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PubMedDate not supplied

Functional instability of the ankle and the role of neuromuscular control: a comprehensive review.

A review of current knowledge of the clinical syndrome of functional ankle instability is presented. Recent evidence has demonstrated that the majority of patients with functional instability of the ankle do not have mechanical hypermobility of the ankle joint. Functional instability of the ankle results from a loss of neuromuscular control. Components of neuromuscular control include proprioception, muscle strength, muscle reaction time, and postural control. Proprioceptive deficits lead to a delay in peroneal reaction time, which appears to be a peripheral reflex. Proprioception and eversion muscle strength improve with the use of passive supportive devices. Balance and postural control of the ankle appear to be diminished after a lateral ankle sprain and can be restored through training that is mediated through central nervous mechanisms. Methods of detecting deficits in neuromuscular control are presented along with rehabilitation techniques to treat functional instability of the ankle.

Ankle Injuries↗

PubMed1978

Intersegmental reflex actions from a joint sensory organ (CB) to a muscle receptor (MCO) in decapod crustacean limbs.

In the walking legs of decapod crustaceans, intersegmental reflex actions originate from various joint proprioceptors. The activity of the 'accessory flexor' (AF) muscle, which with the myochordotonal organ (MCO) constitutes a muscle proprioceptor for the mero-carpopodite (M-C) joint, is modulated by the sensory discharge of a joint receptor (CB chordotonal organ) for the more proximal, coxo-basal (C-B) joint. Selective mechanical stimulation of the CB organ also reflexly modifies the motor activities of the main M-C flexor and extensor muscles (recorded as EMGs). 1. Dynamic CB stretch (as would occur during a dorso-ventral C-B movement - i.e. 'depression' of the limb) stimulates motor discharge to the M-C extensor muscle, while dynamic release of CB (as during a ventrodorsal C-B movement - or leg 'elevation') excites the accessory flexor as well as the main flexor muscle. 2. Successive M-C muscle responses to repetitive sinusoidal changes of CB length differ quantitatively according to the direction (stretch or release) of the first CB movement, in some cases increasing but more commonly 'adapting' with repetition. 3. Reflex discharge frequencies of the extensor, flexor and accessory flexor motoneurones increase with velocity of CB movement. 4. Eye illumination, and spontaneous or other sources of increased central excitability, generally increase the CB reflex drive to the flexor and accessory flexor muscles and, in parallel, decrease the reflex action on the extensor muscle. The results are discussed in terms of the role of proprioceptive reflexes in intersegmental co-ordination of the leg joints. In particular the significance of the reflex regulation of the myochordotonal receptors, and thereby the gain of the M-C resistance reflexes, is considered in the light of the observed 'co-activation' of main flexor and receptor muscle motoneurones.

Action Potentials↗

PubMed1980

[Pathophysiology of tetanus rigidity (author's transl)].

Brainstem reflexes have been studied electrophysiologically in six patients with generalized tetanus. The selective impairment of reflexes with long polysynaptic pathways supports the assumption of an interneuronal dysfunction in tetanus. The behaviour of proprioceptive reflexes suggests that hyperactivity of gamma-motoneurons contributes to the rigidity in an early stage of the disease.

Adult↗

PubMed1990

Significance of dopamine receptor antagonists in human postural control.

The purpose of this study was to investigate the effect of different dopamine receptor antagonists on the function of proprioceptive reflex mechanisms involved in the regulation of stance and gait. Haloperidol as preferential D2 and the 'pure' dopamine D2 receptor antagonist sulpiride significantly reduced the level of the reflex response in the gastrocnemius muscle following backward perturbation. Flupentixol, however, which in addition blocks D1 receptors, had no effect on compensatory gastrocnemius EMG responses. Furthermore, neither the peripherally acting dopamine D2 receptor antagonist domperidon nor the sedative diazepam had any significant influence on this functionally essential reflex mechanism. None of the drugs tested had a significant effect on the tibialis anterior responses elicited following forward perturbation. It is concluded that the reduced stretch sensitivity of the gastrocnemius (but not that of the tibialis anterior) during perturbations of stance described for parkinsonian patients corresponds to these results and arises from an impaired function of central dopamine D2 receptors.

Adult↗

PubMed1986

Behavior of larval and juvenile bullfrogs (Rana catesbeiana) following chronic spinal transection.

