Uncinate processes ref

[John Hutchinson <jrhutch@rvc.ac.uk>]

I think someone asked about this recently on the list; longstanding mystery
about uncinate process function.  Well here's one new study of it, from:
http://jeb.biologists.org/cgi/content/full/208/5/i-a?etoc

BONY BIRDS BREATHE BETTER 

Yfke van Bergen 

A fascination with dinosaur skeletons has led Jonathan Codd of Bonn
University to new insights into birds' breathing physiology. Codd was
puzzled by the role of velociraptors' uncinate processes, `small ossified
structures projecting like little handles from their ribs.' Reflecting on
the evolutionary link between dinosaurs and extant birds, he hoped that our
feathered friends might provide him with some clues regarding the function
of these strange structures. When Codd investigated the muscles associated
with the uncinate processes of giant Canada geese, he found that these bony
projections are integral to bird breathing mechanics (p. 849). 

Codd explains that vertebrate respiratory and locomotor systems are
mechanically linked, so muscles attached to the rib cage could either help
an animal breathe or stabilise it during walking. Together with Steve Perry
he headed across the Atlantic to team up with Dave Carrier, a vertebrate
morphologist at the University of Utah who studies the relationship between
respiratory and locomotor systems. To determine whether the three muscles
associated with birds' uncinate processes primarily assist during breathing
or walking, they decided to measure muscle activity and breathing in
standing, sitting and running geese. 

Muscle activity is normally recorded by sticking needle electrodes into
muscles. `But you can't be sure that the needle is in the right place' Codd
says. So he surgically implanted patch electrodes directly onto the three
muscles, a technique that `allows you to be 100% certain that you have the
right muscle.' To record the birds' breathing, Codd needed to measure
pressure differences in their air sacs, `bags that act as bellows to pump
air in and out of the birds' lungs.' Dona Boggs, a bird respiration expert,
helped Codd insert differential pressure transducers into the birds' air
sacs. Geese can have nasty tempers, but the team used this to their
advantage: they measured the large inspirations and expirations associated
with the birds' threatening hisses. If the three muscles were involved in
breathing, the team reasoned they should see muscle activity during hissing.


Sure enough, just before the birds hissed, the team noticed a burst of
electrical activity from the appendicocostal muscle and larger inspiration,
indicating that this muscle has an inspiratory function. And they saw bursts
of activity from the external oblique muscle during the large expirations
associated with hissing, suggesting that this muscle plays a role in
expiration. But they only saw short bursts of activity in the external
intercostal muscle while the geese were running, not when the birds were
hissing, so the team concluded that this muscle has a locomotor function.
Clearly, only two of the three muscles associated with birds' uncinate
processes help the animals breathe. 

The team were particularly intrigued to see increased appendicocostal
activity in sitting geese. Codd explains that when birds sit, their sternum
movement is restricted, making breathing difficult. `The increased
appendicocostal activity we noticed suggests that when the sternum's
movements are restricted, like when birds are sitting on their nests, this
muscle causes the rib cage to flare sideways and draw air into the birds'
lungs' he says. So thanks to this muscle, birds can breathe easy during
those long periods of egg incubation. 

References

Codd, J. R., Boggs, D. F., Perry, S. F. and Carrier, D. R. (2005). Activity
of three muscles associated with the uncinate processes of the giant Canada
goose Branta canadensis maximus. J. Exp. Biol. 208,849 -857.[CrossRef]

============================================
John R. Hutchinson
Structure & Motion Lab
Royal Veterinary College, Univ. London
Hawkshead Lane, Herts AL9 7TA, UK
phone  (+44) (0)1707-666-313
fax    (+44) (0)1707-666-371 or 652-090
mobile (+44) (0)7843-629-162
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