Shivering is a bodily function in response to early hypothermia in warm-blooded animals. Hypothermia is a condition in which an organism's temperature drops below that required for normal Metabolism and bodily functions In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant When the core body temperature drops, the shivering reflex is triggered. Core temperature, also called core body temperature, is the operating Temperature of an Organism, specifically in deep structures of the body such as the A reflex action, also known as a reflex, is an involuntary and almost instant movement in response to stimulus. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by expending energy. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Shivering can also be a response to a fever as a person may feel cold, though their core temperature is already elevated. Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris
Located in the dorsomedial portion of the hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering. The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis The third ventricle ( ventriculus tertius) is one of four connected fluid-filled cavities comprising the Ventricular system within the human Brain. This area is normally inhibited by signals from the heat center in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord. The skin is the outer covering of living tissue of an animal (or plant The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected Therefore, this center becomes activated when the body temperature falls even a fraction of a degree below a critical temperature level.
Increased muscular activity results in wasted heat - here the heat is utilized for warmth.
Shivering can also appear after surgery. This is known as post-surgical shivering.