Different types of slowly conducting afferent units in cat skeletal muscle and tendon.

Abstract

SUMMARY1. In chloralose-anaesthetized cats, the impulse activity of single afferent units conducting at less than 30 m sol and having receptive fields in the triceps surae muscle or the calcaneal tendon, was recorded from thin filaments of the dorsal roots L7 and SI. The receptive fields of the units were tested with a variety of graded natural stimuli (local pressure, stretch, contractions, temperature changes). In addition, the algesic agent bradykinin was injected into the receptive fields, but the sensitivity of the receptors to this substance was not used for classification purposes.2. Four types of receptors could be distinguished using the strongest response to innocuous natural stimulation as the criterion for characterizing a given ending: (a) nociceptors showing no response to innocuous forms of stimulation and requiring noxious (tissue-threatening) stimuli to be clearly activated; (b) low-threshold pressuresensitive receptors responding to innocuous indentation of the tissue but being relatively insensitive to stretch and contractions; (c) contraction-sensitive receptors reaching high discharge frequencies during active contractions of moderate force and innocuous stretch, but being relatively insensitive to local pressure stimulation; (d) thermosensitive receptors responding strongly to small changes in temperature without reacting to innocuous mechanical stimulation.3. The possible involvement of the different receptor types in central nervous functions (nociception, mechanoreception, ergoreception, thermoregulation) is discussed.

Augmented Mechanical Response of Muscle Thin-Fiber Sensory Receptors Recorded from Rat Muscle–Nerve Preparations In Vitro After Eccentric Contraction

“…These values were about the half those of the cutaneous thin fiber receptors measured by our group with the same instruments in vivo and in vitro (Suzuki et al 2002;Takahashi et al 2003). The existence of thin-fiber receptors with low and high mechanical threshold in the muscle has been reported (Mense and Meyer 1985). However, the distribution of the mechanical thresholds was continuous in the present study and no natural segregation into subgroups was observed.…”

Relative effectiveness of C primary afferent fibers of different origins in evoking a prolonged facilitation of the flexor reflex in the rat

“…Small-diameter afferents from muscle, tendons (Mense and Meyer, 1985) and joints (Schiable and Schmidt, 1983) have been studied in the cat and consist of a mixture of low-and high-threshold units, with the majority of C-fibers falling into the latter category. C-fibers terminate in the superficial dorsal horn (Light and Perl, 1979) where many intemeurons are excited directly or indirectly by the arrival ofa volley in C-afferents (Fitzgerald and Wall, 1980;Woolf and Fitzgerald, 1983).…”

Effect of Experimental Muscle Pain on Motor Unit Firing Rate and Conduction Velocity

“…A major proportion of small diameter group III and IV muscle afferents are sensitive to noxious mechanical and chemical stimuli (Mense and Meyer 1985;Mense and Stahnke 1983). According to the pain adaptation model (Lund et al 1991), the activity of thin nociceptive muscle afferents facilitates inhibitory pathways when the muscle acts as an agonist and facilitates excitatory pathways during antagonist activity.…”