The Anatomy of the Ear

The ear is a very important organ which enables vertebrates to hear and maintain balance. From mice to elephants and everywhere in between, most animals are at least somewhat dependent on their ears. A deer uses its ears for signs of an approaching predator. A wolf listens for prey with the opposite intention. Even bats need their ears for ‘seeing’!


Since the ears have so many tiny, fragile parts, many things can go wrong in there. Some doctors are required to study those little parts in order to diagnose and prescribe medicine. In this essay, the anatomy of the ear and the functions of the parts will be explained.

The ear is organized into three main parts: the External Ear, the Middle Ear, and the Inner Ear. We will go in this order as we take a look at all the bones, cartilage, cavities, and nerves.

EXTERNAL EAR:

First, there is the visible portion of the external ear that we are all familiar with. It is the flap of skin and cartilage on the side of the head, scientifically called the pinna, or the auricle. The pinna helps direct/conduct sound waves into the ear canal. (Part of the reason dogs can hear better than humans is because they have such big auricles!) The pinna has anatomical terms by itself. The upper ridge of the pinna is called the helix. The antihelix is a long lump that runs parallel to the helix, and the two are separated by a furrow called the scapha. At the bottom of the auricle there hangs/dangles the earlobe, a.k.a. lobule, which is squishy because it is filled with fatty tissue. The deep depression of the pinna is called the concha. If you were to insert your index finger into your ear, it would only go as far as the concha, and would not be able to fit into the ear canal. (Do not stick anything smaller than your index finger in your ear.)

Beyond the concha there stretches the area of the ear called the ear canal, which is a narrow passage that leads away into the middle ear.

MIDDLE EAR:

The ear canal stops at the tympanic membrane, or eardrum. The eardrum marks where the external ear ends and the middle ear begins. A tool called an auroscope/auriscope is used to visually examine the tympanic membrane. A healthy tympanic membrane is shiny, taut, and tinted gray, whereas an infected eardrum is bright red, perforated, and/or has pus leaking out of it.

When sound waves reach the eardrum, it transmits vibrations over to the auditory ossicles in the tympanic cavity (the tympanic cavity is an air space within the temporal bone). The auditory ossicles are three tiny bones, commonly known as the anvil, hammer, and stirrup (Malleus, Incus, and Stapes). When the bones vibrate, the stirrup transfers sound vibrations into the inner ear through the oval window, which is firmly attached to the cochlea. The cochlea brings us to the next area of the ear.

INNER EAR:

The inner ear is where the organs of hearing and equilibrium are found. There are three main parts of the inner ear: the coiled cochlea, the bony labyrinth, and the membranous labyrinth.

The cochlea is a coiled organ which resembles a snail shell. It holds fluid that contains tiny mineral crystals. The sound vibrations that are gathered from the stirrup (through the oval window) are converted into fluid vibrations when they enter the cochlea. The fluid moves the crystals, which brush against the fibers. The fibers then turn the vibrations into impulses over a nerve into the brain. This nerve (called the vestibulocochlear nerve) also detects sensations for equilibrium.

We now conclude our ear overview by examining the bony labyrinth and the membranous labyrinth.

The sensations for equilibrium come from the bony labyrinth and the membranous labyrinth, a complex system of fluid and canals, which transmit signals to the brain concerning sensations of acceleration and gravity.