Shivering

Your body shakes when you feel cold.

This shake is called shivering. It happens to warm animals. Your muscles move very fast. These small movements make heat. This helps you stay warm.

Sometimes you shiver when you have a fever. A fever can make you feel cold. You might also shiver if you are very afraid.

Small babies do not shiver like adults. They use a different way to stay warm. They use special fat in their bodies. This helps them stay safe in the cold.

Have you ever felt your body shake from the cold?

This shake is called shivering. It is a way to stay warm. Your brain has a part called the hypothalamus. This part helps control your body heat. When you get too cold, it sends a signal. Your skeletal muscles then shake very fast. These quick movements make heat to warm you up.

Sometimes you shiver when you have a fever. A fever is when your body temperature goes up. During a fever, your brain sets a higher heat level. This makes you feel cold until you reach that level.

Babies and young children shiver differently than adults. They lose heat more easily. They use a special kind of fat to stay warm. This is called brown adipose tissue. This fat helps them make heat without shaking.

As people get older, their bodies change. The shiver response may get smaller or go away. This can make it harder for elderly people to stay warm in the cold.

Have you ever felt your body shake when you are cold? This shaking is called shivering. It is a bodily function for warm-blooded animals. It helps keep your body temperature steady. This steady state is called homeostasis. Shivering can also happen when you feel extreme fear. Sometimes, people shiver when they have a fever too. This happens because the brain sets a higher temperature goal. You feel cold until your body reaches that new level.

Your brain has a special control center for this. It is located in a part called the hypothalamus. A specific area there is the primary motor center for shivering. This center stays quiet when you are warm. The heat center in the anterior hypothalamus usually stops it. However, cold signals from your skin can wake it up. When your temperature drops even a tiny bit, the center activates. It then causes your skeletal muscles to contract very fast. These quick movements create heat as a byproduct.

Scientists have studied how different people react to cold. For example, babies and young children are different from adults. They lose heat much faster than grown-ups do. This is because they have a large surface area compared to their size. Little ones cannot shiver to stay warm like we do. Instead, they use a way called non-shivering thermogenesis. They have a special type of fat called brown adipose tissue. This fat has a high density of mitochondria to help.

This special fat works through a very cool process. When a child is cold, they release a chemical called norepinephrine. This chemical reacts with lipases in the brown fat. The fat breaks down into things called triglycerides. These turn into glycerol and fatty acids. Then, the body breaks those down further. This process creates carbon dioxide and water. In the mitochondria, the body bypasses a normal step. Instead of making ATP, it produces heat directly.

Not everyone shivers in the same way as they age. The way the body controls heat changes over time. This can make it harder for elderly people to handle extreme weather. For some older people, the shiver response may be very small. It might even be gone entirely. This can cause their deep body temperature to drop in the cold. We also see shivering after surgery in some patients. This is known as postanesthetic shivering.

Shivering, also known as shuddering, is a vital bodily function for warm-blooded animals. It serves as a defense mechanism against cold temperatures and extreme fear. The main goal of shivering is to maintain homeostasis. Homeostasis is the process of keeping the body's internal environment stable. When the core body temperature begins to drop, the shivering reflex is triggered. This reflex helps the body generate warmth through physical movement.

The biological process begins in a specific part of the brain. This is located in the posterior hypothalamus near the third ventricle. This area is called the primary motor center for shivering. Under normal conditions, a heat center in the anterior hypothalamic-preoptic area inhibits this center. However, cold signals from the skin and the spinal cord can excite it. When the body temperature falls even a fraction of a degree below a critical level, the center becomes activated. Once active, it causes rapid contractions of the skeletal muscles. These quick muscle movements create heat as a metabolic byproduct.

Shivering is not always caused by the external environment being cold. It can also occur as a response to a fever. During a fever, the hypothalamic set point for temperature is raised. This means the brain's internal thermostat is set to a higher level. This change causes the body temperature to rise, a condition known as pyrexia. Because the body is currently below this new, higher set point, the person feels cold. This feeling of coldness triggers the shivering response to reach the new target.

Infants and young children manage heat differently than adults do. Because they have a larger surface-area-to-volume ratio, they experience greater net heat loss. Unlike adults, young children cannot rely on shivering to maintain their body heat. Instead, they use a process called non-shivering thermogenesis. This process relies on a special type of fat called brown adipose tissue. This tissue has a high mitochondrial density and an increased vascular supply. When a child is stressed by the cold, they will have greater oxygen consumption and release norepinephrine.

The chemical process of non-shivering thermogenesis is quite complex. The norepinephrine reacts with lipases, which are enzymes, in the brown fat. This reaction breaks down the fat into triglycerides. These triglycerides are then metabolized into glycerol and non-esterified fatty acids. These components are further degraded in a heat-generating process to form carbon dioxide and water. Inside the mitochondria, a unique chemical bypass occurs. Normally, a proton gradient produces an electromotive force used to synthesize ATP. In this process, that step is bypassed to produce heat directly.

As humans age, their ability to regulate temperature changes. The functional capacity of the thermoregulatory system alters with age. This can reduce the resistance elderly people have to extreme external temperatures. In many elderly individuals, the shiver response may be greatly diminished or even absent. This lack of response can result in a significant drop in mean deep body temperature when they are exposed to the cold. The rate of decline in these thermoregulatory processes varies significantly between different individuals as they age.

Beyond temperature and fever, shivering can be linked to other states. Some people experience shivering after undergoing surgery. This specific condition is known as postanesthetic shivering. There is also a version of shivering linked to the mind rather than the body. This is called psychogenic shivering, which can be caused by cognition. It can also be a response to intense stimuli, such as music. These different types of shivering show how deeply connected our physical reflexes are to our environment, our biology, and our minds.