Fight-or-flight response in the context of "Serotonin"

Fear is an unpleasant subjective emotional state arising in response to perceived dangers or threats and which, when experienced, is typically associated with physiological and psychological changes. These changes frequently lead to behavioral reactions such as fight-or-flight responses or, in extreme cases, immobilization (freeze response). Unlike most (perhaps all) other animals, humans can experience fear in response to a present or anticipated stimulus and to imagined events.

Most internalizing psychopathologies (depression, anxiety, suicidal thoughts and behaviors, and so forth) are associated with and maintained by dysfunctional, anxious, or fearful feelings and thoughts. Phobias, or exaggerated and often disabling fears, are usually similarly dysfunctional.

The horse (Equus ferus caballus) is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of Equus ferus. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature, Eohippus, into the large single-toed animal of today, originally in North America. Humans began domesticating horses around 4000 BCE in Central Asia, and their domestication is believed to have been widespread by 3000 BCE. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses. These feral populations are not true wild horses, which are horses that have never been domesticated. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior.

Horses are adapted to run, allowing them to quickly escape predators, and possess a good sense of balance and a strong fight-or-flight response. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down, with younger horses tending to sleep significantly more than adults. Female horses, called mares, carry their young for approximately 11 months and a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training under a saddle or in a harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years.

In physiology, a stimulus is a change in a living thing's internal or external environment. This change can be detected by an organism or organ using sensitivity, and leads to a physiological reaction. Sensory receptors can receive stimuli from outside the body, as in touch receptors found in the skin or light receptors in the eye, as well as from inside the body, as in chemoreceptors and mechanoreceptors. When a stimulus is detected by a sensory receptor, it can elicit a reflex via stimulus transduction. An internal stimulus is often the first component of a homeostatic control system. External stimuli are capable of producing systemic responses throughout the body, as in the fight-or-flight response. In order for a stimulus to be detected with high probability, its level of strength must exceed the absolute threshold; if a signal does reach threshold, the information is transmitted to the central nervous system (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.

Stress, whether physiological, biological or psychological, is an organism's response to a stressor, such as an environmental condition or change in life circumstances. When stressed by stimuli that alter an organism's environment, multiple systems respond across the body. In humans and most mammals, the autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are the two major systems that respond to stress. Two well-known hormones that humans produce during stressful situations are adrenaline and cortisol.

The sympathoadrenal medullary axis (SAM) may activate the fight-or-flight response through the sympathetic nervous system, which dedicates energy to more relevant bodily systems to acute adaptation to stress, while the parasympathetic nervous system returns the body to homeostasis.

Anxiety is an emotion characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different from fear in that fear is defined as the emotional response to a present threat, whereas anxiety is the anticipation of a future one. It is often accompanied by nervous behavior such as pacing back and forth, somatic complaints, and rumination.

Anxiety is a feeling of uneasiness and worry, usually generalized and unfocused as an overreaction to a situation that is only subjectively seen as menacing. It is often accompanied by muscular tension, restlessness, fatigue, inability to catch one's breath, tightness in the abdominal region, nausea, and problems in concentration. Anxiety is closely related to fear, which is a response to a real or perceived immediate threat (fight-or-flight response); anxiety involves the expectation of a future threat including dread. People facing anxiety may withdraw from situations which have provoked anxiety in the past.

Post-traumatic stress disorder (PTSD) is a mental disorder that develops from experiencing a traumatic event, such as sexual assault, domestic violence, child abuse, warfare and its associated traumas, natural disaster, bereavement, traffic collision, or other threats on a person's life or well-being. Symptoms may include disturbing thoughts, feelings, or dreams related to the events, mental or physical distress to trauma-related cues, attempts to avoid trauma-related cues, alterations in the way a person thinks and feels, and an increase in the fight-or-flight response. These symptoms last for more than a month after the event and can include triggers such as misophonia. Young children are less likely to show distress, but instead may express their memories through play.

Most people who experience traumatic events do not develop PTSD. People who experience interpersonal violence such as rape, other sexual assaults, being kidnapped, stalking, physical abuse by an intimate partner, and childhood abuse are more likely to develop PTSD than those who experience non-assault based trauma, such as accidents and natural disasters. In the United States, about 3.5% of adults have PTSD in a given year, and 9% of people develop it at some point in their lives. In much of the rest of the world, rates during a given year are between 0.5% and 1%. Higher rates may occur in regions of armed conflict. It is more common in women than men.

Surprise (sə(r)ˈprīz) is a rapid, fleeting, mental and physiological state. It is related to the startle response experienced by animals and humans as the result of an unexpected event.

Surprise can have any valence. That is, it can be pleasant/positive, unpleasant/negative, or neutral/moderate. Surprise can occur in varying levels of intensity ranging from very surprised, which may induce the fight-or-flight response, or slightly surprised, which elicits a less intense response to the stimulus.

Freezing behavior, also called the freeze response or being petrified, is a reaction to specific stimuli, most commonly observed in prey animals, including humans. When a prey animal has been caught and completely overcome by the predator, it may respond by "freezing up/petrification" or in other words by uncontrollably becoming rigid or limp. Studies typically assess a conditioned freezing behavior response to stimuli that typically or innately do not cause fear, such as a tone or shock. Freezing behavior is most easily characterized by changes in blood pressure and lengths of time in crouching position, but it also is known to cause changes such as shortness of breath, increased heart rate, sweating, or choking sensation. However, since it is difficult to measure these sympathetic responses to fear stimuli, studies are typically confined to simple crouching times. A response to stimuli typically is said to be a "fight or flight", but is more completely described as "fight, flight, or freeze". In addition, freezing is observed to occur before or after a fight or flight response.