Shivering

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 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 a 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 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 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.