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PubMed1997

Motor and perceptual responses to horizontal and vertical eye vibration in humans.

Previous studies have shown that low amplitude/high frequency mechanical vibration applied to the human eye muscles results in the illusory movement of a luminous spot fixated in total darkness. The aim of the present study was to investigate whether a vibration-induced motor response also occurs in eye muscles, and to check whether the visual illusions actually result from the proprioceptors being activated by the vibration, or whether they are simply due to the retinal slip induced by the reflex eye movement. The effects of the vibratory stimuli on the inferior rectus (IR) and lateral rectus (LR) muscles were evaluated by recording subjects' eye position changes. When applied to the IR muscle, vibration effectively elicited an upward visual illusion accompanied by a small downward ocular rotation, whereas when applied to the LR muscle, it also induced horizontal visual illusion, which was less frequent and weaker than the vertical one, but no ocular rotation. We concluded that visual illusions of this kind cannot be attributable to the retinal motion of the image of the fixated point. The difference between the vertical and horizontal vibratory motor responses is discussed as regards the particular role that oculo-muscular proprioception may play in the vertical muscles.

Eye Movements↗

PubMed1989

Age related decline in postural control mechanisms.

In order to study voluntary and reflexive mechanisms of postural control, young and elderly persons were given large-fast and small-slow ankle-rotation postural disturbances while standing on a movable platform capable of measuring ground reaction forces. Large-fast rotations were employed to activate long-loop reflexes, and small-slow rotations were employed to tap the higher level sensory integration aspects of postural control. Overall, the elderly persons exhibited more perturbation induced sway and showed a slowing in voluntary, as opposed to reflexive mechanisms of correcting postural disturbance. For both age groups, reflexive mechanisms were found to be relatively intact. When small perturbations were given, the elderly persons swayed more than young participants and produced sporadic reflexive activity. Moreover, elderly persons did not adapt to the small perturbations and exhibited increased postural sway to repetitive presentation of the perturbation, whereas young participants substantially decreased their postural sway. These data demonstrate that elderly persons are at some disadvantage when posture is under the control of slower, higher level sensory integrative mechanisms.

Adult↗

PubMed1992

Propriospinal myoclonus: a neurophysiologic analysis.

We are reporting a neurophysiologic analysis of two patients presenting with thoracoabdominal spontaneous muscle jerks. Polymyographic recordings showed myoclonic bursts with onset in the upper rectus abdominis or lower intercostal muscles followed by rostral propagation to the upper intercostal and caudal propagation to the abdominal muscles by slowly conducting pathways. Jerk-locked back-averaging did not show time-locked cortical or premovement potentials. Peroneal somatosensory evoked response, C-reflex, and intercostal nerve conduction were normal. These findings suggest a generator for the myoclonus in the midthoracic region of the spinal cord with up and down propagation by slowly conducting pathways, such as propriospinal fibers. This type of spinal myoclonus may thus be termed "propriospinal myoclonus," as suggested by Brown et al.

Aged↗

PubMed2005

Modulation of flexion reflex induced by hip angle changes in human spinal cord injury.

The flexion reflex can be elicited via stimulation of skin, muscle, and high-threshold afferents inducing a generalized flexion of the limb. In spinalized animal models this reflex is quite prominent and is strongly modulated by actions of hip proprioceptors. However, analogous actions on the flexion reflex in spinal cord injured (SCI) humans have not yet been examined. In this study, we investigated the effects of imposed static hip angle changes on the flexion reflex in ten motor incomplete SCI subjects when input from plantar cutaneous mechanoreceptors was also present. Flexion reflexes were elicited by low-intensity stimulation of the sural nerve at the lateral malleolus, and were recorded from the ipsilateral tibialis anterior (TA) muscle. Plantar skin stimulation was delivered through two surface electrodes placed on the metatarsals, and was initiated at different delays ranging from 3 to 90 ms. We found that non-noxious sural nerve stimulation induced two types of flexion reflexes in the TA muscle, an early, and a late response. The first was observed only in three subjects and even in these subjects, it appeared irregularly. In contrast, the second (late) flexion reflex was present uniformly in all ten subjects and was significantly modulated during hip angle changes. Flexion reflexes recorded with hip positioned at different angles were compared to the associated control reflexes recorded with hip flexed at 10 degrees. Hip flexion (30 degrees, 40 degrees) depressed the late flexion reflex, while no significant effects were observed with the hip set in neutral angle (0 degrees). Strong facilitatory effects on the late flexion reflex were observed with the hip extended to 10 degrees. Moreover, the effects of plantar skin stimulation on the flexion reflex were also found to depend on the hip angle. The results suggest that hip proprioceptors and plantar cutaneous mechanoreceptors strongly modulate flexion reflex pathways in chronic human SCI, verifying that this type of sensory afferent feedback interact with spinal interneuronal circuits that have been considered as forerunners of stepping and locomotion. The sensory consequences of this afferent input should be considered in rehabilitation programs aimed to restore movement and sensorimotor function in these patients.

