Structure of Muscle Tissue

Actin and Myosin Motions in Muscle Tissue The relationship between the macroscopic structure of muscle tissue and its key proteins actin and myosin is illustrated in Figure 14.30 (99). 

Proteins are responsible for the distinct physical structure of a number of foods, e. g. the fibrous structure of muscle tissue (meat, fish), the porous structure of bread and the gel stracture of some dairy and soya products. 

Figure 2.20 Structure of muscle tissue protein myoglobin.

In general, the physical structure of the tissue must be broken down mechanically followed by an extraction procedure, before the sample can be analyzed. Homogenization using blenders, probe homogenizers, cell disrupters, sonicators, or pestle grinders is particularly useful for muscle, liver, and kidney samples. Regardless of the method used for tissue disruption, the pulse, volume of extraction solvent added, and temperature should be validated and standardized in order to ensure reproducible analytical results. During cell disruption, care should be taken to avoid heat build-up in the sample, because the analyte may be heat labile. 

Figure 3.5. Structure of oral tissues. The mouth and esophagus are composed of two layers the mucosa and submucosa. The mucosa is composed of layers of squamous epithelium, lamina propria, and muscularis. The submucosa contains blood vessels, nerves, adipose tissue, and skeletal muscle.

Scleroproteins. Insoluble in water and neutral solvents and resistant to enzymic hydrolysis. These are fibrous proteins serving structural and binding purposes. Collagen of muscle tissue is included in this group, as is gelatin, which is derived from it. Other examples include elastin, a component of tendons, and keratin, a component of hair and hoofs. 

To understand the physiological nature of muscle contractions, it is helpful to examine muscles microscopically. Muscle fibers have an outside membrane called the plasmalemma, an interior structure called a sar-colemma, transverse tubules across the fibers, and an inner network of muscle tissue called sarcoplasma. When a nerve impulse reaches the muscle, an action potential is set up and the current quickly travels in both directions from the motor end plate through the entire length of the muscle fiber. The whole inside of the muscle tissue becomes involved as the current spreads and, aided by calcium, the contractile protein called actin causes the muscle component (myosin) to contract. An enzyme, ATP-ase, helps provide the energy needed for the muscular filaments to slide past each other. Relaxation occurs promptly when Ca flows into the muscle tissue and the cycle is completed. The muscle fiber is now ready to be stimulated again by a nerve impulse. 

Sensory characteristics (texture, flavor, aroma, and color) of a food product are the most important attributes for the consumer (Aktas and Kaya, 2001b). The texture of food is mostly determined by moisture and fat content, as well as the types and amounts of structural carbohydrates and proteins. There are several physical and chemical methods of tenderizing meat. However, the mechanism of muscle tissue tenderization in solutions... 

The isolation of the proteins of fish muscle is still in its beginning, but is a necessary preliminary step to gain a deeper insight into the metabolism and structure of this tissue, thus providing a basis to attack the problems of storage. For the present, our description will be limited to some pure... 

The structure of muscle can be viewed at the electron micrograph level shown in Figure 8.9a, The muscle tissue is composed of bundles of muscle cells called muscle fibers. Within a muscle fiber are myofibrils, which are also arranged in bundles. Individual myofibrils contain the structurally distinct regions described below. Myofibrils have thin filaments composed of actin and thick filaments composed of myosin. Arrangement of the thick and thin filaments in a myofibril produces the distinctive pattern in Figure 8.9a and Figure 8.15. 

Tissue Properties. The properties of human tissues when the body is considered a linear, passive mechanical system are summarized in Table 10.1 (von Gierke et al., 2002 Goldstein et al., 1993). The values shown for soft tissues are typical of muscle tissue, while those for bone depend on the structure of the specific bone. Cortical bone is the dominant constituent of the long bones (e.g., femiu, tibia), while trabecular bone, which is more elastic and energy absorbent, is the dominant constituent of the vertebrae. The shear viscosity and bulk elasticity of soft tissue are from a model for the response in vivo of a human thigh to the vibration of a small-diameter piston (von Gierke et al., 1952)... 

Targets and spirals have been observed in the CIMA/CDIMA system [13] and also in dilute flames (i.e. flames close to their lean flammability limits) in situations of enlianced heat loss [33]. In such systems, substantial fiiel is left unbumt. Spiral waves have also been implicated in the onset of cardiac arrhytlnnia [32] the nomial contractive events occurring across the atria in the mannnalian heart are, in some sense, equivalent to a wave pulse initiated from the sino-atrial node, which acts as a pacemaker. If this pulse becomes fragmented, perhaps by passing over a region of heart muscle tissue of lower excitability, then spiral structures (in 3D, these are scroll waves) or re-entrant waves may develop. These have the incorrect... 

The structure of heart myocytes is different from that of skeletal muscle fibers. Heart myocytes are approximately 50 to 100 p,m long and 10 to 20 p,m in diameter. The t-tubules found in heart tissue have a fivefold larger diameter than those of skeletal muscle. The number of t-tubules found in cardiac muscle differs from species to species. Terminal cisternae of mammalian cardiac muscle can associate with other cellular elements to form dyads as well as triads. The association of terminal cisternae with the sarcolemma membrane in a dyad structure is called a peripheral coupling. The terminal cisternae may also form dyad structures with t-tubules that are called internal couplings (Figure 17.31). As with skeletal muscle, foot structures form the connection between the terminal cisternae and t-tubule membranes. 

In order to exert a force from one end of a muscle to the other, a structure must be continuous from one end to the other. In smooth muscle tissue, this structure is a system of alternating myosin and actin filaments within a cell, firm attachments first to the cell membrane, and beyond that extracellular attachments to the... 

Research in this area advanced in the 1970 s as several groups reported the isolation of potent toxins from P. brevis cell cultures (2-7). To date, the structures of at least eight active neurotoxins have been elucidated (PbTx-1 through PbTx-8) (8). Early studies of toxic fractions indicated diverse pathophysiological effects in vivo as well as in a number of nerve and muscle tissue preparations (reviewed in 9-11). The site of action of two major brevetoxins, PbTx-2 and PbTx-3, has been shown to be the voltage-sensitive sodium channel (8,12). These compounds bind to a specific receptor site on the channel complex where they cause persistent activation, increased Na flux, and subsequent depolarization of excitable cells at resting... 

The musculoskeletal system consists of bones, blood vessels, nerves, ligaments, tendons, muscles, and cartilage, which work together to perform the structural and kinematic functions of the organism. These musculoskeletal tissues all have a composite structure of cells embedded in a matrix produced by the cells themselves. 

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