Hearing is a complicated process involving many different structures, both mechanical and electrical. The human ear is divided into three parts: the outer ear, the middle ear and the inner ear. The three smallest bones in the body are found in the middle ear and play a part in transmitting vibrations and converting them into the sounds we hear, according to Scientific American. These three bones--collectively called the middle ear ossicles--are the malleus, incus and stapes. They connect to one another and receive vibrations from the eardrum, or tympanic membrane. They then transmit these vibrations to the inner ear, from bone to bone, where they are converted into electrical impulses that the brain can interpret as sound.
Malleus
The malleus is also called the hammer and is the bone that is closest to the outer ear. It is the beginning of the chain that transmits sound from the tympanic membrane--the eardrum--to the cochlea of the inner ear. The malleus has two main parts, called the head and the manubrium, or handle, according to 3D Ear, an ear anatomy tutorial created at McGill University. The manubrium articulates with, or attaches to, the tympanic membrane. When the eardrum is vibrated by external sounds, it slightly moves the manubrium. On the other end of the malleus, the head attaches to the next bone in line, the incus. Within the cavity known as the middle ear, there are a couple of muscles called stapedius and tensor tympani. The tensor tympani muscle attaches to the malleus and is responsible for stiffening this bone and dampening very loud sounds that may damage delicate structures.
Incus
The next bone in this chain that extends from the eardrum to the inner ear is the incus, also known as the anvil due to its unique shape. The incus has two projections, the short process and the long process, that arise off the main body. The head of the incus attaches to the malleus and receives vibrations from it. There is a long projection, called the lenticular process, that attaches to the next bone in line, the stapes.
Stapes
The bone closest to the inner ear and cochlea is the stapes, also known as the stirrup. It too is named for its shape. The lenticular process of the incus attaches to the main portion of the stapes, called the head. On the other end of the stapes is a process called the footplate, which attaches to the boundary of the middle ear called the oval window. According to the University of California Santa Cruz, the oval window marks the division between the inner and middle ear and is a thin membrane almost completely covered by the footplate of the stapes. The inner ear is filled with fluid, and when vibrations are passed from bone to bone through the middle ear, they are eventually transmitted into the fluid by the movement of the stapes on the oval window. These vibrations are then transmitted through the fluid in the cochlea, where they are converted into electrical impulses that travel through nerves to the brain.
