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Biology 212: January 28, 2004
Motor Systems: Focus on muscle physiology
I.
Structure and function of vertebrate skeletal muscle
A. Muscles contract actively, relax passively
1. Pairs of antagonistic muscles [Fig. 49.30]
B. Organization of a vertebrate muscle [Fig. 49.31]
1. Muscle Muscle fiber  myofibrils  thick and thin filaments
C. Structure of a sarcomere [Fig. 49.31]
1. Note positioning of thick (myosin) and thin (actin) filaments
2. Z-lines: sarcomere border (striations viewed with light microscopy)
3. In muscle contraction, the sarcomere shortens as filaments slide past each other
a. The individual filaments do not themselves change length.
D. Sliding filament model of muscle contraction: muscle contraction is based on the
interaction of myosin and actin
1. Go through step-by-step! [Fig. 49.33]
2. Focus on step 3, the binding of the myosin head to the actin filament [Fig. 49.34]
E. Neural control of muscle contraction
1. Anatomy [Fig. 49.35]
a. Motor neuron
b. Neuromuscular junction
c. T-tubule system
d. Sarcoplasmic reticulum
2. How the system works [Fig. 49.36]
a. Go through step-by-step
Study questions
1. What is meant by “antagonistic” pairs of muscles?
2. What is a sarcomere? Sketch the basic structure of a sarcomere, showing the relative
positions of thick and thin filaments.
3. What molecule comprises the thick filament? What molecules make up the thin filament?
4. Give a step-by-step description of the contraction of a sarcomere. Be sure to include the
different positions of the myosin head and the role of ATP and its breakdown products in this
movement. Don’t forget the movement of the actin filaments!
5. Why do muscles remain contracted if no ATP is available?
6. Explain the role of Ca++ in muscle contraction. Be sure to name all relevant molecules
associated with the thin filament.
7. What is the role of the T-tubule system?
8. What is the role of the sarcoplasmic reticulum?
9. What causes Ca++ to be released into the muscle tissue?
10. Put it all together: Give a step-by-step description of how an action potential in the motor
neuron leads to the exposure of the myosin-head binding sites.