Don’t scream until you’ve read this. Let’s take a step back. Screaming is good sometimes, i.e., when
chased by a large carnivorous animal, as a warning of eminent danger, or during
a bout of uncontrollable laughter as exemplified by my daughter above.
Screaming, singing, laughing and vanilla-plain conversation
all require a healthy larynx. Known as
the voice-box to you layfolk out
there, the larynx has important functions as cited in a post, Anatomy of the Larynx: A Journey into your
Voice Box. No doubt, many of you
exercise your larynges (the fancy way
medical people pluralize “larynx”) extensively, to the joy or chagrin of unsuspecting
ears receiving the soundwaves generated by your unique voice.
As with most organs in the body, your larynx requires nerves
to function properly. Fundamentally,
nerves are thin, string-like structures that serve as conduits transmitting
information to and from the brain. Think
of nerves as the wires in electronic devices, or the network of cables and
fiber channels of the internet. Nerves
are wonderful structures: they carry electrical impulses much like metal wires,
but do so using amazing biochemical processes to accomplish this. As such, they are capable of bioengineering
new pathways and new networks and perform self-repair where man-made structures
cannot.
The brain is the ultimate Decider-In-Chief: it must tell an
organ what to do, and also receive information from that organ so it can
enhance its “to-do” commands. Nerves
serve to transmit all the input and output data to and from the brain.
Your larynx likewise has nerves delivering and receiving
impulses of information and commands. Much
of this relates to movement of the true
vocal cords. Often these are
referred simply as vocal cords (as opposed to the false vocal cords which play a much less significant role in voice
production). Here are two of the main
nerves:
1. Recurrent laryngeal
nerve. The name for this shifty nerve is
well-deserved. For some reason, known
only to God and nature, the recurrent laryngeal nerves travel an unusual path
in the body to ultimately land at the larynx.
They branch off the vagus nerve,
a major nerve that travels from the brain down to the lungs. After branching off the vagus, each recurrent
nerve descends downward, then loops around major blood vessels, then travels
upwards to innervate the larynx: the right recurrent laryngeal nerve loops around
the subclavian artery in the lower part of the neck, and the left around the
arch of the aortic artery (the giant, hose-sized blood vessel attached to the
heart) farther down in the chest. Upon
coming back upwards in the neck (ie, the reason they’re called recurrent), they travel close to the
sides of the trachea and pass underneath the thyroid gland on each side, and
then enter deep to the cricothyroid muscle to enter deeper into the larynx. These nerves are responsible for moving the
true vocal cords inward (adduction)
and outwards (abduction). The resultant opening and closing of the glottic airspace between these vocal
cords shapes the air as it passes from the trachea below through the larynx
above. These nerves also close the
airway spontaneously when swallowing by adducting the cords together. This is an autonomic response, meaning this is done involuntarily to prevent
food, drink, saliva and any other unwanted substance from passing down into the
trachea; otherwise you’d cough, choke and gag as the trachea tries to expel any
unwanted substance to prevent it from going lower down to affect the lungs,
causing nasty things such as pneumonia
(infection of the lungs). By the way,
the act of coughing also requires closure of the glottis by vocal cord
adduction—this can alter the air pressure below the vocal cords to do the
necessary work of clearing bad stuff from the larynx, trachea and lungs.
2. Superior laryngeal
nerve. You have one of these nerves on
the left and right sides of your larynx.
This nerve splits (or bifurcates—a
fun medical word meaning “to divide into two”) much like a fork in the road to form
two distinct nerves: the external and the internal branches of the superior
laryngeal nerve. The internal branch enters through the thyrohyoid membrane and then divides
into multiple smaller nerve branches to provide sensation to the inside part of
the larynx. Thus, if you feel a tickle
in that area or have an irritation forcing you to cough or clear your
throat—well, thank the internal branch of your superior laryngeal nerve for
that.
The external branch of
the superior laryngeal nerve travels to the cricothyroid muscle. When
this nerve is activated, it causes that muscle to contract, pushing the cricoid
cartilage up and tilting the thyroid cartilage down and forward; the combined
effect creates elongation and tension of the true vocal cords which further
narrows the column of air passing between, contributing to the ability for the
larynx to generate higher frequencies (i.e., higher pitches).
Impaired or altered movement one or both vocal cords causes
changes in voice quality. This can be
due to injury or impairment of one or both of these nerves from a number of
causes. Likewise, alterations of the
vocal cords from nodules, benign or malignant (cancerous) lesions, inflammation
or swelling of one or both vocal cords also causes vocal changes.
Changes to the voice are heard as hoarseness (harsh or rough
quality), raspiness, decreased projection or loudness, weakness, tremor-like
quality, or a gravelly (think of mucous moving on the vocal cords) quality.
We discussed vocal nodules on a prior post. We’ll go into the variety of other causes for
voice problems in the future. In the
meantime, be kind to your larynx—it’s a wonderful organ, especially in its
silent state for some people. Rest it
regularly and don’t abuse it with unnecessary screaming or cringeworthy singing,
particularly if you see people covering their ears and clenching their teeth,
or hear cries for mercy, begging you to stop.
©Randall S. Fong, M.D.
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