J Appl Physiol 93: 1622–1629, 2002.
First published July 19, 2002; 10.1152/japplphysiol.00417.2002.
Mucosal afferents mediate laryngeal adductor
responses in the cat
RICHARD D. ANDREATTA, ERIC A. MANN,
CHRISTOPHER J. POLETTO, AND CHRISTY L. LUDLOW
Laryngeal and Speech Section, National Institute of Neurological Disorders
and Stroke, National Institutes of Health, Bethesda, Maryland 20892
Received 13 May 2002; accepted in final form 17 July 2002
PERIPHERAL AFFERENTS IN THE mammalian larynx provide
a variety of physiological inputs through specialized
end organs, including pneumoreceptor, chemoreceptor,
thermoreceptor, proprioceptive, and mechanoreceptive
afferents (14, 31–33, 35, 51–53). These different afferent populations are contained in the internal branch of
the superior laryngeal nerve (ISLN) and are thought to
modulate activity in the laryngeal motoneuron pools
during cough, swallow, and vocalization (4, 44, 49). Although extensive research has been conducted on the role
of afferents contained in the mucosa on laryngeal control, less is known about the role of proprioceptive joint
and muscle afferents on laryngeal protective reflexes.
Mechanical indentations or vibratory stimulation to
the mucosa of the cat larynx have been demonstrated
to elicit responses in superior laryngeal nerve fibers (8,
9). Similar investigations have confirmed that the activity in these receptors is well correlated with light
touch, air pressure changes, laryngeal muscle contraction, and cartilage displacement in animal models (6,
13, 26, 34) and are in evidence in the human (2). Davis
and Nail (8) found that the glottis is densely populated
with low-threshold, rapidly adapting (RA) mechanoreceptors of small receptive field size. The largest proportion of these RA afferents were in the region surrounding the arytenoid cartilage in the cat (8, 21). The
arytenoid cartilages adjust their position to produce
vocal fold closure during cough, swallow, and vocalization. Recordings have demonstrated that these receptors provide movement-related afferent feedback during evoked vocalization in the cat (44), are contained in
the ISLN, and contribute to muscle activity during
vocalization.
The laryngeal adductor response (LAR) is a rapid
burst of activity in the thyroarytenoid (TA) muscles,
which can assist in closure of the larynx in response to
ISLN stimulation. The spatiotemporal properties of
the LAR have been studied in both humans and animals by using a variety of stimulus conditions (17, 37,
40, 50). Besides the well-known role of the LAR for
airway closure (37), it has been suggested that this
sensorimotor pathway is also involved in regulating
the stiffness of the internal laryngeal musculature
during vocalization in mammals (1, 10, 48, 49). The
LAR pathway is believed to be mediated by afferents
from neurons within the nodose ganglion that project
to the interstitial subnucleus of the tractus solitarius
(11). Interneuronal projections may pass through the
lateral tegmental field to the laryngeal motor neurons
in the nucleus ambiguus (5, 7, 44).
The purpose of this study was to determine the
relative contribution of mucosal mechanoreceptor afferents and cricoarytenoid joint proprioceptors in the
elicitation of the short-latency component of the LAR.
A surgically performed mucosal peel was used to assess
the relative contribution of surface mechanoreceptors
vs. deep proprioceptive receptors in eliciting LAR re-
Address for reprint requests and other correspondence: R. D.
Andreatta, Dept. of Communication Sciences and Disorders, 514
Aderhold Hall, The Univ. of Georgia, Athens, GA 30602 (E-mail:
[email protected]).
The costs of publication of this article were defrayed in part by the
payment of page charges. The article must therefore be hereby
marked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734
solely to indicate this fact.
sensorimotor; electromyogram; servomotor displacement;
thyroarytenoid
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Andreatta, Richard D., Eric A. Mann, Christopher J.
