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Shivering (also called shuddering) is a bodily function in response to cold and extreme
fear Fear is an intensely unpleasant emotion Emotions are mental state, psychological states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavioural responses, and a degree of pleasure ...

fear
in warm-blooded animals. When the core
body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a sy ...
drops, the shivering
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...

reflex
is triggered to maintain
homeostasis In , homeostasis is the state of steady internal, , and conditions maintained by . This is the condition of optimal functioning for the organism and includes many variables, such as and , being kept within certain pre-set limits (homeostatic r ...
. Skeletal muscles begin to shake in small movements, creating warmth by expending
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
. Shivering can also be a response to a
fever Fever, also referred to as pyrexia, is defined as having a temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on th ...

fever
, as a person may feel cold. During fever the hypothalamic set point for temperature is raised. The increased set point causes the body temperature to rise (
pyrexia Fever, also referred to as pyrexia, is defined as having a temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on th ...
), but also makes the patient feel cold until the new set point is reached. Severe
chills Chills is a feeling of coldness occurring during a high fever, but sometimes is also a common symptom which occurs alone in specific people. It occurs during fever due to the release of cytokines and prostaglandins as part of the Inflammation, ...
with violent shivering are called rigors. Rigors occur because the patient's body is shivering in a physiological attempt to increase body temperature to the new set point. Located in the posterior
hypothalamus The hypothalamus (from Ancient Greek wikt:ὑπό, ὑπό, "under", and wikt:θάλαμος, θάλαμος, "chamber") is a portion of the brain that contains a number of small Nucleus (neuroanatomy), nuclei with a variety of functions. One of ...

hypothalamus
near the wall of the
third ventricle The third ventricle is one of the four connected ventricles of the ventricular system The ventricular system is a set of four interconnected cavities known as ventricles in the brain A brain is an organ (anatomy), organ that serves as the c ...

third ventricle
is an area called the primary motor center for shivering. 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 Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differ ...

skin
and
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system In Biology, biology, the nervous system is a Complex system, high ...

spinal cord
. 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 the generation of heat as a byproduct. Most often, when the purpose of the muscle activity is to produce motion, the heat is wasted energy. In shivering, the heat is the main intended product and is utilized for warmth. Newborn babies, infants, and young children experience a greater (net) heat loss than adults because they cannot shiver to maintain body heat . They rely on
non-shivering thermogenesis Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily, and the giant water lilies of the genus ''Vic ...
. Children have an increased amount of
brown adipose tissue Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue White adipose tissue (WAT) or white fat is one of the two types of adipose tissue Adipose tissue, body fat, or simply fat is a loose connective ...
(increased vascular supply, and high mitochondrial density), and, when cold-stressed, will have greater oxygen consumption and will release
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
. Norepinephrine will react with lipases in
brown fat Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue White adipose tissue (WAT) or white fat is one of the two types of adipose tissue Adipose tissue, body fat, or simply fat is a loose connective ...
to break down fat into
triglycerides 300px, Example of an unsaturated fat triglyceride (C55H98O6). Left part: glycerol; right part, from top to bottom: palmitic acid, oleic acid">palmitic_acid.html" ;"title="glycerol; right part, from top to bottom: palmitic acid">glycerol; right par ...
. Triglycerides are then metabolized to
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
and non-esterified fatty acids. These are then further degraded in the needed heat-generating process to form CO2 and water. Chemically, in
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
the proton gradient producing the
proton electromotive force An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in Concentration, solute concentration across a mem ...
that is ordinarily used to synthesize
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
is instead bypassed to produce heat directly. Shivering can also appear after surgery. This is known as
postanesthetic shivering Postanesthetic shivering (PAS) is shivering after anesthesia. The intensity of PAS may be graded using the scale described by Crossley and Mahajan: :0 = no shivering; :1 = no visible muscle activity but piloerection, peripheral vasoconstriction, ...
. In humans, shivering can also be caused by mere cognition. This is known as
psychogenic shivering A psychogenic effect is one that originates from the brain A brain is an organ (anatomy), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sens ...
.


Shivering and the elderly

The functional capacity of the thermoregulatory system alters with aging, reducing the resistance of elderly people to extreme external temperatures. The shiver response may be greatly diminished or even absent in the elderly, resulting in a significant drop in mean deep body temperature upon exposure to cold. Standard tests of thermoregulatory function show a markedly different rate of decline of thermoregulatory processes in different individuals with ageing.Ring, Francis J. and Phillips, Barbara, Recent Advances in Medical Thermology, pp. 31-33; Springer Publishing, 1984


See also

*
Goose bumps Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold , a common physiological response to cold, aiming to reduce the loss of bo ...

Goose bumps
*
Myoclonus Myoclonus is a brief, involuntary, irregular (lacking rhythm) twitching (different from clonus, which is rhythmic/ regular) of a muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are large bio ...
*
Post micturition convulsion syndrome In Urology#Neurourology, neurourology, post-micturition convulsion syndrome (PMCS), also known informally as pee shivers, is the experience of shivering during or after urination. The syndrome appears to be more frequently experienced by males. The ...
*
Tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction Muscle contraction is the activation of tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opp ...


References


External links

* {{MeshName, Shivering Reflexes