A motor unit is a group of muscle fibers that all get their signals from the same, single motor neuron.

运动单元是一组肌肉纤维，它们都从同一个运动神经元接收信号。

First you've got your motor neurons that release the neurotransmitter acetylcholine at the neuromuscular junction, which then binds to nicotinic acetylcholine receptors on muscle cell membranes.

首先，你的运动神经元在神经肌肉接头处释放神经递质乙酰胆碱（ACh），然后与肌肉细胞膜上的N胆碱受体相结合。

Since multiple action potentials don't travel down all the motor neurons at exactly the same time, each motor unit twitches at slightly different times, which helps smooth out the … twitchiness.

由于多个动作电位不会在完全相同的时间沿着所有的运动神经元运动，每个运动单元在稍微不同的时间抽搐，这有助于消除抽搐。

For example, the tack in your right foot ended up activating the motor neurons in your right hip flexors and hamstring, causing that knee to bend and your foot to lift up.

例如，你右脚的图钉最终激活了你右臀部屈肌和腿筋的运动神经元，导致膝盖弯曲，脚抬起。

When we tap your, let's say your patellar tendon that causes a stretch in a muscle spindle, this sends a signal back to the sensory neuron, which activates a motor neuron in the spinal cord to cause your knee to kick up.

当我们敲击你的，比方说你的髌骨腱，它会导致肌肉纺锤体的拉伸，这会向感觉神经元发送信号，这会激活脊髓中的运动神经元，使你的膝盖抬起。