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 answer to this question, we need to compare the characteristics of smooth muscle with those of skeletal and cardiac muscles. Let's break down the options and evaluate them:
A. Intercalated disks: Intercalated disks are specialized cell junctions found in cardiac muscle, not in smooth muscle. Therefore, option A is not the correct answer.
B. Peristalsis: Peristalsis is a characteristic movement found in smooth muscle. It's the rhythmic contraction and relaxation of smooth muscle that helps propel substances through tubes and organs like the intestines. This movement is not seen in skeletal or cardiac muscle. Therefore, option B is a characteristic of smooth muscle and could be the correct answer.
C. Sarcosomes: Sarcosomes are specialized mitochondria found in cardiac muscle, not in smooth muscle. Therefore, option C is not the correct answer.
D. Longer, cylindrical myofibrils: In skeletal muscle, myofibrils are long, cylindrical structures that are responsible for muscle contraction. However, they are also present in cardiac muscle, where they help generate the force for heart contractions. Therefore, option D is not a characteristic unique to smooth muscle.
Based on this evaluation, the correct answer is B. Peristalsis, which is a characteristic of smooth muscle.