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In spiders, retrograde cobalt staining was used to clarify the distribution and detailed innervation of the three types of proprioceptors in the tibio-metatarsal leg joint: internal joint receptors, lyriform slit sense organs, and cuticular spines and hairs. The axons of all these receptors run in just two lateral, ascending nerves, which had previously been associated only with the internal receptors. Each nerve contains several hundred axons ranging in diameter from 0.1 micron to ca. 10 micron. Each slit of the four tibial lyriform organs is innervated by two bipolar sensory neurons. The lateral nerves are entirely sensory and run just beneath the cuticle, a convenient site for electrophysiological recording. We demonstrate simultaneous nerve and muscle recordings from intact spiders; these, in combination with selective sensory ablations, show that a resistance reflex in the flexor metatarsi muscles is elicited by internal joint-receptor units.
Tendon jerk and H-reflexes are both potentiated by the Jendrassik manoeuvre, but the mechanism of potentiation remains uncertain. We investigated several possibilities in human subjects. Evidence for fusimotor activation during the Jendrassik manoeuvre was sought by recording the tendon jerk reflex as surface EMG in triceps surae after the muscles had been conditioned to leave their spindles in a slack, insensitive state. Interposing a Jendrassik manoeuvre between conditioning and the test reflex should have increased reflex amplitude by restoring spindle sensitivity, but this was not the case. In humans, a close synergist of the triceps surae is the quadriceps. A possible presynaptic disinhibitory mechanism was investigated by testing the effect of a Jendrassik manoeuvre on facilitation of the soleus H-reflex produced by a quadriceps afferent volley. The Jendrassik manoeuvre failed to increase facilitation, contrary to what would be expected if it reduced the level of tonic presynaptic inhibition; the assumption being that the inhibition acts on both homonymous and synergist afferent terminals. The Jendrassik manoeuvre did not increase the level of ongoing EMG in the soleus during a weak voluntary contraction, indicating that it does not operate by direct facilitation of motoneurones. There was found to be less potentiation of soleus tendon jerk and H-reflexes by the Jendrassik manoeuvre under conditions when spindles in the soleus were likely to have a high resting discharge rate. A remaining possibility is discussed: that the Jendrassik manoeuvre operates by modulation of oligosynaptic pathways that may contribute to the largely monosynaptic reflex response. These experiments demonstrate, with new, more sensitive methods than previously used, that neither is the fusimotor system involved in reinforcement nor are direct excitatory or presynaptic disinhibitory effects on motoneurones. While this confirms the previously prevailing view, none of the lingering uncertainties associated with the methods used now remains.
Acute adaptations to use have been shown to occur in both the muscle spindle and Golgi tendon organ pathways. This short term activation adaptation increases the excitability of the motoneuron pool, thereby potentially providing a nonvoluntary increase in the excitation of subsequent contractions. It is thought that the intrafusal muscle fibres reset to a higher gain after contraction and that the tendon organ pathway undergoes a brief desensitisation. These phenomena could be important clinically when trying to stretch muscles, i.e. a contraction before a stretch should make the stretch more difficult. Also, this could affect the amount of muscle force generated, thereby altering motor behaviours requiring fine accuracy. Research on the adaptations of proprioceptors during free movement, using locomotion as a model, has found that the hypothesis of consistent alpha-gamma coactivation during motor behaviours is much more complicated and adaptable, depending on the environmental circumstance and the specific motor task. These research findings support the use of selective training, i.e. training to the task, for optimal motor learning. The results of the relatively limited research on chronic adaptations of proprioceptors due to exercise has shown that on a microlevel, the intrafusal muscle fibres may show some metabolic changes but do not show any hypertrophy. However, on a more macro level, with extended training, the latency of the stretch reflex response is found to be decreased and the amplitude is found to be increased in both animals and humans. Through classical conditioning research, proprioceptors may also be necessary for motor learning. Lastly, both primates and humans have been shown to be able to up- or down-grade their stretch reflex responses using operant conditioning techniques and many practice sessions. These findings have important implications both for rehabilitation of persons with abnormal reflex activity and in the training of athletes. This review provides some consolidation of the recent research findings, but much more research needs to be done in order to fully understand the purpose and importance of the proprioceptive sensory system.
