Relationship of the mechanical properties of the cat inferior oblique muscle to the anatomy of its motoneurons and nerve branches.

Physiologically, the contractile characteristics and electromyography (EMG) of cat inferior oblique (IO) muscle fibers supplied by the medial and lateral IO muscle nerve branches were studied by direct nerve stimulation. Anatomically, the brain stem locations and sizes of IO motoneuron soma were evaluated after retrograde labeling by horseradish peroxidase (HRP) through whole IO muscle nerves and/or through each medial or lateral IO muscle nerve branch. Stimulation of the lateral nerve branch elicited significantly (p < 0.005) slower twitch contraction times (8.0 +/- 1.5 ms) and lower fusion frequencies (217 +/- 46 Hz) than when the medial branch of the IO nerve was stimulated (average twitch contraction time = 6.8 +/- 1.1 ms; average fusion frequency = 260 +/- 34 Hz). The EMG wave shape responses in the global and orbital layers could be differentiated when the individual nerve branches were stimulated, but the response differences were not consistent among animals. The average diameter of IO motoneuron soma with axons in the lateral branch of the nerve were significantly smaller (p < 0.001) than the average diameter of those IO motoneuron soma associated with the medial branch of the nerve (27.9 +/- 7.2 vs. 32.9 +/- 7.2 microns). Regardless of which nerve branch was labeled, the full range of motoneuron soma sizes was found, and these were distributed throughout the IO subdivision of the oculomotor nucleus. These findings showed that muscle contraction time and motoneuron soma diameter were correlated with the IO nerve branch subjected to stimulation or exposed to HRP. But no topographic organization of motoneurons was found within the IO division of the oculomotor nucleus.

Prediction of pain in patients with chronic low back pain: effects of inaccurate prediction and pain-related anxiety.

This study investigated predictions of pain intensity, reports of pain and anxiety, frequency of pain-related anxiety symptoms, and range of motion, in 43 patients exposed to pain during a physical examination. All patients had primary complaints of low back pain. The pain stimuli used for this study included back and/or leg pain produced by repeatedly raising the extended leg of the patient to the point of pain tolerance. Generally, findings demonstrated that (a) predictions of pain were a function of discrepancies between previous predictions and experiences of pain, (b) patients reporting greater pain-related anxiety showed a tendency to overpredict new pain events, but corrected their predictions readily, (c) patients reporting less pain-related anxiety displayed a persistent tendency to underpredict pain, and (d) higher predictions of pain, independent of pain reports, related to less range of motion during a procedure that involved painful movement. Discussion focuses on differences between these results and those of previous studies and the implications of inaccurate prediction for continued pain and disability.