Shivering is an involuntary muscular response that occurs when the body senses a drop in temperature, rapidly generating heat through muscle contractions. While the body’s initiation of shivering is understood, the physiological mechanisms that cease this response once thermal balance is regained are equally important. This article explores the internal and external mechanisms that signal the body to stop shivering and restore optimal body temperature.
The Body’s Internal Thermostat
The human body maintains a stable internal temperature, typically around 37 degrees Celsius (98.6 degrees Fahrenheit), a process known as thermoregulation. This stability is crucial for the proper functioning of metabolic processes within cells. The primary control center for this regulation is the hypothalamus, a region located in the brain.
Within the hypothalamus, specifically in the preoptic area, lies the body’s thermoregulatory center, acting much like a thermostat. This center establishes a “set point” temperature that the body strives to maintain. When the body’s core temperature deviates from this set point, the hypothalamus detects the change and triggers appropriate responses, such as initiating shivering when it becomes too cold.
The hypothalamus constantly receives information about the body’s temperature from specialized nerve cells called thermoreceptors. These sensors are distributed throughout the body, both peripherally in the skin and centrally in areas like the viscera, spinal cord, and within the hypothalamus itself. This continuous monitoring allows the brain to assess the thermal state and respond to temperature fluctuations.
Sensing When to Stop Shivering
Once shivering begins and the body starts generating heat, a feedback loop informs the brain that core temperature is rising. This signaling relies on the same network of thermoreceptors that initially detected the cold. As the body warms, these sensors continuously monitor the temperature changes.
Peripheral thermoreceptors in the skin detect the increasing surface temperature, while central thermoreceptors, particularly those in the hypothalamus, sense the warming of core body tissues. These receptors translate the temperature increase into nerve impulses, which are then relayed back to the hypothalamic thermoregulatory center.
The hypothalamus acts as an integrator, comparing the incoming temperature signals with the established set point. As the signals indicate that the core temperature is approaching or has reached the desired range, this input informs the brain that the need for active heat generation, such as shivering, is diminishing. This continuous sensory feedback is important for the precise control of thermoregulation.
How the Brain Turns Off Shivering
Once the hypothalamus receives sufficient signals indicating that core body temperature is returning to the set point, it actively works to inhibit the shivering response. The posterior hypothalamus contains a motor center responsible for initiating shivering, which is normally held in check by inhibitory signals from the anterior hypothalamic-preoptic area.
As warming occurs, the preoptic area of the hypothalamus modulates neuronal activity. It reduces the activity of cold-sensitive neurons and increases the activity of warm-sensitive neurons. This shift leads to a decrease in excitatory signals that drive heat production and an increase in inhibitory signals.
The hypothalamus sends these inhibitory signals through neural pathways to motor centers in the brainstem and spinal cord. This active inhibition effectively reduces or ceases the involuntary muscle contractions that characterize shivering.
External and Internal Aids to Stop Shivering
While the brain controls the cessation of shivering, various internal and external factors contribute to the body warming sufficiently for this process to occur. Shivering itself is an effective internal mechanism for generating heat, as the rapid muscle contractions produce warmth as a byproduct of metabolic activity. This internal heat production helps to raise core body temperature towards the set point.
External measures also accelerate the warming process. Donning additional layers of clothing, seeking shelter from cold environments, or consuming warm beverages can quickly reduce heat loss and introduce external warmth. Engaging in physical activity, such as walking or jumping jacks, further increases internal heat generation.
These actions directly impact the temperature signals received by the thermoreceptors, providing the necessary input for the hypothalamus to activate its “off” switch more rapidly. Without these external and internal aids, the body’s internal mechanisms would take longer to achieve the thermal balance required to stop shivering.