The gross morphology and histochemistry of respiratory muscles in bottlenose dolphins (Tursiops truncatus)

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Pamela B. Cotten (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Heather Koopman

Abstract: Most mammals possess stamina because their locomotor and respiratory (i.e. ventilatory) systems are mechanically coupled. These systems are decoupled, however, in bottlenose dolphins (Tursiops truncatus) as they swim on a breath-hold. Locomotion and ventilation appear to be coupled only during their brief surfacing event, when they respire explosively (up to 90% of total lung volume in approximately 0.3s) (Ridgway et al., 1969). The predominantly slow-twitch fiber profile of their diaphragm (Dearolf, 2003) suggests that this muscle does not likely power their rapid ventilatory event. Based upon Bramble’s (1989) biomechanical model of locomotor-respiratory coupling in galloping mammals, I hypothesized that muscles located within the cranial-cervical and lumbo-pelvic units, which act upon the thoracic unit, function to power ventilation in bottlenose dolphins. I also hypothesized that these muscles would be composed predominantly of fast-twitch fibers to facilitate the bottlenose dolphin’s rapid ventilation. The gross morphology (n=6) of cranio-cervical (sternomastoid, sternohyoid, scalenes), thoracic (intercostals), and lumbo-pelvic (rectus abdominis, abdominal obliques, hypaxialis) muscles and the fiber-type profiles (n=6) of selected muscles (sternohyoid, sternomastoid, and rectus abdominis) of bottlenose dolphins were investigated. Physical manipulations of excised thoracic units were carried out to investigate potential actions of these muscles. Results suggest that the cranio-cervical muscles act to draw the sternum and associated ribs cranio-dorsally, which flares the ribs laterally, and increases thoracic cavity volume required for inspiration. The thoracic muscles physically link the ribs to create a single functional unit; these muscles can also act to control the size of the intercostal space. The lumbo-pelvic muscles act to draw the sternum and caudal ribs caudally, which decreases the volume of the thoracic and abdominal cavities required for expiration. All muscles investigated were composed predominantly of fast-twitch fibers (range 72-88% by area) and appear histochemically poised for rapid contraction. These combined results suggest that dolphins utilize muscles, similar to those used by galloping mammals, to power their explosive ventilation. However, the mechanisms that permit dolphins to selectively couple and uncouple their locomotor and ventilatory systems, depending upon whether they are respiring at the surface or swimming on a breath-hold, remain unknown.

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Bottlenose dolphin--Physiology, Bottlenose dolphin--Morphology, Bottlenose dolphin--Research, Bottlenose dolphin--Respiration
Bottlenose dolphin -- Morphology
Bottlenose dolphin -- Physiology
Bottlenose dolphin -- Respiration
Bottlenose dolphin -- Research

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