Faculty Bibliography

1. In recordings from the human supraorbital nerve with tungsten microelectrodes, eleven afferent units with unmyelinated (C) axons were identified on the basis of their conduction velocities (0.6-1.4 m/s). 2. Eight units had low mechanical thresholds (less than or equal to 0.23 g) and could be activated up to their maximal firing rates of about 100 impulses/s by weak tactile stimuli, whereas three units had higher thresholds (5.5 g) and responded vigorously to noxious stimuli only. 3. During a skin indentation the low-threshold units adapted to an irregular low-frequency discharge, and release of the stimulus elicited a prominent off-response often ending with an after-discharge. Slow stroking was a particularly effective stimulus, even when done with cotton wool, whereas rapid stroking reduced the response. All types of stroking stimuli were occasionally followed by after-discharges. Repeated mechanical stimulation at short intervals resulted in a decline of the response, indicating receptor fatigue. For two units a response to skin cooling was observed. 4. The above low-threshold C units have all the main characteristics of the C mechanoreceptors known from the cat and primates but not previously proven to exist in man. The high-threshold C units are similar to the polymodal nociceptors found in other human skin areas

1. Sympathetic nerve activity occurring as bursts of multi-unit impulses was recorded with tungsten microelectrodes in the supraorbital nerve of awake healthy subjects. Within the fascicular innervation zone on the forehead, skin resistance was measured as an indicator of sweat gland activity, and skin blood flow was measured with laser-doppler flowmetry. 2. At room temperature, there was little or no background burst activity, but arousal stimuli or mental stress evoked bursts followed by a vasodilator response. Provided repeated arousal stimuli were delivered, individual bursts were followed by a decrease in skin resistance. 3. Body heating induced increasing background burst activity. After an initial period without associated electrodermal activity, there were decreases in skin resistance, which showed a positive linear correlation with the amplitude of the preceding burst. Individual bursts were followed by a vasodilator response with an average onset latency of 2.8 s and an average duration of 9.1 s, and rapid increases in blood flow coincided with a marked increase in burst activity. Arousal stimuli evoked bursts followed by both vasodilator and skin resistance responses. 4. During body cooling, there was no background burst activity, but signs of relatively weak, probably neurally mediated vasoconstriction were observed and arousal-evoked bursts were reduced or abolished, as were the associated vasodilator and skin resistance responses. 5. It is concluded that body heating induces active sympathetic vasodilatation in the skin of the human forehead, and that this is either sudomotor-mediated or caused by vasodilator fibres firing in synchrony with sudomotor fibres. A similar sympathetic mechanism probably underlies the vasodilator responses evoked by arousal stimuli and mental stress

The human suffering and economic cost attributable to musculoskeletal disorders cannot be overemphasized. Biomechanical principles have been introduced to explain the microtrauma and macrotrauma as mechanisms of injury. Stress-induced remodeling is a useful paradigm in the study of environmentally induced disorders. The concept of environment should include psychosocial and organizational factors with respect to musculoskeletal complaints and chronic pain. Low back pain, osteoarthritis, osteoporosis and its associated fractures, and cumulative trauma disorders are the most critical and common musculoskeletal disorders. The risk factors for low back pain have been identified, and preventive measures for reducing the chronicity of low back pain have been discussed. Preventive approaches to control or limit the fractures associated with osteoporosis and loss of bone mass are preferred to simple management of the fracture of osteoporotic patients. It can be concluded that too little or too much stress can disturb the homeostatic or the equilibrium state of health and that much remains to be researched to quantify the optimal stress levels

Spatial joint complexes, such as the spine, require multiaxial systems to adequately assess their functional capacity. The B200 Isostation (Isotechnologies, Inc., Carrboro, North Carolina) is a triaxial system that has three hydraulic pumps under control of an IBM-XT. The transducers measure the torque, angular position, and velocity for all axes simultaneously. There is no isoinertial data base available for strength at different resistances in the sagittal, coronal, and transverse planes. A normal data base for dynamic performance against resistances equal to 30%, 50%, and 70% of the maximum isometric strength of trunk muscles in all three planes was established

The purpose of this study was to detect any changes in the erector spinae muscles in patients undergoing surgery for lumbar disc herniation (LDH) and to analyze which factors (sex, age, the level and site of disc protrusion, and duration of symptoms) would be related to these changes. The percentage of mean area of the type I fibers was significantly larger in males and in the older age group (P less than 0.05), due to the decreasing size of type IIa and IIb fibers. Patients with LDH have: 1) angulated and selective atrophy of type II fibers with a higher type IIb/IIa ratio; 2) with increasing age and duration of symptoms, more marked atrophy of type II fibers; and 3) other unspecific pathologic changes

Eighty-four low-threshold mechanoreceptive afferents innervating facial hairy skin or the red zone of the lip were recorded with micro-electrodes from the human infra-orbital nerve. Based on their responses to skin indentations, the units were classified as slowly or fast-adapting, with small or large receptive fields. The responses to hair movement, skin stretching and contraction of facial muscles were also studied. Both hairy skin and the red zone were innervated by slowly and by fast-adapting units. The innervation density was found to be highest at the corner of the mouth and on the upper lip. Slowly adapting units with small fields in hairy skin were most common and included units responding to sustained hair displacement. These units are suggested to have two types of end-organs, either pilo-Ruffini endings or Merkel cell-neurite complexes. The slowly adapting units with large fields were spontaneously active stretch receptors and may have corresponded to Ruffini corpuscles, although the possibility of other, intramuscular, receptors could not be ruled out. Only one afferent possibly innervated a Pacinian corpuscle. Most mechanoreceptors were also activated by skin stretching or contraction of facial muscles. Many of the slowly adapting units with small fields responded to the onset and release of stretch, whereas their discharge in response to sustained stretching adapted more or less completely. Spontaneously active units had the most sustained stretch response. It is concluded that several types of cutaneous mechanoreceptors can operate as sensitive proprioceptors of importance for facial kinaesthesia and motor control

Intrafascicular micro-electrode recordings were made from the human infra-orbital nerve close to the infra-orbital foramen. The fascicular organization was studied and multi-unit activity from low-threshold mechanoreceptive afferents was recorded during tactile stimuli, vibration and facial movements. Attempts were also made to record C-fibre activity. Innervation zones corresponding to 66 fascicles were mapped with tactile stimuli on facial hairy skin and the red zone of the lip. Most of these fields were located on the upper lip, where they overlapped, indicating a high innervation density. The fields had a median size of 3.8 cm2. Skin indentation evoked dynamic on- and off-responses and a much less pronounced static discharge. The afferent double-peaked responses to an oscillating probe applied to the peri-oral region induced similar grouping of the EMG activity during sustained lip protrusion. Contraction of facial muscles and stretching of the skin evoked on- and off-responses, whereas the static discharge was less pronounced, especially during sustained stretching. The dynamic sensitivity to minor variations in contraction and stretching was high, and during normal facial movements, as in speech, there was a barrage of impulses originating from mechanoreceptors within large facial areas. Functional implications of these sensorimotor interactions are discussed. Sympathetic C-fibre activity, frequently seen in recordings from the supra-orbital nerve, was never encountered in the infra-orbital nerve recordings, indicating a lack of such fibres. Failure to detect afferent C-fibre activity could be explained by methodological difficulties