Human Ear Anatomy

Ear Structure and Function

• The ear is responsible for hearing and maintaining balance (equilibrium) of the body.
• The ear is divided into three parts: external ear, middle ear, and internal ear.

External Ear

• The external ear consists of the auricle and external auditory meatus.
• The auricle projects from the side of the head, with a lower fleshy part called the lobule (containing no cartilage).
• The concha is a central depression in the auricle.
• The external auditory meatus is an S-shaped tube, 24 mm in length, extending from the concha to the tympanic membrane.
• The outer part of the meatus is cartilaginous and directed upwards, backwards, and medially, while the inner part is bony and directed downwards, forwards, and medially.
• The nerve supply to the external ear comes from the auriculotemporal nerve and auricular branch of vagus.

Tympanic Membrane

• The tympanic membrane is an oval, semitransparent membrane forming the lateral boundary of the middle ear.
• The lateral surface of the membrane is concave, while the medial surface is convex and receives the attachment of the malleus.
• The nerve supply to the tympanic membrane comes from the auriculotemporal nerve and auricular branch of vagus (lateral surface) and the tympanic plexus (medial surface).

Middle Ear

• The middle ear (tympanic cavity) is a narrow, air-filled cavity within the petrous part of the temporal bone.
• The middle ear contains air, auditory ossicles (malleus, incus, and stapes), auditory muscles (tensor tympani and stapedius), nerves (chorda tympani and tympanic branch of glossopharyngeal nerve), and blood vessels.
• The boundaries of the middle ear include the tegmen tympani (roof), the floor (separating the tympanic cavity from the jugular bulb), and the anterior, posterior, lateral, and medial walls.
• The nerve supply to the middle ear comes from the tympanic plexus.

Auditory Muscles

• The tensor tympani muscle tenses the tympanic membrane and is supplied by the mandibular nerve.
• The stapedius muscle draws the stapes laterally and is supplied by the facial nerve.
• The two muscles lessen transmission of sound vibrations as a protective mechanism against sounds of higher intensity.