The command that makes your muscles contract can come either in the form of a conscious command from the brain or in the form of a reflex. For example, you can order your biceps to contract, causing your arm to flex.

Information travels from the cerebellum to the spinal cord and along the peripheral nervous system to the biceps muscle cells (see the drawing below).

Reflexes are quick reactions, because they are not guided by the commands of the brain. For example, information about a finger hitting a hot plate is quickly transmitted to the spinal cord. From there, the message travels to the hand muscles, which contract and lift the finger from the hot surface. In other words, the information does not pass through the brain at all.