Adolescent↗

PubMed1994

Mechanical actions of heterogenic reflexes linking long toe flexors with ankle and knee extensors of the cat hindlimb.

1. To study the means whereby ankle biomechanics are represented in the interneuronal circuitry of the spinal cord we examined stretch-evoked reflex interactions between the physiological extensors flexor hallucis longus (FHL) and flexor digitorum longus (FDL) as well as their interactions with gastrocnemius (G), soleus (S), and the quadriceps group (Q) in 34 unanesthetized decerebrate cats. To evoke stretch, DC motors provided ramp-hold-release length changes to tendons detached from their bony insertions. Semiconductor myographs measured resultant muscle force response. Reflexes were examined under both quiescent (no active force generation) and activated conditions; muscle activation was achieved through either crossed-extension or flexion reflexes. 2. FHL and FDL share mutual excitatory stretch-evoked interactions under most conditions examined. These interactions depended on muscle length, were asymmetric (with FHL contributing a larger magnitude of reflex excitation onto FDL), and occurred at a latency of 16 ms. Mutual Ia synergism previously described for these two muscles provides a basis for all of the above findings. Our data demonstrate that for this muscle pair, reflex connectivities revealed at the intracellular level can be extrapolated to cover the entire motoneuron pool; further, our data directly demonstrate the net mechanical result of ensemble synaptic events. 3. FHL was found to share strong, mutually inhibitory stretch-evoked interactions with G, S, and Q. Stepwise regression statistical analyses determined that these interactions depended on recipient muscle force and donor muscle force. These reflex interactions all occurred at a latency of 28 +/- 4 (SE) ms. Further, the heterogenic inhibition between FHL/G and FHL/S was attenuated by strychnine infusion (intravenous) but unaffected by either mecamylamine, picrotoxin, or baclofen infusion (intravenous, intrathecal). Disynaptic Ib inhibition previously described among hindlimb extensors provides a basis for the above findings; our data demonstrate that under certain conditions the ensemble activity of this system can cause a dramatic decline in whole muscle force output. 4. By contrast, FDL was found to share mutually inhibitory, stretch-evoked reflex interactions with G, S, and Q that were much weaker than those observed between FHL and these same muscles. The small magnitude of inhibition observed in these interactions made it difficult to assess reflex latency or to determine the factor(s) that best predicted the heterogenic inhibition. 5. This study provides further evidence of intrinsic differences in interneuronal organization between muscles whose activity occurs in a periodic manner during locomotion ("stereotypical") and a muscle whose locomotor activity is characterized by both periodic and nonperiodic components ("facultative").(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed2005

Development of a human neuro-musculo-skeletal model for investigation of spinal cord injury.

This paper describes a neuro-musculo-skeletal model of the human lower body which has been developed with the aim of studying the effects of spinal cord injury on locomotor abilities. The model represents spinal neural control modules corresponding to central pattern generators, muscle spindle based reflex pathways, golgi tendon organ based pathways and cutaneous reflex pathways, which are coupled to the lower body musculo-skeletal dynamics. As compared to other neuro-musculo-skeletal models which aim to provide a description of the possible mechanisms involved in the production of locomotion, the goal of the model here is to understand the role of the known spinal pathways in locomotion. Thus, while other models focus primarily on functionality at the overall system level, the model here emphasizes functional and topological correspondance with the biological system at the level of the subcomponents representing spinal pathways. Such a model is more suitable for the detailed investigation of clinical questions related to spinal control of locomotion. The model is used here to perform preliminary experiments addressing the following issues: (1) the significance of spinal reflex modalities for walking and (2) the relative criticality of the various reflex modalities. The results of these experiments shed new light on the possible role of the reflex modalities in the regulation of stance and walking speed. The results also demonstrate the use of the model for the generation of hypothesis which could guide clinical experimentation. In the future, such a model may have applications in clinical diagnosis, as it can be used to identify the internal state of the system which provides the closest behavioral fit to a patient's pathological condition.

