Muscles Anatomy Physiology

College scientist cites enlarged skeletal muscles as reason birds exist

A developmental biologist at New York Medical College is proposing a new theory of the origin of birds, which traditionally has been thought to be driven by the evolution of flight. Instead, Stuart A. Newman, Ph.D., credits the emergence of enlarged skeletal muscles as the basis for their upright two-leggedness, which led to the opportunity for other adaptive changes like flying or swimming. And it is all based on the loss of a gene that is critical to the ability of other warm-blooded animals to generate heat for survival.

Dr. Newman, a professor of cell biology and anatomy, studies the diversity of life and how it got that way. His research has always centered on bird development, though this current study, "Thermogenesis, muscle hyperplasia, and the origin of birds," also draws from paleontology, genetics, and the physiology of fat.

Dr. Newman draws on earlier work from his laboratory (Mezentseva et al. BMC Biology 6:17; 2008) which provided evidence for the loss, in the common dinosaur ancestors of birds and lizards, of the gene for uncoupling protein-1 (UCP1). The product of this gene is essential for the ability of "brown fat," tissue that protects newborns of mammals from hypothermia, to generate heat. In birds, heat generation is mainly a function of skeletal muscles.

"Unlike the scenario in which the evolution of flight is the driving force for the origin of birds, the muscle expansion theory does not require functionally operative intermediates in the transition to flight, swimming, or winglessness, nor does it require that all modern flightless birds, such as ostriches and penguins, had flying ancestors. It does suggest that the extinction of non-avian dinosaurs may have been related to a failure to evolve compensatory heat-generating mechanisms in face of the loss of UCP1," says the scientist.

New York Medical College, one of the nation's oldest private health sciences universities, offers advanced degrees in medicine, science, public health and the health professions. The leading academic biomedical research institution between New York City and Albany, the university manages more than $35 million in research and other sponsored programs, notably in the areas of cardiovascular disease, cancer, kidney disease, the neurosciences and infectious diseases.

New Voice, New Career: Anatomy and Physiology Series: Intrinstic ...

So...intrinsic vs. extrinsic, what's the deal?  Back in the day when I was in vocal ped ., we were taught that intrinsic muscles are all contained within the larynx itself.  That is, these muscles all have their origin and insertion points within the laryngeal structure (so somewhere on those cartilages we just went through.)  The extrinsic muscles have either their origin or insertion point in the larynx, but the other point is outside of it. That is all absolutely true.  However, another important component of the difference between intrinsic and extrinsic is in their function.   Intrinsic muscles are concerned with fine motor movements and extrinsic are concerned with gross motor movements.   (This is good to remember, because the tongue also has intrinsic and extrinsic muscles with the same distinction.)   So for our purposes, intrinsic muscles will be involved in the minute vocal adjustments required for communication (pitch, volume, etc.), and the extrinsic muscles have more to do with where the larynx is located in the throat, i.e. elevated for swallowing, neutral for speech (ideally), lower for operatic singing (ideally) etc.  Also important for our purposes:  The intrinsic muscles are divided into adductors (or muscles that close the vocal folds) and abductors (muscles that open the vocal folds...there's only really one...I always thought it's sort of weird to have a whole category for one muscle), glottal tensors, and glottal relaxers.* The first adductor is the lateral cricoarytenoid.  It originates from the superior-lateral surface of the cricoid cartilage, which is the top-front/side of the cricoid, and inserts into the muscular process of the arytenoid.  This muscle is a little hard to see in a model, because it is usually blocked from view by the thyroid.  (You can see it on the picture below because this view is from the side, as if the side of the thyroid had been cut away.) The transverse arytenoid muscle originates from the outer side of the arytenoid and inserts into the outer side of the other arytenoid.  Contraction results in pulling the two arytenoids closer together than just the lateral cricoarytenoid by itself.  This muscles as a lot to do with medial compression , which is the degree of force that brings the vocal folds together at the midline.  It's the muscle underneath the criss-cross muscles pictured below.

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