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A Sense of Balance: Understanding the Vestibular Apparatus

Howard Glicksman

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Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

the-designed-body4.jpgEveryone knows that some of the things the gauges on the dashboard of a car warn the driver about are its content of fuel, oil, and anti-freeze. But how do they do it? Each device is essentially a sensory transducer with a mechanism that enables it to sense a physical phenomenon and convert it into useful information. The body too uses devices to detect physical phenomena so it knows what is going on outside and inside. These are likewise sensory transducers. The sensation of balance comes from the vestibular apparatus in the ears that tells the body its position relative to motion and the force of gravity and also helps to stabilize the retinal image.

Common sense teaches that without this special sense our earliest ancestors could never have survived. Evolutionary biologists claim that similarities in the vestibular mechanisms in different life forms indicates that it was easy for chance and the laws of nature alone to bring about the sense of balance. But as with the development of various inventions and technologies, human experience argues that intelligent design is a much more plausible explanation. Darwinism oversimplifies the need for the presence of all of the parts of the vestibular apparatus for human survival, but also fails to take into account how our brain converts what it receives to experience the sensation of balance.

In fact, this sensation is a mystery that nobody, even evolutionary biologists, understands. Given that, nobody should claim to understand how the vestibular apparatus and balance came into being. Yet that doesn’t stop Darwinists. Let’s look now at what makes up the vestibular apparatus, how it works and what the brain receives which it then converts into the sensation of balance.

Besides the cochlea for hearing, the inner ear also houses the vestibular apparatus. This consists of the three semicircular canals, the utricle, and the saccule. Together they provide sensory information to the brain to help the body maintain its position relative to gravity and control eye movement with head motion.

Like the three sides in each corner of a box, the three fluid-filled semicircular canals are oriented at right angles to each other. The lateral canal is positioned like the bottom of the box, but is oriented about thirty degrees above the horizontal plane. The other two sides, the superior and posterior canals, are oriented vertically and at right angles to each other like the front or back and either side of the box. In this way they are set up to provide the brain with three-dimensional information about the angular acceleration caused by head motion.

The lateral canal is most sensitive to spinning or rotating the head from right to left or left to right, whereas the vertically oriented canals are most sensitive to nodding the head up or down or flexing the head to the right or left shoulder and back again. Head motion in any direction naturally moves the fluid within the semicircular canals and stimulates hair cells that are sensory receptors. The messages sent from the semicircular canals are sent through the vestibular branch of the same nerve that carries information on hearing to the brain (vestibulo-cochlear nerve) where they are processed and analyzed so the body can maintain its balance.

However another important function the information from angular head motion provides is to help stabilize the retinal image. Think about it. When you are in motion, unless you focus on something, everything moves across your visual field at the same speed as you do. If you were unable to have controlled eye movements when your head moves in any direction, everything you look at would always be blurry. Imagine our earliest ancestors running up and down over hill and dale trying to find food or avoid becoming food, without being able to focus on anything? So how does the body do it?

It’s called the vestibulo-ocular reflex. Look into a mirror and focus on your eyes as you rotate your head from side to side, up and down and then in any direction. Notice how your eyes automatically move in the opposite direction of your head so you can keep them in focus. This is also known as the doll’s eye reflex and is often used by physicians (along with the corneal and pupillary light reflex) to assess brainstem function. It is the sensory information supplied by the semicircular canals about angular head motion that allows the brain to reflexively move the eyes in the opposite direction to maintain the retinal image so we can focus on things no matter how fast or in what direction we move.

The utricle and the saccule also contain fluid but in addition have tiny calcium crystals that overlie the hair cells within the sensory membrane. In response to linear motion, the weight of the calcium crystals shears across the hair cells, resulting in depolarization and excitation. The utricle and the saccule provide information on linear acceleration and gravity. The sensory neurons of the utricle are oriented in the horizontal plane and provide information on the body’s back to front and side to side motion whereas the ones in the saccule are oriented in the vertical plane and give information on its up and down motion (like in an elevator) and the position of the head with respect to gravity.

As with the semicircular canals, the sensory information from the utricles and saccules travels in the vestibular branch of the vestibulo-cochlear nerve to the brain. It is within the various parts of the brain that this information is processed and integrated with other sensory data. This allows the body to maintain its balance and along with it, its survival capacity within nature.

Evolutionary biologists may seek to explain what it took for humanity to be able to move around while staying balanced and focused. But this only involves what it looked like, without any discussion of how it actually worked within the laws of nature to allow for survival. Each part of the vestibular apparatus had to be present and working properly, while the brain had to know what to do with the information it received to maintain the body in balance and able to keep its eyes in focus. Next time we’ll look at how all of this is maintained by the reflexes.

Photo credit: © lulu — stock.adobe.com.