The physiological mechanisms operating through the temporomandibular joint in the perception of changes in the position of the mandible can determine extremely small discrepancies in the final occlusal position. Some observations on the pathways of neural control and reflexes are discussed and their importance in clinical situations noted.
1. It has been demonstrated that subjects can alter the reflex stiffness of the elbow and wrist in response to imperceptibly slow perturbations applied through a complaint coupling. We used this technique to measure ankle stiffness in standing subjects as a means of examining reflex activity. 2. During unperturbed stance, a linear relationship between ankle torque and ankle angle is expressed as a load stiffness. The load stiffness predicted from a subject's measured physical dimensions corresponds closely with the value measured by standing the subject on a force platform. 3. Slow perturbations were applied at waist level, through a spring, to standing subjects. The perturbations caused sway similar in magnitude and rate to the sway of normal stance. Ankle stiffness was measured during the period when the perturbations were unperceived. The contribution to ankle stiffness of reflexes that use visual information was assessed by eye closure. The ability of reflexes based on sensory information from the legs to maintain upright posture was assessed when subjects balanced a load equivalent to their own body, in a situation where neither visual nor vestibular information could assist. Ankle stiffness was measured while the load was perturbed. 4. The results show that a simple mechanical model of stance predicts the torque-angle relationship at the ankle. This relationship determines the minimal ankle stiffness required to stand, and reflex muscle stiffness is a necessary component of this ankle stiffness. Visual, vestibular and lower limb sensorimotor reflexes each contribute to ankle stiffness; however, the local sensory reflexes alone are sufficient to stand. For responses to unperceived perturbations, standing subjects can alter their reflex ankle stiffness according to intentional set.
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The purpose of this study was to investigate the effects of hip proprioceptors on soleus stretch reflex excitability in standing humans. A custom-made device to stretch the ankle extensors was mounted on the lower leg portion of a gait orthosis and was used to elicit stretch reflex responses while standing. Six subjects with motor complete spinal cord injury (SCI) and six spinal intact subjects were placed in the orthosis, and stretch reflex responses were elicited when static and/or dynamic hip joint angle changes were imposed. We found that static hip extension significantly enhanced the stretch reflex responses as compared to the neutral position and the hip flexion position only in the SCI group. The EMG magnitude induced by hip extension was 142 +/- 16.6% greater than that induced by the neutral position. When the leg was dynamically swung, the reflex responses also changed with the phase of the hip angle in the SCI group; in particular, the reflex amplitude was enhanced with hip extension and in the transition phase from flexion to extension. Although the magnitude of the changes was less than that in the SCI group, a similar type of modulation was found in the normal group. Given the fact that the persons with SCI had lost the neural connection between higher nervous center and the paralyzed lower limb muscles, the mechanism underlying the present results can be attributed to the peripheral afferent input due to the hip angle changes. We concluded that hip mediated afferent input has a significant influence on the excitability modulation of the soleus stretch reflex pathway. Such neural modulation may play a role in the mechanism responsible for the phase-dependent modulation of the stretch reflex while walking.
