Ear

Ear

The organ for hearing consists of three main parts: the external (outer) ear, the middle
ear, and the inner ear.
- The external (outer) ear is made up of the pinna (or auricle) and the auditory canal. The pinna
(pinna-wing) is made up of cartilage covered by skin. It collects the sound which is
transmitted through the external auditory canal, leading to the tympanic membrane (or
eardrum). The tympanic plate forms the floor and anterior wall of the external auditory meatus (the mastoid portion is located behind and below the auditory meatus or opening of the ear)
which is part of the temporal bone.
- The middle ear lies in a cavity in the temporal bone and is separated from the external ear
by the tympanic membrane which transmits sounds to the internal ear. The middle ear is
connected with the nasopharynx by the Eustachian tube. The function of the Eustachian
tube is to equalize pressure on the eardrum. It opens when yawning or swallowing takes
place.
- The inner ear is comprised of membranous tissue contained within a bony structure. The
bony labyrinth has three divisions: the vestibule and two extensions of the vestibule called
the cochlea and the semicircular canals. The cochlea is a spiral canal containing a receptor
for hearing called the Organ of Corti. It has hair cells which pick up impulses transmitted
from the inner ear.

The semicircular canals form the organ of balance. The superior, posterior, and lateral
semicircular canals each connect by an ampulla (jug) to the utricle (a small sac), from which impulses travel to the brain by the vestibular branch of the VIIIth cranial nerve

Conditions in the ear
- Labyrinth hydrops: Excessive fluid in the organ of balance (labyrinth) that can cause pressure or fullness in the ears, hearing loss, dizziness, and loss of balance.
- Mastoiditis: An infection of the mastoid bone of the skull. The mastoid is located just behind the ear.
- Otisis externa: Inflammation of the outer part of the ear extending to the auditory canal.
- Otisis media: Inflammation of the middle ear caused by infection.

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The lymphatics of the external and middle ear drain to parotid (preauricular) lymph nodes. The
middle ear lymphatics, in addition, drain to retropharyngeal nodes. Lymphatics from both parts of
the ear goes directly or indirectly to the internal jugular (upper and lower deep cervical) nodes. The inner ear has no lymphatics.

Acoustic neuroma, a benign tumor of the auditory nerve, is the most common tumor of the ear.

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