All of the following are true about cardiac muscles, EXCEPT:
**Core Concept**
Cardiac muscle is a unique type of striated muscle tissue that is responsible for the contraction and relaxation of the heart, allowing it to pump blood throughout the body. Unlike skeletal muscle, cardiac muscle is self-excitable and has a continuous supply of oxygen and nutrients.
**Why the Correct Answer is Right**
Cardiac muscle cells, or cardiomyocytes, have a high mitochondrial density and a rich network of capillaries to meet their high energy demands. This allows them to maintain a steady contraction rate and generate the forces needed to pump blood throughout the circulatory system. The continuous supply of oxygen and nutrients is essential for the proper functioning of cardiac muscle.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cardiac muscle is not a type of smooth muscle, which is characterized by its ability to contract without being stimulated by a nervous impulse.
**Option B:** This option is incorrect because cardiac muscle does not have a high concentration of glycogen, which is a type of energy storage molecule found in skeletal muscle.
**Option C:** This option is incorrect because cardiac muscle does not have a high concentration of myoglobin, which is a protein found in skeletal muscle that stores oxygen for later use.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that cardiac muscle is highly dependent on oxygen and nutrients, and its function can be compromised by conditions such as coronary artery disease, heart failure, and cardiomyopathy.
**Correct Answer:** A.