In this video, we're going to be learning about proprioceptors. Proprioceptors are located in our musculoskeletal system and they help us with our sense of proprioception, understanding where our body is and how our body is moving through space. There are three types of proprioceptors. First, we have muscle spindles. Muscle spindles are located in our skeletal muscles and are composed of intrafusal muscle fibers, which you see here in red, with sensory fibers wrapped around them, shown in yellow. These are enclosed in a connective tissue capsule, depicted in purple. They monitor muscle stretch. For example, spindles monitor stretch is one way to remember that. These will initiate a stretch reflex if they detect too much stretch in your muscle or very unexpected, sudden stretching. We will have an entire video on those coming up for you later in the course.
Next, we have Golgi tendon organs, located in our tendons, consisting of sensory nerve endings coiled between collagen fibers. These monitor muscle tension. Remembering that tendon organs monitor tension can help. They will initiate a tendon reflex as a protective mechanism if there is excessive muscle tension to the point where the tendon is at risk of tearing. We will have an entire video on this one coming up for you later as well. To visualize, when the muscle gets very tense, it makes these fibers squeeze down on those nerve endings, causing them to send up action potentials.
Finally, our last category is joint kinesthetic receptors. This category is different because it's not just one type of receptor but rather a group of four receptor types found in our synovial joints. This includes lamellar corpuscles, bulbous corpuscles, tendon organs, and free nerve endings. An easy memory tool for this is to imagine ordering a BLT with fries. We have the B for bulbous corpuscle, L for lamellar corpuscle, T for tendon organs, and F for free nerve endings. These receptors monitor joint position and stretch, providing information about the location of the joint, the angle of the joint, any force being applied, and the motion of the joints.
If we were to imagine these all working holistically in our arm, for example, we would have muscle spindles in the muscle giving us information about stretch. You would have these tendon organs in our tendons giving us information about muscle tension, and we have these joint kinesthetic receptors in our synovial joint giving information about the location and position of our joint, and all of that would get sent up to our central nervous system, giving our brain an idea of where we are in space, how we're moving, and any ways that we may need to adjust that accordingly. Those are our proprioceptors, and I will see you guys in our next video. Bye bye.