Chapter 20 Outline
Vertebrate Skeletal Muscle Cells
- Thick and thin filaments are polarized polymers of individual protein molecules
- Muscles require ATP to contract
- Calcium and the regulatory proteins tropomyosin and troponin control contractions
Excitation–Contraction Coupling
Whole Skeletal Muscles
- Muscle contraction is the force generated by a muscle during cross-bridge activity
- A twitch is the mechanical response of a muscle to a single stimulus
- The velocity of shortening decreases as the load increases
- The frequency of action potentials determines the tension developed by a muscle
- A sustained high calcium concentration in the cytoplasm permits summation and tetanus
- The amount of tension developed by a muscle depends on the length of the muscle at the time it is stimulated
- In general, the amount of work a muscle can do depends on its volume
- BOX 20.1 Electric Fish Exploit Modified Skeletal Muscles to Generate Electric Shocks
Muscle Energetics
- ATP is the immediate source of energy for powering muscle contraction
- Vertebrate muscle fibers vary in their use of ATP
- Different animals employ different types of muscles that contribute to their achieving success
- BOX 20.2 Insect Flight
Neural Control of Skeletal Muscle
- The vertebrate plan is based on muscles organized into motor units
- The innervation of vertebrate tonic muscle is intermediate between the vertebrate and arthropod plans
- The arthropod plan employs multiterminal and polyneuronal innervation
Vertebrate Smooth (Unstriated) Muscle
- Smooth muscle cells are broadly classified
- Ca2+ availability controls smooth muscle contraction by myosin-linked regulation
- The autonomic nervous system (ANS) innervates smooth muscles