Whether you're an opera singer or shower singer, public speaker or normal speaker, your voice is something you probably take for granted. Alongside breathing, walking and swallowing, it's one of those things that you've never had to actively learn. According to the hierarchy of competence, you've attained the highest level by not knowing what you know. But not everyone is so lucky.
The Nervous System
In order for this to make sense, we first need to understand the basics of the nervous system. Essentially, it's a bunch of cells (working together as nerves) that transmits information to and from our brains, allowing it to efficiently coordinate our actions in response to changes in the environment.
There are two types of nerves - sensory and motor. The former sends information from receptors in our body to the brain. The latter sends commands from the brain back to our body. It's like there are two different postmen, who only deliver mail one way. Let's call them Sensory Susan and Motor Mike.
Now imagine that you accidentally grab hold of a hot potato. The heat from the potato is detected by the receptor outpost at Hand HQ, where Susan is on standby. She pulls out a pen and records this information immediately, seals it in an envelope and begins running toward the brain through the sensory nerve highway. It reads, 'HOT!'.
As soon as she reaches Brain HQ, her message is interpreted, the Brain HQ board of directors convene and an envelope containing the response is handed to Mike, who runs back to the hand through the motor nerve highway. It reads, 'DROP!'.
Hand HQ complies, and the potato is dropped. Of course, all of this happens in a split second (Susan and Mike run about 10 times faster than Usain Bolt) and there are thousands of Susans and Mikes all over the body.
The Recurrent Laryngeal Nerve
One particular motor nerve highway, called the recurrent laryngeal nerve (RLN), connects the brain to our vocal cords, which in turn is essential for speech, breathing and swallowing. These specific processes are achieved by manipulating the opening between the vocal cords, otherwise known as the glottis.
For a healthy set of cords, respiration results in a symmetrically opened glottis, while phonation results in a closed glottis, as the cords vibrate against each other (column 1 below). The complete closure of the glottis is important because optimal vibration requires maximum interaction between the two cords.
There are two things to point out here. First, while unilateral paralysis is a significant hindrance to speech, bilateral paralysis affects breathing and is thus a much greater threat to quality of life. Second, in unilateral paralysis situations, the resting position of the dormant cord determines the damage done to speech and breathing, and that damage is relative and inversely proportional. For example, where a dormant cord rests in a closed position, quality of speech is largely preserved due to a smaller glottal gap, but that smaller gap also results in less room for air to flow through. (Yes, it was confusing to write too.)
There are three solutions to Vocal cord paralysis - electrical stimulation, voice therapy, and surgery.
The first and most controversial method is electrical stimulation via methods such as TENS. While existing medical literature is on the fence about its effectiveness, the method intuitively makes sense. In essence, a machine replicates a Mike or Susan and sends them running toward the damaged section of the RLN in the hopes that, with enough repetition, one will jump across the damage, thereby 'breaking through' the damaged section.
The second method is voice therapy, with exercises designed to narrow the glottal gap. Since nerve recovery is unlikely, the focus of these exercises is to strengthen the healthy cord rather than to stimulate the unhealthy one. One particular exercise requires the patient to half-swallow before loudly shouting 'Boom!' (lol). Ultimately, the healthy cord will have to reach across the midline of the glottis and make up for the dormant cord. It's like going to gym every day and only working on one bicep.
Finally, when all else fails, there's always surgery. The operation involves injection of material into the outside of the dormant cord, pushing it toward to the middle of the glottis.
Annnd that's it! Enough medicine for a whole week.