Which statement best describes the mechanism initiating shivering thermogenesis in response to cold?

Which statement best describes the mechanism initiating shivering thermogenesis in response to cold?

• A. Cold exposure directly activates brown adipose tissue through parasympathetic signaling to produce heat without neural input.
• B. The hypothalamus reduces sympathetic outflow to skeletal muscles, preventing shivering.
• C. Cold exposure activates skin and core thermoreceptors, signaling the hypothalamus to increase sympathetic outflow to skeletal muscles, producing rhythmic contractions that generate heat.
• D. Thyroid hormones directly cause rhythmic muscle contractions to generate heat.

Answer: (C)

Cold is detected by thermoreceptors in the skin and body core, and these sensors send signals to the hypothalamus, which acts as the body’s thermostat. In response, the hypothalamus increases sympathetic outflow to skeletal muscles. This neural drive leads to rapid, involuntary rhythmic contractions of many muscle fibers—shivering. The energy spent in these contractions raises metabolic heat production, helping to defend body temperature. It’s a neural sequence starting with peripheral and central temperature sensing and ending with motor activity in muscles; parasympathetic input or direct action of thyroid hormones would not initiate this rapid heat-generating response. (Brown fat can contribute to heat via non-shivering thermogenesis when sympathically activated, but the initiation of shivering itself is through skeletal muscle contractions.)