肌肉

肌肉(muscle)

可收缩的肌肉，产生的运动功能如身体动作、消化、聚焦、循环及身体保暖。分类为横纹肌、心肌及平滑肌，或是分为相位肌或兴奋肌（快速或逐渐对刺激反应）。横纹肌的纤维在显微镜下成条纹状，负责随意运动。这种肌肉大多数是相位肌，附着在骨骼上，中枢神经系统传来讯号时就收缩而移动身体；收缩是由细丝（肌动蛋白）在粗丝（肌凝蛋白）之间滑动来完成；组织内的伸长感觉器提供反馈，使肌肉做到平顺运动与细微运动控制。心肌树枝状的纤维就像网状结构；收缩是源自於心脏肌肉组织本身，由天然的节律点产生讯号；迷走神经与交感神经控制心脏的跳动速率。平滑肌是内部器官与血管的肌肉，通常是不随意肌与兴奋肌；细胞可以集体或个别行动（反应分别的神经末端）且有不同的形状。随意肌的疾病造成无力、萎缩、疼痛和抽搐。有些全身性的疾病（如皮肌炎、多肌炎）会造成肌肉发炎。亦请参阅abdominal muscle、muscular dystrophy、myasthenia gravis。

English version：

muscle

Contractile tissue that produces motion for functions including body movements, digestion, focusing, circulation, and body warmth. It can be classified as striated, cardiac, and smooth or as phasic and tonic (responding quickly or gradually to stimulation, respectively). Striated muscle, whose fibers appear striped under a microscope, is responsible for voluntary movement. Most of these muscles are phasic. They are attached to the skeleton and move the body by contracting in response to signals from the central nervous system; contraction is achieved by the sliding of thin filaments (of actin) between thick ones (of myosin); stretch receptors in the tissue provide feedback, allowing smooth motion and fine motor control. The branched fibers of cardiac muscle give it a netlike structure; contraction originates in the heart's muscle tissue itself with a signal from the natural pacemaker; vagus and sympathetic nerves control heart rate. Smooth muscle, the muscle of internal organs and blood vessels, is generally involuntary and tonic; its cells can operate either collectively or individually (in response to separate nerve endings) and have different shapes. Disorders of voluntary muscle cause weakening, atrophy, pain, and twitching. Some systemic diseases (e.g., dermatomyositis, polymyositis) can cause muscle inflammation. See also abdominal muscle, extensor muscle, flexor muscle, muscle tumor, muscular dystrophy, myasthenia gravis.