The behavior of larval and juvenile bullfrogs (Rana catesbeiana) was examined for 32 days following cervical spinal transection. The threshold for cutaneously elicited hindlimb withdrawal was not changed at either stage of development but righting reflexes were abolished. Forelimb postural support of juveniles was abolished by the transection but recovered within 3 days. Hindlimb posture was normal and hopping could be elicited by stimulation of the rump with a blunt wire probe. Undulatory swimming of larvae was abolished by the transection but began to recover approximately 1 week later. The hindlimbs of larvae were very active following the transection and displayed long sequences of coordinated stepping in response to a variety of stimuli. Gross examination of the spinal cord in situ after 32 days suggested that fibers may have grown across the transection site. Retransection at the site of the original transection on Postoperative Day 33 had no discernable effect on the behavior juveniles or on the stepping of larvae, but it abolished recovered swimming of larvae. Deafferentation of lumbar segments of larvae eliminated stepping but had no effect on swimming. Deafferentation of cervical segments eliminated forelimb support in juveniles. These results suggest that recovery of larval swimming depends at least in part upon the growth of fibers across the transection site. Stepping of spinal larvae appears to be mediated by proprioceptive reflexes rather than by central pattern generators, and in the normal animal is probably under the control of descending inhibition. Recovery of posture and hopping in juveniles was much more rapid than that described for adult frogs and does not depend on growth across the transection site.

Animals↗

PubMed1995

Reflex responses associated with manipulative treatments on the thoracic spine: a pilot study.

OBJECTIVE: To test systematically if spinal manipulative treatments (SMT) and the audible release associated with SMT cause activation of spinal muscles. DESIGN: Experimental pilot study. SETTING: Human Performance Laboratory, The University of Calgary. PARTICIPANTS: One male and one female asymptomatic volunteer. INTERVENTION: Slow and fast SMTs to the left transverse process of thoracic vertebrae using a reinforced hypothenar contact. The treatment forces were directed in a posterior-to-anterior direction with the subjects in a prone position. MAIN OUTCOME MEASURES: Forces applied by the chiropractor during SMT. Measurements of the audible release using skin-mounted accelerometers. Electromyographical activity of selected spinal muscles. RESULTS: Electromyographical (EMG) activity was observed consistently 50-100 msec after the onset of each of the fast SMTs, whether the treatment resulted in an audible release or not; for slow SMTs, there was never any visible electromyographical activity of the target muscles, whether the treatment resulted in an audible release or not. CONCLUSION: The results of this study suggest that fast treatment thrusts elicit muscle activation, whereas slow force application does not. The timing of the onset of the EMG response suggests that activation may be produced by a reflex response originating in the muscle spindles. It also appears that the audible release does not (by itself) evoke muscle activation or a joint proprioceptive reflex response as has been speculated in the literature.

Adult↗

PubMed1994

Intercostal muscle compensation for parasternal paralysis in the dog: central and proprioceptive mechanisms.

1. Denervation of the parasternal intercostal muscles in the dog is known to cause a substantial reduction in the inspiratory cranial displacement of the ribs and a compensatory increase in the activation of the other inspiratory intercostal muscles, namely the external intercostals and the levator costae. The present studies were designed to assess the mechanism(s) of that compensation. 2. Denervating the parasternal intercostals bilaterally caused a reduction in tidal volume and an increase in arterial PCO2 (Pa, CO2). Severing the parasternal intercostals selectively produced similar changes. The concomitant increases in external intercostal and levator costae activity, however, were much greater than predicted on the basis of the increased Pa, CO2. 3. Denervating the parasternal intercostals on one side of the chest produced large increases in ipsilateral, but not contralateral external intercostal activity. 4. Manipulating the ribs after the parasternal intercostals were inactivated so as to reproduce the normal inspiratory cranial displacement of the ribs elicited immediate, clear-cut reductions in external intercostal and levator costae activities. 5. The increases in external intercostal and levator costae activities that occur after inactivation of the parasternal intercostals thus result partly from the increased hypercapnic drive but mostly from proprioceptive reflexes, presumably muscle spindle reflexes.

Animals↗

PubMed1985

Motor unit recruitment and firing rates interaction in the control of human muscles.

Muscle contractions are modulated by the number of motor units recruited and their respective firing rates. The work described in this report documents an interplay between recruitment and firing rates of motor units. The recruitment of a new motor unit appears to have a disfacilitatory influence on the firing rates of previously activated motor units. It is speculated that this effect is likely to be mediated, at least partially, via the stretch reflex loop and possibly by the recurrent inhibition of the Renshaw circuit. Such a mechanism would be functionally useful in providing smooth control of muscle output via peripheral circuitry (consisting of proprioceptive reflexes and recurrent inhibition), thus lessening the amount of detailed supervision of the alpha-motoneuron pool required by the central nervous system.

Action Potentials↗

PubMed1978

Control of pedal and parapodial movements in Aplysia. II. Cerebral ganglion neurons.

