Sentient, sensitive, impressible, impressionable, responsive, susceptible can all mean readily affected by stimuli, usually external stimuli.
Sentient implies a capacity to be affected through the senses; it may describe inclusively the lowest thing in animal life that feels, or the infant aware only of rudimentary sensation, or the man with the most highly developed powers of sensation or perception. The term sentient creature or sentient being may apply to a creature or being within these classes or between them or it may apply to something animate or inanimate to which similar powers are ascribed.
Sensitive (see also LIABLE ) applies usually to human beings who are quick or sharp in sensing anything. It may imply senses that respond to the most delicate of stimuli or it may imply quick emotional reactions that are the outward signs of one’s being easily moved or stirred or an acuteness of mind that is linked with acuteness of sense and of emotion.
Sometimes sensitive is applied not only to a part of the body (as a section of skin or an organ) which is abnormally or excessively reactive to stimuli but to inanimate things (as a photographic film, a thermometer, or an explosive) which responds quickly to some specific influencing factor (as light, heat, or shock).
Impressible implies occasionally and impressionable regularly a readiness to be influenced, not only by a stronger power, but by a power that succeeds in producing an impression. They do not imply, as sensitive usually does, a power to judge accurately and delicately; rather they suggest crudeness or immaturity or indifference to the quality of the thing that impresses.
Responsive, which implies sensitiveness to stimuli in particular or in general, suggests in addition a readiness to respond or react in the way that is wanted. Since it usually occurs only in a good sense, it is likely to connote alertness, cooperativeness, and enthusiasm.
Susceptible (see also LIABLE ) suggests a fitness in disposition or in temperament to be affected by certain stimuli. Though it comes close to impressionable or responsive it more often implies weakness than does either of them, the weakness sometimes being stated but more frequently implied or suggested (as by the person considered or the circumstances attending).