Difference between revisions of "Holcombe:TactileReceptors"

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m (Skin receptors)
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===Skin receptors===
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Latest revision as of 18:46, 10 July 2014

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Skin receptors

Screen Shot 2014-07-11 at 11.37.55 am.png


Receptor Depth Skin Type Fave Temp Freq$ Type[a] Afferent Stimulation it responds to Driven by Adapts to Vibration?
Merkel's disk top skin layers glabrous and hairy[b] ~1 Hz, <5Hz 1 SA-1 pressure, orientation spatial period[1] YES
Meissner's corpuscle glabrous ~10 Hz 1 FA-1 (RA/QA) flutter, some stretch (b/c very sensitive to indentation) spatial frequency and also speed, NOT temporal freq[1] YES
Ruffini corpuscle glabrous and hairy? ~100 Hz 2 SA-2 stretching NO [2]
nail beds nails SA-2[3] fingertip force, fingertip direction[3]
Pacinian corpuscle glabrous? ~400 Hz[c] 2 FA-2 (PC/QA) vibration speed AND tf[1]
free nerve ending deep? sometimes on hair, lowww? C,? pain, ache, heat, cold,

a-Type 1 receptors have smaller, more sharply defined receptive fields and are more superficially localised in the skin than Type 2 receptors. b-At high amplitude, all the mechanoreceptors respond to all frequencies. c-Preferred frequency may change with indentation amplitude.

Check out Darian & Oke 1980, they test RA, SA, Pacinian at wide range of temporal frequencies.

when stimuli move across the receptive fields of tactile afferents, the responses are different depending on the direction of movement (Goodwin and Morley, 1987; LaMotte and Srinivasan 1987; Srinivasan et al., 1990; Edin et al., 1995). Directionality of tactile afferent responses most likely results from different strains produced at the receptor site when forces are applied in different directions. In the case of the fingertip, its geometry and composite material properties may account for widespread complex patterns of strain changes that depend on the direction of the applied force (Maeno et al., 1998). Consequently, the site of stimulation, the location of the receptor in the fingertip per se as well as in relation to the stimulation site, and possible inherent directional preferences of the end-organ attributable to its microanatomy, all could contribute to the directionality of an afferent- I. Birznieks

"Both FA-I and SA-I afferents respond to changes in the magnitude and direction of tangential torque, but differ in the relative importance of specific stimulus features. FA-I fibres discriminate the onset and magnitude of changes in torque more accurately and rapidly than SA-I fibres, but rarely distinguish clockwise from anti- clockwise rotations, or signal steady-state torques. FA-I fibres are silent during static grasp or lift actions when normal forces are constant. In contrast, SA-I fibres distinguish the applied normal force with latencies as brief as 250 ms, and also discriminate torque direction more accurately and faster than FA-I fibres. These findings suggest that FA-I fibres provide early warning signals of rotational as well as translational slips when objects held in the hand are manipulated or perturbed by external forces. The absence of tonic activity in FA-I fibres during static grasp enhances the sudden appearance of spike trains signalling object motion, aiding rapid adjustment of grip force in parallel with the onset of tangential motion over the skin (Kinoshita et al. 1997; Goodwin et al. 1998)" [4]

  1. Goodwin AW and Morley JW. Sinusoidal movement of a grating across the monkey's fingerpad: representation of grating and movement features in afferent fiber responses. J Neurosci. 1987 Jul;7(7):2168-80. PubMed ID:3612236 | HubMed [GoodwinMorley87]
  2. Birznieks I, Macefield VG, Westling G, and Johansson RS. Slowly adapting mechanoreceptors in the borders of the human fingernail encode fingertip forces. J Neurosci. 2009 Jul 22;29(29):9370-9. DOI:10.1523/JNEUROSCI.0143-09.2009 | PubMed ID:19625527 | HubMed [BirznieksEtAl09]
  3. Gardner EP. Tangential torque tunes touch. J Physiol. 2010 Apr 1;588(Pt 7):1035. DOI:10.1113/jphysiol.2010.188672 | PubMed ID:20360027 | HubMed [Gardner10]
All Medline abstracts: PubMed | HubMed