1. Intracellular stimulation of individual neurons in the two symmetrical A neuron clusters of the cerebral ganglion evoked contractions of both the foot and parapodia. Electrical stimulation of pedal and parapodial nerves caused antidromic action potentials in A neurons. Units recorded in the nerves followed the driven somatic spike 1:1. This suggests that the A neurons are presumptive pedal and parapodial motor neurons.2. Individual A neurons evoked both bilteral and unilateral contractions of the parapodia or split foot. Contractions in the parapodia were independent of those in the foot. An individual A neuron caused contractions in either the foot or the parapodia, but not both. Sequential transection of parapodial nerves had only a slight effect until a key nerve was cut. The contractions produced by a single A neuron on one side were then abolished. These data suggest that the motor fields of the A neurons are well defined within the foot or the parapodia. 3. Parapodial contractions produced by individual A neurons are not dependent on the excitation of follower motor neurons. Blocking synaptic transmission by the addition of CoCl2 did not eliminate the contractions produced by driving individual A neurons. This is consistent with the A neurons being motor neurons. 4. Intracellular stimulation of individual neurons in the symmetrical B neuron clusters of the cerebral ganglion also evoked pedal and parapodial contractions. Electrical stimulation of the pedal and parapodial nerves elicited antidromic spikes in these neurons. Individual B neurons caused contractions in both the foot and parapodia. This suggests that the B neurons are motor neurons with very large motor fields. 5. Filling the pedal and parapodial nerves with cobalt primarily filled the cell bodies of neurons located in the pedal and pleural ganglia. The somata of A and B neurons were also occasionally filled. This is consistent with the electrophisiological results. 6. Other neurons also evoked parapodial contractions. Intracellular stimulation of neurons in the pedal and pleural ganglia caused parapodial contractions in intact animals. Some of these neurons were excited by stretching the parapodia or touching the tentacles. 7. The B neurons are strongly excited by tactile stimulation of the tentacles. Since they can cause pedal and parapodial contractions they may mediate reflex contractions elicited by tentacular stimulation. Stretching the parapodia only occasionally caused the A neurons to fire. This makes it unlikely that they make a major contribution to pedal and parapodial proprioceptive reflexes. These reflexes are probably controlled by neurons in the pedal and pleural ganglia.

Animals↗

PubMed2006

The 1932 and 1944 Nobel Prizes in physiology or medicine: rewards for ground-breaking studies in neurophysiology.

In 1932 Sherrington and Adrian were awarded the Nobel Prize in Physiology or Medicine "for their discoveries regarding the functions of neurons" and in 1944 Erlanger and Gasser were awarded the same prize "for their discoveries relating to the highly differentiated functions of single nerve fibres." Sherrington made important discoveries on the reflex functions of the spinal cord, formulated the concept of the "synapse," defined the principle of the "final common path," studied "reciprocal innervation" and showed that central inhibition was an active phenomenon. He distinguished three types of receptors: extero-, intero-, and proprioceptive, studied the proprioceptive reflexes in the decerebrate animal and mapped their pathways in the spinal cord. Adrian made fundamental discoveries on the function of single nerve fibers, developed new techniques for the amplification of the weak signals and discovered that increased stimulation resulted in increased frequency of the impulses, the amplitude being unaffected. Erlanger and Gasser introduced the cathode-ray oscillograph and demonstrated the existence of three main groups of nerve fibers, A, B, and C, the conduction velocities of which were in approximately linear relationship with the fiber diameter, the A-fibers being the fastest and thickest and the C-fibers the slowest and having the finest diameter. Together the contributions by the four Laureates paved the way to modern neurophysiology.

History, 20th Century↗

PubMedDate not supplied

Aging of human segmental oligosynaptic reflexes for control of leg movement.

A heteronymous group I oligosynaptic reflex from the common peroneal nerve to vastus medialis muscle was compared with a group I homonymous monosynaptic reflex to soleus, using electrical stimulation of peripheral nerve trunks in two groups of healthy men, mean ages 22 and 65 years. The oligosynaptic reflex was still elicitable with age, its magnitude decreasing similarly to the monosynaptic reflex. A further group of older subjects, mean age 75 years, showed similar results. Clearly, the oligosynaptic reflex is not lost with healthy aging. The motor interneuronal pool may at least partially avoid the age-related cell loss of motoneuronal pools, with consequent maintenance of segmental participation for movements such as gait. The slowing of conduction velocities, for these proprioceptive reflex arcs, may reduce the effectiveness of autoregulation of the gait.

Adult↗

PubMed1976

Neurophysiology of locomotor automatism.

