Reflex: Definition, Types & Examples

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  • 0:00 Definition of Reflex
  • 1:05 Types of Reflexes
  • 3:35 Common Reflexes and Examples
  • 6:25 Lesson Summary
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Lesson Transcript
Instructor: Nadine James

Nadine has taught nursing for 12 years and has a PhD in Nursing research

In this lesson, you will learn about reflexes in the human body. Different types of reflexes will be discussed and examples will be provided when appropriate. Finally you will be able to test your knowledge of the content by taking the quiz.

Definition of Reflex

Have you ever burnt yourself on a stove? What happened when you put your hand on the stove when it was hot? Did you have to say, 'Wow that is hot; I need to remove my hand!'? No! You moved your hand immediately because of a reflex. Reflex, or reflex action, is the involuntary movement of any organ or body part that has received a stimulus. It happens without any consciousness and is immediate. Reflexes protect the body from harm.

So, how did that reflex happen after you touched the stove? In your hand are nerve endings that pick up a stimulus and carry it to the spinal column and brain. The nerve ending (in this case of burning your hand) is called a sensory neuron (also known as an afferent neuron) because it takes the stimulus - heat to the hand - to the spinal column and brain for interpretation. The brain then interprets the stimulus and sends a message back to the muscles in the hand by a motor neuron (also called an efferent neuron).

The process of the sensory neuron carrying the stimulus to the spinal column and brain, and then the brain sending a message to the motor neuron is called a reflex arc.

Types of Reflexes

There are several ways to classify the types of reflexes in the body.

First, let's talk about the type or function of reflex. Reflexes can be classified according to the type and function of the muscles or organs that move or function because of the reflex. Some reflexes that move skeletal muscles are called: flexor, extensor, locomotor, and statokinetic. Reflexes that involve functions of internal organs include digestive, cardiovascular, excretory, and secretory.

Next, we can talk about the degree of complexity of the reflex. Reflexes are classified according to the degree of complexity of the neuron (nerve) organization within the reflex arcs. In this classification, there are monosynaptic (or monosegmental) reflexes, which involve only one segment of the central nervous system, and multisynaptic (or intersegmental) reflexes, which involve more than one segment of the central nervous system.

So, let's dive into this topic a bit more. You probably already know that mono means one and multi means more than one. But, what does that mean in relation to synapses? Monosynaptic means there is only one neuron involved each way on the path to the spinal cord (called an afferent or sensory neuron) and one away from the spinal cord (called an efferent or motor neuron). An example of a monosynaptic reflex is the patellar (knee jerk) reflex.

A multisynaptic reflex, as you can guess, is more complex. In the simplest form, a multisynaptic reflex has more than one neuron (called interneurons) within the reflex arc process. It also involves more than one area of the central nervous system - usually the spinal cord and the brain. An example of this type is the flexor reflex.

Finally, let's look at the influence on muscle or organ of the reflex. Reflexes can have an excitatory (often known as facilitating) action or an inhibitory (weakening and suppressing) activity. For example, we can examine the reflex actions on the heartbeat. The excitatory reflex of the sympathetic nerve will increase the heartbeat. To decrease the heartbeat, or even stop the heartbeat, the vagus nerve is the inhibitory reflex.

Common Reflexes and Examples

The stretch reflex is one of the simplest reflexes and is monosynaptic. It contracts a muscle that is being stretched and contributes to balance and coordination. A deep tendon reflex is an example of a stretch reflex. How does this work? When you're standing up, your knees bend slightly, and without the deep tendon reflex located around your knees, you could fall. That reflex will straighten your knees and keep you standing upright if you lose your balance. Aside from the knees, deep tendon reflexes are located along the outside of your elbows, in the crooks of your arms, and at your wrists and ankles. This is the same reflex that the doctor checks around your knee.

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