MUSCLE PHYSIOLOGY

Detailed explanation-1: -The sodium–potassium ATPase uses cellular energy to move K+ ions inside the cell and Na+ ions outside.

Detailed explanation-2: -The concentration of sodium ions inside the muscle fiber is kept very low by a pump consisting of a sodium/potassium–activated ATPase. The cleavage of one ATP molecule into ADP and phosphate is accompanied by the transport of three sodium ions out of the fiber and two potassium ions into the fiber.

Detailed explanation-3: -Neurotransmitters such as acetylcholine bind to receptors on the muscle surface and elicit a depolarization by causing sodium/calcium ions to enter through associated channels.

Detailed explanation-4: -In skeletal muscle, the Na+, K+ pump is predominantly situated in the sarcolemma (1000-3500 pumps per microns 2).

Detailed explanation-5: -Ca2+ ions play an important role in muscle contraction by creating interactions between the proteins, myosin and actin. The Ca2+ ions bind to the C component of the actin filament, which exposes the binding site for the myosin head to bind to in order to stimulate a muscle contraction.