostratified columnar epithelium with goblet cells.
• Has two openings: nasopharyngeal (proximal, closes at rest and opens when talking, chewing, or yawning) and tympanic orifice.

Eustachian Tube Functions

• Key roles include pressure equalization, mucociliary clearance and drainage, and protection of the middle ear.

Inner Ear Structures

• The scala vestibuli begins at the oval window at the stapes footplate, spirals to the apex of the cochlea, and communicates with scala tympani via the helicotrema.