About the origin of cerebral somatosensory potentials evoked by Achilles tendon taps in humans

This study examines the effects of ischemic hypoxia and cooling of the leg, muscle contraction and vibration on cerebral potentials evoked by Achilles tendon taps and posterior tibial nerve stimulation to obtain indirect evidence leading to the identification of receptors activated by tendon taps. Experiments performed during ischemia of the leg showed that these receptors lie between the ankle and the knee. Cooling of the leg showed that they are located deep in muscles or bone. Experiments performed during vibration and muscle contraction suggest that muscle stretch receptors provide the afferent input responsible for Achilles tendon tap evoked potentials. All of these experiments point to primary muscle spindles in the proximal gastrocnemius-soleus muscle belly as the main source of afferent input for evoking cerebral potentials to Achilles tendon taps in humans.     

Assessment of fusimotor contribution to reflex reinforcement in humans

The contribution of the fusimotor system to reflex reinforcement such as the Jendrassik manoeuvre was investigated by recording single unit activity with tungsten electrodes from muscle spindle afferent nerves in unanaesthetized normal human subjects. Muscle spindle afferent activity was recorded before, during, and after the reinforcement test. When the leg muscles remained relaxed during the Jendrassik manoeuvre, spindle activity recorded in the tibial nerve was accelerated. Also in the median nerve, activity from muscle spindle afferent fibres was increased during a remote contraction of the ipsilateral quadriceps muscle. Comparing the time course of the phasic reflex reinforcement and the muscle spindle facilitation during the remote contraction, a marked after-effect was recorded in both responses. Present results show an increased spontaneous muscle spindle activity in relaxed muscles during a remote muscle contraction, and provide evidence for the contribution of the fusimotor system to the enhancement of phasic reflexes by reinforcement manoeuvres.     

The limitations of the tendon jerk as a marker of pathological stretch reflex activity in human spasticity.

The motor disorders associated with human spasticity arise, partly from a pathological increase in the excitability of muscle stretch reflexes. In clinical practice, reflex excitability is commonly assessed by grading the reflex response to a blow delivered to the tendon of a muscle. This is a much simpler response than the complex patterns of activity which may be elicited following muscle stretch caused by active or passive movement. Changes in the biceps brachii tendon jerk response have been followed over the first year after stroke in a group of hemiparetic patients and compared with changes in short and medium latency reflex responses elicited by imposed elbow flexion of initially relaxed spastic muscle and with the development of the late reflex responses which contribute to spastic hypertonia. A progressive increase in tendon jerk responses occurred over the first year following stroke, whereas reflex responses to imposed displacement, in particular the late reflex responses contributing to muscle hypertonia, reached their peak excitability one to three months after stroke, with a subsequent reduction in activity. The tendon jerk reflex therefore provides an incomplete picture of the pathological changes in the reflex responses in spasticity.     

The relevance of irrelevance to schizophrenia

Jeffrey Gray's neuropsychological theory of the positive symptoms of schizophrenia has been highly influential by enabling a strong link between animal and human research. Central to the development and testing of this theory has been the phenomenon and paradigm of latent inhibition (LI-the retardation of learning that one stimulus predicts the occurrence of another due to pre-exposure of the first stimulus). We review findings relating to its alteration in patients with schizophrenia (acute and chronic), people high on dimensions of schizotypy and the effects of amphetamine and anti-psychotic medication in humans. We suggest that many human-LI paradigms still suffer from theoretical and practical limitations, but that recent developments are beginning to address these. Finally we explore the idea that the paradigm of Learned Irrelevance (LIRR-the retardation of learning that one stimulus predicts the occurrence of another due to pre-exposure of both stimuli but in an unrelated manner) might be used to complement studies on LI in exploring the cognitive distortions suffered by patients with schizophrenia.     

