40 - Skeletal Muscle Action Potentials

Abstract

Publisher Summary This chapter discusses skeletal muscle action potentials. The chapter focuses on sarcolemmal electrophysiological properties that are the bases of the action potential (AP) generation. The chapter also reviews briefly general electrophysiological principles that can be applied to skeletal muscle fibers. The chapter discusses several related concepts, including ion channel activation and inactivation, electrogenesis of depolarizing afterpotentials, and excitation delivery to fiber interior. Conduction into the T-tubular system and evidence for T-tubule communication with the sarcoplasmic reticulum across the triadic junction are also discussed under excitation delivery to fiber interior. It is mentioned that the AP spike in skeletal muscle fibers is followed by a prominent depolarizing afterpotential, also called a negative afterpotential. The skeletal AP is considerably different from the AP of cardiac muscle cells, which has a very long duration with a pronounced plateau and a substantially lower rate of rise and propagation velocity. A general overview of electrogenesis of the AP and the ion channel activation and inactivation are discussed. The skeletal AP is terminated partly by the turn-on of the K+ conductance. The Cl– conductance (gCl)of skeletal muscle fibers is generally very high, and it is important for producing a sharp repolarization of the AP. ATP-dependent K+ (KATP) channels are characterized by the inhibition of channel openings by ATP. The cell membranes of most excitable cells apparently pass through similar stages of differentiation during development. One type of skeletal muscle fibers, known as slow fibers, subserves tonic functions, including posture. When the end plate potential (EPP), generated at the neuromuscular junction, reaches threshold for eliciting an AP in the skeletal muscle fiber, an AP is propagated down the muscle fiber in both directions from the end plate.