Arousal

Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the reticular activating system in the brainstem, the autonomic nervous system, and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, mobility, and readiness to respond.

The arousal system involves many different neural systems. Five major systems originating in the brainstem, with connections extending throughout the cortex, are based on the brain's neurotransmitters: acetylcholine, norepinephrine, dopamine, histamine, and serotonin. When these systems are in action, the receiving neural areas become sensitive and responsive to incoming signals, producing alertness and cortical activity.

Arousal is important in regulating consciousness, attention, alertness, and information processing. It is a crucial for motivating certain behaviours, such as mobility, the pursuit of nutrition, the fight-or-flight response and sexual activity (the arousal phase of Masters and Johnson's human sexual response cycle). It is also important in emotion and has been included in theories such as the James-Lange theory of emotion. According to Hans Eysenck, differences in baseline arousal level lead people to be extraverts or introverts.

...
Wikipedia