Modeling and simulation of excitation- contraction coupling of fast-twitch skeletal muscle fibers.

BACKGROUND: The current excitation-contraction coupling model of fast-twitch skeletal muscle fibers cannot completely simulate the excitation-contraction process. OBJECTIVE: To solve this problem, this study proposes an excitation-contraction model of fast-twitch skeletal muscle fibers based on the physiological structure and contractile properties of half-sarcomeres. METHODS: The model includes the action potential model of fast-twitch fiber membranes and transverse tubule membranes, the cycle model of 𝐶𝑎2+ in myofibril, the cross-bridge cycle model, and the fatigue model of metabolism. RESULTS: Finally, detailed analyses of the results from the simulation are conducted using the Simulink toolbox in MATLAB. Two conditions, non-coincidence and coincidence, are analyzed for both the thick and thin myofilaments. CONCLUSIONS: The simulation results of two groups of models are the same as the previous research results, which validates the accuracy of models.

[Histomorphology observation of canine whole facial nerve treated with chemically extracted acellular methods].

OBJECTIVE: Using chemically extracted acellular methods to treat extracranial section of the canine whole facial nerve, to evaluated its effects on nerve structure and the removal extent of Schwann cells and myelin. METHODS: Twenty whole facial nerves were exposed from 10 canines [weighing (18 +/- 3) kg]. The extracranial trunk of canine facial nerve and its branches (temporal branch, zygomatic branch, buccal branch, marginal mandibular branch, and cervical branch) were dissected under light microscope. Twenty facial nerves were divided into the experimental group (n = 12) and control group (n = 8) randomly. In experimental group, the nerve was extracted with the 3%TritonX-100 and 4% sodium deoxycholate. In control group, the nerve was not extracted. HE staining and immunofluorescence histological stainings for Hoechst33258, P75, Zero, and Laminin were performed. RESULTS: After histological staining, it was found that myelin and Schwann cells were removed from the facial nerve while the basal lamina tube remained intact. The whole canine facial nerves (one nerve trunk and multiple nerve branches) had the similar result. CONCLUSION: The canine whole facial nerve has natural structure (one nerve trunk and multiple nerve branches) by extracted with chemically extracted acellular methods, so it is an available graft for repairing the defect of the whole facial nerve.

[Treatment of degenerative lumbar spondylolisthesis through posterolateral fusion and fixation with pedicle screws].

OBJECTIVE: To explore internal fixation whether can improve the clinical outcomes of decompression and posterolateral fusion in patients with degenerative lumbar spondylolisthesis. METHODS: From December 1998 to December 2005, 49 patients who had degenerative lumbar spondylolisthesis underwent decompression and posterolateral fusion without (group A, 21 cases) or with (group B, 28 cases) internal fixation (CD HORIZON M8 system). There were 12 males and 37 females with a mean age of 58.5 years (range, from 49 to 68 years). Among them,32 cases were grade I and 17 were grade II according to Meyerding grade system. All patients were followed up with an average of 58 months (range from 12 to 90 months). The pain of low back and leg (VAS scoring), spinal active function and neurologic function were evaluated according the assessment system of Yuan. RESULTS: The VAS score of low back in group A and B were respectively 41.9 +/- 7.5 and 32.8 +/- 6.2 at follow-up; and VAS score of leg in group A and B were respectively 33.9 +/- 7.3 and 30.8 +/- 6.2. Spinal active function of patients, 15 cases obtained improvement, 6 cases aggravation or no improvement in group A; 25 cases obtained improvement, 3 cases aggravation or no improvement in group B. Neurologic function of patients, 15 cases obtained improvement, 6 cases aggravation or no improvement in group A; 26 cases obtained improvement, 2 cases aggravation or no improvement in group B. The group B was better than group A in the aspect of low back pain, spine active function and neurologic function (P < 0.05). There was no statistically significant difference in improvement of leg pain between two groups (P > 0.05). CONCLUSION: Using internal fixation in decompression and posterolateral fusion for degenerative lumbar spondylolisthesis can improve low back pain and clinical function. Decompression is necessary for the surgical treatment of degenerative spondylolisthesis, which is major effect on the improvement of leg pain.