People refer to an abnormal change in voice as "hoarseness." This can mean many different things to different people. The voice can be:
- A higher or lower pitch
What Is the Difference Between Speech and Voice?
As air passes from the lungs via the trachea (windpipe) and through the larynx (voice box) it causes the vocal folds to vibrate. This vibration creates the sound - like a reed on a wind instrument - that is voice. The vibration then passes through the resonator, which is comprised of the pharynx (throat), mouth and nose. We manipulate the shape of these tubes and that reforms the vibration into words that make speech.
Voice problems arise at the level of the larynx (voice box) causing distortions in the vibration.
Speech problems arise at the level of the resonator, which is, most often, the mouth. Impaired tongue, lip or palate mobility can make it difficult to shape the vibratory sound, generated by the larynx (voice box), into words.
Individuals can have difficulty with voice or speech or both components.
What Are the Vocal Folds and What Do They Do?
The vocal folds (also known as vocal cords) are folds of tissue located within the larynx (voice box), specifically the thyroid cartilage.
The thyroid cartilage should not be confused with the thyroid gland. The thyroid cartilage can be felt as the Adam's apple on most men; it is present, though less prominent, in women. The thyroid cartilage is a firm framework structure. The thyroid gland, on the other hand, is a soft tissue structure located lower in the neck just above the collar bones. It is involved in the regulation of metabolism.
In addition to producing voice, the vocal folds are the gate keepers to the trachea (windpipe) and the lungs. When you speak the vocal folds come together so that they can vibrate against one another. When you swallow, the vocal folds also close, to help prevent food or liquids from trickling into your airway. This helps protect you from choking or getting food into the airways or lungs (aspiration). Aspiration is dangerous because it can lead to pneumonia.
What Are the Vocal Folds Made Of?
The vocal folds are made of several layers. The most superficial (top layer) is the epithelium (also known as the skin). The next layer is called the lamina propria, which is itself divided into three layers: superficial, intermediate and deep. The lamina propria is a gelatinous layer that allows the epithelium (skin) to move over the deepest layer. This last layer is a muscle layer comprised of the vocalis and thyroarytenoid muscles.
How Do the Vocal Folds Make Voice?
When you talk, the muscles place the focal folds in approximation. Air passing between the vocal folds causes the epithelium (skin) to vibrate against one another, thus generating sound.
Have you ever made a whistle from a blade of grass? The principle is the same. Your hands holding the blade of grass are like the muscles (vocalis and thyroarytenoid) holding the vocal folds together. When you blow at your hands across the grass, it is like the air being exhaled from your lungs passing through the larynx (voice box). The blade of grass vibrating between your hands is like the vocal fold epithelium (skin) vibrating against one another and making sound.
The muscles of the larynx (voice box) can also adjust the tension on the vocal folds, like tension on a rubber band. The change in tension affects the rate at which the epithelium (skin) vibrates. This then changes the pitch of the sound. Take a rubber band and stretch it gently between your fingers and pluck it. Now stretch it further and pluck again. The sound it makes should be a higher pitch when there is more tension.
What Causes Hoarseness (or a Change in Voice)?
There are many potential causes of voice change. They can be grouped into three broad categories:
- Voice misuse
- Gastrointestinal reflux
- Vocal fold paralysis
- Systemic neurologic disorders