This is chapter 26. THE EAR, Lab Reports of Anatomy

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THE EAR

In this exercise we will study the anatomy of the human ear and its involvement in both hearing and equilibrium. The ear is the organ of hearing and balance. The ear is anatomically divided into three parts:

1. external ear

B. External Auditory meatus/canal/tube

• this is the tube that connects the outer ear to the inside or middle ear.
• is the canal that extends from the auricle about an inch into the temporal bone and terminates at the tympanic membrane, or tympanum (eardrum).

The skin lining the canal contains some small hairs and modified apocrine sweat glands that produce a waxy secretion called cerumen. The auricle collects sound waves and directs them through the external auditory meatus to the tympanum.

2. Middle ear (Tympanic Cavity) , consists of a small cavity within the temporal bone. This air-filled cavity lies between the tympanum and the inner ear, and it contains three small bones, the ear ossicles. These tiny bones form a sensitive lever system that transmits the vibrations of the tympanum to the fluids within the inner ear.

The bones are called: A. Malleus – the outermost ossicle

• is a hammer-shaped or club- shaped bone that is attached to the tympanum by the end of its handle. B. Incus – the middle ossicle
• it is an anvil-shaped bone.

The auditory tube leads downward from the middle ear to the nasopharynx. This slender duct allows the air pressure in the middle ear to be equalized with that of the outside atmosphere. A valve at the nasopharynx end of the tube normally keeps the tube closed. However yawning or swallowing temporarily opens the valve to allow air

important roles in hearing and equilibrium. The bony labyrinth consists of three semicircular canals, vestibule and the cochlea. The vestibule is the portion that contains the oval window. The semicircular canals branch off one end of the vestibule, and the cochlea is the coiled

Two branches of the vestibulocochlear nerve , the eight cranial nerve carry impulses to the brain from the inner ear. The vestibular nerve leads from the vestibule, and the cochlear nerve emanates from the cochlea.

The bony labyrinth of the cochlea contains three chambers. The upper chamber, the scala vestibuli , is continuous with the vestibule. The lower chamber, the scala tympani , is so named because it contains the membranous round window. Both of these chambers are filled with perilymph. The middle chamber, the cochlear duct , is bounded by the vestibular membrane above and the basilar membrane below.

On the upper surface of the basilar membrane is the spiral organ , or organ of Corti , which contains hair cells that act as receptors for sound stimuli. The hair cells sit on top of the basilar membrane with the tips of the hairs embedded in a gelatinous flap, the tectorial membrame.