1. Mechanical actions of heterogenic (intermuscular) reflexes arising from proprioceptors in flexor and extensor ankle muscles were measured in intercollicular and premammillary decerebrate cats. Length inputs were applied to the freed tendons of one of a pair of muscles crossing the ankle joint and resulting changes in force in both muscles were measured. Interactions between autogenic and heterogenic reflexes were studied by applying length changes to both muscles. 2. A consistent asymmetry was observed in the heterogenic inhibition between the single-joint antagonists soleus and tibialis anterior (TA). Inhibition from soleus to TA was weak or absent during the reflex activation of TA. In contrast, a strong heterogenic inhibition was consistently observed from TA to soleus during the activation of soleus by a crossed-extension reflex. The effect of this inhibition in the intact joint is to increase the apparent mechanical stiffness of soleus. 3. Mutual synergism among soleus, medial gastrocnemius (MG) and lateral gastrocnemius (LG) was demonstrated only at low to moderate forces by the observation of excitatory reflexes among them. During a naturally or electrically evoked crossed-extension reflex, however, a unidirectional inhibitory reflex from MG and LG to soleus was observed. This inhibition increased with force in MG or LG. These results suggest that the knee and ankle joints become more tightly linked mechanically at high forces since the stiffness of the biarticular gastrocnemius muscle predominates over that of the uniarticular soleus. 4. Under quiescent conditions (no resting muscle activation), mutual synergism was obeyed among the ankle extensors soleus, LG and MG and also between the pretibial flexors TA and extensor digitorum longus (EDL). Moreover, inhibition was generally observed between a pretibial flexor and an ankle extensor. Departures from this expected pattern of heterogenic reflexes occurred when the muscle groups were activated by crossed-extension and flexion reflexes. Reflexes onto soleus, TA and EDL reversed in sign or increased in magnitude. 5. The observed patterns of reflex connectivity among the ankle flexors and extensors were similar in both intercollicular and premammillary preparations, although changes in reflex strength were sometimes noted in cases where a second, lower transection was performed during the experiment. 6. It is argued from the large magnitudes of certain heterogenic reflexes that the mechanical response properties of muscles crossing the ankle joint in the intact animal are not dominated by autogenic reflexes and intrinsic mechanical properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Recent studies have described sensory-motor function alterations resulting from vibrations applied to various parts of the body. The present work describes the effects produced at the myotatic loop level by long-term vibration. Hoffmann and Tendon reflexes as well as tendon vibration response were substantially depressed by 18 Hz, +/- 0.25 G vibration applied to the whole body or to the legs of seated human subjects. The reflex inhibition lasted throughout the 15-min vibration period and persisted minutes after stimulus cessation. In contrast, vibration limited to the S's head and trunk showed much weaker effects. This suggests that the vibration acts mainly upon extero- and proprioceptive receptors rather than upon the vestibular organs. The results are discussed in relation to findings derived from experiments involving locally applied short-duration vibration.
This review focuses on the role of the cerebellum in regulating cutaneomuscular reflexes and provides a hypothesis regarding the way in which this action contributes to the coordination of goal-directed movements of the extremities. Specific attention is directed towards the cerebellum's role in conditioned and unconditioned eyeblink reflexes and limb withdrawal reflexes as models of its interactions with the cutaneomuscular reflex systems. The implications regarding the cerebellum as a storage site for motor engrams also is discussed in the context of these two behaviors. The proposed hypothesis suggests that the cerebellum regulates important features of the cutaneomuscular reflex circuits including the integration of their activity with descending pathways in a manner that implements these fundamental reflex circuits in the organization and control of goal-directed movements of the extremities.
Evoked electromyograms (EMGs) induced by galvanic stimulation of the labyrinth were examined in the muscles of the lower limbs. The labyrinthine-evoked EMGs appeared in the muscles of the femoral and gluteal regions and of the legs, and these muscle activities were changed by the head position in spite of the labyrinthine stimulation being the same. The vestibulo-spinal reflexes fulfil these functions in coordination with the neck proprioceptor.
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In order to obtain a complete functional balance in the patient suffering from vestibular disorders it is necessary to examine the spinal reflexes. Computerized posturographic systems allow quantitative and qualitative analysis of body sway. The posturographic test must be preceded by an accurate clinical examination to identify the anomalies of the osteo-arthro-muscular structure that can cause disorders in motor programs and in proprioceptive inputs. A battery of complementary posturographic tests can clarify the influence of the vestibular, proprioceptive and visual inputs. The posturographic tests allow us: to observe particular aspects of postural control which are not usually detected by the common clinical examination; to identify the most correct kind of functional reeducation and to monitor the spontaneous evolution of the disease and the results of the therapy; to show the voluntary simulators or accentuators of unsteadiness in medico-legal reports.
