The Middle & Inner Ear

The Middle Ear

The middle ear is a small air-filled cavity that is bordered by the tympanic membrane on one side, and the oval and round windows on the other side. Inside the middle ear are the three smallest bones in the body, collectively know as the auditory ossicles:

The malleous

Commonly known as the hammer, this bone attaches to the internal surface of the tympanic membrane and articulates with the incus.

The incus

Commonly known as the anvil, this bone acts as a hinge joining the malleous to the stapes, so that pressure changes caused by sound waves can be accommodated.

The stapes

Commonly known as the stirrup, this bone fits into the oval window of the inner ear and hammers the sound into the fluid filled cochlea.

Internal Ear

The internal ear is also called the labyrinth due to its many canals, and is comprised of a bony labyrinth and a membranous labyrinth.

The bony labyrinth

This is a number of small holes in the temporal bone of the skill and is divided into three areas:

The semicircular canals - which sense equilibrium

The vestibule - which also senses equilibrium,contains two sacs called the utricle and the saccule.

The cochlea - which contains receptors for hearing

The membranous labyrinth

This lies inside the bony labyrinth, and is surrounded by a fluid called perilymph. The membranous labyrinth is a series of sacs and tubes which contain endolymph. The endolymph has unusually high levels of potassium ions, which are important in transducing auditory signals. 

 

Images courtesy of Wiki Commons