skeletal muscle excitation and contraction coupling SummaryKey Structures of the muscle cell See: Muscle Cell • The sarcolemma (its plasma membrane). • A myofibril. - The A band refers to the length of the thick filaments, "think "A" for d-a-rk – they are aniosotropic (or birefringent) in polarized light. - The I band is the region along the thin filaments (between the thick filaments). Think "I" for L-i-ght: they are "isotropic" (do not alter polarized light). • Sarcoplasmic reticulum (SR) - Form web-like rows. - Store calcium. - Are a key component to coupling muscle cell excitation to myofibril contraction. • Terminal cisternae (aka lateral cisternae) of the sarcoplasmic reticulum. - Flank the transverse tubules (T-Tubules) • Transverse tubules (T-Tubules) - Are tubular invaginations of sarcolemma. • Sarcoplasm - The muscle cell cytoplasm. - Muscle cell nuclei lie within the periphery of the cell. - During development, the nuclei transition from a central location to a peripheral one. - Muscle cells comprise numerous mitochrondria: they are the energy powerhouses of the cell – the site of aerobic respiration, which by definition requires oxygen but is capable of generate the most amount of ATP. • The synaptic terminal (aka terminal bouton, terminal button, synaptic bouton) of a typical motor nerve. - Within it are molecules of acetylcholine.Key aspects of myofilaments See: myofilaments Thin filaments • Actin - Spherical molecules joined in pairs of strands (like beads on a string). It is referred to as F-actin for filamentous actin, and comprises a polymer of G-actin monomers that are arranged in a double helix. Tropomyosin • Threadlike strands Troponin • Protein complexes that bind tropomyosin, actin, and also calcium (show their calcium-binding sites). Thick filaments • Comprise myosin molecules, which form a golfclub shape, and comprise two heavy chains and two light chains.Excitation Acetylcholine binds a post-synaptic receptor on mu...