This study was undertaken to determine the effect of spinal cord damage on motor development, and to determine whether there is greater survival of motor function in those motor patterns with a later onset of function than in those which are present at birth. The postnatal development of postural reflexes and locomotion was examined during the first 4 months of life in normal kittens and in those which had received a spinal cord lesion (at high cervical or low thoracic levels) at birth. The results suggest that there are some similarities in normal development, recovery of function after adult lesions and recovery and/or development of function after neonatal lesions. After neonatal lesions, just as after lesions in adults, reflex recovery appears to underlie recovery of locomotion. After spinal lesions, the pattern and sequence of motor development was identical to that seen in normal animals. Hindlimb motor development was normal for some time after the spinal lesion, but deficits appeared later. These observations suggest that postural reflexes and locomotion are not dependent upon ipsilateral descending input for their onset, but only for their maturation. Unexpectedly, tactile placing developed after neonatal spinal cord lesions. This represents sparing of function, for tactile placing is abolished and does not recover after the same lesion sustained in adulthood. Tactile placing is the last of the series of postural reflexes to develop. It depends on the last of the spinal pathways to develop, the corticospinal tract. Two aspects of this study support the hypothesis that later developing motor patterns will have a greater chance for survival and subsequent development than those which are present at birth. First, the immediate effects of spinal cord lesions on postural reflexes are more severe on those reflexes that are more mature at birth. Second, the spinal cord lesions produce more severe impairment of the more mature forelimb motor function than of the less mature hindlimb motor function. The hypothesis is not supported, however, when the long-term effect of spinal cord lesions on the maturation of motor behavior is considered. All postural reflexes and locomotion fail to mature fully, i.e. they retain characteristics of the immature responses.
BACKGROUND: The use of external ankle support is widespread throughout sports medicine. However, the application of ankle bracing to a healthy ankle over a long period has been scrutinised because of possible neuromuscular adaptations resulting in diminished dynamic support offered by the peroneus longus. OBJECTIVE: To investigate the immediate and chronic effects of ankle brace application on the amplitude of peroneus longus stretch reflex. METHODS: Twenty physically active college students (mean (SD) age 23.6 (1.7) years, height 168.7 (8.4) cm, and mass 69.9 (12.0) kg) who had been free from lower extremity pathology for the 12 months preceding the study served as subjects. None had been involved in a strength training or conditioning programme in the six months preceding the study. A 3 x 3 x 2 (test condition x treatment condition x time) design with repeated measures on the first and third factor was used. The peroneus longus stretch reflex (% of maximum amplitude) during sudden foot inversion was evaluated under three ankle brace conditions (control, lace up, and semi-rigid) before and after eight weeks of ankle brace use. RESULTS: A 3 x 3 x 2 repeated measures analysis of variance showed that peroneus longus stretch reflex amplitude increased immediately after application of a lace up brace (67.1 (4.4)) compared with the semi-rigid (57.9 (4.3)) and control (59.0 (5.2)) conditions (p<0.05). Peroneus longus stretch reflex also increased after eight weeks of use of the semi-rigid brace compared with the lace up and control conditions (p<0.05). CONCLUSIONS: Initial application of a lace up style ankle brace and chronic use of a semi-rigid brace facilitates the amplitude of the peroneus longus stretch reflex. It appears that initial and long term ankle brace use does not diminish the magnitude of this stretch reflex in the healthy ankle.
This paper raises new questions about the relationship between occlusion and periodontics. Specifically, it raises questions about the effect of periodontal diseases on mechanoreceptors in the periodontal ligament. Periodontal mechanoreceptors transmit information from the periodontium to various reflexes coordinated by the central nervous system. One of these reflexes is the trigemino-neck reflex. Its function is to change the position of the head, neck, and jaws on a moment-to-moment basis, and it powerfully influences the occlusal position. This paper raises questions about the consequences of periodontal diseases on all reflexes that depend on periodontal mechanoreceptors, and specific questions are raised about the effect of periodontal disease on the trigemino-neck reflex because of its extreme importance to the way we analyze and treat occlusion.
Gluteal activation and pelvic stability often are decreased in chronic low-back pain sufferers, but the importance of motor control and programming in treatment has not been fully evaluated. This study investigated whether gluteal muscles could be activated more effectively by stimulating the proprioceptive mechanism during walking. Labile support, through wearing "balance shoes," offered facilitation of cerebellovestibular circuits. Electromyographic recordings of gluteus maximus and medius in 15 healthy subjects were made during barefoot and balance shoes walking before and after 1 week of facilitation. Significant increases (P < 0.0002) in gluteal activity and significant decreases (P < 0.01) in time to 75% maximum contraction, demonstrated the value of sensorimotor elicitation of subconscious and automatic responses in muscles often weakened in back pain sufferers.