A characteristic of smooth muscle, not seen in skeletal or cardiac muscle, is?

A. intercalated disks
B. peristalsis
C. sarcosomes
D. longer, cylindrical myofibrils

To find the characteristic of smooth muscle that is not seen in skeletal or cardiac muscle, we can first understand the differences between these three types of muscles.

Skeletal muscle is responsible for voluntary movements of the body. It is attached to bones and helps us move and maintain posture. Cardiac muscle is found only in the heart and is responsible for pumping blood. Smooth muscle, on the other hand, is found in various organs such as the walls of blood vessels, gastrointestinal tract, and respiratory tract. It is responsible for involuntary movements like contracting and relaxing to control the flow of substances through these organs.

Now, let's examine the options:

A. Intercalated disks: Intercalated disks are specialized structures found in cardiac muscle. They provide a structural and functional connection between adjacent cardiac muscle cells, allowing synchronized contractions. Therefore, intercalated disks are seen in cardiac muscle, not in smooth or skeletal muscle.

B. Peristalsis: Peristalsis is a rhythmic contraction and relaxation of smooth muscles that propels substances through organs like the intestines or esophagus. Peristalsis is a characteristic feature of smooth muscle, so it is not unique to smooth muscle only.

C. Sarcosomes: Sarcosomes are mitochondria-like structures found in cardiac muscle cells. They are responsible for energy production and play a role in contracting the heart muscle. Sarcosomes are seen in cardiac muscle, not in smooth or skeletal muscle.

D. Longer, cylindrical myofibrils: Myofibrils are contractile structures found in both skeletal and cardiac muscles. They are responsible for muscle contraction. While smooth muscle also contains some myofibrils, they are shorter and not as organized compared to those found in skeletal and cardiac muscles. So, longer, cylindrical myofibrils are seen in skeletal and cardiac muscles, not in smooth muscle.

Therefore, the characteristic of smooth muscle not seen in skeletal or cardiac muscle is: C. sarcosomes.