Effect of supraspinal influences on the manifestation of presynaptic inhibition Ia afferents in different types of muscle contraction in humans

Relevance. Тhe biological role of presynaptic inhibition is to regulate excessive skeletal muscle tone, which prevents the execution of arbitrary muscle contractions. In the modern literature, there is information devoted mainly to the study of various types of spinal inhibition in the isometric type of contraction. The aim: determining the role of supraspinal influences from brain stem structures on the activity of presynaptic inhibition when performing various types and sizes of muscle contractions in humans. Materials and methods: 20-22 year-old healthy men (n=6) took part in the research. Presynaptic inhibition was registered at rest; at rest in combination with the performance of Jendrassik maneuver; when performing concentric, eccentric, isometric contractions of 50 % and 100 % of the individual maximum without and against the background of Jendrassik maneuver. Results: During the execution of concentric, eccentric and isometric contractions of different sizes, the severity of presynaptic inhibition decreases in comparison with rest, both without taking Jendrassik maneuver, and against the background of its execution. With an increase in the strength of concentric, eccentric, and isometric contractions from 50 % to 100 % of the individual maximum, the severity of presynaptic inhibition progressively decreased under the same experimental conditions. Without taking Jendrassik maneuver, the greatest severity of presynaptic inhibition was observed with concentric and isometric contractions of 50 % and 100 % of the MVC, and against the background of taking Jendrassik maneuver - with an isometric type of reduction of 50 % and 100 % of the MVC. Conclusion. Supraspinal descending effects caused by the Jendrassik maneuver modulate the state of presynaptic inhibition Ia of the afferents of the flexor muscle of the foot, depending on the type and strength of muscle contraction.

A biomedical Engineering Laboratory module for exploring involuntary muscle reflexes using Electromyography

Background Undergraduate biomedical engineering (BME) students interested in pursuing a career in research and development of medical or physiological monitoring devices require a strong foundation in biosignal analysis as well as physiological theory. Applied learning approaches are reported to be effective for reinforcing physiological coursework; therefore, we propose a new laboratory protocol for BME undergraduate physiology courses that integrates both neural engineering and physiological concepts to explore involuntary skeletal muscle reflexes. The protocol consists of two sections: the first focuses on recruiting soleus motor units through transcutaneous electrical nerve stimulation (TENS), while the second focuses on exploring the natural stretch reflex with and without the Jendrassik maneuver. In this case study, third-year biomedical engineering students collected electromyographic (EMG) activity of skeletal muscle contractions in response to peripheral nerve stimulation using a BioRadio Wireless Physiology Monitor system and analyzed the corresponding signal parameters (latency and amplitude) using the MATLAB platform. Results/protocol validation Electrical tibial nerve stimulation successfully recruited M-waves in all 8 student participants and F-waves in three student participants. The students used this data to learn about orthodromic and antidromic motor fiber activation as well as estimate the neural response latency and amplitude. With the stretch reflex, students were able to collect distinct signals corresponding to the tendon strike and motor response. From this, they were able to estimate the sensorimotor conduction velocity. Additionally, a significant increase in the stretch reflex EMG amplitude response was observed when using the Jendrassik maneuver during the knee-jerk response. A student exit survey on the laboratory experience reported that the class found the module engaging and helpful for reinforcing physiological course concepts. Conclusion This newly developed protocol not only allows BME students to explore physiological responses using natural and electrically-induced involuntary reflexes, but demonstrates that budget-friendly commercially available devices are capable of eliciting and measuring involuntary reflexes in an engaging manner. Despite some limitations caused by the equipment and students’ lack of signal processing experience, this new laboratory protocol provides a robust framework for integrating engineering and physiology in an applied approach for BME students to learn about involuntary reflexes, neurophysiology, and neural engineering.

Classification and Assessment of the Patelar Reflex Response through Biomechanical Measures

Clinical evaluation of the patellar reflex is one of the most frequent diagnostic methods used by physicians and medical specialists. However, this test is usually elicited and diagnosed manually. In this work, we develop a device specifically designed to induce the patellar reflex and measure the angle and angular velocity of the leg during the course of the reflex test. We have recorded the response of 106 volunteers with the aim of finding a recognizable pattern in the responses that can allow us to classify each reflex according to the scale of the National Institute of Neurological Disorders and Stroke (NINDS). In order to elicit the patellar reflex, a hammer is attached to a specially designed pendulum, with a controlled impact force. All volunteer test subjects sit at a specific height, performing the Jendrassik maneuver during the test, and the medical staff evaluates the response in accordance with the NINDS scale. The data acquisition system is integrated by using a tapping sensor, an inertial measurement unit, a control unit, and a graphical user interface (GUI). The GUI displays the sensor behavior in real time. The sample rate is 5 kHz, and the control unit is configured for a continuous sample mode. The measured signals are processed and filtered to reduce high-frequency noise and digitally stored. After analyzing the signals, several domain-specific features are proposed to allow us to differentiate between various NINDS groups using machine learning classifiers. The results show that it is possible to automatically classify the patellar reflex into a NINDS scale using the proposed biomechanical measurements and features.

