Question

Smooth muscle lacks

A. actin and myosin.
B. transverse tubules and striations.
C. myofibrils.
D. nuclei and mitochondria.

Answer 1

Smooth muscle lacks striations and myofibrils, and it has its own distinct characteristics compared to skeletal and cardiac muscles.

Step-by-step explanation:

Smooth muscle differs from skeletal and cardiac muscles in that it lacks striations and myofibrils.

Smooth muscle fibers are spindle-shaped and have a single nucleus. They do have actin and myosin contractile proteins, although they are not arranged in the same regular fashion as in skeletal muscles.

Smooth muscle is found in the walls of blood vessels, the tubes of the digestive system, and the tubes of the reproductive systems.

Answer 2

Smooth muscle lacks transverse tubules and striations, but still contains actin and myosin for muscle contractions. It has a single nucleus and a nonstriated, uniform appearance.The correct option is:

**B. transverse tubules and striations.**

Step-by-step explanation:

The student has asked what smooth muscle lacks. The correct answer is B. transverse tubules and striations. Unlike skeletal and cardiac muscles, smooth muscle cells have a spindle shape with a single, centrally located nucleus and do not exhibit the banded appearance because they lack the organized sarcomeres of striated muscles.

However, smooth muscle does contain the contractile proteins actin and myosin, which are necessary for muscle contraction but are not arranged in the same regular pattern as in skeletal and cardiac muscle, giving the smooth muscle its nonstriated, uniform appearance.The correct option is:

**B. transverse tubules and striations.**