Muscle
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The amount of tension developed by a muscle fiber during tetanic contraction can be as much as three to four times greater than that of a single muscle twitch. The mechanism involved with this increased strength of contraction involves the concentration of cytosolic calcium. Each time the muscle fiber is stimulated by an action potential, Ca++ ions are released from the sarcoplasmic reticulum. However, as soon as the Ca++ ions are released, a continuously active calcium pump begins returning the Ca++ ions to the sarcoplasmic reticulum. Consequently, fewer Ca++ ions are available to bind with troponin and only a portion of the binding sites on the actin become available to the myosin cross bridges. Each subsequent stimulation of the muscle fiber results in the release of more Ca++ ions from the sarcoplasmic reticulum. In other words, as the frequency of nerve stimulation increases, the rate of Ca++ ion release exceeds the rate of Ca++ ion removal. Therefore, the cytosolic concentration of calcium remains elevated. A greater number of Ca++ ions bind with troponin, resulting in a greater number of binding sites on the actin that become available to the myosin cross bridges. As the number of cycling cross bridges increases, the amount of tension that is developed increases.
Effects of Dopamine on The Digestive System
M.D. Francesco Amenta in Peripheral Dopamine Pathophysiology, 2019
It has been suggested recently that the release of opioid peptides from the myenteric plexus in the guinea pig ileum is under the inhibitory modulation of a dopaminergic nervous system.75 When a low frequency of stimulation (e.g., 0.1 or 0.2 Hz, inducing twitch contractions) in the longitudinal muscle preparation of the guinea pig ileum is increased to 10 Hz, a tetanic contraction is induced. Upon returning to the basal low frequency, e.g., after 30 s, twitch contractions are again induced, but their amplitude is less pronounced. Since this inhibitory response to high frequency stimulation is antagonized by naloxone, it is thought to be due to the release of endogenous opioids. This inhibitory response can be increased by acute or chronic pretreatment of the guinea pigs with haloperidol,76 and by chronic pretreatment with sulpiride and 6-hydroxydopamine.75,77 This led to the hypothesis that interruption of an inhibitory dopaminergic nervous system increases the release of the endogenous opioids involved. This hypothesis thus suggests the presence of dopaminergic neurons in the myenteric plexus, but the evidence for the presence of dopaminergic neurons in the gastrointestinal tract is poor. (See Section V.A., this chapter.)
Regulation of Sympathetic Nerve Activity in Humans: New Concepts Regarding Autonomic Adjustments to Exercise and Neurohumoral Excitation in Heart Failure
Irving H. Zucker, Joseph P. Gilmore in Reflex Control of the Circulation, 2020
The role of the muscle mechanoreflex in regulation of SNA during exercise in humans is uncertain. There is convincing evidence that activation of muscle mechanoreceptors with type I and II afferents does not increase muscle SNA, heart rate, or arterial pressure since tendon vibration that activates these receptors does not effect these variables (Mark et al., 1985). The uncertainty regarding the mechanoreflex surrounds the influence of mechanoreceptors with type III afferents. This question is difficult to answer because of the problem of separating mechanoreceptor influences from the effect of central command and metaboreceptors. There are, however, several findings that provide insight into the issue of whether mechanosensitive type III muscle afferents exert influences on muscle SNA in humans. First, muscle SNA does not increase abruptly with voluntary static or rhythmic handgrip as would be expected if muscle mechanoreceptors were exerting an excitatory influence on muscle SNA (Mark et al., 1985; Victor et al., 1987; Seals et al., 1988). Second, Pryor et al. (1989) have recently reported that involuntary, electrically evoked tetanic contraction of the brachioradialis muscle fails to produce an abrupt increase in muscle SNA characteristic of a muscle mechanoreflex.
How many nerve fibres can be separated as donor from an integral nerve trunk when reconstructing a peripheral nerve trauma with amplification method by artificial biochitin conduit?
