The vertebrate larynx: Adaptations and aberrations

Abstract

The complex anatomy of the vertebrate larynx shows a steady progression from the simple slit on the floor of the lungfish's pharynx to the fine-tuned mechanism of the human vocal apparatus. The frog's larynx acts as a check valve to prevent collapse of the lungs during a dive, since the animal has no rib cage. The crocodile's laryngeal framework has acquired an epiglottic analogue which fits snugly into the nasopharynx and protects the lower respiratory tract from inundation while the animal drowns its prey. The snake's larynx lies intraorally and can be extended beyond the lower teeth while the reptile leisurely swallows its prey intact. The mammal has acquired a cricothyroid joint, allowing its membranous vocal folds to be stretched during phonation. In Homo sapiens, vocal performance has reached its highest degree of versatility, with a vocal fold capable of adjustment in length, tension and shape. In the course of organic evolution, man appears to have chosen the ability to speak and sing over the security that an intranarial epiglottis would have given him.

Ultrafast sound production mechanism in one of the smallest vertebrates

“…Although the mechanism for sound production varies across vertebrates, it is common to use specialized striated muscles that manipulate air ( 2 ). In tetrapods, sounds are controlled by vocal folds in the larynx ( 3 ) or the syrinx in birds ( 4 ), which modulate airflow. In these cases, sound production and respiration are coupled, but fishes, with some exceptions ( 5 ), do not breathe air; therefore, the mechanisms they use for sound production are not coupled with airflow and they instead rely on other mechanisms ( 2 ).…”

Rapid evolution of the primate larynx?

“…A first possibility is that differences in relative larynx size between primates and carnivorans reflect the role of the larynx in protecting the respiratory system during feeding [ 27 ]. Although the trachea is mainly occluded by the epiglottis (not examined here) during swallowing, the larynx protects against aspiration of food or liquid via reflex closure and coughing when the epiglottis is bypassed [ 28 ]. Accordingly, increased variation in primate larynx size may be partially explained by a relaxation of selective forces related to diet and associated feeding behaviors relative to carnivorans.…”

“…A second possibility is that differences in relative larynx size between primates and carnivorans reflect the role of the larynx in respiration, e.g., in regulating the amount of oxygen that can enter the lungs and intrapulmonary pressure [ 30 ]. For example, differences in locomotor behavior between primates and carnivorans may place different demands on oxygen metabolism [ 31 ] and the capacity to stiffen the thorax by increasing intrapulmonary pressure [ 28 ]. Both factors are closely related to substrate use, which although variable in both orders, is more often terrestrial for carnivorans and arboreal for primates [ 32 , 33 ].…”

Serotonin therapies for opioid-induced dysphagia and respiratory depression: sex differences in a rat electromyography model

“…Precise coordination of the upper aerodigestive tract is essential for functional swallowing, breathing, and airway protection [1][2][3]. Swallow is the critical mechanism of energy intake for mammals [4], while breathing ventilates the lower airways to permit gas exchange [5].…”

“…Failure to maintain separation of the airway from ingested material can result in aspiration of food or liquid into the lower airway [2,3]. Sequelae of aspiration can be fatal if airway obstruction (acute) or aspiration pneumonia (chronic) occur [12].…”