Anatomy of the sense of touch in sea otters: Cutaneous mechanoreceptors and structural features of glabrous skin

2021 ◽  
Author(s):  
Sarah McKay Strobel ◽  
Melissa A. Miller ◽  
Michael J. Murray ◽  
Colleen Reichmuth





1980 ◽  
Vol 43 (6) ◽  
pp. 1558-1570 ◽  
Author(s):  
B. H. Pubols

1. The on- and off-responses of 50 raccoon median nerve fibers associated with rapidly adapting cutaneous mechanoreceptors in glabrous skin were examined under experimental conditions designed to allow comparable opportunities for on- and off-responses to occur. Trapezoidal stimuli were utilized, providing for equal stimulus indentation and retraction velocities and equal static displacement times and intertrial intervals. Principal findings were as follows: 2. At stimulus levels well above displacement and velocity thresholds for on-responses, 80% of units yielded a more vigorous on-response than off-response (as measured by the total number of ramp impulses); in 6%, the reverse was true; while in the remaining 14%, the off-discharge was absent. 3. On and off displacement thresholds were approximately equal (on median, 43 micron; off median, 42 micron). However, on velocity thresholds were significantly lower than off velocity thresholds (on median, 1.0 micron/ms; off median, 3.8 micron/ms). 4. Exponents (b) of power functions relating discharge rate to ramp velocity (frequency = a x velocityb) were consistently greater for on-responses than for off-responses, but intercept constants (a) were consistently greater for off-responses than for on-responses. 5. Previous findings that mammalian rapidly adapting (RA) mechanoreceptors possess a “linear directionality” generally favoring on-responses were confirmed. 6. Results are discussed in relation to the role of viscoelastic properties of RA mechanoreceptors and neighboring skin. It is suggested that, when considerations is also given to the mechanical properties of surrounding tissues, the Loewenstein and Skalak (18) analysis of the mode of operation of Pacinian corpuscles might also apply, at least qualitatively, to the simple dermal (rapidly adapting) corpuscle of raccoon glabrous skin.



1986 ◽  
Vol 55 (4) ◽  
pp. 644-659 ◽  
Author(s):  
K. H. Sanders ◽  
M. Zimmermann

In the glabrous skin of the rat's hindfoot the same triple set of low-threshold mechanoreceptors is present as has been found in other mammals: slowly adapting (SA), rapidly adapting (RA), and very rapidly adapting Pacinian corpuscle-like (PC) receptors. Their functional characteristics were examined in normal rats and compared with those of sensitive mechanoreceptors found in the glabrous skin of the foot 2-24 wk after crush of the plantar nerves, resulting in regeneration of the transected nerve fibers. After 2 wk of nerve regeneration, low-threshold RA and SA cutaneous mechanoreceptors reappeared in the foot skin. Responses of PC receptors were recorded again after 3 wk, at which time the proportion of fibers that could be identified as low-threshold cutaneous mechanoreceptors had regained control level. Discharge patterns of regenerated cutaneous mechanosensitive receptors were very similar to those of normal skin mechanoreceptors. Their sensitivity to controlled mechanical stimulation was, however, still reduced 4 wk after the lesion. After 8 wk RA and SA receptors had regained their normal dynamic sensitivity, i.e., the responsiveness to the velocity of skin indentation. The static sensitivity of SA receptors, i.e., responsiveness to maintained skin indentation, was not consistently reestablished within 24 wk. No shift in sensitivity could be deduced from tuning curves of PC receptors examined 3-24 wk after nerve crush. In addition to the low-threshold mechanoreceptors, high-threshold (HT) mechanoreceptive fibers were found in controls and in animals with regenerating nerves. This type of fiber was most frequently found 1 wk after the nerve crush, when reinnervation of the foot started. They probably represent fibers not connected to specific mechanoreceptor end organs. Thus, functional restitution of the highly specific cutaneous mechanoreceptors occurs fairly soon after invasion of the original territory by the regenerating nerve. It is assumed that the underlying mechanism is the rapid reconnection of fibers with the end organs that have either survived during the period of denervation or regenerated subsequent to reinnervation of the skin.



2000 ◽  
Vol 23 (2) ◽  
pp. 153
Author(s):  
Yaojun Li ◽  
Shaozong Chen ◽  
Xueyong Li ◽  
Biao Cheng


1979 ◽  
Vol 42 (5) ◽  
pp. 1461-1478 ◽  
Author(s):  
R. W. Dykes ◽  
J. K. Terzis

1. A total of 791 fibers were isolated from the ulnar nerves of five baboons. Over half of these were obtained from the right ulnar nerves subsequent to reinnervation following a nerve crush; the other fibers were obtained from the undamaged left ulnar nerves. 2. The conduction velocities in the proximal portion of the injured axons dropped below normal, and this reduction persisted until reinnervation appeared nearly complete. 3. The response properties of 65 cutaneous afferent fibers serving reinnervated glabrous skin were compared to 80 fibers from normal skin. 4. Of the afferent fibers reinnervating skin, the proportion judged to have abnormal response properties was not significantly greater than the proportion in normal skin. 5. After reinnervation, cutaneous rapidly adpating fibers displayed tuning curves characteristic of their submodality, while some cutaneous slowly adapting fibers could still be differentiated into type I and type II fibers. However, both types of slowly adapting fibers displayed an increased rate of adaptation and a lowered sensitivity to sustained displacements even at 5 mo following reinnervation. 6. In conclusion, the cutaneous mechanoreceptors in reinnervated glabrous skin regained response properties that allowed them to be assigned to the same submodalities found in normal skin. Submodality was recognizable at an early stage when the receptive field was still immature and when the threshold was elevated. With time, the receptive-field sizes and shapes returned to normal, the thresholds approached normal, and the remaining differences from normal cutaneous afferent fibers became minor.



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