Question

Explain 3 differences on the regulatory process of myofilament contraction between skeletal and smooth muscles

Answer 1

Muscle tissue is largely composed of actin (thin) and myosin (thick) filaments, which work in a coordinated effort to generate force and, in turn, muscle contraction. Depending on the intracellular arrangement of these myofilaments, muscle tissue is classified as either striated (skeletal and cardiac) or nonstriated (smooth) muscle. The myofilaments of striated muscle are arranged into sarcomeres; smooth muscle lacks this arrangement. Although the different types of muscle follow very similar principles on a molecular level (sliding filament mechanism), their functions vary greatly. Skeletal muscle is attached to the skeleton and provides voluntary movement. Smooth muscle possesses greater elasticity and is primarily found in the walls of hollow internal organs, where it contracts and relaxes involuntarily to fulfill a wide range of functions. In the intestine, for example, smooth muscle is responsible for transporting the bolus, whereas in the blood vessels it is primarily responsible for ensuring vascular resistance in circulation.

	Skeletal muscle	Cardiac muscle	Smooth muscle
Cell morphology	Large elongated cells with multiple nuclei located at the periphery	Branched cells with a central nucleus	Spindle-shaped with a central nucleus
Invaginations of the sarcolemma	One T-tubule and two terminal cisternae form a triad	One broad T-tubule and one terminal cistern of the SRform a dyad	Caveolae

Comparison of contractile filaments

	Skeletal muscle/cardiac muscle	Smooth muscle
Organization/orientation	Sarcomere	Disorganized
Interaction with calcium	Troponin	Calmodulin
Myosin binding site blockage	Tropomyosin	Tropomyosin with caldesmon and calponin
Anchorage	Z lines (skeletal muscle)/intercalated discs (cardiac muscle)	Dense bodies
Phosphorylation of the light myosin chain required	No	Yes

Skeletal muscle	Cardiac muscle	Smooth muscle
Initiating structure or stimulus	Alpha motor neuron via motor endplates	Cardiac pacemaker cells	Hormones (especially from autonomic neurons Pacemaker cells Metabolic factors (e.g., pH value) Mechanical stimulus (e.g., stretching of a sphincter)
Special features of electromechanical coupling	Direct protein-protein interaction between the ryanodine receptor and dihydropyridine receptor Conformational change in dihydropyridine receptorresults in release of intracellular calcium from the sarcoplasmic reticulum	Calcium-induced calcium release	No action potential required for contraction Calcium influx in the cell, especially from the extracellular space The light myosin chains require phosphorylationfor interaction with actin.
Function as a unit	All skeletal muscle fibers must be stimulated individually by their motor endplate.	Organized transfer of the stimulus from cell to cell via gap junctions in intercalated discs	Two types: single-unit and multi-unit Single-unit smooth muscle cells are connected via gap junctions and mutually contract (functional syncytium). Multi-unit smooth cells are separate and must also be stimulated separately.