Computer Simulation↗

PubMed1979

Effects of the vestibular system on human development, Part I. Overview of functions and effects of stimulation.

Studies concerned with the effects of vestibular stimulation on human development and function are reviewed and some implications for therapy are suggested in this paper. Studies are included that relate to changes in the vestibulo-ocular reflex with age, effects of vestibular stimulation on smiling, crying, general activity, and visual attentiveness of infants; and studies that show that typical sequelae to vestibular stimulation are reduced following long-term stimulation. The importance of reviews of the literature and transference of research results to therapeutic use are stressed, with the implication that vestibular-based therapy will improve as occupational therapists become more aware of related research.

Adolescent↗

PubMed1991

The effects of 4-aminopyridine on neurological deficits in chronic cases of traumatic spinal cord injury in dogs: a phase I clinical trial.

A Phase I trial of 4-aminopyridine (4-AP) was carried out in 39 dogs referred to the veterinary teaching hospital with naturally occurring traumatic paraplegia or paraparesis. The rationale for the study was provided by the observation that 4-AP restores conduction in demyelinated nerve fibers in experimental spinal cord injury. Most injuries (77%) resulted from degenerative disk disease, occurring at or near the thoracolumbar junction, and producing chronic, complete paraplegia. Neurological examination of each dog was recorded on videotape before and at intervals after administration of 4-AP. The drug was administered systemically in total doses between 0.5 and 1 mg/kg body weight. Three areas of neurological status changed significantly at 15-45 minutes following administration of 4-AP: (a) striking improvements in hindlimb placing occurred in 18 animals; (b) increased awareness of painful stimuli to the hindlimb in 10 animals; (c) partial recovery of the cutaneus trunci muscle reflex of the back skin in 9 animals. These effects reversed within a few hours of administration. Other animals (36%) showed no change in neurological signs except a slight enhancement of hindlimb reflex tone. Significant side effects were seen in 6 dogs receiving higher intravenous doses, with elevation of body temperature and apparent anxiety, leading to mild seizures in 3 of the animals. These seizures were controlled with diazepam. The results indicate that conduction block may contribute significantly to functional deficits in closed-cord injuries and that potassium channel blockade may prove to be a valid, if limited approach to therapeutic intervention in chronic paraplegia and paraparesis.

4-Aminopyridine↗

PubMed1991

Cervico-ocular function in patients with spasmodic torticollis.

The cervico-ocular (COR) and active and passive vestibulo-ocular reflexes (VOR) were measured in seven patients with spasmodic torticollis (ST) and six normal controls. The COR was found to be weak or absent in both groups. The VOR gain was similar in the two groups but five patients had a significant asymmetry of the response. There was no evidence of abnormal cervico-vestibular interaction during active head rotation. The study suggests that the VOR asymmetry frequently found in ST cannot be explained on the basis of an abnormal cervical input.

Adult↗

PubMed2000

Upper limb H reflexes and somatosensory evoked potentials modulated by movement.

In the human lower limb, the magnitudes of both Hoffmann (H) reflexes and primary somatosensory evoked potentials (SEPs) from scalp electrodes, are reduced by active and/or passive movement. We surmised that similar effects occur for the upper limb and specifically hypothesised that amplitudes of median nerve induced flexor carpii radialis H reflexes and cortical SEPs are reduced with passive movement about the wrist or elbow. The results showed (P<0. 05) that either movement significantly attenuated mean magnitudes of SEPs elicited from stimulation at elbow or wrist and that reflex magnitudes attenuated with wrist movement. Thus, the upper limb shows similar movement-induced modulation to the lower limb. These attenuations of fast conducting sensory paths consequent to movement per se, may be a basic level of motor control, initiated from muscle mechanoreceptor discharge. Upon this basic level, more complex modulations then may be laid as appropriate for the particular characteristics of active motor tasks.

Adult↗

PubMed2006

Modelling spinal circuitry involved in locomotor pattern generation: insights from the effects of afferent stimulation.

