When your infant wakes up from the slightest squeak of your rocking chair, you can thank his middle ear for his quick reaction to sound. Although the ear seems like a relatively simple body part, a complex system actually lies behind the floppy organ. Although the outer, middle and inner ear work together to ensure successful transmission of sounds to the brain, the anatomy of the middle ear in infants plays an extremely important role in the process.
Function
At all stages of life, the main function of the middle ear is to quickly and efficiently transmit external sounds from the external environment into the inner ear. Since external sounds are delivered to the ear via air, they must be converted to move through fluids. The middle ear plays an important role to ensure the successful transmission of sounds from an air medium to a fluid medium.
Overall Structure
The middle ear consists of an air-filled cavity, which is commonly referred to as the tympanic cavity. This cavity is carved out of the skull's temporal bone. When taking the entire anatomy of the ear into consideration, the middle ear is just a very small portion. According to the University of Pennsylvania Health System, the middle ear begins to develop around the fifth month of fetal development and continues until birth.
Eustachian Tube
The Eustachian tube is a narrow tube that connects the middle ear to the throat. Its main function is to equalize the air pressure in the middle ear with the air pressure in the outer ear. Normally, this tube remains closed. However, the passageway opens when the pressure needs to be equalized. For example, when an airplane takes off, the Eustachian tube quickly opens and closes to equalize the air pressure in the middle and outer ear. This reaction typically causes the ear to "pop." Since the Eustachian tube also opens while yawning, sneezing or swallowing, frequent flyers use these techniques to adjust to the air pressure change. Since an infant's Eustachian tube works the same as an adult's, you can help an infant adjust to air pressure changes by feeding him during take-off and landing.
Eardrum
Although the eardrum is not technically part of the middle ear, it does serve as the dividing membrane between the outer and middle ear. This thin membrane, commonly known as the tympanic membrane, sits at the end of the auditory canal. When sound waves from the external environment enter the ear, they cause the eardrum to vibrate. These vibrations then move on to the ossicles, which sit directly behind the eardrum.
Ossicles
Three very tiny bones lie within the structure of the middle ear, just past the eardrum. These bones consist of the malleus, incus and stapes. Because of their shape, they are also commonly referred to as the hammer, anvil and stirrup, respectively. When sound waves enter the ear, they vibrate the eardrum and set the hammer in motion, which is connected to the eardrum. The hammer then pushes the anvil, which is fused with the stirrup. When the stirrup moves, it quickly opens and closes the oval window of the cochlea, sending sound vibrations into the inner ear. Even as an adult, these bones remain the smallest bones within the body. At an infant's young age, these bones are extremely miniscule. However, they play an extraordinarily important role. According to the Scientific American website, "Without the middle ear ossicles, only about 0.1 percent of sound energy would make it into the inner ear."
References
- Scientific American: How do the hammer, anvil and stirrup bones amplify sound into the inner ear?
- Science Clarified: Ear
- University of Wisconsin-Madison: Functions and Pathophysiology of the Middle Ear
- WebSchool Solutions: The Ear: Auditory and Vestibular Systems
- The University of Pennsylvania Health System: Fetal Ear Development
