A key difference in the mechanism of excitation-contraction coupling between the muscle of the pharynx and the muscle of the wall of the small intestine is that

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[Chapter 1, VI B; VII B; Table 1.3]. The pharynx is skeletal muscle, and the small intestine is unitary smooth muscle. The difference between smooth and skeletal muscle is the mechanism by which $\mathrm{Ca}^{2+}$ initiates contraction. In smooth muscle, $\mathrm{Ca}^{2+}$
binds to calmodulin, and in skeletal muscle, $\mathrm{Ca}^{2+}$ binds to troponin C. Both types of muscle are excited to contract by action potentials. Slow waves are present in smooth muscle but not skeletal muscle. Both smooth and skeletal muscle require an increase in intracellular $\left[\mathrm{Ca}^{2+}\right]$ as the important linkage between excitation (the action potential) and contraction, and both consume adenosine triphosphate (ATP) during contraction.

A Key Difference in the Mechanism of Excitation-Contraction Coupling Between [Ca2+]\left[\mathrm{Ca}^{2+}\right][Ca2+]

A Key Difference in the Mechanism of Excitation-Contraction Coupling Between $\left[\mathrm{Ca}^{2+}\right]$