Final answer:
Both skeletal and cardiac muscle cells use sarcomeres for contraction and demonstrate a striated appearance, but differ in the stimulus for depolarization and the length of individual muscle cells.
Step-by-step explanation:
The similarities between skeletal and cardiac muscle cells include their use of sarcomeres to contract and their striated appearance due to the organized arrangement of actin and myosin filaments. A sarcomere is the basic functional unit of muscle fiber in both muscle types and is responsible for the muscles' striated look. Both muscle types demonstrate striations from the regular arrangement of these contractile proteins, which are visible under high magnification. However, there are differences in how they are stimulated for depolarization and contraction. While skeletal muscles require an electrical impulse from nerves, often involving the neurotransmitter acetylcholine, cardiac muscles have built-in pacemaker cells that regulate contractions independently. Furthermore, the length of individual muscle cells markedly varies between these muscle types, with skeletal muscle cells being much longer than those of cardiac muscle.