Poletto, and Christy L. Ludlow. Mucosal afferents mediate laryngeal adductor responses in the cat. J Appl Physiol
93: 1622–1629, 2002. First published July 19, 2002; 10.1152/
japplphysiol.00417.2002.—Laryngeal adductor responses
(LAR) close the airway in response to stimulation of peripheral afferents in the superior laryngeal nerve. Although both
mucosal afferents and proprioceptive receptors are present in
the larynx, their relative contribution for reflex elicitation is
unknown. Our purpose was to determine which receptor
types are of importance in eliciting the LAR. A servomotor
with displacement feedback was used to deliver punctate
displacements to the body of the arytenoid cartilage and
overlying mucosa on each side of the larynx in eight anesthetized cats. The same displacements were delivered both before and after surgical excision of the overlying mucosa. With
the mucosa intact, early short-latency component R1 LAR
responses recorded from the thyroarytenoid muscles were
frequent (ipsilateral ⬎ 92%, contralateral ⬎ 95%). After the
mucosa was removed, the LAR became infrequent (⬍3%) and
was reduced in amplitude in both the ipsilateral and contralateral thyroarytenoid muscle recording sites (P ⬍
0.0005). These findings demonstrate that mucosal mechanoreceptors and not proprioceptive afferents contribute to the
elicitation of LAR responses in the cat.
MUCOSAL AFFERENTS MEDIATE THE LAR
METHODS
Subjects and surgical procedures. Eight cats of either sex
were used (weight range: 2.6–4.4 kg). All care and treatment
procedures were in compliance with and in accordance to the
rules and regulations of the National Institute of Neurological Disorders and Stroke Intramural Program (National Institutes of Health Manual 3040-2, revised 1999). Before
study, each animal had a cephalic vein port placed in the
forelimb for intravenous administration and was preanesthetized with acepromazine (0.1 mg/kg im). Deep anesthesia was
induced with a mixture of 3–5% isoflurane and 100% oxygen
(3 l/min) delivered via a ventilator into an enclosed induction
chamber. After anesthesia to effect, the animal was removed
from the induction chamber, laid supine on the surgical
carriage, and fitted with a nose cone to support ventilation
with 0.5–1% isoflurane (2 l/min of oxygen), and the skull was
fixed to a stereotaxic frame with ear bars.
A tracheotomy was performed at a level superior to the
thoracic inlet to provide an independent airway and to allow
for discrete stimulation to the laryngeal area without producing airway interruption or stimulating pressure receptors
within the lungs. After placement of the endotracheal cannula, ␣-chloralose (40 mg/kg) was administered intravenously to effect during gradual withdrawal of isoflurane to
engender long-lasting anesthesia. Spontaneous breathing
was supported throughout the remainder of the protocol via
the endotracheal cannula (100% oxygen at 2 l/min). Core
body temperature was monitored and maintained between
36 and 38°C by using a warm-water circulating blanket. Vital
signs, including heart rate, respiratory rate, PCO2, oxygen
saturation, and checks for the lack of a withdrawal response
to painful stimuli, were recorded every 30 min. A pediatricsize adhesive grounding electrode was affixed to the shaved
dorsal spine region of the animal.
To expose the laryngeal region for mechanical stimulation,
a midline separation of the thyroid and cricoid lamina was
performed. The free ends of the divided cartilaginous tissue
were sutured and secured to the stereotaxic frame to maintain the larynx in a constant open position. Bipolar stainless
steel bifilar hooked-wire electrodes contained in a 27-gauge
J Appl Physiol • VOL
hypodermic needle were inserted into the anterior portion of
the TA muscles bilaterally under visual guidance. The lower
abdomen was opened to visualize the inferior surface of the
diaphragm, and a bipolar hooked wire electrode was inserted.
The electromyographic (EMG) signal of the diaphragm was
routed to an audio speaker and used to time the delivery of
the mechanical stimulus during the expiratory phase of respiration to control for respiratory modulation of the LAR. The
exposed mucosa was kept moist by administration of physiological saline periodically throughout the experiment.
