Proprioceptive system: Difference between revisions - VR & AR Wiki

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Studies that observed motor cortical neurons concluded that the brain is not concerned with information about muscle length changes from individual afferents, but with the population of muscles afferent input signals that arises in groups of muscles. Another area that has been explored is the relation between proprioception and fatigue from exercise. Some of the clumsiness in movements felt after intense exercise could have an origin in proprioception. An important point is age and proprioception. Evidence shows that a decline in proprioception due to age is responsible for an increase in falls in the elderly <ref name=”2”></ref>.

==The proprioceptive senses==

The proprioceptive senses include the senses of position and movement of limbs and trunk, the sense of effort, the sense of force, and the sense of heaviness. Like previously mentioned, the receptors that are involved in proprioception are located in skin, muscles, and joints <ref name=”2”></ref>.

When limbs move or change position, the tissues around the relevant joint are deformed. These include skin, muscles, tendons, fascia, joint capsules, and ligaments, all of which are innervated by mechanically sensitive receptors. Their density varies across muscles and different regions of the body. A specific type of receptor, the muscle spindles, play an essential role in proprioception, along with some skin receptors that provide additional information. Another receptor that contributes to proprioception is the Golgi tendon organs. These have been gaining prominence recently. They identify changes in muscle tension, and contribute to the senses of force and heaviness. In general terms, the information that is received by the receptors is sent through the spinocerebellar tract into the cerebellum. It accepts the information provided by every muscle and joint in the body, and calculates where limbs must be in space <ref name=”2”></ref> <ref name=”3”></ref> <ref name=”11”></ref>. The sense of limb position is complex, with different sources of information interacting to produce perception, such as tactile, visual, and proprioceptive. The brain continuously matches visual and kinaesthetic inputs during movements to link what is seen with what is felt <ref name=”5”></ref> <ref name=”7”></ref>.

Presently, regarding peripheral afferents, it is considered that “muscle spindles provide the kinaesthesia sense, Golgi tendons organs provide the sense of tension, the vestibular system provides the sense of balance, and the central nervous system provides the sense of effort. In short, limb placement is achieved by combining motor command signals and afferent signals in order to produce the best estimate of body part positioning, although how these sources of information combine to give the normal positional acuity remain the subject of further experiments <ref name=”5”></ref>.

Proske (2015) has proposed “the idea of the existence of two kinds of position sense, served by different classes of sensory receptors.” The first relates to signaling the position of one body part relative to another. In this case, the principal receptors are the muscle spindles, with cutaneous receptors acting as proprioceptors in a supporting role. The second kind of position sense would determine the location in space of the body or one of its parts. For this, vision would contribute the most, supported by cutaneous receptors acting as exteroceptors and auditory receptors signaling spatial information <ref name=”10”></ref>.

===Joint and skin receptors===

Joint receptors were thought to be all important in kinaesthesia, but the present view is that they only have a minor contribution. They may contribute proprioceptive information as limb displacement approaches the limits of joint movement, but not inform about position. There is evidence, however, of a contribution by joint receptors in the mid-range of movements at the finger joints <ref name=”2”></ref> <ref name=”7”></ref> <ref name=”10”></ref>.

According to Proske (2015), skin receptors can act both as proprioceptors and exteroceptors. When a joint rotates it causes the skin to stretch on one side and to be slackened or folded on the other side. These deformations will stimulate the skin mechanoreceptors, leading to sensations of elbow movement. Moreover, the elbows may come in contact with external objects, which is signaled by cutaneous receptors acting as exteroceptors. These contribute to kinaesthesia at the index finger, elbow, and knee <ref name=”2”></ref> <ref name=”9”></ref> <ref name=”10”></ref>. In this way, the skin contributes to kinaesthesia, and the sensitivity of human skin stretch receptors is similar to that of muscle spindles afferents (when expressed as impulses per degree of joint motion) <ref name=”2”></ref>.

The contribution of the skin receptors to kinaesthesia is essential in the skin adjacent to the finger joints. Their presence at each finger joint allows them to provide joint-specific information <ref name=”2”></ref> <ref name=”7”></ref> <ref name=”9”></ref>. However, the activation of cutaneous receptors can produce illusory movements of the index finger, elbow, and knee, supporting the hypothesis that cutaneous receptors can generate proprioceptive sensation at other joints beside those of the hand <ref name=”9”></ref>. Therefore, skin afferents have a significant role in kinaesthesia, likely contributing to movement sensation at most joints. Nonetheless, their contribution to position sense at the more proximal joints is likely to be less relevant than the input from muscle spindles <ref name=”2”></ref>.

A note will be given to auditory input as an exteroceptor, with the ability to localize sounds, providing spatial information about the surroundings. Recent reports describe how hearing can affect the perceived size of a limb <ref name=”10”></ref>.

===Some factors that can affect proprioception===

Some researches indicate that pain can interfere with the perception of the position of the painful limb, although others did not find such an association between proprioception and pain. In another study, it was found that pain did not affect ankle joint position sense but that it affected the ankle movement detection threshold. This leads to the suggestion that the relationship between pain and proprioception is complex and that more research is necessary to clarify the connections between these two concepts <ref name=”5”></ref>.

Another factor that can impact proprioception is the increased exposure to relevant proprioceptive stimuli. This was observed in studies of visually guided reaching, where the accuracy of matching performance was improved <ref name=”8”></ref>.

==References==