When your quadriceps contract, your foot kicks up. The muscle spindles in your quadriceps sense the sudden increase in length and automatically send the message to contract your quadriceps to prevent injury and overstretching. When the doctor taps your patellar tendon just below your knee, it stretches your patellar tendon, your quadriceps tendon, and your quadriceps muscles. The knee-jerk reflex is a great example of the stretch reflex. The stretch reflex also prevents us from tearing our muscles, tendons, and ligaments. We’re rarely consciously aware of how the stretch reflex automatically maintains our balance and keeps us from falling over-but we sure would notice if it wasn’t working properly.
When the muscle spindles in those muscles sense that they’re being lengthened, they automatically send the message to contract to correct your posture.
If you suddenly lean to the right side, the postural muscles on the left side of your vertebral column are stretched. One critical function of the stretch reflex is that it helps us stand upright. This means that their messages travel faster and are more important to our survival than the sensations of pain, touch, and temperature. In fact, the neurons carrying the stretch reflex messages back and forth from the spine are among the most heavily myelinated (insulated) in the body. In general, reflexes exist to help us stay alive and avoid injury. Why? To keep us standing upright and to prevent our muscles, tendons, and ligaments from being torn. The alpha motor neuron then tells the skeletal muscle fibers to contract. When one of your skeletal muscles is stretched-either by you pulling on it, someone else pulling on it, or by someone giving you a deep massage-the muscle spindles within that muscle are stretched too.Īs you can see in the diagram below, the sensory axons wrapped around the muscle spindle sense the increase in length and send that information to the alpha motor neuron in the spine. Muscle spindles detect changes in the length of our muscles, and for this reason they’re also referred to as stretch receptors.
Muscle spindles are sensory receptors located within our skeletal muscles (the type of muscles that move our skeleton around, in contrast to the smooth muscle of our internal organs). Muscle spindles play an important role in our stretch reflex. If you’re not familiar with the gamma loop, you can read What is the Gamma Loop? The stretch reflex is a function of the gamma loop, a feedback loop in our nervous system that regulates the level of tension in our muscles. Unfortunately, stretching usually doesn’t accomplish much, mainly due to the myotatic reflex, more commonly referred to as the stretch reflex. If we’re involved in sports or physical training, we stretch to warm up, cool down, and during breaks to help us stay loose. What is the stretch reflex (myotatic reflex)?įrom a young age, we’re taught that stretching is a necessary part of any workout routine.
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