Knee joint angular velocities and accelerations during the patellar tendon jerk

Tendon jerk (TJ) is one of the most commonly used clinical tests in differential diagnosis of human motor disorders. There remains some ambiguity in the physiological interpretation of the test, especially with respect to its association to the functional status of patients. The TJ test inputs a non-physiological stimuli, but it is unclear to what degree the kinematics generated during the TJ test exceed the ranges that muscles encounter in activities of daily living (ADLs). The aim of our pilot study was to determine the range of angular knee kinematics (angular velocities and accelerations) corresponding to the muscle stretch elicited by TJ. We measured the longitudinal kinematics (velocities and accelerations) of the rectus femoris muscle in vivo using vector tissue Doppler imaging, an ultrasound-based method, and measured the angular kinematics of the knee in response to tendon taps with an electrogoniometer. We concluded that muscle longitudinal elongation accelerations elicited during the standard TJ test exceed angular accelerations (104.40-4534.20 rads?2) encountered in typical ADLs, but the velocities (0.82-6.21 rads?1) elicited do not exceed those elicited by ADLs.     

Reproducibility of tendon jerk reflexes during a voluntary contraction.

OBJECTIVES: The present study explored whether testing tendon jerks during voluntary contraction of the test muscle would improve reproducibility by effectively 'clamping' the excitability of the motoneurone pool at firing threshold. METHODS: Tendon jerk reflexes of soleus, tibialis anterior and vastus lateralis and the soleus H reflex were recorded in 12 healthy subjects at rest and during voluntary contractions of 10-20% of maximum. Recordings were repeated 8-10 times in 5 subjects, in whom reflex symmetry was also determined. RESULTS: Not all tendon jerk reflexes could be recorded at rest, and the variability of latency and amplitude was high. All reflexes could be recorded in each subject during contractions. The latency of tendon jerk reflexes decreased by approximately 2 ms during contractions, but H-reflex latency decreased by only 0.2-0.3 ms. For the tendon jerks, an asymmetry of >3.0 ms at rest and >2.5 ms contracting would be outside 3 SD of the normal mean. In repeat studies, the coefficient of variation of reflex latency was <4% for the tendon jerk. CONCLUSIONS: A voluntary contraction could potentiate the tendon jerk by a number of mechanisms, but the most important is probably enhancement of the excitability of the motoneurone pool. The present techniques should increase the value of tendon reflex testing when assessing possible peripheral nerve, plexus and root disturbances.     

不同生物材料修复跟腱损伤的应用

背景：构建组织工程化肌腱的关键是寻找适于肌腱细胞黏附、生长及功能分化的支架材料。 目的：评价不同生物材料在跟腱损伤修复中的效果。 方法：以“生物材料,跟腱,修复” 为关键词在万方数据库中检索1985-01/2011-01关于生物材料治疗跟腱缺损的文章。 结果与结论：陈旧性跟腱断裂难以自行愈合及修复,易遗留疼痛及功能障碍。长期以来,不少学者对跟腱缺损的治疗进行了较多的研究,从自体肌腱移植、同种异体肌腱移植到人工肌腱移植、组织工程肌腱移植等,实践证明这些方法手段都存在一定的优点和缺点。虽然肌腱组织工程中支架材料的研究与应用已经取得了一些成功,但是目前应用的材料或存在生物相容性问题、降解性问题或存在力学性能差、难加工成型等缺陷,与理想的支架材料还存在很大差距。     

Repeated measurements of learned irrelevance by a novel within-subject paradigm in humans

Learned irrelevance (LIrr) refers to the retardation of classical conditioning following preexposure of the to-be-associated stimuli. Healthy volunteers have been tested on three occasions with a new LIrr paradigm avoiding methodological problems which afflict traditional paradigms. A significant LIrr effect was demonstrated on each occasion. Thus, the new paradigm enables repeated measurements of LIrr and might be useful in evaluating long-term effects of medication in psychiatric disorders exhibiting aberrant LIrr.     

Human muscle afferent responses to tendon taps. 2. Effects of variations in fusimotor bias.

