Nerve reflexes

Ouch. Leon burned his hand. Did you notice how he pulled his hand back in a flash? You've surely done that yourself a few times, if you burned your hand on a stove or a candle. You pull your hand back, without controlling it.

It just happens. But why? How does it work? To understand that, we need to understand some things about the nervous system. If you haven't seen that film, please watch it first.

The nervous system is a network of cords, nerves, throughout the body that sends signals back and forth. The brain is also a part of the nervous system. From the brain runs a collection of nerve cords. It's contained in the spine and is called the spinal cord. Together, the nerves, the brain, and the spinal cord form the nervous system.

The nerves send signals about everything we feel. When a cat rubs against your leg, the touch is registered by sensory cells. The touch is converted into a nerve signal that's transmitted, first to the spinal cord, and then on, to the brain. Then the brain can detect and interpret the signal. "A cat is rubbing against my leg", the brain analyses. But if it's a sensation of pain, like when you burn your finger, something else happens.

The sensory nerves in Leon's hand registered that he burned it. They sent a pain signal to the spinal cord. And then the nifty thing happened. The spinal cord sent an instant signal to the muscle of the arm with the message: "Pull the hand away at once!" Leon's arm obeyed straight away. It couldn't do anything else.

At the same time, the spinal cord passed the signal on to the brain and made Leon aware of what happened. "Ow! I burned my finger, and pulled my hand away", the brain noted. This function in the spinal cord is there to protect us from whatever can hurt us, for instance heat that may cause damage to the skin. The function is a reflex. So now you know what made Leon pull back his arm when he burned a finger.

The nerves and the spinal cord acted on their own, without asking the brain: A reflex. Are there other kinds of reflex? Yes, several of them. One example - which you surely have experienced yourself - is when something touches your open eye. The reflex from the spinal cord makes you close the eye immediately.

This is nothing you can decide. It happens, without the brain being involved. And a newborn child shows a number of reflexes, already when it's a few seconds old. For example, it grasps what's placed in its palm. All infants do that.

The reflexes mentioned so far are with us from birth. We don't need to practice them. Such reflexes are innate. But you can train certain reflexes. Whoever has learnt to ride a bike can perform a complex interplay of muscles and sensory input, where a series of reflexes are combined.

Such reflexes are learned. -- Feel better, Leon? Good. So hey! Think fast! Nice learned reflex, Leon!