MUSCULAR CONTRACTIONS

Contracting and Relaxing Skeletal Muscle

Anatomy of a Muscle Fiber (Cell)

Sarcolemma Myofibril Sarcomere Z line

Anatomy of a Sarcomere

Actin Myosin

Contraction Overview

Lovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

Steps of a Muscle Contraction

Nerve causes release of acetylcholine (ACh)

Steps of a Muscle Contraction

Reception of ACh causes an action potential (electrical nerve signal) in muscle cell

Steps of a Muscle Contraction

Action potential causes release of calcium in muscle cell

Meanwhile…

Steps of a Muscle Contraction

Calcium binds, forming troponin complex and revealing myosin binding sites.

Steps of a Muscle Contraction

Sliding filament theory

Contraction Overview

Lovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

Relaxation

Acetylcholinesterase breaks down Ach Active transport prepares the muscle cell for

future action potentials Active transport removes free calcium from

muscle cells ATP breaks actin-myosin linkage

Relaxation

Interference

Botox & botulism – block acetylcholine release

Rigor mortis – can’t keep calcium out of cells so muscles contract, lack of ATP prevents myosin from releasing actin