We have located links that may give you full text access.
The histomorphologic structure of the levator ani muscle and its functional significance.
The levator ani muscle (LAM), unlike other striated muscles has resting myoelectric activity, the cause of which is not precisely known. In a recent study this activity was suggested to be related to the presence of smooth muscle bundles in the LAM. The present study investigated this point in 25 cadaveric specimens (10 neonates, 15 adults). Histologic examination of the LAM was performed in 12 specimens, three to six slices being taken from the lateral to the medial side of each muscle, processed and stained with H&E and Masson's trichrome stain. The remaining 13 specimens were studied by direct dissection and photographed. Microscopic examination of specimens from adult cadavers showed that the lateral part of the LAM consisted of purely skeletal muscle bundles, mostly of the small-caliber type and few of the large or intermediate type. As we proceeded medially, smooth muscle bundles started to appear. Examination of slices medial to the midportion of the LAM showed that the muscle began to be separated into two layers: a deep (pelvic) one formed of smooth fibers and a superficial (perineal) one of skeletal fibers, separated by a neurovascular plane. Microscopic examination of specimens from neonates showed that the whole LAM consisted of skeletal fibers; no smooth fibers or separation into two layers were identified. By direct dissection of the adult specimens the medial part of the LAM consisted of two layers, superficial and deep, which were separated by fascia containing vessels and nerves. The muscle was thicker at its medial part and tapered laterally, with loss of demarcation, into two layers. Specimens from neonates showed no differentiation of the LAM, into two layers. It is suggested that the deep layer of the LAM, which was formed of smooth fibers, acts involuntarily, supporting the pelvic viscera by its tone and responding to variations in intra-abdominal pressure by adaptation of this tone. The superficial layer of the LAM, made of skeletal fibers, appears to represent the functional mobile part that acts voluntarily during urination or defecation. The presence of the smooth fibers in the adult LAM and not in neonates seems to be adaptational, caused by the action of intra.abdominal pressure and visceral weight. The skeletal fibers pass into various histologic stages before they transform to smooth fibers.
Full text links
Related Resources
Trending Papers
Heart failure with preserved ejection fraction: diagnosis, risk assessment, and treatment.Clinical Research in Cardiology : Official Journal of the German Cardiac Society 2024 April 12
Proximal versus distal diuretics in congestive heart failure.Nephrology, Dialysis, Transplantation 2024 Februrary 30
Efficacy and safety of pharmacotherapy in chronic insomnia: A review of clinical guidelines and case reports.Mental Health Clinician 2023 October
World Health Organization and International Consensus Classification of eosinophilic disorders: 2024 update on diagnosis, risk stratification, and management.American Journal of Hematology 2024 March 30
Get seemless 1-tap access through your institution/university
For the best experience, use the Read mobile app
All material on this website is protected by copyright, Copyright © 1994-2024 by WebMD LLC.
This website also contains material copyrighted by 3rd parties.
By using this service, you agree to our terms of use and privacy policy.
Your Privacy Choices
You can now claim free CME credits for this literature searchClaim now
Get seemless 1-tap access through your institution/university
For the best experience, use the Read mobile app