Shivering (also called shuddering) is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by expending energy. Shivering can also be a response to a fever, as a person may feel cold, though their core temperature is already elevated.
Located in the posterior hypothalamus near the wall of the third ventricle is an area called the primary motor centre for shivering. This area is normally inhibited by signals from the heat centre in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord. Therefore, this centre 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.
Shivering can also appear after surgery. This is known as postanesthetic shivering.
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. Children have an increased amount of Brown Fat (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 CO2 and water. 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.
Shivering should not be confused with chills or rigor, which is a shaking occurring during a high fever.
Famous quotes containing the word shivering:
“As in hoary winter’s night stood shivering in the snow,
Surprised I was with sudden heat which made my heart to glow;
And lifting up a fearful eye to view what fire was near,
A pretty Babe all burning bright did in the air appear;”
—Robert Southwell (1561?–1595)
“The shivering birds beneath the eaves
Have sheltered for the night.”
—Claude McKay (1889–1948)
“... it is an uneasy lot at best, to be what we call highly taught and yet not to enjoy: to be present at this great spectacle of life and never to be liberated from a small hungry shivering self—never to be fully possessed by the glory we behold, never to have our consciousness rapturously transformed into the vividness of a thought, the ardour of a passion, the energy of an action, but always to be scholarly and uninspired, ambitious and timid, scrupulous and dim-sighted.”
—George Eliot [Mary Ann (or Marian)