MICROANATOMY

Detailed explanation-1: -the actin: myosin ratio is higher in smooth muscle averaging 15:1 in vascular smooth muscle in comparison to 6:1 in skeletal or cardiac muscle. There are no intercalated disks or z-disks, however, dense bodies in smooth muscle are thought to be analogous to z-disks (Figure 2.2).

Detailed explanation-2: -Smooth muscle lacks the striations of skeletal and cardiac muscle because the actin and myosin filaments are not regularly arrayed along the length of the cell. Instead, the arrangement of filaments is less regimented and occurs as a spiral.

Detailed explanation-3: -Smooth muscle contraction depends on calcium influx. Calcium increases within the smooth muscle cell through two different processes. First, depolarization, hormones, or neurotransmitters cause calcium to enter the cell through L-type channels located in the caveolae of the membrane.

Detailed explanation-4: -In smooth muscle, actin filaments are attached to the dense bodies on the plasma membrane and within the cytoplasm. These dense bodies are the functional equivalent of Z-disks in skeletal and cardiac muscle.