 Nerve action. The human body has four types of nerves, sensory, motor, mixed and reflex. Sensory nerves, also called afferent nerves, carry messages from the sense organs to the brain. Sensory nerve endings are called receptors. The receptors send to the brain the sensation messages of touch, pain, pressure, cold, heat, sight, hearing, taste and smell. Motor nerves, also called afferent nerves, carry messages from the brain to the muscles. The messages produce movement. A complete circuit is formed when the sensory nerve sends a message from the sensory receptors to the brain, which then sends the message to the motor nerves and onto the muscle. Mixed nerves contain both sensory and motor fibers. They have the ability to both send and receive messages. A reflex nerve is unconscious and involuntary. A reflex is an automatic nerve response to a stimulus that causes muscular movement. This is the simplest type of nerve response and does not have to be learned. You have completed this learning activity, Nerve Action.