The ear's anatomy and physiology allow for two functions: hearing and maintaining balance. According to the book "How the Body Works" by Dr. Peter Abrahams, when a sound enters the external ear, sound waves vibrate the tympanic membrane, or eardrum. The vibration of the eardrum moves the three bony ossicles within the middle ear. These three bones conduct sound by transmitting the sound waves to the oval window which marks the border of the middle and inner ear. The uniform movement of the three ossicles allows for sound amplification, states the Lucille Packard Children's Hospital at Stanford.
Malleus
Also called the hammer, malleus is the first ossicle attaching to the inner surface of the eardrum on one end and the incus, the second ossicle, on the other end. The malleus is also the largest of the three bones, measuring at approximately 8mm. A small muscle called the tensor tympani attaches to the base of the malleus and helps to regulate its movement.
Incus
The second, or middle ossicle is interchangeably called the incus or anvil. The large and round body of the incus allows for articulation with the malleus and stapes, the third ossicle. According to "How the Body Works," like the other bones, a ligament holds incus in place within the middle ear. Sound vibrations from the malleus reach the incus, which then transmits it to the stapes.
Stapes
Stapes, also known as stirrup, is the smallest of the three ossicles. According to Enchanted Learning, stapes measures 0.25 to 0.33cm making it the smallest bone in the human body. On one end, it articulates with the end portion of the incus, called the lenticular process of incus. Attached at the neck of stapes is the smallest muscle in the human body, called the stapedius. The contraction of the stapedius muscle muffles down loud sounds before the sound waves transmit to the cochlea. At the opposite side of the ossicle's neck, the flat base of stapes attaches to the oval window leading into the inner ear.
References
- "How the Body Works"; Dr. Peter Abrahams; 2007
- LPCH at Stanford: Anatomy and Physiology of the Ear
- Enchanted Learning: Ear Anatomy Diagram