Mechanical stimuli. A custom-designed servomotor operating under displacement feedback was used to deliver punctate mechanical transients to three different locations along
the exposed vocal fold margin: 1) the tissues encompassing
the body of the arytenoid cartilage, 2) the area of the vocal
process, and 3) the anterior aspect of the TA muscle (Fig. 1).
A 5-ms Transistor-Transistor Logic pulse produced by a Master 8 pulse generator provided the control signal to the
servomotor’s controller. The stimulator system consisted of a
high-performance audio speaker with a permanently affixed
and rigid shaft extending from the speaker’s diaphragm.
Displacement of the shaft was monitored by an optoelectrical
sensor located distal to the motor and a servo-feedback circuit to the speaker driver. The distal end of the rigid shaft
was fitted with a miniature load cell (Schaevitz Sensors,
Hampton, VA) serially coupled to a probe tip. The probe tip
consisted of a 30-gauge hypodermic needle hub with its
cannula trimmed to ⬍2 mm in length. The trimmed cannula
was inserted into the mucosa and operated to anchor the
probe tip securely in place at each stimulus site. After cannula insertion, the probe was carefully advanced with the use
Fig. 1. Line illustration of the experimental procedure. The orientation of the servo-displacement system is shown with reference to the
exposed larynx. The load cell was serially coupled to the shaft of the
motor and was monitored on an oscilloscope to maintain a constant
loading bias of 30–40 g. Stimulus locations are shown by the arrows
and are labeled for each site. TA, thyroarytenoid.
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sponses in the anesthetized cat. Mucosal excision was
used because of possible variations in the degree of
tissue diffusion and the duration of effect when applying lidocaine to the mucosa. Access to the vocal folds
and the arytenoid region was possible via a carefully
performed midline anterior incision through the thyroid and cricoid cartilages. Because the recurrent laryngeal nerve (RLN), which innervates the laryngeal
adductor muscles, enters the larynx posteriorly and
from an inferior direction, the anterior midline incision
of the thyroid cartilage did not interfere with the
course of the RLN innervating the TA muscle. Demonstration that the RLN was intact, as evidenced by TA
muscle LAR responses, was required before beginning
the study. In addition, it was assumed that because the
afferents from the region beneath the vocal folds,
which join the recurrent nerve, do so in the posterior
inferior region (51–54), disturbance of these fibers by
an anterior midline section through the thyroid cartilage was unlikely. This approach for accessing the
vocal folds also allowed us to study the spatial distribution and displacement characteristics of stimulation
that evoked the LAR.
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MUCOSAL AFFERENTS MEDIATE THE LAR
Table 1. Studies conducted in each animal
Animal
1
2
3
4
5
6
7
8
Procedure
totals
Stimulation
Site Study
Stimulus Magnitude
Study
Mucosal Peel
Study
R
R
R
R
R
R
L-ary
R-ary
L-ary
L-ary
L-ary
L and R-ary
L and R-ary
R-ary
L and R-ary
R-ary
L and R-ary
L-ary
L and R-ary
L and R-ary
L and R-ary
n⫽6
n⫽9
n ⫽ 13
ary, Arytenoid cartilage; L, left side; R, right side.
peel conditions, results of displacement of an arytenoid cartilage were compared on one side of the larynx. Given the
delicate nature and sensitivity of vocal fold tissues to external manipulations, the order of data acquisition was designed to maximize data collection and minimize physical
damage at each stimulus site. Therefore, the site condition
was typically performed first on one side, followed by the
displacement magnitude condition on the opposite side, with
the mucosal peel condition performed on the same side as the
displacement magnitude condition. For several of the animals, we were able to complete a second set of displacement
magnitude and mucosal peel experiments on the remaining
intact arytenoid body after completion of the former two
experimental conditions (Table 1).
