China
Africa
Explore chapters and articles related to this topic
Pathophysiology of Heart Failure with Reduced Ejection Fraction
Published in Andreas P. Kalogeropoulos, Hal A. Skopicki, Javed Butler, Heart Failure, 2023
Jacob Cao, John O'Sullivan, Sean Lal
Excitation contraction coupling refers to the coordinated process that starts when the action potential arrives at the sarcolemmal membrane and ends with sarcomere contraction and relaxation (Figure 3.4). Calcium plays a pivotal role in this entire process. Upon activation of the voltage-gated L-type calcium channels on the T tubules by the action potential, there is an initial small inward current of calcium. This small current acts on the closely apposed ryanodine receptors 2 and triggers a large release of calcium from the sarcoplasmic reticulum (calcium-induced calcium release). The cytosolic calcium subsequently binds to the cardiac troponin C. This induces conformational changes of the contractile proteins, leading to cross-bridge formation and sarcomeric contraction. The peak cytosolic calcium concentration is a major determinant of contractility. Relaxation occurs when the calcium is transported from the cytosol to either the sarcoplasmic reticulum via the SERCA-2a transporter (major mechanism) or out of the cells via the sodium-calcium exchanger (minor mechanism).
Basic medicine: physiology
Published in Roy Palmer, Diana Wetherill, Medicine for Lawyers, 2020
Muscle cells are also excitable by electrical, chemical or physical stimuli. Their contraction is activated by the action potential conveyed down the relevant nerve. There are three different types of muscle. Striated muscle makes up the mass of musculature that moves the skeleton and is under voluntary control; its cross-striations give a characteristic striped appearance under the microscope. Filaments of contractile proteins—actin and myosin—undergo shortening when the muscle is stimulated to contract. Smooth muscle lacks striations, and its contraction is involuntary. It is typically found in the wall of the gut where it undergoes spontaneous activity, but it is also under the control of the autonomic nervous system. Cardiac muscle is also striated; it is only found in the heart, where it contracts rhythmically without the need for external stimulation.
Ultrastructure of The Myometrium and The role of Gap Junctions in Myometrial Function
Published in Gabor Huszar, The Physiology and Biochemistry of the Uterus in Pregnancy and Labor, 2020
Arie Verhoeff, Robert E. Garfield
The protein components of the cell that respond to the Ca2+ fluctuations and utilize the chemical energy of ATP to result in either shortening or tension development are termed collectively the contractile apparatus. In smooth muscle, the major contractile proteins are myosin, actin, and tropomyosin, and minor components of the contractile apparatus include the proteins that are involved in the Ca2+-dependent regulatory mechanism.27
Effect of eccentric exercise on markers of muscle damage in patients with chronic obstructive pulmonary disease
Published in Physiotherapy Theory and Practice, 2021
Aqsa Mujaddadi, Jamal Ali Moiz, Deepika Singla, Irshad Hussain Naqvi, Mir Shad Ali, Deepak Talwar
In the present study, both the groups showed MVC decrement up to 48 h after eccentric exercise. The maximum decrement was noted at 48 h in both the groups with 20.3% change in the control group versus 45.7% in the COPD group. Significantly greater decrease in strength in COPD group can be possibly explained by two mechanisms. The first can be the impairment in excitation-contraction coupling forces due to metabolic changes in muscles such as phosphocreatine (PCr) depletion, accumulation of lactate (Sahlin, 1986), and structural and metabolic disorganization of contractile proteins which tends to be more in COPD leading to depressed force production (Westerblad and Allen, 2003). Second reason can be nitrosative stress induced in the body due to smoking which results in greater production of nitric oxide (NO) which further depresses force production of the muscle (Reid, 2001).
Passive stretching-induced changes detected during voluntary muscle contractions
Published in Physiotherapy Theory and Practice, 2020
Haris Begovic, Filiz Can, Suha Yağcioğlu, Necla Ozturk
QF muscle; formed by four parts, primarily functions as knee extensor while relative contribution of each part changes to the changing force output (Blazevich, Gill, and Zhou, 2006). The force output is affected by architectural differences between the parts, in which the RF is a bi-articular muscle while others mono-articular (Blazevich, Gill, and Zhou, 2006), posing different cross-sectional areas (Waryasz and McDermott, 2008), and changing intramuscular activation (Hug et al, 2015a; Hug, Hodges, and Tucker, 2015b). The total force output, which results from summation of the passive forces (i.e., compliance of noncontractile elements) and the active forces (i.e., interaction between actin and myosin contractile proteins) (Gajdosik, 2001) is further affected while being transmitted through regions of musculo-tentinous and osteo-tendinous junctions (Abate et al., 2009). Additional to this, an increase in muscle compliance, hence decrease in stiffness manifested by lengthened EMD after stretching would happen (Esposito, Limonta, and Cè, 2011) affecting a discharge level (Costa et al., 2010; Torres, Duarte, and Cabri, 2012).
Modulation of the airway smooth muscle phenotype in a murine asthma model and effects of nuclear factor-κB inhibition
Published in Journal of Asthma, 2019
Chen Qiu, Jie Li, Jian Zhang, Qi He, Lingwei Wang, Xuanwen Weng, Minjie Guan
Three genes encoding the contractile proteins of ASMC were studied by real-time PCR: α-smooth muscle actin, calponin and SM-MHC. α-Smooth muscle actin, calponin and SM-MHC mRNAs were dramatically decreased in OVA + vehicle mice compared with those in naive controls in the chronic model (Figure 1(B)). In the acute model, only one out of three genes (calponin) was down-regulated with statistical significance in OVA + vehicle mice (Figure 1(C)). PDTC treatment partially reversed the down-regulation of contractile gene expression in both the acute and chronic models. We also assessed COLIA1 mRNA expression in the intrapulmonary airways. Although OVA + vehicle mice demonstrated increased expression of COLIA1 that was significantly decreased by PDTC treatment in the acute model, there were no significant differences between the groups in the chronic model.