As a subject matter expert in the field of physiology, I can provide you with an accurate explanation of depolarization in muscle cells, specifically in the context of muscle contraction. Depolarization is a critical step in the process of muscle contraction. It refers to the reversal of the electrical charge across the muscle cell membrane, known as the sarcolemma, from the resting state. In a healthy muscle cell at rest, the sarcolemma is polarized, meaning it has a negative charge inside and a positive charge outside. This is known as the resting membrane potential, which is typically around -90 millivolts (mV). During depolarization, the muscle cell membrane allows an influx of positively charged ions, such as sodium (Na+), which enter the cell through voltage-gated ion channels. This influx of positive ions causes the inside of the cell to become more positively charged, reducing the membrane potential and leading to a state known as depolarization. When the membrane potential reaches a certain threshold, typically around -55 mV, it triggers the opening of additional ion channels, which further depolarizes the cell and initiates the contraction process. Depolarization is essential because it sets off a series of events within the muscle cell that ultimately lead to the sliding of actin and myosin filaments past one another, resulting in muscle contraction. This process is regulated by the nervous system and is a part of the excitation-contraction coupling mechanism. Here is the translation of the above explanation into Chinese: 作为生理学领域的专家，我可以为您提供关于肌肉收缩过程中肌肉去极化的准确解释。 去极化是肌肉收缩过程中的关键步骤。它指的是肌细胞膜，即肌膜，从静息状态的电荷逆转。在静息状态下的健康肌细胞中，肌膜是极化的，意味着内部带有负电荷，外部带有正电荷。这被称为静息膜电位，通常在-90毫伏（mV）左右。 在去极化过程中，肌细胞膜允许正电荷离子，如钠离子（Na+），通过电压门控离子通道进入细胞。这些正离子的流入导致细胞内部变得更正电荷，减少膜电位，导致所谓的去极化状态。当膜电位达到某个阈值，通常在-55 mV左右时，它会触发额外的离子通道打开，这进一步去极化细胞并启动收缩过程。 去极化至关重要，因为它在肌细胞内引发了一系列事件，最终导致肌动蛋白和肌球蛋白丝相互滑动，从而产生肌肉收缩。这个过程由神经系统调节，是兴奋-收缩耦联机制的一部分。 read more >>

An action potential in the skeletal muscle cell is what triggers muscle cell contraction. We have seen that calcium ions regulate whether or not contraction can occur. Thus, what is needed is a way to link muscle excitation (the depolarization of the action potential) to Ca++ release from the sarcoplasmic reticulum.read more >>