For the site condition, the servomotor was positioned on
each of the stimulation sites in a random order. The servo
device was programmed to deliver a constant displacement of
⬃350–400 ␮m with a loading bias maintained between ⬃30
and 40 g at each site. Ten tokens were delivered, with 1-min
intervals between tokens, at each stimulus site. For the
displacement magnitude condition, the servomotor was positioned on the body of the arytenoid cartilage and stimulated
Fig. 2. TA muscle responses for ipsilateral
(LTA) and contralateral (RTA) recording sides
for the prepeel condition (A) and postpeel condition (B). Stimulus displacement (DISP) levels
for each condition were 325 ␮m. Stimulation of
the arytenoid body before mucosal peel evoked
bilateral short-latency R1 responses. No R1
responses occurred bilaterally postmucosal
peel. EMG, electromyogram.
J Appl Physiol • VOL
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of a micrometer until the flat and blunt surface of the hypodermic’s plastic hub contacted the tissue surface. During
placement of the probe tip over the arytenoid, the 2-mm
trimmed cannula was inserted through the mucosa and anchored into the body of the arytenoid cartilage. The probe
tip’s loading was monitored and controlled throughout the
experiment for all stimulation sites (preload bias of 30–40 g
for all experimental conditions). The direction of stimulation
was generally posterolateral.
During placement of the stimulation probe, care was taken
to assure that the probe tip was not over the region of the
hooked wire electrodes within the TA muscle. This was of
particular concern during stimulation of the anterior region
of the TA muscle site. The EMG signal was reviewed during
the experiment to ensure that movement artifacts were not
observed, such as a direct current offset during probe displacement, which might alter the measurement of a muscle
response. TA muscle EMG signals were band-pass filtered
(30–3,000 Hz) (Fig. 2). After antialiasing with a low-pass
filter at 2,500 Hz, stimulus-triggered digitization of the TA
EMG and the servo displacement signals were conducted at
5,000 Hz by using a customized routine written in LABVIEW
command language (National Instruments).
Experimental conditions. The effects of three different experimental conditions on the ipsilateral and contralateral TA
response were studied: 1) a stimulation site condition comparing evoked responses to the same displacement over the
arytenoid body, the vocal process, and the TA muscle (on the
same vocal fold margin); 2) a displacement magnitude condition comparing evoked responses to different mucosal displacements over the right and/or left arytenoid body, and,
lastly; 3) a mucosal peel condition that sought to compare
LAR responses to the same displacement of the arytenoid
body with and without the overlying mucosa intact. Six of the
eight animals received each of the three experimental conditions (Table 1). The remaining two animals received only one
or two of the three experimental conditions. For the stimulation site condition, all three loci were on the same side of
the larynx. For the displacement magnitude and mucosal
MUCOSAL AFFERENTS MEDIATE THE LAR
J Appl Physiol • VOL
comparisons to examine any omnibus significant main effects
after each of the repeated-measures analyses.
RESULTS
Site of stimulation effects. As shown in Fig. 3, the
magnitude of the LAR evoked by a constant servomotor
displacement of ⬃350–400 ␮m increased significantly
as mechanical inputs were delivered closer to the body
of the arytenoid cartilage for both ipsilateral and contralateral recording sites (F ⫽ 62.96, P ⬍ 0.0005). The
main effect of response side (ipsi- vs. contralateral) was
nonsignificant (F ⫽ 3.09, P ⫽ 0.139), as was the interaction effect for site of stimulation by response side
(F ⫽ 2.03, P ⫽ 0.183). Post hoc testing for the significant main effect of stimulation site revealed that the
pairwise comparisons of arytenoid body stimulation
with vocal process stimulation and with TA muscle
stimulation were significantly different (P ⫽ 0.0024
and P ⫽ 0.004, respectively). The pairwise comparison
between vocal process stimulation and TA muscle stimulation was nonsignificant (P ⫽ 0.74).
Fig. 3. Mean integrated EMG responses with stimulation at 3 locations along the vocal fold margin for individual animals. Each point
is the average of 10 trials at each of the following sites: anterior TA
muscle body, vocal process, arytenoid body. Lines connect the integrated response amplitudes at each site for the same animal. A:
ipsilateral TA muscle response amplitudes. B: contralateral TA muscle response amplitudes.