It had long been known that the decapitated cock can cross a yard. During the last century an automatic mechanism controlling stepping movements has also been found in other vertebrates. The system controlling locomotion has many features similar to these systems controlling other natural movements: respiration (28), micturition (98), scratching (154), mastication (33), etc. Today we know that there are spinal automatisms for each limb generating its stepping movements. Activity of these automatisms depends essentially on the afferent inflow from the moving limbs. There also is interaction of the limbs during locomotion that promotes their coordination. The existence of two descending systems with different functions in the control of locomotion (Fig. 1) also can be considered as an established fact. Activity of a number of neurons involved in the control of locomotion has been studied directly during locomotion in decorticate, thalamic, and mesencephalic cats. To explain the experimental data at hand, several hypotheses of organization of the spinal automatism of stepping have been forwarded: a chain-reflex hypothesis, a hypothesis of two reciprocal half-centers, and a ring hypothesis (Fig. 2). Although general features of the system controlling locomotion are more or less clear, many questions are not yet answered. It is unknown what relative contributions to motoneuronal activity are made by proprioceptive reflexes versus influences from the automatism of stepping. Furthermore the structure of the spinal stepping automatism is not known. It is not clear if the spinal stepping automatisms of the forelimbs are as potent as those of the hindlimbs. The descending system responsible for activation of the spinal automatism of stepping has not yet been identified in direct experiments. The inputs and outputs of the subthalamic and midbrain "locomotor" regions have not been found, and we know almost nothing about intrinsic interaction of neurons in these regions. The role of inhibitory thalamic influences is scarcely known. Finally, we have no data concerning the influence of either cortical (42, 186) or visual mechanisms in locomotor control.

Afferent Pathways↗

PubMed1986

Effects of pressure stimulation of the body surface on posture and vestibulospinal reflexes.

The effects of pressure stimulation of the body surface on postural activities as well as on the response gain of limb extensors to natural stimulation of labyrinth receptors were investigated in intact, as well as in decerebrate cats. In intact, unanesthetized cats, slight pressure applied symmetrically to the body surface at the chest level decreased the tonic activity of the axial (neck) and limb extensor musculature, as well as the proprioceptive reflexes induced by passive flexion of the limbs. The positive supporting reaction caused by pressure applied to the pad of the foot was also depressed. If the cats were suspended in the air by their nape, slight pressure applied to the upper part of the body greatly reduced the tonic contraction of the forelimb extensors to linear acceleration after downward movement of the animal, a response which can be attributed to stimulation of macular receptors located in the sacculus. Moreover, the prominent myotatic reflexes which occurred in all four limbs as soon as the animal touched the floor were greatly depressed, as shown by the fact that the forelimbs displayed only a slight tonic contraction of the extensor musculature during landing, while the hindlimbs collapsed under the weight of the body. In precollicular decerebrate cats there was a good postural activity in all four limbs. Moreover, the multiunit EMG activity of the medial head of the triceps brachii responded to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees) leading to selective stimulation of labyrinth receptors. These responses, characterized by an increased EMG activity during side-down tilt and a decreased activity during side-up tilt, were related to animal position and not to velocity of animal displacement, and are thus attributable to stimulation of macular, utricular receptors. Slight pressure applied to the chest greatly decreased not only the postural activity of the limbs, but also the amplitude of EMG modulation and then the gain in the first harmonic component of the multiunit EMG responses of the triceps brachii to animal tilt. This reduced gain was due, in particular, to a reduced number of motor units being recruited during labyrinth stimulation, although a reduced modulation of firing rate of the active motor units should not be ruled out. However, no changes in the phase angle of the responses were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Late spinal dislocation after treatment of spinal arteriovenous malformation. A case of Charcot spinal arthropathy.

Neuropathic arthropathy of the spine is a destructive condition of the spine which is secondary to a loss of the protective proprioceptive reflexes. In the majority of cases, it occurs in patients who have suffered from traumatic medullary lesions and is responsible for destruction of the vertebral bodies and considerable spinal deformity. We report a case of neurogenic lumbar arthropathy in a patient with a spinal arteriovenous malformation. This vascular lesion caused considerable disturbances of proprioception. The course was favorable with regard to the deformity after correction and fusion by posterior approach.

Adult↗

PubMed1975

Alpha motoneuron responses to natural stimuli in decerebellate cats.

