ear

Introduction to the Ear

  • The ear is an engineering marvel and plays a critical role in hearing and balance.

  • The structure of the ear includes three sections: external ear, middle ear, and internal ear.

Anatomy of the Ear

External Ear

  • Auricle (Pinna):

    • The visible part of the ear, made of elastic cartilage and skin.

    • Divided into various parts including helix, antihelix, concha, tragus, and lobule.

    • The lobule is soft and contains fibrofatty tissue, allowing for wearing earrings.

  • External Auditory Meatus:

    • Conducts sound waves to the tympanic membrane. It is about 24 mm long with a cartilaginous and bony portion.

    • The canal is S-shaped and can be straightened for examination by pulling the auricle.

Middle Ear

  • Structure and Function:

    • Comprises the tympanic cavity, which is a narrow air-filled space. It communicates anteriorly with the nasopharynx through the auditory tube and posteriorly with the mastoid antrum and air cells.

    • Contains three ossicles: malleus, incus, and stapes, which transmit sound waves to the inner ear.

  • Tympanic Membrane (eardrum):

    • Oval in shape, measuring about 9 x 10 mm. It is concave, with the umbo being the most prominent point.

    • Composed of three layers: outer cuticular layer, middle fibrous layer, and inner mucous layer.

  • Muscles:

    • Tensor Tympani: Arises from the auditory tube and attaches to the malleus, dampening loud sounds.

    • Stapedius: Located in the pyramid of the middle ear, controls the stapes bone and also dampens loud noises.

Internal Ear (Labyrinth)

  • Components:

    • Bony Labyrinth: Composed of cochlea, vestibule, and semicircular canals. Contains perilymph.

    • Membranous Labyrinth: Contains endolymph and houses structures for hearing and balance (e.g., organ of Corti).

  • Cochlea:

    • Resembles a snail shell and contains the organ of Corti, responsible for hearing.

    • Contains scala vestibuli and scala tympani, which transmit fluid movements caused by sound waves.

  • Vestibule and Semicircular Canals:

    • Utricle and Saccule: Detect static balance; contain hair cells sensitive to gravity.

    • Semicircular Canals: Detect dynamic balance with the cristae providing sensory input during head movements.

Blood Supply and Nerve Supply

Blood Supply of the Ear

  • Supplied mainly by the mastoid and posterior auricular arteries.

Nerve Supply

  • External Ear: Lateral surface innervated by the auriculotemporal nerve and great auricular nerve.

  • Middle Ear: Supplied by branches of the glossopharyngeal nerve and facial nerve.

  • Internal Ear: Innervated by branches from the vestibulocochlear nerve.

Clinical Anatomy

Common Ear Conditions

  • Otitis Media: Inflammation of the middle ear, often leading to fluid accumulation and pressure.

  • Mastoiditis: Infection of the mastoid air cells, can occur as a complication of otitis media.

  • Hyperacusis: Increased sensitivity to certain frequency and volume ranges of sound, often due to stapedius muscle paralysis.

Procedures

  • Myringotomy: Incision in the tympanic membrane to relieve pressure or drain fluid.

  • Syringing: Removing wax or foreign bodies from the ear.

Clinical Signs

  • Displacement of the auricle in infections, and the presence of discharge can indicate otitis media.

  • Pain during swallowing can suggest eustachian tube dysfunction.