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at three discrete displacement levels: ⬃400, ⬃250, and ⬃150
␮m (⫾25 ␮m for each displacement level). The order of
displacement level presentation was randomized with 10
tokens, presented at 1-min intervals, for each displacement
magnitude. Lastly, for the mucosal peel condition, a series of
10 tokens at ⬃325 ␮m displacement were delivered to the
body of the arytenoid cartilage (prepeel condition) at 1-min
intervals before surgical removal of the mucosa. The probe
tip was then retracted. The peel procedure consisted of undermining and excising the mucosa overlying the arytenoid
cartilage with microdissection instruments under highpower magnification. Care was taken to selectively excise the
soft tissue and maintain minimal bleeding in the region.
After removal of the mucosa, the bare surface of the arytenoid cartilage could be seen, and the probe tip of the servomotor was subsequently repositioned in the exact same position by using the previous tip insertion puncture in the
arytenoid cartilage as a location marker. The area was mechanically restimulated at the same displacement level and
by using the same preload as in the prepeel condition to
assess the effect of mucosal removal on the LAR. On completion of the study, the animals were euthanized by a barbiturate overdose.
Data analysis. Digitized signals were visually inspected
and marked by use of a customized routine written in MATLAB (v 5.3). The servomotor displacement signal was used to
synchronize the graphical display to aid in identification of
the evoked TA responses, bilaterally (Fig. 2). Onset and offset
points were marked on the data records and were saved to an
ASCII output file. The mean level of rectified TA EMG activity during a 20-ms period before stimulus onset was used to
compute and subtract the baseline activity from the response. The initial deflection of the TA EMG response from
baseline was identified as the onset of the short-latency
component of the TA response, referred to as R1 (⬃17 ms
after the servomotor displacement signal). Response offset
was marked as the point when the EMG signal returned to
baseline and remained stable for at least 20 ms. Automated
signal-processing routines were later used to compute various measures from each marked R1 component of the TA
signal, including 1) response latency, 2) response duration,
and 3) the total area under the curve (mV ⫻ ms), as a
measure of response magnitude. The mean baseline was
multiplied by the R1 duration and subtracted from the total
R1 integral to correct for differences in overall muscle activity independent from the response.
Repeated-measures ANOVAs (␣ ⫽ 0.05) were conducted
separately for the site and growth curve conditions using the
calculated R1 integral values as the dependent measure. For
the site condition, the main effects of stimulus location and
side of response were tested along with the interaction of
location and side. For the growth curve condition, the main
effects of stimulus magnitude and side of response were
tested along with the interaction of magnitude and side.
Finally, for the mucosal peel condition, mean response rates
were calculated by dividing the total number of evoked TA
responses by the total number of tokens presented for each
animal in the pre- and postpeel condition. Any EMG activity
beyond a latency of ⬃10 ms that differed from the pretrigger
baseline and that had a clear onset/offset location was measured and counted as an evoked TA response. The frequencies of LAR responses were compared using a repeatedmeasures ANOVA. For this analysis, the main effects of peel
condition (pre- vs. postpeel) and side of response were tested
along with the interaction effect of peel condition and side.
Post hoc testing used Tukey’s test for simultaneous pairwise
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MUCOSAL AFFERENTS MEDIATE THE LAR
component of the LAR, bilaterally. The mean percent
response rate (pooled across all animals and response
sites) was 93.7% (225 responses out of 240 tokens). In
contrast, after the mucosa was surgically removed, the
LAR mean percent response rate dropped to 1.2%,
bilaterally (3 responses out of 237 tokens). A repeatedmeasures ANOVA (␣ ⫽ 0.05) comparing the mean
response frequency for each animal pre- and postpeel
on each side was significant (F ⫽ 713.36, P ⬍ 0.0005).
The pronounced effect of the mucosal peel condition
can be clearly seen in Fig. 5, bilaterally. The main
effect for response side was nonsignificant (F ⫽ 0.01,
P ⫽ 0.922), as was the response side by peel condition
interaction (F ⫽ 0.68, P ⫽ 0.443).
