Autonomic nervous system The autonomic nervous system is a control system that acts largely unconsciously and regulates heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the<unk>  and its role is mediated by two different components: the sympathetic nervous system and the parasympathetic nervous system. Sympathetic nervous system The sympathetic nervous system originates in the spinal cord and its main function is to activate the physiological changes that occur during the<unk> . This component of the autonomic nervous system utilises and activates the release of norepinephrine in the reaction. Parasympathetic nervous system The parasympathetic nervous system originates in the sacral spinal cord and medulla, physically surrounding the sympathetic origin, and works in concert with the sympathetic nervous system. Its main function is to activate the "rest and digest" response and return the body to homeostasis after the<unk>  or<unk>  response. This system utilises and activates the release of the neurotransmitter acetylcholine. Reaction An infographic displaying the<unk>  The reaction begins in the amygdala, which triggers a neural response in the hypothalamus. The initial reaction is followed by activation of the pituitary gland and secretion of the hormone ACTH. The adrenal gland is activated almost simultaneously, via the sympathetic nervous system, and releases the hormone epinephrine. The release of chemical messengers results in the production of the hormone cortisol, which increases blood pressure, blood sugar, and suppresses the immune system. The initial response and subsequent reactions are triggered in an effort to create a boost of energy. This boost of energy is activated by epinephrine binding to liver cells and the subsequent production of glucose. Additionally, the circulation of cortisol functions to turn fatty acids into available energy, which prepares muscles throughout the body for response. Catecholamine hormones, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), facilitate immediate physical reactions associated with a preparation for violent muscular action and: * Acceleration of heart and lung action * Paling or flushing, or alternating between both * Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops * General effect on the sphincters of the body * Constriction of blood vessels in many parts of the body * Liberation of metabolic energy sources (particularly fat and glycogen) for muscular action * Dilation of blood vessels for muscles * Inhibition of the lacrimal gland (responsible for tear production) and salivation * Dilation of pupil (mydriasis) * Relaxation of bladder * Inhibition of erection * Auditory exclusion (loss of hearing) * Tunnel vision (loss of peripheral vision) * Disinhibition of spinal reflexes * Shaking Function of physiological changes The physiological changes that occur during the<unk>  or<unk>  response are activated in order to give the body increased strength and speed in anticipation of<unk> ing or running. Some of the specific physiological changes and their functions include: * Increased blood flow to the muscles activated by diverting blood flow from other parts of the body. * Increased blood pressure, heart rate, blood sugars, and fats in order to supply the body with extra energy. * The blood clotting function of the body speeds up in order to prevent excessive blood loss in the event of an injury sustained during the response. * Increased muscle tension in order to provide the body with extra speed and strength.
Fight-or-flight response
Withdrawal reflex
Accommodation reflex
Decompensation
Inflammatory reflex
Snout reflex
Instinctive drowning response
Cushing reflex