Now, the next muscles that we are going to talk about is the extrinsic laryngeal muscles.
The extrinsic laryngeal muscles, as I said, determine the position of the larynx in the
neck, whether it's high up in the neck or low down in the neck. The extrinsic laryngeal
muscles can be divided into two groups, they can be divided as laryngeal elevators (or
supra,hyoids) and laryngeal depressors (or infra,hyoids), ok, like that. The laryngeal
elevators elevate the larynx meaning they lift the larynx high up in the neck, specifically
involved during swallowing. Some of the muscles I've listed there are the digastricus, stylohyoid,
geniohyoid, and the mylohyoid. Now I'm not going to go into details about that but all
I want you to know is laryngeal elevators are muscles that elevate the larynx and they
are situated above the hyoid, supra hyoid meaning they have one point of attachment
to the hyoid and the other point of attachment outside the hyoid, above. Laryngeal depressors
are also called infra hyoids and they depress the larynx meaning it decreases or lowers
the larynx in the neck. So the examples are omohyoid, sternohyoid, sternothyroid, and
thyrohyoid. These are muscles that have one point of attachment to the hyoid and the other
point of attachment to structures below the hyoid and that is why they are called infra
hyoid. OK? Suprahyoids, infrahyoids, laryngeal elevators, and laryngeal depressors. OK? So
that is an example, this is the hyoids, so the muscles above the hyoid, mylohyoid, stylohyoid,
digastricus, these are elevators. The depressors are the thyrohyoid, the sternothyroid, the
omohyoid, and the sternohyoid, which have connections to the hyoid and to structures
below the hyoid. OK? Those are extrinsic laryngeal muscles. Now this is an overview of how do
you look at the vocal folds. I've been talking to you about the vocal folds so far. This
is the vocal fold, a pearly white structure that has point of attachment to the inner
side of the thyroid notch and the posterior aspect of the vocal folds that are attached
to the vocal process of the arytenoid cartilage, ok. This is the position of the vocal folds
when you're breathing quietly. Look at the opening of the vocal fold. It has about eight
millimeter width. So let me back up here and say the opening that you see between the vocal
folds is called the glottis. G,l,o,t,t,i,s, glottis. OK? The width between the glottis
is going to be eight millimeters during quiet respiration. This is the position of the glottis
when you are under vigorous respiration, meaning when you're trying to do a physical activity,
and exerting yourself, your vocal folds have to be widely open to take in a lot more air.
It's about twice the glottal width as quiet respiration. This position that you see here
is the phonatory position of the vocal folds, and they are completely adducted, meaning
the vocal folds have to come together for phonatory position when you have to phonate.
This is the whisper position where your vocal folds are adducted, but you still see a gap
between the glottis and your vocal folds are not vibrating here. And that's the whisper
position of your vocal folds. This is the view of the vocal folds when you see through
an indirect laryngoscopy. If you go to the dentist office and the dentist uses a mirror
to see the back of your mouth or the tooth, kind of so he can see just by opening your
mouth and he has to use a mirror. The same kind of mirror but bent with an angle at 45
degrees, is placed in the back of your mouth, to be able to view the vocal folds. OK? This
is called an indirect laryngoscopy. Alright, and those are the positions of the vocal folds.
OK? Alright, now having talked about the structures in our phonatory system, how do these structures,
how does the phonatory system help us in speech? Remember when we talked about adduction or
bringing the vocal folds together and abduction, taking the vocal folds apart. Some speech
sounds can be categorized into voiceless speech sounds and voiced speech sounds. Voiceless
speech sounds are speech sounds that does not require vocal folds to come together.
And voiced speech sounds are speech sounds that needs your vocal folds to come together.
So if you try these sounds with me as I'm doing this lecture, as you're listening to
this lecture, I want you to go 'ssssssssss'. And then I want you to go 'zzz zzzzzzzz'.
When you do both these sounds I want you to place your hand on your neck and I want you
to feel the difference in your neck when you produce these two sounds. Or you can go 'hhhhhhh',
'aaahhhhhh'. When you produce voice speech sounds, like the 'zzzzzz', or the 'aaaahhh'
with, all vowels are voiced speech sounds, you should be able to feel a vibration in
your neck, that's because of the vibration of the vocal fold. When you produce voiceless
speech sounds, there is no vibration of the vocal folds. Ok. Also, any changes that we
have with pitch, pitch changes when i have an inflection, or when I go 'aaaaaAAAAA' (pitch
rise). Any pitch change that I have is because of the increased and decreased tension of
the vocal folds. So in our speech, how does this phonatory system, affect. It helps us
in producing different speech sounds, the speech sounds could be voiced or voiceless
speech sounds, and how we change our pitch and vary our intonation and speaking patterns
is because of our vocal fold movements. Now we talked about the vocal folds needing to
vibrate, and the source for the vibration is going to come from our lungs. Right? So
lungs have to produce this air, and the air has to come and build below the vocal folds
and it creates something called the subglottic pressure. The subglottic pressure is nothing
but the air pressure that is built up under, or below, the vocal folds. Ok. Now, if I were
to bring my vocal folds together, there should be some force to set these vocal folds apart
or to blow these vocal folds apart. That force is going to be the subglottic pressure that
builds below the vocal folds or under the vocal folds. Now the subglottic pressure has
to increase, above the pressure to increase, to be more than the pressure above the vocal
folds. When that happens, it forces the vocal folds to open. Now, when I say forces the
vocal folds to open, it's not like it goes and it's a one shot open, it's a nice, smooth
movement of the vocal folds from the posterior aspect to the anterior aspect. So the vocal
folds are blown apart from the posterior aspect to the anterior aspect in a nice, wave,like
motion. Ok. So, when those open apart, now what happens to that pressure? The pressure
is going between the vocal folds as air flow, right? Well now the air passes between the
vocal folds and it goes above the vocal folds, what happens to the pressure in between the
vocal folds? The pressure in between the vocal folds drop, right? When the pressure in between
the vocal folds drop, your vocal folds are going to get sucked again to midline, okay?
