Chapter 5
Contraction
Many biological tissues can exert and are subjected to both passive and active forces.
Passive forces, e.g., elastic and viscous forces, are caused by deformation involving
the exchange of mechanical energy, while active forces require a source of metabolic
energy derived from biochemical reactions. Contractile forces are the most common
type of active force. Contraction plays an important role in numerous biological processes, including locomotion, cell division, and morphogenesis. Vision, breathing,
digestion, and the heartbeat involve contraction of various types of muscles. Many
non-muscle cells also can undergo some form of active contraction.
At the subcellular level, contraction involves the activity of motor proteins
moving along passive filaments. According to the sliding filament theory for
muscle contraction (McMahon 1984; Fung 1993), the motor protein myosin (more
specifically myosin II) attaches its globular head to actin filaments, forming a crossbridge. Next, ATP hydrolysis causes the myosin head to rotate and displace the
myosin relative to the actin, but the filaments themselves do not change in length
(Fig. 5.1a). Finally, the head releases and rotates back to its starting position, and the
cycle repeats. Significant shortening at the tissue level requires thousands of these
cycles by thousands of cross-bridges. Likewise, the motor protein kinesin walks
along microtubules (Howard 2001).
This chapter focuses on actomyosin contraction from a continuum mechanics
point of view. Rather than dealing with the details of contraction at the molecular
level, we use a phenomenological approach that lumps these details into macroscopic mechanisms. While this approach does not provide biophysical explanations
for observed behavior, it serves as a useful tool for solving complex problems. In
addition to describing the contraction of different types of muscle, the basic theory
can be used to simulate contraction of stress fibers at the cellular level.
© Springer Nature Switzerland AG 2020
L. A. Taber, Continuum Modeling in Mechanobiology,
https://doi.org/10.1007/978-3-030-43209-6_5
209
Contraction
Many biological tissues can exert and are subjected to both passive and active forces.
Passive forces, e.g., elastic and viscous forces, are caused by deformation involving
the exchange of mechanical energy, while active forces require a source of metabolic
energy derived from biochemical reactions. Contractile forces are the most common
type of active force. Contraction plays an important role in numerous biological processes, including locomotion, cell division, and morphogenesis. Vision, breathing,
digestion, and the heartbeat involve contraction of various types of muscles. Many
non-muscle cells also can undergo some form of active contraction.
At the subcellular level, contraction involves the activity of motor proteins
moving along passive filaments. According to the sliding filament theory for
muscle contraction (McMahon 1984; Fung 1993), the motor protein myosin (more
specifically myosin II) attaches its globular head to actin filaments, forming a crossbridge. Next, ATP hydrolysis causes the myosin head to rotate and displace the
myosin relative to the actin, but the filaments themselves do not change in length
(Fig. 5.1a). Finally, the head releases and rotates back to its starting position, and the
cycle repeats. Significant shortening at the tissue level requires thousands of these
cycles by thousands of cross-bridges. Likewise, the motor protein kinesin walks
along microtubules (Howard 2001).
This chapter focuses on actomyosin contraction from a continuum mechanics
point of view. Rather than dealing with the details of contraction at the molecular
level, we use a phenomenological approach that lumps these details into macroscopic mechanisms. While this approach does not provide biophysical explanations
for observed behavior, it serves as a useful tool for solving complex problems. In
addition to describing the contraction of different types of muscle, the basic theory
can be used to simulate contraction of stress fibers at the cellular level.
© Springer Nature Switzerland AG 2020
L. A. Taber, Continuum Modeling in Mechanobiology,
https://doi.org/10.1007/978-3-030-43209-6_5
209