DISCUSSION
Fig. 4. Mean integrated EMG responses at 3 displacements magnitudes: low (150 ␮m), middle (250 ␮m), and high (400 ␮m). Each point
is the average of 10 trials for a single animal at each displacement.
Lines connect responses within the same animal. A: ipsilateral TA
muscle response amplitudes. B: contralateral TA muscle amplitudes.
Stimulation magnitude effects. As expected, the magnitude of the evoked LAR changed systematically as a
function of the displacement level delivered to the body
of the arytenoid cartilage (F ⫽ 26.91, P ⬍ 0.0005) (Fig.
4). The main effect for stimulation magnitude was
significant (F ⫽ 26.91, P ⬍ 0.0005). The main effect for
response side (ipsi- vs. contralateral) was nonsignificant (F ⫽ 2.96, P ⫽ 0.123), as was the interaction effect
for stimulation magnitude by response side (F ⫽ 1.77,
P ⫽ 0.203). Post hoc testing for the significant main
effect of stimulation magnitude revealed that the comparison between the highest displacement magnitude
vs. the lowest displacement level was significant (P ⬍
0.0005) and therefore accounted for the significant
omnibus F value. Pairwise comparison of the highest
displacement magnitude with the middle level was
nonsignificant (P ⫽ 0.106), as was the comparison
between the middle displacement magnitude vs. the
lowest magnitude (P ⫽ 0.1082).
Mucosal peel effects. Stimulation of the arytenoid
mucosa during the prepeel condition with a 325-␮m
displacement consistently evoked the short-latency
J Appl Physiol • VOL
Fig. 5. Mean percentage of trials with R1 responses pre- vs. post
mucosal peel by animal. A: ipsilateral TA muscle responses. B:
contralateral TA muscle responses.
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The most important finding in this experiment was
that surgical removal of the mucosa overlying the arytenoid body effectively abolished the LAR response in
both the ipsilateral and contralateral TA muscles in
the cat. The mean percent response rate dropped dramatically immediately after the mucosal peel, and the
area was restimulated with the same displacement
MUCOSAL AFFERENTS MEDIATE THE LAR
J Appl Physiol • VOL
the human larynx have been suggested to form the
basis for patient complaints such as foreign body sensations (22) and spasmodic dysphonia (18). Abnormally
heightened responses to typical laryngeal stimulation
may be life threatening when laryngospasm causes
airway obstruction and prolonged apnea (23–25, 39,
46). Unfortunately, few physiological studies address
the contribution and central effects of general somatic
afferents on laryngeal motoneuron pool excitability
during coordinative actions in the human larynx. Behavioral data in humans suggest that mucosal afferents are sensitive to physiologically relevant inputs
such as airflow, air pressure, and touch (2, 15, 36).
Furthermore, Sanders and Mu (29) studied the territory supplied by the ISLN in excised human larynges
and found a rich distribution of mechanoreceptive endings to the ventricular and vocal folds, the mucosa
overlying the arytenoids, the posterior glottis, and the
joint capsule of the cricoarytenoid joint. Similar distributions of ISLN afferent endings have been described
for the cat larynx (54), suggesting that the cat may be
an accurate model for testing the sensitivity of different receptor types contributing to movement dynamics
during coordinated laryngeal behaviors.
Although our investigation has detailed the importance of mucosal afferents for evoking the LAR in the
cat, this is not the only channel through which the LAR
may be elicited. Stimulation of chemoreceptors, which
are scattered throughout the laryngeal complex, will
produce central apnea, alter respiratory rhythms, and
elicit the LAR (6, 30, 47). Also, it is likely that other
classes of receptors, such as joint or other mechanical
receptors in muscle, were active during mucosal displacement. Although the LAR was not elicited after
removal of the mucosa, these other receptors may have
continued to be active. Without microneurography,
however, the degree to which these afferents continued
to be active after mucosal removal is not known.
