The ear serves the important functions of allowing us to hear sounds produced by our environment, as well as maintaining our sense of balance. It is
made up of three major parts: the outer, middle and inner ear.
The outer ear consists of the part of the ear that you can see, in addition to the narrow, tube-like opening called the ear canal. At the end of the ear canal is a tightly stretched tympanic membrane, the eardrum, which separates the outer ear from the middle ear.
The inner ear is made up of two components: one involved with hearing, the cochlea ("coke-lee-a"), and the other with balance, the vestibular
system. The cochlea is a snail-shaped chamber filled with fluid and
lined with sensory receptors in the form of tiny hair cells. It is attached to the auditory, or hearing, nerve that leads to the brain. The vestibular system is made up of a network of tubes (semicircular canals) and sacs (vestibule).
Outer, middle and inner ear. Click on the
image for a larger and more detailed diagram.
Like the cochlea, the vestibular system also contains sensory receptors and is attached to the vestibular, or balance, nerve that leads to the brain. The inner ear is also referred to as the labyrinth.
How We Hear
We hear sound when a series of sound waves, or vibrations, pass through our outer, middle and inner ear and reach our brain for interpretation.
Sound waves are first collected in our outer ear, pass through our
ear canal and cause our eardrum to vibrate. These vibrations are in
turn transmitted to our inner ear by the bones of our middle ear.
Click on the right arrow to learn more about how we hear.
Our inner ear plays a vital role in the
transformation of these mechanical vibrations into electrical impulses, or signals, which can be recognized and decoded by our brain. When
the vibrations reach the cochlea through movement of the bones in
the middle ear, the fluid within it begins to move, resulting in
back and forth motion of tiny hairs (sensory receptors) lining the
cochlea. This motion results in the hair cells sending a signal
along the auditory nerve to the brain. Our brain receives these
impulses in its hearing centers and interprets them as a type of
sound.
For a more in-depth discussion, see The
Search for the Mechanisms of Hearing, by Dr. Peter Dallos.
How We Maintain Our Balance
Our balance is maintained through the interaction of the visual, vestibular
and sensory systems. These systems function individually and in combination
to keep us stable with respect to our postural orientation. We may experience
feelings of dizziness, lightheadedness or imbalance in the event of a disturbance of any one or more of these systems.
The visual system contributes to the maintenance of balance by making
us aware of our surroundings and the position of our bodies in relation
to those surroundings. The vestibular system detects rotational (circular)
and linear (back and forth) motion produced when we engage in actions
such as stopping, starting or turning. The sensory system keeps track
of the movement and tension of our muscles and joints as well as the position
of our body with respect to the ground. Upon receiving signals from these
systems, the brain processes the information gathered to produce a sensation
of stability.
The tubes and sacs within the vestibular system are filled with fluid.
When we move our heads, this fluid is set into motion, causing the hair
cells of the sensory receptors to bend. This change results in the generation
of an electrical impulse which is carried along the vestibular nerve to
the brain for interpretation.
Once the brain has interpreted the impulses as head movement, it responds
by signaling our eyes to move in a manner that will allow us to maintain
clear vision during the motion. Our brain will also send signals to our
muscles so that their corresponding action serves to ensure balance regardless
of the position our body (sitting, standing, moving).
The vestibular systems of our left and right inner ears must work equally
to send uninterrupted impulses to our brain. Balance is disrupted if the
signals are unequal, resulting in a type of dizziness called vertigo.
