The contraction of the muscle causes your lower leg to kick out. You might wonder why such a reflex exists. This type of reflex is important in keeping your balance. When you're standing up, gravity might cause your knee to bend slightly, and this could make you fall if you didn't have the protective DTR to straighten that knee and keep you standing upright.
A doctor often checks for DTRs to make sure that the nervous system is working properly. Aside from the knee, they also can be checked along the outside of the elbows, in the crooks of the arms, and at the wrists and ankles. So the next time your doctor taps you with that little rubber hammer, say, "Hey doc, how are my DTRs? Reviewed by: KidsHealth Medical Experts. Larger text size Large text size Regular text size. This knee-jerk reflex is an example of a simple monosynaptic reflex.
Have you ever noticed that when you touch a sharp or hot object, you pull your hand away rapidly without even thinking about the action? This reaction of removing your hand very quickly is a natural response within your body, designed to protect you [ 1 ].
This quick response is called a reflex , and reflexes occur without conscious thinking or planning, meaning the brain is not involved in them.
This is very different than most behaviors that you do every day, such as playing Lego, combing your hair, cutting your food, or fist bumping, which all involve using the brain. Actually, many reflexes are even faster than the blink of an eye! Although reflexes are super-fast and just happen without you thinking about them, this does not mean that they are bad.
Reflexes protect you and allow you to move around without thinking about every single action and response your body needs to make. It is important that reflexes occur without the need for thinking about them because there are things that happen to your body and forces acting in your body when you move that need to be responded to very quickly. Reflexes allow your body to react in ways that help you to be safe, to stand upright, and to be active. 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 three main types of neuron: sensory, motor and relay. These different types of neurons work together in a reflex action. A reflex action is an automatic involuntary and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot.
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.
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