Muscles and Cavities

The middle ear is composed of two muscles which are the tensor tympani and stapedius muscle.

Wageih Felfela (2017) said that the tensor tympani muscle is housed within the tensor tympani semicanal superior to the Eustachian tube. The tendon bends around the cochleariform process and proceeds to its insertion in the manubrium malli. Moreover, the tensor tympani is innervated by the cranial nerve V (trigeminal nerve) via the otic ganglion. Its function is to stiffen the ossicular chain and pull the malleus anteromedially. It also dampens loud sounds such as the sounds produced when chewing or shouting.

The other muscle in the middle ear is the stapedius muscle. This is the smallest skeletal in the body, with a length of only 6.3 millimeters and a thickness of roughly 5 square millimeters in the cross-sectional area. This is also embedded in the bone of the posterior wall of the middle ear. Wageih Felfela (2017) stated that the posterior neck of the stapes is the point of insertion of the stapedius tendon from the pyramidal eminence apex which runs anteriorly towards it. Moreover, there are muscle spindles in the stapedius muscle. Furthermore, the stapedius’s contraction, which is less than 80 dB, pulls the stapes posteriorly. This then causes the stiffening of the ossicular chain and the reduction of the energy delivered to the inner ear.

Wageih Felfela (2017) said that cavities refer to the hollow spaces or landmarks in the body. The middle ear has cavities which include the mesotympanum, epitympanum, and the hypotympanum. The total volume of the middle ear cavities excluding the mastoid air cells is 2 cubic centimeters. However, if the volume of the mastoid air cells is taken into account, then the total volume is 10 cubic centimeters.

The mesotympanum cavity is located between the wall of the inner ear and the tympanic membrane. This is at the level of the pars tensa. Moreover, the mesotympanum cavity is divided into three pouches – the inferior incudal space, anterior pouches of Von Troeltschm, and the posterior pouches of the Von Troeltsch.

The epitympanum cavity contains the head of the malleus and the body of the incus. This is above the level of the pars tensa.

The hypotympanum cavity is at the lower area of the middle ear cavity below the tympanic membrane level.