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 sensing receptors in the skin and core detect the drop in temperature and signal the hypothalamus. The hypothalamus then increases sympathetic output to skeletal muscles, triggering rhythmic, involuntary contractions that constitute shivering. This rapid muscle activity raises heat production by boosting metabolic activity in the muscles, helping to restore body temperature. This process is distinct from non-shivering thermogenesis in brown adipose tissue and from the longer-term effects of thyroid hormones, which do not initiate the immediate shivering response.