The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Balance

Balance, or the ability to maintain body position over a center of gravity, involves many different sensory systems integrated together. The three main sources of the required sensory information are the muscles, the eyes, and the vestibular organs. Vestibular information comes from specialized organs within the inner ear and provides information about where the body is in space relative to motion. Balance is something that most people do not think about on a regular basis. However, when there are issues with balance, everyday actions become extremely difficult. Some diseases involving the balance system include benign paroxysmal positional vertigo, Meniere’s disease, multiple sclerosis, and Parkinson’s disease. These diseases can be related to issues arising from the vestibular system in particular or general problems involving the nervous system and brain.

Sensory Inputs

Sensory inputs originate from three main sensory systems: proprioceptive, visual, and vestibular. Information from these sensory systems is integrated in the brainstem and processed in the cerebellum. The cerebellum is responsible for sending out motor signals to help maintain balance in posture and movement.

Muscles and Joint Position

One of the biggest cues that the brain uses to determine where the body is and how it needs to move to maintain balance is the location of the joints relative to itself (proprioception). This is accomplished through joint position sense provided by receptors within the joint itself, muscle spindles (providing information about the length and motion of the muscle itself), and Golgi tendon organs (which are responsible for providing information about a sense of force on the muscle). All of these receptors help the brain determine where the body is in space and how it moves. It allows the brain to make decisions about how to move specific muscles to keep the body where it needs to be in order to maintain balance. For instance, these sensory inputs help tell you to clench your toes on your right foot if you are leaning forward too far.

Romberg Test

The ability to balance oneself is dependent on the cooperation of a minimum of two out of three subjective factors: an individual’s vision, their proprioception, and the proper functioning of the vestibular organs of the inner ear. Analyzing these three factors is the basis for the Romberg test. When giving a patient a complete neurological exam, doctors will often employ the Romberg test as one of many tools designed to screen for problems with balance, particularly to determine disorders of proprioception and the vestibular apparatus.

In clinical practice, the Romberg test does not always give very precise results, and today it is used most often to monitor the progress of a patient diagnosed with a particular disease or as a general indication that the patient has difficulty with balance. The test was not designed to assess vestibular function, though it has come to be used for that purpose. There is still a lack of consistency regarding when to use the test and how to interpret the results; however, a positive Romberg’s sign, meaning a loss of balance, certainly indicates a need for further testing.

One of the most common uses of the test today is by law enforcement officials to confirm positive results from standardized roadside sobriety tests. The Romberg test removes visual stimuli that a person might use to maintain balance and can therefore detect problems with proprioception or the vestibular apparatus.

Materials:

Volunteer

Enough space for two people to stand safely

Timer or watch with a second hand

Directions:

For safety, the experimenter should stand next to the volunteer with his or her arms in front of and behind the subject in all balance tests to provide support and to reduce the risk of a fall.

Test 1: Have the volunteer stand with both feet together. Ask the person to pick up one foot and balance on the other foot for 10 seconds. A normal response is that the person will not sway or need to hold on to anything for balance. Repeat this test with the other foot and compare responses.

Test 2: Have the volunteer stand with one foot in front of the other touching heel to toe. The subject can choose which foot is in front. Next, have the person fold their arms across their chest or hanging down at their sides. Have the individual stand in this position with their eyes closed for 30 seconds. Mild rotational swaying may be perceptible and is considered a normal occurrence. For a true negative test, there should be no marked swaying or loss of balance, nor should the subject have to move their feet for stability.

Erin Slocum

Visual Input

Information from the eyes comes in from light hitting the rods and cones (photoreceptors) in the retina. This information is processed in visual centers within the brain and tells the brain important information about the surrounding area. This visual input provides cues to where the body is relative to space—whether it is upright, sitting, moving in a certain direction, and so on.

Vestibular Sense

Vestibular organs reside within the inner ear and are made up of the utricle, saccule, and the three semicircular canals. The utricle and saccule are responsible for vertical and horizontal orientation within space (as relative to gravity—which way is up and which way is down), and the semicircular canals are responsible for detecting rotational motion. Typically the vestibular system works symmetrically. Ideally information from both sets of vestibular organs will match. When this sensory information does not match, it can cause a feeling of dizziness or vertigo and cause the individual to lose his or her balance.

Diseases

Diseases of the balance system typically consist of symptoms of dizziness, vertigo, and unsteadiness. One of the more common reasons for these diseases is issues involving the vestibular system. Benign paroxysmal positional vertigo (BPPV) is one of these. BPPV is due to loose vestibular crystals (otoconia). These otoconia will move when the head is tilted or jolted and will then weigh down the semicircular canals, causing them to send incorrect messages about motion to the brain. This causes a brief but intense episode of vertigo in the patient. There are multiple causes of dislodging the otoconia including head injury, age, and dehydration. Meniere’s disease, another balance disorder, is still not well understood but it is believed to be related to issues with fluid filling the semicircular canals. This disease is characterized by episodes of vertigo, tinnitus (ringing in the ears), and buzzing in the ears.

Other diseases of balance are due to issues within the brain and nervous system itself. Parkinson’s disease is one such disease. Parkinson’s disease is a disease of the motor system characterized by tremors and muscle rigidity. Additionally, patients afflicted with Parkinson’s disease may have postural instability and lose balance easily. This instability is thought to be due to problems making minute adjustments in posture to maintain a standing position.

Riannon C. Atwater

See also: Dizziness; Golgi Tendon Organs; Meniere’s Disease; Tinnitus; Vestibular System

Further Reading

National Institute on Deafness and Other Communication Disorders (NIDCD). (2015). Balance disorders. Retrieved from https://www.nidcd.nih.gov/health/balance-disorders

Tassinari, Mariateresa, Daniele Mandrioli, Nadia Gaggioli, & Paola Roberti di Sarsina. (2015). Ménière’s disease treatment: A patient-centered systematic review. Audiology & Neurotology, 20(3), 153—165.