A computational model of the mammalian spinal cord circuitry incorporating a two-level central pattern generator (CPG) with separate half-centre rhythm generator (RG) and pattern formation (PF) networks has been developed from observations obtained during fictive locomotion in decerebrate cats. Sensory afferents have been incorporated in the model to study the effects of afferent stimulation on locomotor phase switching and step cycle period and on the firing patterns of flexor and extensor motoneurones. Here we show that this CPG structure can be integrated with reflex circuits to reproduce the reorganization of group I reflex pathways occurring during locomotion. During the extensor phase of fictive locomotion, activation of extensor muscle group I afferents increases extensor motoneurone activity and prolongs the extensor phase. This extensor phase prolongation may occur with or without a resetting of the locomotor cycle, which (according to the model) depends on the degree to which sensory input affects the RG and PF circuits, respectively. The same stimulation delivered during flexion produces a temporary resetting to extension without changing the timing of following locomotor cycles. The model reproduces this behaviour by suggesting that this sensory input influences the PF network without affecting the RG. The model also suggests that the different effects of flexor muscle nerve afferent stimulation observed experimentally (phase prolongation versus resetting) result from opposing influences of flexor group I and II afferents on the PF and RG circuits controlling the activity of flexor and extensor motoneurones. The results of modelling provide insights into proprioceptive control of locomotion.

Action Potentials↗

PubMed1983

[Cervical nystagmus caused by proprioceptors of the neck].

A pathological nystagmus, occurring during turning of the trunk in relation to the head, which is held stationary in space, clearly points towards a cervical origin of vestibular vertigo. Such a cervical nystagmus may have a vascular origin by the compression of the arteriae vertebrales, or a proprioreceptive origin via the upper neck joints, or it may possibly be due to functional disturbances of the upper cervical spine. The dynamic characteristics of the so-called cervico-ocular reflex can be examined only in patients with non-functioning labyrinths, since in a healthy person the reflex is so strongly suppressed that it cannot be analyzed any more. In five patients with isolated bilateral complete vestibular deficiencies, we found a strong cervico-ocular reflex. Detailed examinations showed that nystagmus occurred during turning of the body in relation to the head ("phasic neck reflex"). On the other hand, when remaining in the extreme positions, the proprioreceptive nystagmus does not persist. Contrary to this, a cervical nystagmus due to vascular causes shows a latency period after torsion of the neck and increases if the head remains in the extreme position. Before assuming a cervical origin of a vestibular vertigo, an examination for cervical nystagmus should be carried out. Such a cervical nystagmus is the only definite pointer towards a relation between an upper cervical spine syndrome and vertigo, which is sometimes assumed rather uncritically.

Adult↗

PubMed1996

Exercise-induced muscle cramp. Proposed mechanisms and management.

Muscle cramp is a common, painful, physiological disturbance of skeletal muscle. Many athletes are regularly frustrated by exercise-induced muscle cramp yet the pathogenesis remains speculative with little scientific research on the subject. This has resulted in a perpetuation of myths as to the cause and treatment of it. There is a need for scientifically based protocols for the management of athletes who suffer exercise-related muscle cramp. This article reviews the literature and neurophysiology of muscle cramp occurring during exercise. Disturbances at various levels of the central and peripheral nervous system and skeletal muscle are likely to be involved in the mechanism of cramp and may explain the diverse range of conditions in which cramp occurs. The activity of the motor neuron is subject to a multitude of influences including peripheral receptor sensory input, spinal reflexes, inhibitory interneurons in the spinal cord, synaptic and neurotransmitter modulation and descending CNS input. The muscle spindle and golgi tendon organ proprioceptors are fundamental to the control of muscle length and tone and the maintenance of posture. Disturbance in the activity of these receptors may occur through faulty posture, shortened muscle length, intense exercise and exercise to fatigue, resulting in increased motor neuron activity and motor unit recruitment. The relaxation phase of muscle contraction is prolonged in a fatigued muscle, raising the likelihood of fused summation of action potentials if motor neuron activity delivers a sustained high firing frequency. Treatment of cramp is directed at reducing muscle spindle and motor neuron activity by reflex inhibition and afferent stimulation. There are no proven strategies for the prevention of exercise-induced muscle cramp but regular muscle stretching using post-isometric relaxation techniques, correction of muscle balance and posture, adequate conditioning for the activity, mental preparation for competition and avoiding provocative drugs may be beneficial. Other strategies such as incorporating plyometrics or eccentric muscle strengthening into training programmes, maintaining adequate carbohydrate reserves during competition or treating myofascial trigger points are speculative and require investigation.

Central Nervous System↗

PubMed1997

Aviation spatial orientation in relationship to head position and attitude interpretation.