Jendrassik Maneuver Facilitates cVEMP Amplitude: Some Preliminary Observations

Background: The cervical vestibular evoked myogenic potential (cVEMP) is an acoustically driven electrophysiological measure of saccular and inferior nerve function that requires tonic sternocleidomastoid muscle (SCM) activity in order to be elicited. The cVEMP is gaining increased interest in the clinical and research communities based on the anatomical specificity it adds to vestibular test batteries, because it is noninvasive, and since it can be performed with instrumentation commonly found in audiology clinics worldwide. Purpose: Because maintaining a constant level of tonic background electromyography (EMG) over the entire course of the recording epoch is a requirement for response elicitation, active participation for some individuals including the elderly and those with cervical problems can be difficult. As a way to facilitate the response for some clinical populations, this study addressed whether cVEMPs could be modulated by remote or local changes in EMG related neural activity by applying various maneuvers during the course of the recording epoch. Research Design: Keeping acoustic stimulation and recording parameters constant, three separate experimental conditions, Jendrassik maneuver, jaw (teeth) clenching, and forced-eye closure, were used to determine whether cVEMP amplitudes could be enhanced from the control condition. Study Sample: Nine adults (2 males; 7 females) ranging in age from 24 to 42 yr with normal pure-tone hearing sensitivity and a negative history of otological disease, neurological disease, and head trauma. Data Collection and Analysis: Cervical vestibular evoked myogenic potentials were recorded from the SCM using surface electrodes in response to suprathreshold 500 Hz Blackman windowed tone bursts under a control and three experimental conditions. Three separate one-way repeated measures analyses of variance (ANOVAs) were used to evaluate the effects of these maneuvers on P1/N1 peak-to-peak amplitudes and P1 and N1 peak latencies. Results: A significant main effect of experimental condition was shown to increase P1/N1 peak-to-peak cVEMP amplitude. Post hoc analysis found that Jendrassik maneuver versus control was the only the condition that produced significantly increased response amplitudes in comparison to all other post hoc contrasts. P1 and N1 peak latencies were unchanged across the various experimental conditions. Conclusions: In adults with normal hearing sensitivity and a negative history of otological disease, neurological disease, and head trauma, Jendrassik maneuver increased cVEMP amplitude by over 39% in comparison to the control condition. Such a simple modulation effect warrants further investigation for application in clinical studies.

Tonic Central and Sensory Stimuli Facilitate Involuntary Air-Stepping in Humans

Air-stepping can be used as a model for investigating rhythmogenesis and its interaction with sensory input. Here we show that it is possible to entrain involuntary rhythmic movement patterns in healthy humans by using different kinds of stimulation techniques. The subjects lay on their sides with one or both legs suspended, allowing low-friction horizontal rotation of the limb joints. To evoke involuntary stepping of the suspended leg, either we used continuous muscle vibration, electrical stimulation of the superficial peroneal or sural nerves, the Jendrassik maneuver, or we exploited the postcontraction state of neuronal networks (Kohnstamm phenomenon). The common feature across all stimulations was that they were tonic. Air-stepping could be elicited by most techniques in about 50% of subjects and involved prominent movements at the hip and the knee joint (∼40–70°). Typically, however, the ankle joint was not involved. Minimal loading forces (4–25 N) applied constantly to the sole (using a long elastic cord) induced noticeable (∼5–20°) ankle-joint-angle movements. The aftereffect of a voluntary long-lasting (30-s) contraction in the leg muscles featured alternating rhythmic leg movements that lasted for about 20–40 s, corresponding roughly to a typical duration of the postcontraction activity in static conditions. The Jendrassik maneuver per se did not evoke air-stepping. Nevertheless, it significantly prolonged rhythmic leg movements initiated manually by an experimenter or by a short (5-s) period of muscle vibration. Air-stepping of one leg could be evoked in both forward and backward directions with frequent spontaneous transitions, whereas involuntary alternating two-legged movements were more stable (no transitions). The hypothetical role of tonic influences, contact forces, and bilateral coordination in rhythmogenesis is discussed. The results overall demonstrated that nonspecific tonic drive may cause air-stepping and the characteristics and stability of the evoked pattern depended on the sensory input.