The textbook excerpt is as follows:

"In the field of cardiac muscle regulation, the following research articles provide valuable insights: Gordon AM, Homsher E, Regnier M. Regulation of contraction in striated muscle. Physiol Rev. 2000;80(2):853-924. Imbrici P, Altamura C, Pessia M, Mantegazza R, Desaphy JF, Camerino DC. ClC-1 chloride channels: state-of-the-art research and future challenges. Front Cell Neurosci. 2015;9:156. Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev. 2015;95(2):549-601. Nelson CR, Fitts RH. Effects of low cell pH and elevated inorganic phosphate on the pCa-force relationship in single muscle fibers at near-physiological temperatures. Am J Physiol Cell Physiol. 2014;306(7):C670-C678. Sandri M. Protein breakdown in cancer cachexia. Semin Cell Dev Biol. 2016;54:11-19. Schiaffino S, Reggiani C. Fiber types in mammalian skeletal muscles. Physiol Rev. 2011;91(4):1447-1531.

After studying these articles, students will be able to answer the following questions:

1. Explain the structure of cardiac muscle and how it meets the demands of the organ.
2. Describe the molecular mechanisms involved in excitation-contraction coupling in cardiac muscle and its suitability for this organ.
3. Discuss the molecular mechanisms that result in an increase in the force of contraction of the heart.
4. Analyze the length-tension relationship and the force-velocity curve for cardiac muscle, including the molecular basis for both curves.

If the student has already completed the section on skeletal muscle, they will be able to compare cardiac and skeletal muscle for each of the learning objectives listed above.

The heart's primary function is to pump blood through the circulatory system, which relies on the organized contraction of cardiac muscle cells. These cells are interconnected to form an electrical syncytium, with strong electrical and mechanical connections between neighboring cells. This allows for the rapid transmission of action potentials throughout the heart, facilitating synchronized contraction of the cardiac muscle cells. Synchronized relaxation is also crucial for the heart's refilling process, as abnormal relaxation can lead to pathological conditions.

This chapter begins by describing the organization of cardiac muscle cells within the heart, including their tight electrical and mechanical connections. It also explores the mechanisms behind contraction, relaxation, and regulation of the force of contraction in these cells. While cardiac muscle and skeletal muscle are both striated muscles, they differ significantly in terms of their organization, electrical and mechanical coupling, excitation-contraction coupling, and mechanisms for regulating contraction force. These differences are highlighted throughout the chapter.

The basic organization of cardiac muscle cells involves smaller dimensions compared to skeletal muscle cells, with cardiac cells typically measuring 10 µm in diameter and approximately 100 µm in length.
Gordon AM, Homsher E, Regnier M. Regulation of contraction in striated muscle. Physiol Rev. 2000;80(2):853-924.
Imbrici P, Altamura C, Pessia M, Mantegazza R, Desaphy JF, Camerino DC. ClC-1 chloride channels: state-of-the-art research and future challenges. Front Cell Neurosci. 2015;9:156.
Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev. 2015;95(2):549-601.
Nelson CR, Fitts RH. Effects of low cell pH and elevated inorganic phosphate on the pCa-force relationship in single muscle fibers at near-physiological temperatures. Am J Physiol Cell Physiol. 2014;306(7):C670-C678.
Sandri M. Protein breakdown in cancer cachexia. Semin Cell Dev Biol. 2016;54:11-19.
Schiaffino S, Reggiani C. Fiber types in mammalian skeletal muscles. Physiol Rev. 2011;91(4):1447-1531.
Upon completion of this chapter, the student should be able to answer the following questions: 1.
Describe the organization of cardiac muscle and how it meets the demands of the organ.
2.
Describe the molecular mechanisms involved in excitation-contraction coupling in cardiac muscle and its suitability for this organ.
3.
Describe the molecular mechanisms that lead to an increase in the force of contraction of the heart.
4.
Discuss the length-tension relationship and the force-velocity curve for cardiac muscle, including the molecular basis for both curves.
If the student has already completed on skeletal muscle, the student will be able to compare cardiac and skeletal muscle for each of the learning objectives just listed.
he function of the heart is to pump blood through the circulatory system, and this is accomplished by the highly organized contraction of cardiac muscle cells. Specifically, the cardiac muscle cells are connected together to form an electrical syncytium, with tight electrical and mechanical connections between adjacent cardiac muscle cells. An action potential initiated in a specialized region of the heart (e.g., the sinoatrial node) is therefore able to pass quickly throughout the heart to facilitate synchronized contraction of the cardiac muscle cells, which is important for the pumping action of the heart. Likewise, refilling of the heart requires synchronized relaxation of the heart; abnormal relaxation often results in pathological conditions.
This chapter begins with a description of the organization of cardiac muscle cells within the heart, including discussion of the tight electrical and mechanical connections. The mechanisms that underlie contraction, relaxation, and regulation of the force of contraction of cardiac muscle cells are also addressed. Although cardiac muscle and skeletal muscle are both striated muscles, they are significantly different in terms of organization, electrical and mechanical coupling, excitation-contraction coupling, and mechanisms to regulate the force of contraction. These differences are also highlighted.
Basic Organization of Cardiac Muscle Cells
Cardiac muscle cells are much smaller than skeletal muscle cells. Typically, cardiac muscle cells measure 10 µm in diameter and approximately 100 µm in length. As shown in