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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
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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
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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
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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


Atrophy- Decrease in muscle cell size.


This occurs with consistently applied external loads
and an abundance of nutrients.
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
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1. Progressive Overload Resistance Training

2. Proper Nutrition

Carbohydrates and Protein
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3. Genetics

4. Hormone Secretion

Testosterone

HgH
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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_hyper
trophy_and_regeneration_Interplay_between_the_myogenic_regulatory_fac
tors_(MRFs)_and_insulin-like_growth_factors_(IGFs)_pathways [accessed Sep
6, 2015].

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 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