Chapter 2
Structure of
Muscle Tissue &
Muscle Contraction
Learning Objectives
• Be able to describe differences b/n
smooth, skeletal & cardiac muscle.
• Understand the basic structure of skeletal
muscle.
• Know the characteristics that differentiate
fast twitch from slow twitch muscle fibers.
• Be familiar with the sliding filament model
of muscle contraction.
3 Types of Human
Muscle Tissue
1
Structure of Smooth Muscle
• Long, spindle-shaped fibers
• An external shape that may change to
conform to the surrounding elements
• One nucleus per fiber
Structure of Skeletal Muscle
Structure of Cardiac Muscle
2
Skeletal Muscles Showing
Cross-Striations
Muscle Fibers & Connective
Tissue Sheaths
Adapted from J.W. Hole, Jr. Human Anatomy and Physiology, 5th edition (1990),
with permission of the McGraw-Hill Companies.
Structure of the Muscle Fiber
• Sarcolemma:
• Sarcoplasm:
• Myofibrils:
3
Classification of
Muscle Fiber Types
•
•
•
•
Anatomical appearance
Muscle function
Biochemical properties
Histochemical properties
Characteristics of
Muscle Fiber Types
3 Primary Fiber Types in Human
Skeletal Muscle
4
Significance of Fiber Type
for Athletics
• Slow oxidative (SO) fibers:
• Fast twitch (FT) fibers:
A Sarcomere—
The Functional Unit of the Myofibril
Structure of a Sarcomere
• Z-line—
• Myofilaments—
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Myofilaments
• Myosin:
– Its length is equal to the length of the A band
(the dark band seen in the striation effect); the
area b/n the ends of the thick filaments is the I
band.
• Actin:
– A thin filament; the amount by which its two
ends don’t meet is the H zone (a lighter band
within the A band).
Actin, Myosin, Troponin,
& Tropomyosin
Aspects of the Sliding Filament
Model of Muscle Contraction
Contraction
6
ATP Breakdown & Muscle
Contraction — 1st Theory
1.
2.
3.
4.
5.
Actin–myosin binding activates myosin ATPase, which breaks
down an ATP molecule & liberates energy.
Energy causes the myosin cross-bridge to swivel toward the
center of the sarcomere, which pulls Z-lines closer together &
shortens sarcomeres.
A fresh ATP molecule binds to the myosin cross-bridge,
causing it to release from the actin molecule. The myosin
cross-bridge stands back up & binds to a different actin
binding site.
This binding again activates myosin ATPase to break down
the new ATP molecule bound to the myosin cross-bridge.
The process repeats—cross-bridge recycling or cross-bridge
recharging.
ATP Breakdown & Muscle
Contraction — 2nd Theory
1.
2.
3.
4.
5.
The myosin cross-bridge is energized and bound to
ADP & inorganic phosphate (Pi).
The binding of actin & the myosin cross-bridge
releases stored energy, which causes the myosin
cross-bridge to swivel; this then results in muscle
contraction.
During the swiveling, ADP & Pi are released from
the myosin cross-bridge
After actin & myosin dissociate, fresh ATP is broken
down & liberated energy is used to reenergize the
myosin cross-bridge.
The cross-bridge recycling process repeats.
What do you think?
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Where to Learn More
• Muscles:
– http://users.rcn.com/jkimball.ma.ultranet/BiologyPa
ges/M/Muscles.html
• Muscle physiology—myofilament structure:
– http://muscle.ucsd.edu/musintro.fibril.shtml
• Histology of muscle:
– http://views.vcu/edu/ana/OB/Muscle~1/index.htm
• Sliding filament theory:
– http://users.rcn.com/jkimball.ma.ultranet/BiologyPa
ges/M/Muscles.html
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