Shivering (also called shuddering) is a bodily function in response to cold and extreme
fear in
warm-blooded animals. When the core
body temperature drops, the shivering
reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
is triggered to maintain
homeostasis. Skeletal muscles begin to shake in small movements, creating warmth by expending
energy. Shivering can also be a response to
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), 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 inflammatory r ...
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.
Biological basis
Located in the posterior
hypothalamus 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 and
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 of greater
surface-area-to-volume ratio. As they cannot shiver to maintain body heat, they rely on
non-shivering thermogenesis. Children have an increased amount of
brown adipose tissue (increased vascular supply, and high mitochondrial density), and, when cold-stressed, will have greater oxygen consumption and will release
norepinephrine. Norepinephrine will react with lipases in
brown fat to break down fat into
triglycerides. Triglycerides are then metabolized to
glycerol 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 Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
, the proton gradient producing the
proton electromotive force that is ordinarily used to synthesize
ATP
ATP may refer to:
Companies and organizations
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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 mere 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
*
Goose bumps
*
Myoclonus
*
Post micturition convulsion syndrome
*
Chattering teeth
Chattering teeth is a bodily function in animals that occurs primarily in response to cold; the jaw muscles begin to shiver leading teeth to crash together. It may also occur as a result of bruxism where emotional stress causes the jaw movements. C ...
*
Tremor
A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, fa ...
References
External links
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* {{MeshName, Shivering
Reflexes