The responses of single alpha motoneurons to various "natural' stimuli were recorded from dissected ventral root filaments in lightly anesthetized control and recently decerebellate cats. The identity of the motoneurons was established by recording the unitary responses to orthodromic stimulation of nerves innervating the triceps surae muscles in the hindlimb. We recorded only the activity of units which responded to electrical stimulation of the medial or lateral gastrocnemius nerves, though some units responded to stimulation of both these nerves, and some also responded to stimulation of the posterior tibial nerve. The distributions of unit latencies and amplitudes did not differ between the two groups of animals. Baseline firing rates were also similar. However, unit firing rates in response to neck extension, ipsilateral hindfoot dorsi- or ventral-flexion were significantly higher in decerebellate than in control cats. The discharge rates in response to other stimuli, including neck flexion, pinna stimulation, and noxious stimulation in the hindlimb, were not significantly different between the two groups. Since the alpha motoneurons showed an increase in responsiveness only to some stimuli, specific mechanisms probably explain this release. The most important mechanism seems to be a loss of inhibition normally exerted by the cerebellum on vestibular and joint proprioceptive reflexes. The pathways to the ventral horn cells are thought to involve the vestibulo-spinal and reticulo-spinal tracts.

Animals↗

PubMed1983

The role of stress, occlusion, and condyle position in TMJ dysfunction-pain.

Lateral transcranial TMJ radiographs are duplicable within +/- 0.2 mm and are cross-sectional views of the lateral third of the condyle and fossa. The innate asymmetry of humans, when the right and left sides of the fossa and condyle are compared, was clinically insignificant. Tomograms are not indicated because they lack appropriate resolution and detail to evaluate qualitative bone changes; and because they are not an in-office procedure, the condylar position in the fossa is completely unreliable. A correlation was reported between condylar position in the fossa and TMJ dysfunction in over 320 patients. This observation suggests that a new definition of centric relation is indicated, a definition that differentiates whether it is functional or dysfunctional. The criterion is the correlation between the occlusal findings and the condylar position in the fossa as recorded by the lateral TMJ radiographs (when the teeth are in maximum occlusion). Stress response was found to be greater in males than in females (in all vertebrates, including humans); therefore stress cannot be a direct cause of craniomandibular pain since more women have the disorder. It was concluded that stress is an indirect contributing factor that usually works through the medium of clenching. The role of the neuromuscular mechanism in craniomandibular pain was discussed. Proprioception reflex activity forms the basis for muscle length, mandibular positional sense, as well as masticatory function. Occlusal disharmonies increase noxious input to the neuromuscular system, as well as stress-induced clenching, causing increased muscle activity and spasm-pain. Condylar displacement also contributes to TMJ dysfunction-pain, depending on its direction. Anterior condylar displacement can initially affect the muscles by inducing overfunctional response in the proprioceptive system. Posterior condylar displacement usually results in an intrajoint response consisting of a disk derangement, reciprocal clicking, possible anterior disk dislocation, possible pathologic swallowing pattern, and noxious stimulation to the proprioceptive system. These factors contribute to subsequent trismus, muscle spasm and pain, and long-term pathologic remodeling of the joint. A detailed history is necessary to evaluate the role of stress. The physical occlusal findings are correlated with the condylar displacement observed in the TMJ radiographs to diagnose and plan corrective treatment.

Dental Occlusion, Centric↗

PubMed1989

Human postural reflexes and gravity--an under water simulation.

This study represents the first attempt to investigate the influence of gravity on postural adjustments. Subjects were displaced while standing under water on a movable platform, while the buoyancy of the body was adjusted by using a variety of lead vests. Under water, an approximately linear relationship was found between body weight and impulse directed electromyographic response amplitudes in the leg and thigh muscles. Loading of the subjects out of water resulted in a saturation of the response amplitude. The biomechanical signals recorded during the displacements indicated that neither vestibulospinal nor muscle proprioceptive reflex mechanisms can account for the effect observed under water. It is suggested that the EMG responses are mediated by reflexes which are activated by pressure receptors within the body in order to hold the centre of gravity over the feet.

Adult↗

PubMed1976

Habituation of exteroceptive suppression and of exteroceptive reflexes in man as influenced by voluntary contraction.

Habituation kinetics were found to vary considerably in different polysynaptic pathways of the brain stem in man. The exteroceptive reflex of the digastric muscle habituates markedly, even for stimuli repeated at 1-min intervals. The second component of the blink reflex habituates for intervals below about 8 sec, but this can largely be prevented by steady voluntary contraction of the muscle. On the other hand the exteroceptive suppressions of the masseter muscle only disclose slight habitaution of their late component ES2 and no habituation of the early component ES1. This does not appear to be affected by voluntary activation since the suppressive effects present the same pattern in relaxed masseter muscles tested by proprioceptive reflex activation. Exteroceptive reflexes and exteroceptive suppressions of similar latencies disclose genuine and important differences in their habituation kinetics.

Adult↗