What is the gamma loop?
The gamma loop (also referred to as the alpha-gamma loop) is a feedback loop in our nervous system that regulates the level of tension in our muscles. The way the gamma loop works can get a little confusing, so in this post I’m going to explain it as simply as possible and focus on why the gamma loop is so important.
In future posts I’ll talk about two closely related topics: how the stretch reflex (myotatic reflex) works, and how we build up residual muscle tension.
What is a muscle spindle?
Before I explain the components of the gamma loop and how it works, I want to introduce an important part of the gamma loop: the muscle spindle.
Muscle spindles are a specific type of sensory receptor known as proprioceptors. Proprioception is how we sense our body in space, and muscle spindles help us sense the position of our body by giving us feedback about the length of our muscles.
Muscle spindles are located within our skeletal muscles, where they detect changes in the length of our muscles. For this reason they are also referred to as stretch receptors.
How the gamma loop works
The gamma loop is made up of alpha and gamma motor neurons, sensory neurons, muscle spindles, and skeletal muscle. The gamma loop operates between the spinal cord and the muscles, quickly and automatically regulating the level of tension in our muscles.
Alpha motor neurons control the contraction of skeletal muscle, while gamma motor neurons control the contraction of muscle fibers located within the muscle spindle.
When our brain sends the message down to the alpha motor neurons to contract a muscle, our gamma motor neurons get the message to contract the muscle fibers within the muscle spindle as well. This is called alpha-gamma coactivation, and it occurs so that the muscle spindle always stays active and able to sense changes in muscle length.
As you can see in the diagram below, there are sensory neurons wrapped around the muscle spindle. These sensory neurons sense changes in the length of the muscle spindle and send this information to the alpha motor neuron, allowing it to regulate the length of the skeletal muscle. So, our muscle length is determined both by descending messages from the central nervous system (CNS) and by the automatic activity that occurs within the gamma feedback loop.
We could get into more detail about how the gamma loop works, but I think it’s more important that you understand how the gamma loop affects you and how you can control its function.
Why is the gamma loop so important?
When the gamma loop is working properly, everything is great. We contract our muscles when we need to use them, and they automatically relax when we’re done moving.
However, throughout our lives we develop learned motor patterns—habitual ways of standing and moving. As a result of this process of developing muscle memory, we tend to contract certain muscles in the same patterns over and over. When repeated muscle contraction is signaled by the brain, the gamma loop can get out of whack.
When gamma motor neurons become overactive, or when the firing of alpha and gamma motor neurons becomes imbalanced, we experience an increased level of muscle tension, muscle spasms, and even spasticity or rigidity.
This is why the gamma loop is so important. When we lose the ability to fully control and release our muscles, bad things happen. Tight muscles are sore and painful, they pull our skeleton out of alignment, compress our joints, increase our risk of injury, and elevate our blood pressure. Muscle spasticity and rigidity limit our ability to walk, go about our normal daily life, and do any activity requiring fine motor control.
If you’re thinking, “Gosh, those poor people whose gamma loops have gotten out of whack,” take a look in the mirror. Virtually everyone has a higher than normal level of tension in some muscles in their body, and this tension is a result of gamma loop activity.
As we develop habitual ways of standing and moving, and contract our muscles in the same ways over and over, our gamma loop activity adapts by gradually allowing the resting level of tension in our muscles to get higher and higher. Without conscious intervention, this buildup of muscle tension continues throughout our lives. This is why we tend to become stiff, tight, and have limited movement as we get older: it’s a buildup of muscle tension, plain and simple.
Can we control gamma loop activity?
Yes, we can! Even though our muscle tension and habitual posture and movement can feel out of our control, we can absolutely retrain our learned motor patterns and adjust gamma loop activity by providing our nervous system with biofeedback.
Our pandicular response is the way that we instinctively respond to a buildup of tension in our muscles. If you’ve ever seen a dog or cat arch their back when they get up from a nap, or watched a baby stretch their arms and legs as they wake up, you’ve witnessed the pandicular response.
Thomas Hanna used our natural pandicular response as the basis for his movement technique of voluntary pandiculation. This technique of voluntary pandiculation is the basis of Hanna’s method of Clinical Somatic Education, which releases muscle tension, relieves pain, restores natural posture and movement, and alleviates many common musculoskeletal conditions.
Our natural pandicular response and voluntary pandiculation both provide our nervous system with information about the level of contraction within our muscles. Pandiculating our muscles gradually restores a normal level of gamma motor neuron firing and reduces the level of muscle tension being set by the gamma loop.
It’s important to understand that external manipulation like passive stretching, massage, and chiropractic work has little to no lasting effect on gamma loop activity because it doesn’t involve any active movement on your part. Slow, conscious, active movement is necessary to change learned motor patterns and to adjust the level of gamma motor neuron firing.