The effect of varying the fusimotor bias on the muscle spindle responses to light tendon taps has been studied in normal human volunteers using surface electrodes at the wrist for recording whole nerve activity. Reinforcement manoeuvres were found to increase the sensitivity of the afferent responses to the mechanical stimulus. Such sensitisation was found to be exhibited more commonly as a decrease in the latency of the peak of the afferent waveform than as an increase in amplitude. Increase in amplitude of the response was seen in cases where the subject was well relaxed and the test muscle quiescent. A change in furimotor drive was also achieved by asking the subjects to close their eyes voluntarily during the test, thus depriving themselves of the visual feedback. The results under these conditions were found to be variable, though showing considerable changes from control recordings. The effect of reinforcement manoeuvres may perhaps result in increasing the dynamic fusimotor drive. Such an effect may be simulated on occluding the blood supply to the test muscle since ischaemia produces an immediate rise in the rate of afferent discharge. The method of recording is suggested as a convenient technique for clinical use.     

Dependence of the Achilles tendon reflex on the excitability of spinal reflex pathways

Muscle afferent activity from the triceps surae was recorded during experimentally induced alterations in amplitude of the Achilles tendon jerk. No changes in the neural afferent response to tendon percussion or in the background level of neural activity occurred when the reflex response was altered by discomfort, distraction, changes in attention, or changes in the rate of tendon percussion. Reinforcement of the Achilles tendon jerk by forceful contraction of the forearm muscles did not alter the relationship between intensity of the tendon tap and amplitude of the evoked neural afferent volley. Nevertheless, such maneuvers lowered the reflex threshold and raised reflex sensitivity so that a smaller afferent volley was required to produce a tendon jerk, and an increase in the afferent volley produced a disproportionately greater increase in reflex electromyographic activity than would have occurred at rest. Reinforcement maneuvers potentiated the H-reflex but did not alter the electrically induced afferent volley or the background level of neural activity. It is concluded that these changes in reflex responsiveness occurred through intrinsic spinal mechanisms independent of the fusimotor system.     

Independence of skeletomotor and fusimotor activity in man?

The activity of human muscle spindle afferents from finger extensor muscles has been studied during voluntary movements in a visual tracking paradigm. With an elastic load the spindle discharge rate was disproportionately high when the opposing force was close to zero, suggesting that the fusimotor drive was high when the direct afferent information about the size of the load that the subject had to handle was poor.     

生物补片材料进展与运动性跟腱断裂的修复

文章采用文献资料调查与分析的方法，根据研究目的查阅运动性跟腱损伤以及手术修复的相关论著, 为分析提供依据。结果表明运动性跟腱断裂与跟腱的解剖结构、跟腱局部的病变及运动技术等因素有关，当跟腱完全断裂时目前主张手术治疗。随着组织工程化肌腱研究的发展，临床上已经越来越多的将生物补片用于跟腱的修补治疗，从防止术后粘连到替代跟腱方面生物补片均有一定的优势。     

The responses of muscle spindles to small, slow movements in passive muscle and during fusimotor activity

We have previously shown that movement detection thresholds at the human elbow joint were less than a degree of joint rotation in the passive limb but were higher if they were measured while subjects co-contracted elbow muscles [A.K. Wise, J.E. Gregory, U. Proske, J. Physiol., 508 (1998) 325-330]. Here we report observations on the responses of muscle spindles of the soleus muscle of the anaesthetised cat to determine their ability to signal small length changes in the passive muscle and during a contraction, under conditions resembling those of the human experiments. After appropriate conditioning of the muscle to control for history effects, primary endings of muscle spindles showed thresholds to ramp stretch at 20 micrometers s-1 of between less than 5 micrometers and 15 micrometers, which translates to 0.05 degrees -0.15 degrees of human elbow joint rotation. Thresholds were much higher following conditioning to introduce slack in the muscle. Since during a voluntary contraction there is likely to be alpha:gamma co-activation, responses of spindles were also recorded during slow stretches (100 micrometers at 20 micrometers s-1) during static fusimotor stimulation, dynamic fusimotor stimulation, combined fusimotor stimulation and fusimotor plus skeletomotor stimulation. Invariably, responses to passive stretch were larger than during motor stimulation. It is concluded that spindles are sensitive enough to signal fractions of a degree of elbow joint rotation and that the rise in threshold observed during a voluntary contraction may be accounted for by the actions of fusimotor and skeletomotor axons on spindle stretch responses.