The brain stem maps information both from the outside world and from inside the body. Nerves originating in the skin, muscles, skeletal system, blood vessels, and viscera (internal organs) all connect to neurons in the brain stem. The firing patterns of these nerves are then mirrored in the firing patterns of the brain stem neurons. In this way, the brain forms a representation of the internal state of the body, and this representation is updated on a moment-by-moment basis. Likewise, some types of sensory information, such as sound and touch, are sent to the brain stem in the initial stages of perception.