Which type of muscle tissue is characterized by the absence of sarcomeres?

The correct answer is Smooth muscle.

Muscle tissue in the human body is broadly classified into three types: skeletal muscle, cardiac muscle, and smooth muscle. One of the key distinguishing features among these muscle types is the presence or absence of sarcomeres.

- Sarcomeres are the basic contractile units of muscle fibers, composed of organized arrangements of actin and myosin filaments that create a characteristic striated appearance.
- Both skeletal muscle and cardiac muscle exhibit striations, which means their fibers contain well-organized sarcomeres.
- In contrast, smooth muscle lacks these organized sarcomeres, which is why it is called "smooth." The contractile proteins in smooth muscle are arranged more randomly, leading to a non-striated appearance under the microscope.
- This structural difference allows smooth muscle to perform slower, sustained contractions typically found in the walls of internal organs such as the intestines, blood vessels, and the bladder.

Important points:
- Skeletal muscle – striated with sarcomeres
- Cardiac muscle (also called myocardial muscle) – striated with sarcomeres
- Smooth muscle – non-striated, no sarcomeres

Reference: Ganong's Review of Medical Physiology, 26th Edition, Chapter 6: Muscle Physiology / Page 87