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Xiaofeng Yin, Xiaomeng Zhang, Yuhui Kou, Yanhua Wang, Lijia Zhang, Baoguo Jiang, Dianying Zhang
The CMAP of skeletal muscle is integrated by multiple single action potentials of nerve fibres under stimulation [7]. As a typical and mature method in the diagnosis of PNI [8], the maximal CMAP amplitudes quantify the complete structure of “axon – motor endplate – muscle fibre” and reflects the overall function of the motor units [9,10]. If the peripheral nerve is injured, the structural integrity will be lost due to axonotmesis with the decline of maximal CMAP amplitude [11,12]. Another method used in the assessment of PNI is to measure the contractility of the skeletal muscle. According to the stimulus frequency, skeletal muscle contractions include single contraction and tetanic contraction. Overall, the complex movements of limbs, the maintenance of postures and the preservation of body temperature mainly depend on the tetanus contraction. The maximal tension produced by complete tetanic contraction is much larger than that of single contraction tension, and it reflects the number of functional motor endplates as well [13].
Blood perfusion changes during sacral nerve root stimulation versus surface gluteus electrical stimulation on in seated spinal cord injury
Published in Assistive Technology, 2019
Liang Qin Liu, Martin Ferguson-Pell
In theory, all muscles consist of a number of motor units, and the fibers belonging to a motor unit are dispersed and interlink among fibers of other units. A motor unit normally consists of one motor neuron and all of the muscle fibers it stimulates. The muscle fibers belonging to one motor unit can be spread throughout a part, or most of the entire muscle, depending on the number of fibers and size of the muscle. When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contracted. The activation of single motor neuron results in a weak distributed muscle contraction (twitch contraction). In contrast, the activation of more motor neurons will result in more muscle fibers being activated, and therefore, a stronger muscle contraction (tetanic contraction) was produced. The higher the recruitment of motor unit, the stronger the muscle contraction will be. The activation of more motor neurons will result in more muscle fibers being activated, and therefore, a stronger muscle contraction (Guyton & Hall, 0000). In comparison, between sacral nerve root stimulation versus traditional surface FES of gluteal muscles, the larger numbers of motor neurons recruitment in sacral nerve roots stimulation may produce stronger contraction than surface FES. Therefore, it can activate gluteus muscles more efficiently. Sacral nerve root stimulation can efficiently activate all motor neurons that innervate gluteal maximus, whereas surface FES of gluteus maximus may be limited by the size of electrodes and the depth of electrical signal to reach the muscle motor points.
An in vivo study of a custom-made high-frequency irreversible electroporation generator on different tissues for clinically relevant ablation zones
Published in International Journal of Hyperthermia, 2021
Bing Zhang, Fanning Liu, Zheng Fang, Lujia Ding, Michael A. J. Moser, Wenjun Zhang
Miklavcic et al. [4] first showed that muscular contractions can be reduced by increasing the frequency of electric pulses above the frequency of tetanic contraction, while maintaining the antitumor efficacy in an in vivo rat model study. Using eight 100-μs unipolar pulses at a frequency of 5 kHz, they resulted in a single contraction instead of 8. However, this approach had the potential to generate significant temperature increases when more pulses are delivered, like the 90 pulses used clinically. The notion of H-FIRE was proposed by Arena et al. [5]; they used a burst of high-frequency and bipolar pulses (P-D-N: 2-0-2 or 2-2-2) to replace the single monopolar pulse in IRE. They demonstrated that the H-FIRE pulse waveforms at 4000 V/cm did not cause muscle contractions in a rat model, nor did they cause a significant temperature increase. Since then, much work has been done to further explore the use of H-FIRE with various pulse waveforms by computational [3,5], in vitro [6–8], ex vivo [9–11], and in vivo [12–15] studies. Sano et al. [6] looked at the use of H-FIRE pulse waveforms with a sub-microsecond pulse width (i.e., 0.25-2-0.25 and 0.5-2-0.5) in a pancreatic tumor cell in vitro cell suspension model and showed this modality was effective at causing cell death. and Ivey et al. [16] (i.e., 0.5-2-0.5) using a similar treatment protocol were able to demonstrate a visible ablation zone in a 3 D collagen glioma stem cell model, respectively at high electric field strengths (e.g., 4000 V/cm). Dong et al. in a first in human trial of H-FIRE prostate cancer [17] demonstrated the effectiveness of H-FIRE (250 pulse bursts with a pulse waveform of 5-10-5).