Auditory System Hearing Mechanism

The mechanism of hearing comprises a highly specialized set of structures. The anatomy of ear structures and the physiology of hearing allow sound to move from the environment through the structures of the ear, and to the brain. We rely on this series of structures to transmit information so it can be processed, giving us information about our surroundings.

Anatomy of the Ear - The Human Auditory System

The Outer Ear

The outer ear is the first structure of the auditory system to take in sound from the environment. The “pinna,” or the external ear structure, works as a funnel to take in sound waves and transmit them into the outer ear canal. The function of the outer ear is to trap and concentrate sound waves so their specific messages can be communicated to the other ear structures.

The Middle Ear

The middle ear begins to process sounds specifically, and reacts specifically to the types of sounds being heard. The first structure sound waves hit in the middle ear is the tympanic membrane, commonly known as the eardrum. This thin membrane of skin works like a drum, vibrating when it is struck by sound waves.

Attached to the tympanic membrane are three tiny bones, called the “ossicles.” These bones form a chain, which transmits sound energy from the tympanic membrane to the cochlea. The ossicles are the:

  • Malleus (or hammer)
  • Incus (or anvil)
  • Stapes (or stirrup).

The malleus is connected to the tympanic membrane. The incus connects the malleus to the stapes. The stapes, the final link in this chain of bones, is connected to the cochlea and transmits the sound waves into the inner ear.

The Inner Ear

The inner ear is made up of a series of bony structures, which house sensitive, specialized sound receptors. These bony structures are the cochlea, which resembles a snail shell, and the semicircular canals. They are filled with fluid, which helps to transmit sound. The cochlea contains microscopic hairs called cilia. When moved by sound waves traveling through the fluid, they facilitate nerve impulses along the auditory nerve.

The Auditory Nerve

The auditory nerve is one of the twelve cranial nerves that connect to the brain. This nerve also carries vestibular (balance) information to the brain. The cochlea transmits information to the brain via electrical nerve impulses.

The Brain

Once the auditory signal is transmitted to the brain via the auditory nerve, the brain must assign meaning to the sound. The ear structures themselves do not allow us to differentiate between a flute and a trumpet, recognize a dog’s bark, or understand speech. The brain’s auditory cortex processes sound and assigns meaning to what we hear based on our knowledge and previous experiences. For most of us, it seems that we process speech and sound effortlessly. However, our brains are always at work assigning meaning to the sound that we take in from the environment.

Resources

Martin, F.M.