ANESTHESIOLOGY FAST REVIEW

ANESTHESIOLOGY_FAST_REVIEWKAPAK1-0-25

NEUROMUSCULAR PHYSIOLOGY

Nuran Akıncı Ekinci

Konya City Hospital, Department of Anesthesiology and Reanimation, Konya, Türkiye

Akıncı Ekinci N. Neuromuscular Physiology. In: Kazancı D, editor. Anesthesiology Fast Review. 1st ed. Ankara: Türkiye Klinikleri; 2025. p.55-64.

ABSTRACT

  • A thorough understanding of neuromuscular physiology is critical for the proper use of muscle relaxants inanesthesia, the management of neuromuscular diseases such as myasthenia gravis, and the treatment of certain poisonings.
  • Neuromuscular transmission occurs through nicotinic acetylcholine (Ach) receptors, which are located on themuscle cell membrane and bound to the rapsin protein. These receptors are cylindrical complexes composed of five protein subunits. When Ach binds to the a subunits, ion channels open, allowing the entry of Na+ and Ca2+ ions and the exit of K+, initiating membrane depolarization.
  • Muscle contraction begins with the formation of an action potential in the motor neuron, leading to the openingof voltage-gated Ca2+ channels and the release of Ach. Ach binds to postsynaptic receptors, causing Na+ entry and K+ exit, and once the threshold potential is reached, an action potential is generated in the muscle cell. This results in the release of Ca2+ from the sarcoplasmic reticulum (SR) and the interaction of actin and myosin, leading to muscle contraction. When depolarization ends, Ca2+ is reabsorbed by the SR, and muscle contraction ceases.
  • Extrajunctional receptors increase in conditions such as burns, sepsis, and muscle inactivity, which canparticularly elevate the risk of hyperkalemia, especially with the use of succinylcholine.
  • Local anesthetics, ketamine, and inhaled anesthetics are among other agents that affect neuromusculartransmission. These agents create neuromuscular block by altering the opening and closing dynamics of ion channels, without directly interacting with the acetylcholine binding site.
  • Neuromuscular monitoring is used to evaluate neuromuscular transmission by applying electrical stimulation toa peripheral motor nerve. The presence and degree of neuromuscular blockade are determined by the reduction in muscle response.

Keywords: Neuromuscular junction; Receptors, cholinergic; Neuromuscular monitoring; Neuromuscular blockade

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