The Contractors  Vince Bendotti  Chris Hoepfner  Taylor Stephenson  Cory Worthey

How did this happen?!

Myogenesis!  The formation of muscle fibers and muscles in embryonic development  Due to  Satellite cells  Myogenic pathways  Hormones

Satellite cells  Population of cells located in adult skeletal muscle  Are responsible for muscle growth and regeneration  Located in the indentation between sarcolemma and basal lamina  Satellite cells become activated and expressed and then become myoblasts  These cells fuse together to generate new myofibers during regeneration of torn and damaged skeletal muscle

Myogenic pathways  In the early development of an embryo, myoblasts can either proliferate, or differentiate into a myotube.  Differenitiation - When an undifferentiated cell is given the features of a specific cell  Proliferation - Duplication through cell division  “Skeletal myogenesis is then initiated in myogenic cells originating form the dermomyotome lips that differentiate to form primary muscle fibers (see [1] for review). Subsequently, a progenitor population that expresses Pax3 and Pax7 arise from the central portion of the dermomyotome and is maintained throughout embryogenesis within the developing skeletal muscles “

Myogenic proteins  MyoD and Myf5  Have defined specific roles in satellite cell biology  MyoD is required for the differentiation potential of skeletal myoblasts  Myf5 regulates their proliferation rate and homeostasis

What happens to the cell  Hypertrophy - An increase in the size of existing muscle cells  This occurs with consistently applied external loads and an abundance of nutrients.  Atrophy - Decrease in muscle cell size.  Can occur from disease, lack of physical activity, aging and lack of nutrients.  Hyperplasia - An increase in the numbers of cells/fibers in a normal tissue or organ.

Hypertrophy  Neuroelectrical activity with greater impulses over short periods of time signal growth.  Different growth factors are secreted during muscle repair among which insulin-like growth factors (IGFs) are the only ones that promote both muscle cell proliferation and differentiation and that play a key role in muscle regeneration and hypertrophy.  Myostatin is a protein that limits muscular hypertrophy.

Criteria for Hypertrophy  1. Progressive Overload Resistance Training  2. Proper Nutrition  Carbohydrates and Protein  3. Genetics  4. Hormone Secretion  Testosterone  HgH  Androgens  IGF-1

Atrophy  Neuroelectrical activity of low-intensity signal input over longer periods of time signal for greater muscular efficiency, decreasing the size (therefore, energy needs) of the muscle cells.  Decreased protein kinase signaling  Protein degradation via ubiquitin-proteosome pathway  AMP-activated protein kinase (AMPK) pathway, which can lead to decreased muscle protein synthesis.

References  Farrel, P. A., Joyner, M. J., & Caiozzo, V. J. (2012). ACSM's Advanced Exercise Physiology (2nd ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.  Le Grand, F., & Rudnicki, M. A. (2007). Skeletal muscle satellite cells and adult myogenesis. Current Opinion in Cell Biology, 19(6), 628–  Skeletal muscle hypertrophy and regeneration: Interplay between the myogenic regulatory factors (MRFs) and insulin-like growth factors (IGFs) pathways. Available from: trophy_and_regeneration_Interplay_between_the_myogenic_regulatory_fac tors_(MRFs)_and_insulin-like_growth_factors_(IGFs)_pathways [accessed Sep 6, 2015]. trophy_and_regeneration_Interplay_between_the_myogenic_regulatory_fac tors_(MRFs)_and_insulin-like_growth_factors_(IGFs)_pathways  THOMAS J. HAWKE1 AND DANIEL J. GARRY1,2 1Department of Internal Medicine and 2Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas   