MUSCULAR CONTRACTIONSContracting and Relaxing Skeletal Muscle

Anatomy of a Muscle Fiber (Cell)SarcolemmaMyofibrilSarcomereZ line

Anatomy of a SarcomereActinMyosin

Contraction OverviewLovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

Steps of a Muscle ContractionNerve causes release of acetylcholine (ACh)

Steps of a Muscle ContractionReception of ACh causes an action potential (electrical nerve signal) in muscle cell

Steps of a Muscle ContractionAction potential causes release of calcium in muscle cellMeanwhile

Steps of a Muscle ContractionCalcium binds, forming troponin complex and revealing myosin binding sites.

Steps of a Muscle ContractionSliding filament theory

Contraction OverviewLovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

RelaxationAcetylcholinesterase breaks down AchActive transport prepares the muscle cell for future action potentialsActive transport removes free calcium from muscle cellsATP breaks actin-myosin linkage

Relaxation

InterferenceBotox & botulism block acetylcholine releaseRigor mortis cant keep calcium out of cells so muscles contract, lack of ATP prevents myosin from releasing actin