Basic Ear Anatomy and Physiology

Your ears have tremendous careers

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Your sense of hearing and balance are precious gifts from your auditory system. Its anatomy is confusing, but it can be divided into a peripheral and a central auditory system.

Your peripheral auditory system consists of three connected parts: the outer ear, the middle ear, and the inner ear.
- The outer ear includes the auricle (also called pinna), external acoustic meatus (external ear canal), and tympanic membrane (eardrum).
- The middle ear is a tiny air-filled space that houses three cute and wonderfully named tiny bones. As a group, they’re called the ossicles, and they’re made up of the malleus (hammer), incus (anvil), and stapes (stirrups). The stapes is the smallest bone in your body, and it connects the middle ear to the inner ear. An often forgotten member of your middle ear is the auditory tube (eustachian tube). It's a canal that connects your middle ear with the posterior part of your nose. It aids in proper transmission of sound waves through pressure equalisation in your middle ear.
- The inner ear provides a home to both your hearing and balancing (vestibular system) organs. The hearing part is called the cochlea. It connects to your central auditory system through the cochlear nerve. It also has numerous hair cells (sensory cells) and contains fluid.
Your central auditory system includes the cochlear nerve and the auditory cortex deep within your brain. For purposes of simplicity, we shall only be talking about your peripheral auditory system.

Enough about ear anatomy, let’s go to the physiology of hearing. How can we hear then?

The auricles collect air vibrations (sound waves) around us and funnel them into the external ear canals. The air vibrations make your eardrums vibrate and mobilise the ossicles. The ossicles, particularly the stapes, in turn, transmit the vibrations to the cochlea in the inner ear.

The cochlear fluid produces tiny waves as a result of the vibrations and stimulates the hair cells. The hair cells are extremely sensitive to the frequency or pitch of sounds. They then generate nerve impulses which travel fast along the cochlear nerve to the auditory cortex deep within your brain, giving you the perception of sound. All of these processes happen instantaneously in a fraction of a second.

How about balance? How do our ears give us a sense of balance?

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The vestibular system of the inner ear is the part responsible for your sense of balance. It contains three semi-circular canals, the saccule, and the utricle. The three canals are positioned at right angles to each other similar to a gyroscope. There is fluid in these canals that detect changes in your body movements through the hair cells. Yes, they’re the same hair cells that detect vibrations for your sense of hearing. The saccule and utricle detect your head movements.

Fluid movement in the canals, utricle, and saccule stimulate the hair cells and generate nerve impulses that are transmitted through the vestibular nerve which joins the cochlear nerve. Together they’re called the vestibulocochlear nerve or simply auditory nerve. The nerve impulses from the vestibular nerve are relayed to your brainstem, cerebellum, and spinal cord, giving you a sense of balance.

The Major Difference between Adult and Paediatric Ears

The major difference in the anatomy of the ear between adults and children is in the eustachian tube. Children have a lesser ability to equilibrate pressure and drain fluid in their middle ear due to the small diameter and horizontal positioning of their eustachian tubes. This makes them more prone to middle ear infections compared to adults. As they grow older, the diameter increases and the eustachian tube assumes a more diagonal position allowing drainage of fluid.

Our ears don’t get much attention like our eyes or the other parts of our head. You can’t imagine your world without your sense of balance and hearing, that’s how essential your ears are. We have more articles about ears you may want to take a look at: