Sence organ Ear I

EAR I
GENERAL FEATURES
Ear is a peripheral sense organ concerned with hearing and equilibrium.
It is subdivided into three parts, the external ear, middle ear or tympanic cavity and the internal ear or labyrinth.

STRUCTURE
External Ear
• The external ear consists of the auricle that collects sound waves and the external acoustic meatus that conducts these waves to the tympanic membrane (ear drum).
• The auricle and the outer third of external acoustic meatus are made of elastic cartilage covered by thin skin. This skin is provided with hair, sebaceous and ceruminous (modifi ed sweat glands) glands.
• The tympanic membrane separates the external ear from the middle ear. It is a trilaminar structure, lined externally by stratifi ed squamous epithelium and internally by simple cuboidal epithelium and is supported in the middle by fi brous tissue.

Middle Ear
• The middle ear is a narrow air space compressed mediolaterally, occupying the petrous part of temporal bone. It contains a chain of three tiny auditory ossicles (malleus, incus and stapes) whose function is to transmit the vibrations of tympanic membrane to the perilymph of internal ear.
• The middle ear also has two small muscles (tensor tympani and stapedius) attached to the ear ossicles. These muscles refl exly contract to dampen excessive vibration caused by loud noise.
• Middle ear cavity communicates anteromedially with the nasopharynx through auditory tube. This helps to equalize air pressure on both surfaces of tympanic membrane.