Shivering
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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 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 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.
Understanding shivering
[edit]When understanding the concept of shivering it is important to understand the human physiological responses to cold exposure. There are many reactions that humans have to the cold such as “cutaneous vasoconstriction and shivering thermogenesis” these processes “decrease heat loss and increase metabolic heat production”. [1]
Cutaneous vasoconstriction is the narrowing of blood vessels in the skin reducing blood flow and heat loss to environmental temperatures. This process is one of the many natural defenses' humans have against cold temperatures.
Thermogenesis (shivering) is when the body comes in contact with cold temperatures in the environment and the body feels as though it needs to raise its core body to protect itself. This is a primary trigger for the mechanism of heat production in mammalian bodies when exposed to cold. This process generates heat though high speed contractions of the skeletal muscles. It begins by having the hypothalamus triggering a signal in the muscles to contract and relax making heat the excess product of the rapid muscle movement that the process causes.[1]
Biological basis
[edit]Located in the posterior hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering.[2] 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.[3]
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.[4]
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,[5] 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.[6] Norepinephrine will react with lipases in brown fat to break down fat into triglycerides.[7] Triglycerides are then metabolized to glycerol and non-esterified fatty acids.[8] These are then further degraded in the needed heat-generating process to form CO2 and water.[8] Chemically, in mitochondria, the proton gradient producing the proton electromotive force that is ordinarily used to synthesize ATP is instead bypassed to produce heat directly.[9]
Shivering can also appear after surgery. This is known as postanesthetic shivering.
In humans, shivering can also be caused by cognition.[10] This is known as psychogenic shivering.[11][12]
Shivering and the elderly
[edit]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.[13]
See also
[edit]References
[edit]- ^ a b Castellani, John W.; Young, Andrew J. (2016-04-01). "Human physiological responses to cold exposure: Acute responses and acclimatization to prolonged exposure". Autonomic Neuroscience. Thermoregulation. 196: 63–74. doi:10.1016/j.autneu.2016.02.009. ISSN 1566-0702.
- ^ Bear, Matthew H.; Reddy, Vamsi; Bollu, Pradeep C. (2022-10-10), "Neuroanatomy, Hypothalamus", StatPearls [Internet], StatPearls Publishing, PMID 30252249, retrieved 2025-03-10
- ^ "Regulation of body temperature by the nervous system".
- ^ McCuller, Christopher; Jessu, Rishita; Callahan, Avery L. (2025), "Physiology, Skeletal Muscle", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30725824, retrieved 2025-03-10
- ^ "Muscle Non-shivering Thermogenesis and Its Role in the Evolution of Endothermy".
- ^ Gilsanz, Vicente; Hu, Houchun H.; Kajimura, Shingo (2012-10-22). "Relevance of brown adipose tissue in infancy and adolescence". Pediatric Research. 73 (1): 3–9. doi:10.1038/pr.2012.141. ISSN 0031-3998. Archived from the original on 2025-02-04.
- ^ Zhou, Anqiang; Kondo, Mari; Matsuura, Yukinaga; Kameda, Kenji; Morimoto, Chie; Tsujita, Takahiro; Okuda, Hiromichi (1995-04-01). "Mechanism of norepinephrine-induced lipolysis in isolated adipocytes: evidence for its lipolytic action inside the cells". Pathophysiology. 2 (1): 29–34. doi:10.1016/0928-4680(95)00004-K. ISSN 0928-4680.
- ^ a b "Triglycerides". eClinpath. Retrieved 2025-03-10.
- ^ Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2002), "Electron-Transport Chains and Their Proton Pumps", Molecular Biology of the Cell. 4th edition, Garland Science, retrieved 2025-03-10
- ^ Goldstein A. (1980). Thrills in response to music and other stimuli. Physiol. Psychol. 8, 126–129.
- ^ Schoeller, F., Eskinazi, M., Garreau, D. (2018) Dynamics of the knowledge instinct: Effects of incoherence on the cognitive system. Cognitive Systems Research 47: 85-91.
- ^ Oka, T. (2015). Psychogenic fever: how psychological stress affects body temperature in the clinical population. Temperature: Multidisciplinary Biomedical Journal, 2(3), 368–378. http://doi.org/10.1080/23328940.2015.1056907
- ^ Ring, Francis J. and Phillips, Barbara, Recent Advances in Medical Thermology, pp. 31-33; Springer Publishing, 1984
External links
[edit]
Media related to Shivering at Wikimedia Commons- Shivering at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