Then again, the vocal folds are closed, subglottic pressure builds below the vocal folds, when
the subglottic pressure below the vocal folds increases above the vocal folds, it blows
open the vocal folds. When the vocal folds open apart, this pressure flows as air flow
between the vocal folds. When the air flow between the vocal flows rises up and goes
above the vocal folds, there is negative pressure between the vocal folds, and it sucks the
vocal fold again. Right? That phenomenon of sucking the vocal folds together due to negative
pressure is called the Bernoulli effect. Okay, I think I might have that right here, there
you go. Bernoulli effect. Bernoulli effect is when the air passes through the vocal fold
and it passes beyond and goes about the vocal fold, there is negative pressure between the
vocal folds. The negative pressure between the vocal folds causes the vocal folds to
be sucked together and it's aided by elastic properties of the vocal folds as well. Elastic
properties, meaning that, the, the ability of the body to come back to its original position.
Okay, now, when we talked about subglottic pressure, I want you to understand certain
subglottic pressures involved in speech. In order for somebody to initiate phonation,
meaning I need to bring my vocal folds together, and to start phonation, I need an approximate
subglottic pressure of about three centimeters of water. When I mean three centimeters of
water, I'm not saying that there is a buildup of water below your vocal folds. All I'm saying
is the air molecules that build up as pressure is measured in centimeters of water, meaning
your pressure is measured in depth of centimeters of water. In order to sustation phonation,
meaning if I have to go 'ahhhh p p p p p p', that is when I sustain phonation, I need about
five to seven centimeters of water. In order to produce a loud speech, in order to say
something really loud, 'HEY', I need to build a subglottic pressure of about ten centimeters
of water, to be able to produce a loud speech. Now for shouting which I'm not going to depict
what shouting is, if you're at a ball game or if you're cheering somebody, the subglottic
pressure for shouting is about twenty centimeters of water. As you can see, how the increase
is, there is a need to increase your subglottic pressure as the need to, initiate or sustain
or produce different various phonations, your subglottic pressure is changing, okay. Alright,
I need you to keep this slide in mind because I will be asking you this question, what is
the minimum subglottic pressure required to initiate phonation?' or 'what is the minimum
subglottic pressure required to sustain phonation?'. These are things that I really need you to
know. Ok. Finally, what I want to talk about is a theory of phonation, it's called the
myoelastic theory of phonation. This is exactly what we talked about so far, but I'm putting
it in sum under the theory of phonation. In order to phonate, we need air flow and pressure
which is where we get the air flow from the lungs. That air flow builds below the vocal
folds as a subglottic pressure. Once that subglottic pressure increases and is more
than a subglottic pressure above the vocal folds, it drives the vocal folds apart. And
then when it drives the vocal folds apart, this elastic component of muscle and soft
tissues and the Bernoulli effect will suck the vocal folds together, leading to the cycle
of vibration that continues until you decide to stop phonation. Ok. The last thing that
we are going to talk about here is certain properties that are associated or a certain
parameters that are associated with phonation. One thing that I want to talk about is the
frequency of phonation. How does somebody know it's a male voice versus a female voice?
That is because there is a change in the frequency of phonation or the frequency of vibration
of the vocal folds. For males, the frequency of vibration is lower, resulting in a lower
pitch when compared to females. If I go 'ahhhh' (low pitch), 'ahhhh' (higher pitch), 'ahhh'
(even higher pitch), 'ahhhh' (highest pitch). You see how the frequency changed from a lower
pitch, when i say pitch because that's what you are percieving, a low pitch, to a higher
pitch there was a change in frequency which is what we can measure. Now this frequency
depends on elasticity, tension, mass of the vocal folds, okay. So if you look at this
formula right here, frequency is proportional to the tension and length of the vocal folds
and inversely proportional or reciprocal to the mass of the vocal folds. Now think about
this, if I am trying to, remember the cricothyroid muscle that we talked about, the CT muscle?
What does the CT muscle do, it stretches the vocal fold. When it stretches the vocal fold,
it increases the elasticity of the vocal fold. When it increases elasticity of the vocal
fold, the mass per unit area of your vocal fold is decreasing. All of this results in
an increased pitch, okay. The frequency is directly proportional to the tension and length
of the vocal fold. As the length of the vocal fold increases, the tension and stiffness
of the vocal fold increases, while mass per unit area decreases. When it decreases, you
have an increased pitch. So if I go 'ooooOOOOOO' (low to high pitch), that results in an increase
in my vocal fold length, an increase in tension of my vocal fold, decrease in mass of the
vocal fold, resulting in increased pitch. Okay, what I'm going to probably do, is I
will post a link, a YouTube link, that shows different pitch variations, and you can see
how the vocal fold is changing in length and tension when you observe the speech changes
as well. I will post that quick link, as a quick link on your YouTube, okay. So that
sums up our phonatory system. So we talked about
the rest. Then I will talk in part three, the central nervous system and how it serves
as a controller in the final output to speech.