Final answer:
Smooth muscle differs from skeletal muscle in structure, having spindle-shaped cells with a single nucleus and lacking striations. It is controlled involuntarily, contracts over a wider range of lengths, and has a limited SR and no T-tubules, relying on calveoli for calcium ion sequestration. Additionally, smooth muscle tissue can regenerate from pericytes, whereas skeletal muscle repairs via satellite cells. The correct option is d.
Step-by-step explanation:
Smooth muscle differs significantly from skeletal muscle in structure, control, and function. Firstly, smooth muscle cells are spindle-shaped with a single, centrally located nucleus, whereas skeletal muscle fibers are cylindrical with multiple nuclei peripherally located.
Smooth muscle cells lack striations, which are the banded appearance seen in skeletal muscle due to the regular arrangement of sarcomeres. In terms of regulation, smooth muscle contraction is under involuntary, autonomic nervous system control, or can be excited by local conditions in tissues, hormones, or pacesetter cells.
On a cellular level, smooth muscle cells have a limited sarcoplasmic reticulum (SR) and lack T-tubules because their smaller diameter allows calcium ions to easily diffuse throughout the cell. Instead of T-tubules, smooth muscle uses membrane structures called calveoli to facilitate the sequestration of calcium from the extracellular fluid.
Additionally, smooth muscles can contract over a wider range of resting lengths than skeletal muscle and can maintain contractions for longer periods because of latch bridges that do not require continual ATP consumption. The correct option is d) Smooth muscle can be excited in a multitude of ways while skeletal muscle is excited by a neuron