BACKGROUND: Conventional wisdom describing aviation spatial awareness assumes that pilots view a moving horizon through the windscreen. This assumption presupposes head alignment with the cockpit "Z" axis during both visual (VMC) and instrument (IMC) maneuvers. Even though this visual paradigm is widely accepted, its accuracy has not been verified. The purpose of this research was to determine if a visually induced neck reflex causes pilots to align their heads toward the horizon, rather than the cockpit vertical axis. HYPOTHESIS: Based on literature describing reflexive head orientation in terrestrial environments it was hypothesized that during simulated VMC aircraft maneuvers, pilots would align their heads toward the horizon. METHODS: Some 14 military pilots completed two simulated flights in a stationary dome simulator. The flight profile consisted of five separate tasks, four of which evaluated head tilt during exposure to unique visual conditions and one examined occurrences of disorientation during unusual attitude recovery. RESULTS: During simulated visual flight maneuvers, pilots tilted their heads toward the horizon (p < 0.0001). Under IMC, pilots maintained head alignment with the vertical axis of the aircraft. CONCLUSION: During VMC maneuvers pilots reflexively tilt their heads toward the horizon, away from the Gz axis of the cockpit. Presumably, this behavior stabilizes the retinal image of the horizon (1 degree visual-spatial cue), against which peripheral images of the cockpit (2 degrees visual-spatial cue) appear to move. Spatial disorientation, airsickness, and control reversal error may be related to shifts in visual-vestibular sensory alignment during visual transitions between VMC (head tilt) and IMC (Gz head stabilized) conditions.

Aerospace Medicine↗

PubMed1996

Octopamine induces steady-state reflex reversal in crayfish thoracic ganglia.

1. This paper investigates the effect of octopamine on spontaneous and reflex motor output of crayfish leg motor neurons. Octopamine modulated spontaneous activity, both rhythmic and tonic, and dramatically modulated the pattern of reflex motor output elicited by stimulating identified proprioceptors of the basal limb. 2. Spontaneous reciprocal motor patterns, involving alternating bursts of promotor and remotor motor neuron activity, were reversibly abolished by octopamine. The threshold concentration for this effect was approximately 1 microM. 3. At concentrations greater than approximately 10 microM octopamine inhibited spontaneous promotor nerve activity in both bursting and nonbursting preparations. In some experiments promotor inhibition was correlated with the induction of tonic remotor nerve activity. The EC50 for complete inhibition of promotor nerve activity by octopamine was 20-30 microM. 4. Reflexes mediated by two basal limb proprioceptors, the thoracocoxal muscle receptor organ (TCMRO; which signals leg promotion) and the thoracocoxal chordotonal organ (TCCO; which signals leg remotion) were analyzed in a number of promotor and remotor motor neurons. In both cases assistance reflexes (excitation of promotors by the TCCO and remotors by the TCMRO) were restricted to subgroups of the motor pool. Among remotor motor neurons, the first two units recruited during bursts of spontaneous activity were members of the assistance reflex group (group 1). A third unit, sometimes recruited during more intense spontaneous bursts, was excited by TCCO stimulation and was therefore a member of the resistance reflex group (group 2). Other resistance group remotors were also excited by the TCCO, but this input normally remained subthreshold. 5. Stimulation of the TCCO afferent nerve elicited excitatory postsynaptic potentials (EPSPs) in group 2 (resistance group) remotor motor neurons at a latency compatible with a monosynaptic connection. The same stimulation excited group 1 (assistance group) promotor motor neurons, but at a greater and more variable latency. Thus the remotor resistance reflex from the TCCO is probably monosynaptic, but the promotor assistance reflex, also elicited by TCCO stimulation, is likely to be di- or polysynaptic. Assistance group (group 1) remotor motor neurons are inhibited by mechanical stimulation of the TCCO, or electrical stimulation of its nerve. 6. Octopamine had selective effects on individual remotor units. First, assistance group remotor motor neurons were affected in two ways. One unit was inhibited, so that reflex spiking in response to TCMRO stimulation was abolished. A second unit was not inhibited, but its reflex response mode changed, so that instead of responding to TCMRO input with an assistance reflex, it responded to TCCO input with a resistance reflex. Second, among motor neurons that normally respond to TCCO input with resistance reflexes, these responses were enhanced by octopamine. 7. Promotor motor neurons were inhibited by octopamine and reflex responses were also affected selectively. Responses to TCCO input (assistance reflexes) were abolished; whereas, responses to TCMRO input (resistance reflexes) were relatively less affected. 8. Intracellular recordings revealed that the majority of remotor motor neurons depolarized in the presence of octopamine. In preparations where these could be classified on the basis of TCMRO/ TCCO inputs, all were identified as group 2 (resistance group). A minority of remotor motor neurons were hyperpolarized by octopamine. All of these were identified as group 1 (assistance group), with strong TCMRO input. 9. The majority of promotor motor neurons were depolarized by octopamine. This depolarization was nevertheless inhibitory since it reversed slightly positive to rest and was associated with a substantial fall in inp

Animals↗

PubMed1993

Contribution of the tonic vibration reflex to muscle stress and muscle fatigue.

