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), 628–633. http://doi.org/10.1016/j.ceb.2007.09.012

Skeletal muscle hypertrophy and regeneration: Interplay between the myogenic regulatory factors (MRFs) and insulin-like growth factors (IGFs) pathways. Available from: http://www.researchgate.net/publication/236103945_Skeletal_muscle_hypertrophy_and_regeneration_Interplay_between_the_myogenic_regulatory_factors_(MRFs)_and_insulin-like_growth_factors_(IGFs)_pathways [accessed Sep 6, 2015].

THOMAS J. HAWKE1 AND DANIEL J. GARRY1,21Department of Internal Medicine and 2Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390

www.muscle.ucsd.edu/musintro/hypertrophy.html

www.nlm.nih.gov/medlineplus/ency/article/003441.htm

www.physiologyonline.physiology.org/content/23/3/160