physiology lecture
Smooth Muscle Physiology
General Characteristics
* Smooth muscle lacks cross-striations, giving it a smooth appearance. * It is involuntary, meaning it is not under voluntary control. * Contraction depends on Ca²⁺ and actin–myosin cross-bridge cycling.
Differences from Skeletal Muscle
Compared with skeletal muscle, smooth muscle differs in its arrangement of contractile filaments and mechanism of excitation–contraction coupling.
A. Arrangement of Contractile Filaments * In skeletal muscle, actin and myosin are arranged regularly within sarcomeres, producing cross-striations. * In smooth muscle, actin and myosin are not arranged in sarcomeres, so there are no cross-striations. B. Mechanism of Excitation–Contraction Coupling * Excitation–contraction coupling is the process by which stimulation leads to muscle contraction. * In skeletal muscle: Ca²⁺ → Troponin C → contraction * In smooth muscle: Ca²⁺ → Calmodulin → MLCK (Myosin Light Chain Kinase) → contraction
Arrangement
Usually arranged in sheet-like layers
Cell Shape
Spindle-shaped
Instructor
Dr. Zahraa Majid
Stage
Second Stage
Diameter
2–10 μm
Length
50–400 μm
Smooth Muscle Type
Single