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Abnormal Uterine Contractions
Published in Gowri Dorairajan, Management of Normal and High Risk Labour During Childbirth, 2022
In this condition, the lower segment contraction predominates and tends to go into spasm. The woman gets an urge to pass urine repeatedly, is in constant pain, and has an urge to bear down prematurely. On abdominal examination, the pelvic grip will trigger more uterine contraction and pain. The woman may not allow the pelvic grip examination, though the uterus is relaxed, allowing other grips. The pelvis grip findings become obscured. On vaginal examination, the cervix appears thick and hanging loose, not well applied to the presenting part. Meconium-stained liquor may be manifested due to fetal compromise. Ruling out cepahlopelvic disproportion is important. Treatment is in the same lines as generalised tetanic contractions.
The heart
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
As in neurons, cardiac muscle cells undergo an absolute or effective refractory period in which the voltage-gated fast Na+ channels become inactivated at the peak of the action potential and are incapable of opening regardless of further stimulation. Therefore, the fast Na+ channels cannot reopen, Na+ ions cannot enter the cell, and another action potential cannot be generated. These channels do not return to their resting position and become capable of opening in sufficient numbers to generate a new action potential until the cardiac muscle cell has repolarized to approximately −70 mV. The absolute refractory period lasts almost as long as the duration of the associated contraction, about 250–300 ms. The physiological significance of this phenomenon is that it prevents the development of tetanus or spasm of the ventricular myocardium. By the time the cardiac muscle cell can be stimulated to generate another action potential, the contraction from the previous action potential is over. Therefore, the tension from sequential action potentials cannot accumulate and become sustained. This contrasts with skeletal muscle where tetanic contractions readily occur to produce maximal strength (Chapter 12). The pumping action of the heart, however, requires alternating contraction and relaxation so that the chambers can fill with blood. Sustained contraction or tetanus would preclude ventricular filling.
Neuromuscular blockade and opioids
Published in Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor, Manual of Neuroanesthesia, 2017
Prasanna U. Bidkar, Lakshmi K. Narmadha
Stimulus and response: A frequency of 50–200 Hz with a supramaximal stimulus is used for tetanic stimulation. The stimulus is usually delivered over 5 s. Normal skeletal muscle will show sustained tetanic contraction.
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.
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].
In complete SCI patients, long-term functional electrical stimulation of permanent denervated muscles increases epidermis thickness
Published in Neurological Research, 2018
Giovanna Albertin, Christian Hofer, Sandra Zampieri, Michael Vogelauer, Stefan Löfler, Barbara Ravara, Diego Guidolin, Caterina Fede, Damiana Incendi, Andrea Porzionato, Raffaele De Caro, Alfonc Baba, Andrea Marcante, Francesco Piccione, Paolo Gargiulo, Amber Pond, Ugo Carraro, Helmut Kern
The progressive FES training was begun with bursts, each having a stimulation duration (SD) of 4 s which was followed by a stimulation pause (SP) of 2 s. Each 4 s stimulation burst was composed of impulses lasting (impulse duration, ID) 150 ms and an impulse pause (IP) of 500 ms. The protocol was performed for two months to activate degenerated denervated muscle fibers. According to the improving activation response of trained muscles, the ID can be reduced to 80 and then 40 ms and the SP decreased to 1 s for another 2 months. The next training phase implements tetanic burst contractions of 3 s SD (with each stimulatory burst composed of a 40–50 ms ID and 10 ms IP) followed by a 3 s SP to reach the requested stimulation frequency of 20 Hz. This frequency is enough to obtain fused contractions and therefore external work, since the denervated muscle is and will remain a slow contracting muscle tissue never attaining the speed of innervated muscles. Daily series of tetanic contractions will further increase muscle fiber diameter, muscle mass, and muscle force with leg extensions performed in the sitting positions initially without, and then with, additional weights on the ankles of the patients. If very good muscle condition is achieved, depending not only on the amount of weekly training but also on the duration of denervation, then standing, stepping-in-place, and walking exercises may also be performed with a series of stimulations (40 ms ID and 10 ms IP) under the volitional control of the patient by external switches [6–12].