Which of the following is an example of negative feedback in the human body?

While waiting for a bus on a very cold winter day, your body temperature starts to drop. Specialized cells in your preoptic area (POA) of the hypothalamus register a drop in your internal body temperature. Cells in the hypothalamus integrate that information and activate nerve cells that cause muscles around the blood vessels leading to the skin and extremities to contract. When these muscles contract, less blood flows to the skin and extremities. What is the effector in this scenario?