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The patient with acute neurological problems
Published in Peate Ian, Dutton Helen, Acute Nursing Care, 2020
Axons transmit information away from the cell body. Axons vary in length from less than 1mm to over a metre. The proximal portion of the axon is called the initial segment and is the origin of the action potential required for nerve transmission. Action potentials are electrical signals that travel along the surface of a neurone. The signal is maintained (or propagated) by the movement of ions (electrolytes) across the membrane of the neurone.
Bioelectric and Biomagnetic Signal Analysis
Published in Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam, Introduction to Computational Health Informatics, 2019
Arvind Kumar Bansal, Javed Iqbal Khan, S. Kaisar Alam
The depolarization causes muscles to contract based upon electromechanical coupling involving multiple proteins: actin, troponin, myosin and tropomyosin. Calcium ions cause the triggering of the contraction. Depolarization is followed by repolarization when Na+ ions exit out of the cells, and K+ ion maintains an ion-equilibrium. Action potential threshold for depolarization is around −40 mV. During the depolarization, the action potential shoots up to +30 mV before dropping back to −80 mV during relaxation. The range of surface voltage measured for EMG ranges from 0 to 10 mV.
Neurobiology of the Gustatory Zone of Nucleus Tractus Solitarius
Published in I. Robin A. Barraco, Nucleus of the Solitary Tract, 2019
The neurons in these four groups also differ in other passive membrane properties.18 For example, Group I and Group III neurons are capable of initiating the highest frequency of action potentials when depolarized. In response to a short depolarizing pulse, Group II neurons have the longest latency to the first spike and respond with the fewest spikes. A subset of neurons in each neuron group shows membrane after hyperpolarization (AHP) following a burst of action potentials induced by depolarization. Postburst AHP durations are of longest duration in neurons belonging to Group III. Group II neurons, which have the largest postburst AHP magnitude, have the shortest postburst AHP duration.
Brugada syndrome
Published in Acta Cardiologica, 2021
Haarika Korlipara, Giridhar Korlipara, Srinivas Pentyala
There are two types of cardiac cells that assist with conduction in the heart: pacemaker and non-pacemaker cells. Pacemaker cells drive the rate and rhythm of the heart and include the sinoatrial (SA) and atrioventricular (AV) nodes. They undergo spontaneous depolarisation and therefore have no true resting membrane potential, and once they reach a threshold voltage of about −40 mV, they trigger an action potential with rapid and complete depolarisation followed by repolarization [4]. Non-pacemaker cardiac cells include the cardiomyocytes in the atria and ventricles as well as the Purkinje conduction system within the ventricles. Contrasting to pacemaker cells, they have true resting potentials (between −90 and −80 mV) and undergo rapid depolarisation followed by a prolonged phase of depolarisation, known as the plateau phase [4]. Specifically, rapid inward movement of
Chronic cough: Investigations, management, current and future treatments
Published in Canadian Journal of Respiratory, Critical Care, and Sleep Medicine, 2021
I. Satia, M. Wahab, E. Kum, H. Kim, P. Lin, A. Kaplan, P. Hernandez, J. Bourbeau, L. P. Boulet, S. K. Field
Cough can be under both voluntary and automatic control at the same time, but it is widely recognized that the cough reflex is the archetypal airway defensive reflex to prevent aspiration of foreign bodies or inhalation of noxious chemicals like smoke. The lungs are innervated by two sub-types of the vagus afferent nerve”34 unmyelinated c-fibers and myelinated A-delta fibers projecting sensory nerve terminals to the epithelium and sub-epithelium, respectively. The c-fibers are predominantly chemically sensitive and express ion channels and g-protein coupled receptors on their terminals that, upon activation, allow cations to flow inside resulting in membrane depolarization. The A-delta fibers are mainly mechanosensitive, but also respond to change in pH and osmolarity. Depolarization generates action potentials that are transmitted to the central nervous system. Once the signal reaches the first order synapse in the nucleus tractus solitarius (NTS) and paratrigeminal nuclei, second order neurons relay the signal to the thalamus, and third order neurons to the primary somatosensory cortex. This causes the unpleasant conscious sensation of urge to cough, which if strong enough, will evoke coughing (Figure 2). Importantly, cough is also under voluntary control and recent evidence suggests the presence of descending inhibitory control neurons that inhibit impulses arriving at the brainstem, thus limiting the urge to cough40,50 (Figure 3).
The effects of pulsed electromagnetic field on experimentally induced sciatic nerve injury in rats
Published in Electromagnetic Biology and Medicine, 2021
Gülten Bademoğlu, Nurten Erdal, Coşar Uzun, Bahar Taşdelen
Wallerian degeneration is a peripheral nerve injury by crush causes by the axons and their myelin sheaths to degenerate with the distal stump (Güven et al. 2005). In the literature, the axonotmesis method, which causes second-degree injury, is widely used (Landers and Altenburger 2003; Robinson 2000). The conduction velocity of action potentials depends on the diameter of axons and the thickness of the myelin sheath of the sciatic nerve (Mohammadi et al. 2014; Ullén 2009). Electrophysiological evaluations were used to evaluate the number of stimulated motor fibers, synchronization of their responses, and the number of innervated motor units to evaluate peripheral nerve regeneration. The most commonly used method for electrophysiological evaluation of nerve healing is recording compound muscle action potentials (Chen et al. 2015; Navarro and Kennedy 1989; Nijhuis et al. 2013). Although the parameters obtained from these methods are useful, it is also extremely influential selection of an appropriate method to evaluate the degree of functional recovery of nerve regeneration (Grasso et al. 2004; Monte-Raso et al. 2006). Walking track analysis has frequently been used effectively to determine functional recovery following sciatic nerve repair in rat models (Mohammadi et al. 2014).