Increasing stimulation of the parasympathetic nervous system decreases heart rate and blood pressure as well as the size of the pupil. At the same time, it increases digestion, urination, defecation and sexual arousal. T... More »

The autonomous nervous system controls the nervous system, normally by the constant input of the parasympathetic nervous system that keeps the heart rate down. The more active the parasympathetic nervous system input is,... More »

Stress can cause dilated pupils if it stimulates the sympathetic branch of the autonomic nervous system, which triggers a fight or flight response, according to Scientific American. Stress can also inhibit the parasympat... More »

Neuroscience for Kids states that smoking affects the nervous system by causing an increase in blood pressure, heart rate and respiration as well as constriction of arteries and stimulation of the central nervous system.... More »

Adrenaline, also known as epinephrine, primarily boosts the heart rate, raises blood pressure, expands the lung air passages and dilates the pupil in the eye. It acts on various kinds of cells and generates numerous acti... More » Science Human Anatomy Glands & Hormones

Vasovagal syncope, the medical term for fainting due to suppression of the functions of the vagus nerve, occurs when this essential part of the nervous system that controls the heart rate and blood pressure malfunctions,... More »

Adrenaline, a natural stimulant created in the kidney's adrenal gland, travels through the bloodstream and controls functions of the autonomous nervous system, including the secretion of saliva and sweat, heart rate and ... More »