Smooth Muscle Physiology
Start with the big picture
Smooth muscle cells are small and spindle-shaped, with thin filaments anchored to dense bodies rather than Z lines. They lack T-tubules; caveolae in the cell membrane help concentrate calcium channels. Contraction follows a rise in cytosolic calcium, which binds calmodulin and activates myosin light-chain kinase (MLCK), enabling cross-bridge cycling. Relaxation involves myosin light-chain phosphatase (MLCP) and removal of calcium from the cytosol. Single-unit and multi-unit smooth muscle differ in coupling and neural control. Slow waves can support spontaneous gastrointestinal activity, while chemical signals can regulate contraction without membrane depolarization. Slow, sustained force, the latch state, stress-relaxation, and a broad length-tension range help smooth muscle meet varied functional demands.
What you'll learn
- Describe smooth muscle cell structure and the role of dense bodies and caveolae.
- Distinguish single-unit from multi-unit smooth muscle organization.
- Explain how calcium–calmodulin signaling initiates contraction and how relaxation occurs.
- Identify mechanisms that support sustained force and adaptation to stretch.
- Summarize electrical, pharmacological, and neural regulation of smooth muscle.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