The degree to which muscle spindles provide feedback to the motor neuron pool and alter muscle tone is
unknown for the larynx. Few if any muscles spindles
have been found in the intrinsic laryngeal muscles of
primates and humans (3, 16, 19), and they seem to be
absent in the cat. The extent to which muscle spindles
are distributed and functionally active within the TA
muscle of the human (3, 28) remains controversial.
Because species may differ in the presence of muscle
spindles and their possible physiological role in laryngeal control, caution must be taken in generalizing our
results to the human.
Regardless of these limitations, this study has provided data on the functional contribution and spatial
sensitivity of mucosal mechanoreceptor afferents for
the elicitation of the LAR in the cat. Continuing to
differentiate the functional effects of each receptor
class contained within the ISLN may help clarify the
specific channels through which central changes may
occur in humans with laryngeal disorders. This information is considered to have potential for understanding the pathophysiology of various sensorimotor laryngeal disorders.
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magnitude as in the prepeel condition. It appears,
therefore, that cricoarytenoid joint afferents do not
contribute to the elicitation of the LAR. This conclusion
is further strengthened in that servomotor displacement was readily observed to move the arytenoid cartilage and therefore would have activated cricoarytenoid joint receptors during both the pre- and postpeel
conditions. Thus it is suggested that mucosal mechanoreceptors overlying the arytenoid complex represent
the dominant source of somatosensory input needed to
evoke the LAR in the cat.
Our investigation also found that the contribution of
mucosal mechanoreceptors for eliciting the LAR was
greatest in the posterior glottis. When the same displacement was administered to the mucosa overlying
the thyroarytenoid muscle, no LAR responses occurred,
and few occurred when stimulation was over the vocal
process (Fig. 4). Because the magnitude of the reflex
response grew with increased displacements of the
arytenoid, the excitability of laryngeal motoneurons
may be influenced by mechanical stimuli to this region.
Collectively, these data are consistent with others’
results. Immunohistochemical staining of intraepithelial nerve fibers in the epithelium of the laryngeal
mucosa showed sharp territorial differences between
the anterior and posterior regions of the glottis (20).
These authors found that the posterior glottis contained the heaviest density of labeled fibers and suggested that this disproportionate distribution of fibers
in the posterior glottis may be important for the perception of stimuli and the elicitation of reflexes in the
larynx. Microneurographic recordings of ISLN afferent
fibers in the cat by Davis and Nail (8) also showed
greater density levels in the posterior glottis with a
disproportionate number of RA mechanoreceptive afferents with small receptive fields over the arytenoid
complex. Slowly adapting receptor profiles were also
found but primarily populated the lumen of the larynx
and to a lesser extent the aryepiglottic fold, the vocal
process, and the base of the epiglottis. More importantly, Davis and Nail demonstrated that laryngeal
mucosal receptors were exquisitely sensitive to both
the static and dynamic features of indentation and
were capable of faithfully after vibratory inputs up to
400 Hz. Given that the posterior glottal region normally undergoes rapid biomechanical adjustments for
airway protection, a high distribution of afferents and
their apparent high-frequency sensitivity in this region
may provide for precise monitoring of sensory events
during rapid laryngeal control. These data, in conjunction with our findings, suggest that mucosal afferents
may effectively contribute to laryngeal sensorimotor
responses. In addition, as the arytenoid cartilages are
moved, the mechanoreceptors within the mucosa overlying them may operate as a primary source of sensory
input necessary for laryngeal motor control.
An understanding of the distribution and integrity of
ISLN-mediated afference in the human is of importance to normal and disordered laryngeal behavior
such as chronic cough and irritable laryngeal disorders
(22). Sensory abnormalities due to disease or injury of
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MUCOSAL AFFERENTS MEDIATE THE LAR
Gratitude is expressed to Erich Luschei for technical assistance
and advice, Frank Evans for the development of signal processing
routines, and Carlos Cyrus for procedural support during data collection.
This project was funded by the Intramural Program at the National Institute of Neurological Disorders and Stroke, The National
Institutes of Health, Bethesda, MD.
22.
23.
24.
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