Anatomy of the Ear

• External ear is formed by the 8th week of gestation and comprises 10% of the ear

Key Components of the Outer Ear

• The outer ear includes the pinna/auricle, and external auditory canal/meatus.
• The pinna has a cartilage covered portion that projects and consists of raised and ridged structures.
• Pinna collects and funnels sound waves into the ear canal.
• External auditory canal is 0.1-10 IC L:1 is one third is surrounded by elastic cartilage.
• The remaining two thirds of the ear canal is within the temporal bone.
• The canal contains modified sweat glands that secrete cerumen (ear wax), helping trap foreign materials like dust, insects, and microbes.
• Cerumen, combined with hairs, prevents these foreign materials from reaching the tympanic membrane.

Middle Ear Characteristics and Components

• In the middle ear, acoustic energy is transformed to mechanical energy.
• The ossicles include malleus, incus, and stapes.
• The middle transforms acoustic that shaped by the Outer Ear and is connected to the middle ear via the ossicles.
• Area of the tympanic membrane is 55 mm2 while the stapes footplate is 3.2 mm2.
• This difference in area creates a pressure increase of around 17:1 to overcome the impedance of the fluid filled inner ear.
• The tensor tympani muscle is innervated by cranial nerve V and it inserts into Malleus.
• The stapedius muscle, innervated by cranial nerve VII, inserts into stapes.
• Air pressure in the middle ear is equalized via the eustachian tube to nasopharynx.

Inner Ear Components and Function

• Oval and round windows are apart of the bony labyrinth lined by perilymph fluid.
• The membranous labyrinth contains endolymph fluid.
• The cochlea contains three chambers scala vestibuli, scala tympani and scala media.
• The Scala vestibuli and Scala tympani contain perilymph fluid.
• The Scala media contains endolymph fluid and the organ of corti which is responsible for converting mechanical energy into electrical energy.