Which of the following words does not belong to the group?
brain, glands, motor neuron, movement, muscles, sensory neuron, stimuli

I believe that the word "glands" is incorrectly added to the group. My reasoning for this stems from the fact that the rest seem to show the process of reacting to an external stimuli. When reacting to an external stimuli in a quick manner, your body will use the neuron pathways it has created throughout itself. As the sensory neuron senses the stimuli, it sends the message up the neuron to the brain, where it makes the decision to react, sends it down the motor neuron and created movement. This all happens in a very quick manner, while glands secrete hormones much more slowly.