As unlikely as it might sound, there thought to be a tenuous link between detection of movement and emotions. The James-Lange theory of emotions states that emotions result from physiological responses of the body to the environment. The diametrically opposite theory is the Cannon-Bard theory of emotions which states that physiological responses in the body occur subsequent to emotional experiences. The Williams-Lange theory has been refined by A Craig (see here, here and here). In Craig’s model our sense of our own body – interoception – is an important part of emotional experience and he suggests that emotions and interoceptive information are integrated in the Insular Cortex. The model is elaborated on and it is well worth reading Craig’s original works.
So detecting movements in our arms – a type of interoception might be an important component of our emotional experience. However it’s not too far-fetched when you think of the fight-or-flight response. With a lion fast approaching, the sensation of rapid movement in your arms and legs as you exit the scene complements the ‘there’s a Lion right behind me’ thought and the associated anxiety you are experiencing. So now we get onto the slightly more technical bit. How do we detect movements in our body. Well the answer is through mechanoreceptors. These are receptors in the body which are deformed in response to various changes in the body including movements.
So if we want to understand what’s going on as we’re running away from the Lion, part of the picture is provided by considering the movements of our arms. It turns out that our arms are covered in these tiny mechanoreceptors and in this post I am looking at a special type of receptor known as the Ruffini end-organ or Ruffini receptor.
Since they are so tiny, they are usually visualised with a microscope or with special types of staining. In anatomical studies, specimens are obtained post-mortem, prepared using special techniques and then examined using microscopy. It turns out from a review of the literature that this very specialised area of research consists of a very small number of studies which show that the Ruffini endings are found throughout the arm.
Glenohumeral Joint, Gray’s Anatomy, 1918, 20th Edition, Public Domain, Wikimedia Commons
Ruffini end organs were identified in the Inferior, Middle, Superior and Posterior Glenohumeral Ligaments in this study (Vangsness et al, 1995). Ruffini endings were not found in the Glenoid Labrum and the researchers didn’t report the identification of Ruffini endings in the Subacromial Bursa. The researchers suggest that removal of an inflamed bursa may also reduce pain signals from this part of the shoulder.
Flexor Tendons of the Hand, Gray’s Anatomy, 1918, 20th Edition, Public Domain, Wikimedia Commons
In a histological study, flexor tendons of the hand were examined (Zimny et al, 1989). The researchers identified Ruffini endings but these were outnumbered by Pacinian corpuscles and Golgi Tendon organs.
In an immunohistological study researchers examined the index finger of donors and were able to identify only a single Ruffini corpuscle (Paré et al, 2003). They concluded that human glabrous skin was not well supplied with Ruffini endings. In another study, the researchers examined 10 hands using immunofluorescence techniques and looked at the thumb ligaments – the Dorsal, Posterior and Anterior Oblique, Central, Carpometacarpal and Ulnar Collateral Ligaments (Lee et al, 2011). They found evidence of Ruffini endings in the ligaments.
Volar Aspect of Interphalangeal Joints of the Finger, Gray’s Anatomy, 20th Edition, 1918, Public Domain, Wikimedia Commons
The researchers in this immunohistochemical study examined 12 right index finger distal interphalangeal joints and surrounding structures (Chikenji et al, 2011). The specimens were divided into three regions longitudinally these being proximal, middle and distal and these areas were further subdivided. Although other types of endings were more prevalent – the researchers identified type I endings which includes Ruffini Endings. The same research team also studied the 12 right index finger proximal interphalangeal joints and surrounding structures (Chikenji et al, 2010). The specimens were again divided into three regions longitudinally (proximal, middle and distal) and these areas were further subdivided. The researchers found that type I endings (e.g Ruffini-like endings) were more prevalent in the volar plate of the proximal interphalangeal joints.
Chikenji T, Suzuki D, Fujimiya M, Moriya T, Tsubota S. Distribution of nerve endings in the human proximal interphalangeal joint and surrounding structures. J Hand Surg Am. 2010 Aug;35(8):1286-93. Epub 2010 Jul 13.
Chikenji T, Berger RA, Fujimiya M, Suzuki D, Tsubota S, An KN. Distribution of nerve endings in human distal interphalangeal joint and surrounding structures. J Hand Surg Am. 2011 Mar;36(3):406-12.
Lee J, Ladd A, Hagert E. Immunofluorescent Triple-Staining Technique to Identify Sensory Nerve Endings in Human Thumb Ligaments. Cells Tissues Organs. 2011 Aug 10.
Paré M, Behets C, Cornu O. Paucity of presumptive ruffini corpuscles in the index finger pad of humans. J Comp Neurol. 2003 Feb 10;456(3):260-6.
Vangsness CT Jr, Ennis M, Taylor JG, Atkinson R. Neural anatomy of the glenohumeral ligaments, labrum, and subacromial bursa. Arthroscopy. 1995 Apr;11(2):180-4.
Zimny ML, DePaolo C, Dabezies E.Mechano-receptors in the flexor tendons of the hand. J Hand Surg Br. 1989 May;14(2):229-31.
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