Central nervous system control of the laryngeal muscles in humans

Abstract

Laryngeal muscle control may vary for different functions such as: voice for speech communication, emotional expression during laughter and cry, breathing, swallowing, and cough. This review discusses the control of the human laryngeal muscles for some of these different functions. Sensori-motor aspects of laryngeal control have been studied by eliciting various laryngeal reflexes. The role of audition in learning and monitoring ongoing voice production for speech is well known; while the role of somatosensory feedback is less well understood. Reflexive control systems involving central pattern generators may contribute to swallowing, breathing and cough with greater cortical control during volitional tasks such as voice production for speech. Volitional control is much less well understood for each of these functions and likely involves the integration of cortical and subcortical circuits. The new frontier is the study of the central control of the laryngeal musculature for voice, swallowing and breathing and how volitional and reflexive control systems may interact in humans.

Fig. 1

A schematic drawing showing the laryngeal muscles and their attachments on the thyroid, arytenoid and/or the cricoid cartilages. (A) A superior view shows the thyroarytenoid muscle (TA), the lateral cricoarytenoid muscle (LCA) and the interarytenoid muscles (IA). The arrows show the effects of muscle contraction on arytenoid movement. (B) A posterior view shows the lateral (l) and medial (m) compartments of the posterior cricoarytenoid muscle (PCA) and the interarytenoid muscle (IA). (C) A frontal view shows the rectus (r) and oblique (o) compartments of the cricothyroid muscle (CT). (D) A lateral view of changes in position of the thyroid cartilage thought to occur as a result of contraction of the rectus (r) compartment of the CT muscle (a–r) and as a result of the oblique (o) compartment of the CT muscle (b–o). Lengthening of the thyroarytenoid muscle (TA) is shown with contraction of either the rectus or oblique compartments of the CT.

Fig. 2

A schematic diagram illustrates the motions of the arytenoid cartilage during abduction on the left, and adduction on the right. The numbers illustrate the starting position of the arytenoids cartilage (1), the intermediate position (2) and the final position on the completion of either motion (3). Note that during abduction the tip of the arytenoid, the vocal process, moves from a medial inferior position (1) to a superior lateral position lengthening and elevating the vocal fold (3), while during adduction, the vocal process moves from a superior lateral position (1) to an inferior medial position (3).

Fig. 3

A thyroarytenoid muscle response is shown in the second tracing from the top following an air pressure puff to the laryngeal mucosa. The air pressure change is shown in the uppermost tracing. The bottom tracing shows the thyroarytenoid muscle response to an electrical stimulation to the internal branch of the superior laryngeal nerve (SLN). Responses to SLN electrical stimulation are labeled as R1 (beginning at approximately 17 ms) and R2 (beginning at approximately 65 ms). The time calibration bar for 100 ms refers to all three tracings.

Fig. 4

A schematic illustration shows the mechanical effects of a servomotor application of force to the thyroid cartilage. The left top diagram shows the position of the thyroarytenoid muscle (TA), the cricothyroid muscle (CT), and the sternothyroid muscle (ST) at rest. The middle diagram illustrates the change in position as force is applied to the thyroid cartilage (horizontal arrow) pushing it posteriorly and lengthening the CT and the ST muscles. The right top diagram illustrates the change in position of the thyroid cartilage as force is released returning it to the initial position and lengthening the TA muscle. The middle line shows the timing of change in the servomotor force relative to the changes in the fundamental frequency of the voice (bottom tracing). Immediately following force application there is an initial lowering of the fundamental frequency with a later raising (at around 100 ms) and lowering of the fundamental frequency. After a release of force there is a raising of the fundamental frequency followed by a later lowering.

Fig. 5

A schematic diagram summarizing the results of functional brain imaging studies during volitional breathing (A), during voicing for speech (B), and during volitional swallowing (C). The studies are described in the text. Abbreviations are supplementary motor area (SMA), anterior cingulate cortex (ACC), premotor cortex (PM), motor cortex area for the diaphragm (M1), the laryngeal motor cortex (LX), the cerebellum (CBL), the motor cortex for the diaphragm and chest wall (mc), the motor area active for jaw lips and tongue (smc), the superior temporal lobe area active audition (tc), Broca’s area (BA), medulla (M), a large area for taste and tongue movement from the precentral to postcentral gyrus (M1–S1), the insula (In), and the posterior parietal area (PA).