1. Easily excited
   "The excitable child couldn't sit still during the movie"
    
2. (physiology) capable of responding to stimuli
   "The excitable nerve cells fired rapidly in response to the stimulus";
   - irritable

See also: flighty, nervous, quick, sensitive, skittery, skittish, spooky [N. Amer, informal], warm

Antonym: unexcitable

Encyclopedia: Excitable