Hearing and Balance
Discussion of Dizziness
Dizziness is a symptom not a disease. It may be defined as a sensation of unsteadiness, imbalance, or disorientation in relation to an individual's surroundings. The symptom of dizziness may vary widely from person to person and be caused by many difference diseases. It varies from a mild unsteadiness to a severe whirling sensation known as vertigo. As there is little representation of the balance system in the conscious mind, it is not unusual for it to be difficult for the patient to describe his symptom of dizziness to the physician. In addition, because the symptom of dizziness varies so widely from patient to patient and may be caused by many different diseases, the physician commonly requires testing to be able to provide the patient with some knowledge about the cause of his dizziness. Dizziness may or may not be accompanied by a hearing impairment
Function of the Normal Ear
The ear is divided into three parts: external ear, middle ear, and inner ear.
The external ear structures gather sound and direct it toward the eardrum. The middle ear chamber consists of an eardrum and three small ear bones. These structures transmit sound vibrations to the inner ear fluid.
The inner ear chamber (labyrinth) is encased in bone and filled with fluid (endolymph and perilymph). This fluid bathes the delicate nerve endings of the hearing and the balance mechanism.
Fluid waves in the hearing chamber (cochlea) stimulate the hearing nerve endings which generate an electrical impulse. These impulses are transmitted to the brain for interpretation as sound. Movement of fluid in the balance chambers (vestibule and three semicircular canals) also stimulates nerve endings, resulting in electrical impulses to the brain, where they are interpreted as motion.
Maintenance of Balance
The human balance system is made up of four parts. The brain acts as a central computer receiving information in the form of nerve impulses (messages) from its three input terminals: the eyes, the inner ear, and the muscles and joints of the body. There is a constant stream of impulses arriving at the brain from these input terminals. All three systems work independently and yet work together to keep the body in balance.
The eyes receive visual clues from light receptors that give the brain information as to the position of the body relative to its surroundings. The receptors in the muscles and joints are called proprioceptors. The most important ones are in the head and neck (head position relative to the rest of the body) and the ankles and joints (body sway relative to the ground).
The inner ear balance mechanism has two main parts: the three semicircular canals and the vestibule. Together they are called the vestibular labyrinth and are filled with fluid. When the head moves, fluid within the labyrinth moves and stimulates nerve endings that send impulses along the balance nerve to the brain. Those impulses are sent to the brain in equal amounts from both the right and left inner ear. Nerve impulses may be started by the semicircular canals when turning suddenly, or the impulses may come from the vestibule, which responds to changes of position, such as lying down, turning over or getting out of bed.
When one inner ear is not functioning correctly the brain receives nerve impulses that are no longer equal, causing it to perceive this information as distorted or off balance. The brain sends messages to the eyes, causing them to move back and forth, making the surroundings appear to spin. It is this eye movement (called nystagmus) that creates a sensation of things spinning.
Remember to think of the brain as a computer with three input terminals feeding it constant up-to-date information from the eye, inner ear and muscles and joints (proprioceptors). The brain itself is divided into several different parts. The most primitive area is known as the brainstem, and it is here that processing of the input from the three sensory terminals occurs. The brainstem is affected by two other parts of the brain, the cerebral cortex and the cerebellum.
The cerebral cortex is where past information and memories are stored. The cerebellum, on the other hand, provides automatic (involuntary) information from activities which have been repeated often.
The brainstem receives all these nerve impulses: sensory from the eyes, inner ear, muscles and joints; regulatory from the cerebellum; and voluntary from the cerebral cortex. The information is then processed and fed back to the muscles of the body to help maintain a sense of balance.
Because the cortex, cerebellum and brainstem can eventually become used to (ignore) abnormal or unequal impulses from the inner ear, exercise may be helpful. Exercise often helps the brain to habituate to (get used to) the dizziness problem so that is does not respond in an abnormal way, does not result in the individual feeling dizzy. An example of habituation is seen with the ice skaters who twirl around, stop suddenly, and do not apparently have any balance disturbance.
Types of Dizziness
Sensations of unsteadiness, imbalance or disorientation in relationship to one's surroundings may result from disturbances in the ear, neck, muscles and joints, the eyes, the nervous system connections of these structures, or a combination of any of the above.
Ear dizziness, one of the most common types of dizziness, results from disturbances in the blood circulation or fluid pressure in the inner ear chambers, from direct pressure on the balance nerve, or physiologic changes involving the balance nerve. Inflammation or infection of the inner ear or balance nerve is also a major cause of ear dizziness.
The inner ear mechanism is about the size of a pea, and is extremely sensitive. There are two inner ear chambers: One for hearing (cochlea), and one for balance (vestibule and semicircular canals). These chambers contain a fluid which bathes the delicate nerve endings. These nerve endings are stimulated when there is movement of the fluid. Nerve impulses are then transmitted to the brain by the hearing and balance nerves. The nerves pass through a small bony canal (internal auditory canal), accompanied by the facial nerve.
Any disturbance in pressure, consistency or circulation of the inner ear fluids may result in acute, chronic, or recurrent dizziness, with or without hearing loss and head noise. Likewise, any disturbance in the blood circulation to this area or infection of the region may result in similar symptoms. Dizziness may also be produced by over stimulation of the inner ear fluids, such as one encounters when he spins very fast and then stops suddenly.
Central dizziness is usually an unsteadiness brought about by failure of the brain to correctly coordinate or interpret the nerve impulses which it receives. An example of this is the “swimming feeling” or unsteadiness that may accompany emotional stress, tension states, and excessive alcohol intake. Circulatory inefficiency, tumors, or injuries may produce this type of unsteadiness, with or without hearing impairment. A feeling of pressure or fullness in the head is common. Occasionally true vertigo (spinning) may be caused by central problems.
Neck Dizziness (cervical vertigo) results from abnormal or uncoordinated nerve impulses being sent to the brain from the neck muscles.
The neck muscles are constantly sending nerve impulses to the balance centers of the brain to help maintain equilibrium. Spasm (tenseness) of the muscles may result in an abnormal nerve discharge, leading to unsteadiness or dizziness. This spasm may result from injury, arthritis of the spine, or from pressure on nerves in the neck.
Muscle-joint dizziness is relatively uncommon. Any disturbance of sensation arising from the muscles and joints in the limbs (such as occurs in the muscular dystrophies and other abnormalities) produces this type of unsteadiness. Such an example is the unsteadiness experienced when one tries to walk on a leg that has “gone to sleep.”
There are many causes of dizziness. This dizziness may or may not be associated with hearing loss. In most instances the distressing symptoms of dizziness can be greatly benefited or eliminated by medical or surgical management.