Why are reflexes involuntary

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Neuroscience in the News Check out the latest news from the field. Neuromyths Do you believe any of these common neuromyths? Like Subscribe Follow Follow Subscribe. About BrainFacts. Imagine a typical day. You might be thinking of practicing your sport or musical instrument, walking to school, or making a snack. In all of these actions, you are thinking, but at the same time, there are also reflexes that you are unaware of happening inside your body.

These reflexes are built naturally into the body, and they exist at birth and change as we grow older. Reflexes are kind of like safety features for survival that allow us to move in response to something in the environment.

Reflexes can act to protect you in many ways, including removing your hand from a hot or sharp object, or ducking when a loud and sudden sound occurs. These fast actions are reflex responses! The fact that these responses are automatic shows that reflexes occur at a rate that is far too fast for the brain to be involved with the response. Actions that occur without the involvement of the brain are called involuntary actions, while planned actions from the brain, like throwing a ball or strumming a guitar, are called voluntary actions.

After the reflex action has happened, the brain does become aware and tells you what happened. At this point, the brain might even add to the action. For example, you might have ducked as an involuntary response to a very loud noise, but when the brain becomes involved you learn why you ducked down and the brain sends the voluntary action to respond—maybe to stand back up.

In order for reflexes to work, messages need to move around the body. These messages are action potentials , and they travel along the neurons and send messages, special parts of the neurons are involved. The neuron has three different parts that allow signals to be sensed, to travel, and then move to another neuron or muscle. These three parts are called the dendrites, the axon, and the nerve ending Figure 1. The dendrites receive information from the sensor or other neurons. This information then moves to the axon, which travels to or from the spinal cord.

The action potential travels from the nerve endings at one end of the neuron to the next neuron. Many reflexes start at the muscle or skin and go to the spinal cord. When the action potential reaches the nerve ending, the signal is transferred to another neuron, such as an interneuron or motor neuron.

The action potential then travels outside the spinal cord to a muscle. But the neurons do not touch each other in the spinal cord and do not touch at the muscle. There are tiny spaces called synapses that the action potential must jump across. Reflex actions are therefore essential to the survival of many organisms. A reflex action follows this general sequence and does not involve the conscious part of the brain. This is why the response is so fast.

The nerve pathway followed by a reflex action is called a reflex arc. While this is considered a simple reflex, many pages could be filled exploring its technical details. A muscle is stretched by the hammer hitting a tendon, and an electrical signal is sent to the spinal cord, which sends out a signal to tense the muscle to return it to its proper length.

The result is a brief jerking motion, and the knee kicks out. No electrical signal ever needs to reach the brain for this reflex to occur. Neurologists use different reflexes to see how different parts of the nervous system are functioning.

For example, for the knee-jerk reflex to work, the nerves to and from the muscle must be intact, and the spinal cord needs to be working at that level. Similarly, a brainstem reflex, such as the pupils constricting to light, can help a neurologist know that the brainstem is working properly. Furthermore, reflexes are moderated by many other things in the body.

For example, the brain usually sends impulses down the spinal cord that keeps reflexes like the knee-jerk relatively calm.

After a stroke or other injury to the brain, the calming influence on the reflex is slowly lost, and this results in reflexes being hyperactive. Sometimes a reflex can look a lot like conscious behavior.

This can happen even if an electrical signal never reaches the brain—it can be completely orchestrated by the spinal cord. Not knowing everything that reflexes do for us saves us a lot of trouble in day-to-day life. However, knowing about reflexes and how to test them can shed a lot of light on how the nervous system works and where a problem may lie in a nervous system disorder.

Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. What is a reflex? A guide for understanding disorders of consciousness.