Reflex

In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes help organisms react quickly to things around them without needing to think first.

Reflexes are found in animals that have a nervous system. They work through special paths in the nervous system called reflex arcs. When something touches or startles an animal, a signal travels through these paths to create a quick reaction. Often, these signals do not go to the brain, allowing the animal to respond fast.

Many reflexes help keep animals safe. For example, the startle reflex makes an animal jump or move quickly when something sudden happens. Another example is the feline righting reflex, which helps a cat twist its body when falling to land safely. These quick actions help animals protect themselves and survive.

Types of human reflexes

A reflex is a quick, automatic response to something that happens around you. It happens without you thinking about it first. Your body uses special paths in the nervous system to make these responses happen very fast.

Some reflexes happen when a muscle is stretched, like when a doctor taps your knee and your leg jumps up. Others happen when something touches a tendon, like a special spot in your arm. Babies are born with many reflexes that help them respond to the world before they learn anything. For example, a baby might grasp your finger when you touch their palm or turn their head when something touches one side of their cheek. These reflexes help babies stay safe and healthy until they can think and learn more.

Grading

In medicine, reflexes help doctors check how well the nervous system is working. Doctors look at how strong a reflex is and give it a number from 0 to 4. A score of 2 or higher is usually normal. Some people might have weaker reflexes, scoring around 1, while others might have stronger reflexes, scoring around 3.

Reflex modulation

Some people think reflexes are always the same, but they can actually change to help us move better. For example, when a muscle is stretched while we are standing still, it tightens up to help us stay balanced. But when we start moving on purpose, this tightening lessens so it doesn’t get in the way.

We still don’t fully understand how these changes happen, but we know that special cells in our nerves help control reflexes. These changes happen in parts of our spinal cord or nerve system and also get help from signals sent from our brain.

Other reflexes

Breathing is both something we do without thinking and something we can control. For example, we can hold our breath by using special muscles in our chest called internal intercostal muscles.

History

The idea of reflexes began in the 1600s with René Descartes. In his work "Treatise on Man", Descartes explained how the body can react automatically to things around it without thinking. He compared this to a statue that moves in response to touch.

Later, in the 1800s, Marshall Hall introduced the term "reflex". He studied how the body makes quick, automatic movements in response to stimuli, using the spinal cord and nervous system instead of the brain's conscious control. Hall shared his findings in a paper from 1833 in the Philosophical Transactions of the Royal Society.