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Table 6:
Numbers and Types of Large Diameter Afferent Fibers in the Spinal Cord.
Fiber Type/Sensation Number of Collaterals Conduction Speed/Diameter Rexed Laminae Innervated/Bouton Density 
Ia afferents (1) Stretch, length, or rate of length change of muscle 3–9, mean 5.8 ±1.9 >80 m/s >13 μVI, VII, IX 
Ib afferents (2) Contraction or stretch of muscle 5–11, mean 7.4 ±>80 m/s >13 μIV, V, VI, dorsal VII 56–384, strongest in medial VI 
FAII Pacinian corpuscles (5) Tickling or vibration over 20–50 Hz 4–12, mean 7.11 ±3.55 57–75 m/s 9.5–12.5 μm 11.5 and 12.8 in our model 2/3 in III (strong), IV (weaker) 1/3 in V, VI 47–367 
FAI rapidly adapting (RA, Krause's end bulb, Meissner corpuscle) afferents (6) Tapping at 1 Hz; flutter at 10 Hz; vibration at 50 Hz Mean 5 54–60 m/s 11.7–13.0 μm 11.5 and 12.8 μm in our model Almost all in III, rest in IV (number of boutons not given) 
SAII afferents (Ruffini; subtype: claw base) (5) Usually no sensation (occasionally position) Mean 9.89 28–51 m/s 6.1–11.1 μm 8.7 μm in our model III–dorsal IV (40–50) V, VI < ventral IV < III, dIV V–VI (10–20) 
SAI afferents (Merkel cell of glabrous and hairy skin origin) (3) Sustained pressure over 5–10 Hz 4–16, mean 8.6 Not given in (3); from (4): 33–95 m/s 7.2–15.8 μm 7.5 μm in our model III, IV, dorsal V hairy (16–46, mean 24.2) glabrous (9–26, mean 15.3) 
Hair follicles (7) Hair movement 2–12, mean 4.8   
Three types of low-threshold mechanoreceptors (RA, hair follicles, SAI) lumbar (8) See sensations above RA: 10.06 ±0.93 hair follicle: 9.33 ±0.56 SAI: 9.75 ±0.75   
Aβ hair follicle afferents in different lumbar spinal levels corresponding to 5 dermatomes (9) Hair movement 9.83 ±0.64 (over 5 dermatomes)   
Aβ RA afferents from various parts of the rat foot (10) Tapping at 1 Hz; flutter at 10 Hz; vibration at 50 Hz 10.82–14.00 (range of means)   
Fiber Type/Sensation Number of Collaterals Conduction Speed/Diameter Rexed Laminae Innervated/Bouton Density 
Ia afferents (1) Stretch, length, or rate of length change of muscle 3–9, mean 5.8 ±1.9 >80 m/s >13 μVI, VII, IX 
Ib afferents (2) Contraction or stretch of muscle 5–11, mean 7.4 ±>80 m/s >13 μIV, V, VI, dorsal VII 56–384, strongest in medial VI 
FAII Pacinian corpuscles (5) Tickling or vibration over 20–50 Hz 4–12, mean 7.11 ±3.55 57–75 m/s 9.5–12.5 μm 11.5 and 12.8 in our model 2/3 in III (strong), IV (weaker) 1/3 in V, VI 47–367 
FAI rapidly adapting (RA, Krause's end bulb, Meissner corpuscle) afferents (6) Tapping at 1 Hz; flutter at 10 Hz; vibration at 50 Hz Mean 5 54–60 m/s 11.7–13.0 μm 11.5 and 12.8 μm in our model Almost all in III, rest in IV (number of boutons not given) 
SAII afferents (Ruffini; subtype: claw base) (5) Usually no sensation (occasionally position) Mean 9.89 28–51 m/s 6.1–11.1 μm 8.7 μm in our model III–dorsal IV (40–50) V, VI < ventral IV < III, dIV V–VI (10–20) 
SAI afferents (Merkel cell of glabrous and hairy skin origin) (3) Sustained pressure over 5–10 Hz 4–16, mean 8.6 Not given in (3); from (4): 33–95 m/s 7.2–15.8 μm 7.5 μm in our model III, IV, dorsal V hairy (16–46, mean 24.2) glabrous (9–26, mean 15.3) 
Hair follicles (7) Hair movement 2–12, mean 4.8   
Three types of low-threshold mechanoreceptors (RA, hair follicles, SAI) lumbar (8) See sensations above RA: 10.06 ±0.93 hair follicle: 9.33 ±0.56 SAI: 9.75 ±0.75   
Aβ hair follicle afferents in different lumbar spinal levels corresponding to 5 dermatomes (9) Hair movement 9.83 ±0.64 (over 5 dermatomes)   
Aβ RA afferents from various parts of the rat foot (10) Tapping at 1 Hz; flutter at 10 Hz; vibration at 50 Hz 10.82–14.00 (range of means)   

1. Brown and Fyffe (1978). 2. Brown and Fyffe (1979). 3. Brown and Fyffe (1978). Brown, Rose, and Snow (1978). 4. Willis and Coggeshall (2004a) 5. Brown, Fyffe, Rose, and Snow (1981). 6. Brown, Fyffe, and Noble (1980). 7. Brown, Rose, and Snow (1977). 8. Woolf (1987). 9. Shortland, Woolf, and Fitzgerald (1989). 10. Shortland and Woolf (1993). FAI: Fast-adapting receptor type I (aka rapidly-adapting or RA). RAII: Fast-adapting/rapidly adapting receptor type II (aka Pacinian corpuscle). SA: Slowly adapting receptor. Aβ: A-beta fiber (large-diameter sensory fiber).

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