Listen To This: All About the Auditory System

The ability to hear is made possible courtesy of the auditory system. This system consists of organs and other structures that turn sound waves into something that people hear, understand, and recognize. The ears are the two sensory organs of the auditory system. Each ear is divided into parts that contain specific and important structures. The auditory system also includes the auditory nervous system, which features nerve fibers that carry signals to the cortex and brain stem. For people who have difficulty hearing, a hearing aid may be necessary to assist the auditory system and enable them to hear more clearly.

Outer-Ear Structures

The structures of the outer ear include the pinna and the ear canal. The pinna is the part of the ear that is visible. It is made of cartilage covered by skin, and when it collects sound, it acts as a preamplifier. The ear canal extends from the pinna and leads to the tympanic membrane, which is also known as the eardrum. Within the ear canal, wax is produced to help keep the ears clean by collecting dirt and debris. It also helps prevent infection.

Middle-Ear Structures

The tympanic membrane is where the middle ear begins. Other structures of the middle ear include the three ossicles, which are the malleus, incus, and stapes. Together, these structures turn sound waves into vibrations that will carry to the inner ear. The vibrations begin when sound waves hit the eardrum. The vibration causes the ossicles, which are tiny bones, to move. This movement causes sound waves to be transmitted to the inner ear. The eustachian tube is also a part of the middle ear. It keeps the air pressure on both sides of the eardrum equalized and also drains fluids.

Inner-Ear Structures

The inner ear is located in the skull in an area that is known as the labyrinth. This portion of the auditory system contains structures that not only help hearing but also help with balance. The structures of the inner ear include the cochlea and the semicircular canals. The cochlea is a snail-shaped structure that is filled with liquid. Inside of the cochlea is the organ of Corti, which has tiny hair cells. When the vibration from the ossicles causes the cochlea to move, this movement causes waves in the liquid inside. The waves then cause the hairs to move and start the process of sending signals to the brain. The signals that are sent by these hairs are sent as nerve impulses through the auditory nerve.

The semicircular canals are also a part of the inner ear, as are the utricle and the saccule. The semicircular canals also have fluid and contain tiny hairs called cilia. When the head turns, the fluid moves the hairs, which communicate with the brain about how to keep the body in balance. The utricle and saccule are also important in terms of equilibrium. They are both membranous sacs that contain fluid and are located near the semicircular canals; however, the utricle is larger in size than the saccule. They rely on hair cells that are located in an area called a macula to help maintain one’s equilibrium by sending information about the position of one’s head when it is not in motion.

Auditory Pathways

The auditory pathways begin in the cochlea, where the nerve impulses travel from nerve fibers located in the organ of Corti to the cochlear nucleus. From the cochlear nucleus, the auditory nerve fibers cross at the brainstem. At this juncture, a large number of the impulses move to the opposite side of the brain; however, both crossed and uncrossed fibers will continue along pathways that take them to the superior olive or superior olivary complex, which receives information from both ears. From there, impulses travel to the inferior colliculus and the medial geniculate body, then to the auditory cortex, where the information is processed in the brain.