WolfmanHarris Posted January 4, 2009 Share Posted January 4, 2009 So my A&P textbook offers no answer as to the role of pectinate muscles in the Right Atrium and Auricle of the Left Atrium. I did a quick google/wiki search and found that they are supposed to increase force of contraction without greatly increasing muscle mass. These weren't particularly reputable sources though and I'm still left with a lack of understanding of the how/why on this. A little direction would be appreciated. Thanks, - Matt Link to comment Share on other sites More sharing options...
Richard B the EMT Posted January 4, 2009 Share Posted January 4, 2009 Per an online search, check this one out. disclaimer: no guarantee of veracity. <a href="http://medical-dictionary.thefreedictionary.com/pectinate+muscle">pectinate muscle</a> Link to comment Share on other sites More sharing options...
WolfmanHarris Posted January 5, 2009 Author Share Posted January 5, 2009 Thanks Richard, but that didn't have what I needed. I know what they are and think I know what they're supposed to do (increase contractile force while not greatly increasing muscle mass), it's the how and why of their function I don't understand and am having trouble finding a source on. Link to comment Share on other sites More sharing options...
Just Plain Ruff Posted January 5, 2009 Share Posted January 5, 2009 pectinate muscles The right atrium has a forward extension into its auricle. This space is lined by ridges of muscle called pectinate muscles and are not shown in the diagram Blood leaves the right ventricle and passes through the pulmonary trunk to the lungs. Oxygenated blood returns to the left atrium of the heart from the lung through the pulmonary veins. The left atrium doesn't have much to talk about. There is an extension into the small auricles which have pectinate muscles in its walls. The muscles line the atrium and look like the ridges of a leaf. They assist in providing additional contractile force for the atrium. If you look at any diagram of the heart or drawing and you will see in the atrium what looks like ridges in the drawing. those ridges are the pectinate muscles. It seems that all they do is to provide additional musculature to help the atrium contract a little more forceful. Link to comment Share on other sites More sharing options...
Just Plain Ruff Posted January 5, 2009 Share Posted January 5, 2009 In the right atrium, behind the crest the internal surface of the atrium is smooth, while in front of it the muscular fibers of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati (pectinate muscles). In the left atrium, the musculi pectinati, fewer and smaller than in the right auricula, are confined to the inner surface of the auricula. This is due to the embryological origin of the auricles, which are the true atria. Some sources cite that the musculi pectinati are useful in increasing the power of contraction without increasing heart mass substantially http://faculty.ucc.edu/biology-potter/heart.htm go here this is interesting reading Link to comment Share on other sites More sharing options...
WolfmanHarris Posted January 5, 2009 Author Share Posted January 5, 2009 Okay, so maybe I should just discount the part on "without greatly increasing muscle mass"? Now here's something I don't quite understand, if the pectinate muscles are helping to increase strength of contraction in the atria, why does the anterior wall of the RA have pectinate but only the auricle of the LA does? Wouldn't you expect more musculature on the left side pumping into the LV? Edit: I hadn't even considered evolutionary basis for this. Thanks Ruff! I'll take a look at that link. So does that mean that the pectinate muscles are more an evolutionary hold over from before we developed the atria we have now and that their purpose is less important than it once was? Maybe I'm jumping the gun. I'll read that now. Edit 2: I think I get it now. Two quotes from that link put it into focus for me. The interior of the atrial walls shows woven ridges of cardiac muscle called pectinate muscle. The woven nature of this muscle permits a great strength of contraction with a minimum of muscle mass. AND A thickly woven arrangement of cardiac muscle called trabeculae carneae. The appearance and function of this woven muscle is essential the same as the pectinate muscle. Once I drew a conceptual relationship to the trabeculae carneae it made more sense. I still don't quite know why there would be more pectinate muscle in the RA vs. the LA but I definitely have a better handle on this one. Thanks Ruff, this little part of the heart's been bugging me all evening. Link to comment Share on other sites More sharing options...
Just Plain Ruff Posted January 5, 2009 Share Posted January 5, 2009 I think that the mass thing you are having problems with I can help you with. Take a single strand of spiders silk. By itself it can really only catch a small insect like a gnat. But when you add the entire web you can get insects as large as butterflys and the like. The single strand by itself is strong but you add the entire web you get Greater strength. I hope that helps. Link to comment Share on other sites More sharing options...
WolfmanHarris Posted January 5, 2009 Author Share Posted January 5, 2009 It does help a bunch. I'd figured that from your previous help, but the confirmation is nice too. Link to comment Share on other sites More sharing options...
mstovall Posted January 5, 2009 Share Posted January 5, 2009 Just thinking out loud here, but I would think that the RA would need more contractile strength as the blood that is coming in from the Venae Cavae would be at a lower pressure than that returning from the pulmonary veins. I don't know this for fact, but it seems that something in the back of my head was pointing to this as the reason. I am trying to find something in some of my books. Someone please correct me if I am on the wrong track, as I am trying to pull a 8 sec. sound byte out of about a 40 hour lecture series. Michael Link to comment Share on other sites More sharing options...
WolfmanHarris Posted January 5, 2009 Author Share Posted January 5, 2009 Good thought but, the pressure in the RV only goes as high as ~30mmHg and only needs to go as high as ~20mmHg to open the pulmonary SL valve so I'd imagine that the RA pressure would be lower still. Not saying you're wrong, I'm just not seeing it. Link to comment Share on other sites More sharing options...
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