The aim of the investigation was to determine the influence of vibration displacement amplitude (200, 300 microns peak-to-peak), as opposed to acceleration effects at selected frequencies (40, 80, 100, 120, 150, 200 Hz), on a commonly observed but often undesired motor response elicited by local vibratory stimulation, that is, the tonic vibration reflex (TVR). Vibration was applied to the distal tendons of the hand flexor muscles. Changes in the activity of hand flexor and extensor muscles were analyzed as a function of both their initial contraction level (0, 10, 20% of maximal voluntary contraction) and the vibration parameters. The main results indicate that TVR increases with the initial muscle contraction and increases with vibration frequency up to 100-150 Hz but decreases beyond. High-frequency vibration seems to induce less muscle and tendon stress. This result is particularly important for the design of handheld vibrating tools.

Adult↗

PubMed1982

The inhibitory effect of acupuncture on the tonic vibration reflex (TVR) in man.

The effect of acupuncture on the tonic vibration reflex (TVR) has been examined in healthy men. Vibrations (100 Hz) were applied over the muscle bellies of either finger flexion muscles or extension muscles, while finger flexions and extensions were measured by a strain attached to the middle finger. A stainless steel acupuncture needle was inserted for 10 min into an acupuncture point named "Chu-Chih (LI-II)". After the application of acupuncture, TVRs in both flexion and extension muscles were significantly less than those observed before the application of acupuncture. The inhibitory effect of acupuncture almost disappeared 10 min after removing the needle. Acupuncture transiently inhibits TVR in extension and flexion muscles in man.

Acupuncture Therapy↗

PubMed1966

Reflex and cerebellar influences on alpha and on 'rhythmic' and 'tonic' gamma activity in the intercostal muscle.

1. Efferent intercostal alpha and gamma activity and afferent intercostal muscle spindle activity were studied in decerebrate cats in response to stimulation of the anterior lobe of the cerebellum and to postural and other reflexes.2. Low threshold intercostal responses were elicited from lobuli IV and V of the anterior lobe of the cerebellum.3. The existence of two functionally different types of intercostal gamma neurones has been confirmed. These are the ;rhythmic' or ;specifically respiratory' gamma neurones, and the ;tonic' gamma neurones.4. In response to cerebellar stimulation, facilitatory, inhibitory and diphasic tetanic and post-tetanic effects were obtained from alpha and the two types of gamma fibres in both external and internal intercostal nerve branches.5. Generally both inspiratory and expiratory alpha and gamma activity was facilitated in response to tetanic stimulation at contralateral stimulus sites, and inhibited in response to stimulation of ipsilateral sites.6. ;Rhythmic' gamma activity appeared to be rather closely linked to the respiratory alpha activity but the balance between ;rhythmic' gamma and alpha was often changed in response to cerebellar stimulation, as indicated by the responses of primary muscle spindle afferents.7. The ;tonic' gamma neurones were as a rule more responsive to cerebellar stimulation than were the alpha and ;rhythmic' gamma neurones. Long-lasting post-tetanic effects were much more prominent in the ;tonic' gamma fibres than in the alpha or ;rhythmic' gamma fibres.8. ;Rhythmic' gamma activity was abolished after cervical transections of the cord. ;Tonic' gamma activity remained in the spinal preparations although usually at a different discharge rate.9. ;Tonic' gamma neurones were more responsive than the ;rhythmic' gamma neurones to the proprioceptive gamma reflex elicited by passive movements of the chest wall as well as to other spinal and supraspinal reflexes.10. Both ;dynamic' and ;static' gamma fibres seem to be represented in the group of ;tonic' intercostal gamma neurones.11. The significance of the results are discussed with regard to the following two main points: (a) integration of respiratory and postural functions of the intercostal muscles; (b) cerebellar control of the alpha-gamma balance in active contractions and passive relaxations.

Animals↗