Shivering (also called shuddering) is a bodily function in response to cold and extreme
fear
Fear is an unpleasant emotion that arises in response to perception, perceived dangers or threats. Fear causes physiological and psychological changes. It may produce behavioral reactions such as mounting an aggressive response or fleeing the ...
in
warm-blooded
Warm-blooded is a term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species (including birds and mammals) maintain a stable body temperature by regulating ...
animals.
When the core
body temperature
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
drops, the shivering
reflex is triggered to maintain
homeostasis
In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...
.
Skeletal muscles begin to shake in small movements, creating warmth by expending
energy
Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...
. Shivering can also be a response to
fever
Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...
, 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), but also makes a person feel cold until the new set point is reached.
Biological basis
Located in the posterior
hypothalamus
The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...
near the wall of the
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 animal coverings, such as the arthropod exoskeleton, have different ...
and
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
and becomes activated when the body temperature falls even a fraction of a degree below a critical temperature level. The center then causes rapid contractions of skeletal muscles, producing heat as a byproduct.
Newborn babies, infants, and young children experience a greater (net) heat loss than adults because of greater
surface-area-to-volume ratio
The surface-area-to-volume ratio or surface-to-volume ratio (denoted as SA:V, SA/V, or sa/vol) is the ratio between surface area and volume of an object or collection of objects.
SA:V is an important concept in science and engineering. It is use ...
. As they cannot shiver to maintain body heat, they rely on
non-shivering thermogenesis. 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 (or white fat). Brown adipose tissue is found in almost all mammals.
Classification of brown fat refers to two distinct cell populations with si ...
(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 compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...
. Norepinephrine will react with lipases in
brown fat to break down fat into
triglycerides
A triglyceride (from ''wikt:tri-#Prefix, tri-'' and ''glyceride''; also TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids.
Triglycerides are the main constituents of body fat in humans and oth ...
. Triglycerides are then metabolized to
glycerol
Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...
and non-esterified fatty acids.
These are then further degraded in the needed heat-generating process to form CO
2 and water.
Chemically, in
mitochondria
A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...
, the proton gradient producing the
proton electromotive force that is ordinarily used to synthesize
ATP is instead bypassed to produce heat directly.
Shivering can also appear after surgery. This is known as
postanesthetic shivering.
In humans, shivering can also be caused by cognition. This is known as
psychogenic shivering.
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
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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 Tickling, tickled, cold or experiencing strong emotions such as fear, euphoria or sexual arousa ...
*
Myoclonus
*
Post micturition convulsion syndrome
In neurourology, post-micturition convulsion syndrome (PMCS), also known informally as pee shivers or piss shivers, is the experience of shivering during or after urination. The syndrome seems to be experienced more often by men than women.
The ...
*
Chattering teeth
*
Tremor
A tremor is an involuntary, somewhat rhythmic muscle contraction and relaxation involving neural oscillations, oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the h ...
References
External links
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* {{MeshName, Shivering
Reflexes