Muscle anatomical structure

Anatomical structure. The striated muscles of vertebrates consist of bundles of muscle fiber cells covered with connective tissue. A muscle fiber is composed of bundles of striated myofibrils surrounded by sarcoplasmic reticulum, mitochondria and other organelles. The unique structure of the striated myofibrils, composed of thin(actin)-filaments and thick(myosin)-filaments, is common to all striated muscles of vertebrates including fish (19,20). 

All cells produce movement internally, and many are capable of motility or of changing shape. In some, movement is related to the function of individual cells, as in the migratory and engulfing movements of phagocytic cells or the swimming movements of sperm cells. In other cases, cells generate movement as one aspect of tissue function, as in the ciliary transport of mucus by the bronchial epithelium. Cells specialized for changing the dimensions or shape of anatomical structures or for movement of body parts with respect to each other are called muscle cells. 

Giuriato L, ScatenaM, Chiavegato A, Guidolin D, Pauletto P, Sartore S (1993) Rabbit ductus arteriosus during development anatomical structure and smooth muscle cell composition. Anat Rec 235 95-110... 

The anatomical unit of muscle is an elongated cell called a fibre. Each individual fibre cell consists of myofibrils which are bundles of contractile protein filaments composed of actin and myosin (Figure 7.1). Differences in structure indicate that muscles have evolved to perform particular functions. Although the structure of fibres, myofibrils and filaments of actin and myosin, is similar in all muscle types, their arrangement, action and control allow identification of three tissue types ... 

In summarizing the material on anatomical variations, it may be pointed out that the observed variations encompass all structures, brain, nerves, muscles, tendons, bones, blood, organ weights, endocrine-gland weights, etc. Data are presented which show that these structures often vary tremendously from one individual to another and that their structural differences in general are under genetic control. 

The lower urinary tract consists of the bladder, urethra, urinary or urethral sphincter, and the surrounding musculofascial structures including connective tissue, nerves, and blood vessels. The urinary bladder is a hollow organ composed of smooth muscle and connective tissue located deep in the bony pelvis in men and women. The urethra is a hollow tube that acts as a conduit for urine flow out of the bladder. The interior surface of both the bladder and urethra is lined by an epithelial cell layer termed transitional epithelium, which is in constant contact with urine. Previously considered inert and inactive, transitional epithelium may actually play an active role in the pathophysiology of many lower urinary tract disorders, including interstitial cystitis and UI. The urinary or urethral sphincter is a combination of smooth and striated muscle within and surrounding the most proximal portion of the urethra adjacent to the bladder in both men and women. This is a functional but not anatomic sphincter that includes a portion of the bladder neck or outlet as well as the proximal urethra. 

Because phospholipids are typically the other main lipid class found in fish flesh, the leaner the fish and the higher the proportion that phospholipids contribute to total lipids. For this reason, phospholipids comprise almost 90% of total lipids of lean fish such as cod, with TAG contributing as little as about 1%. Due to anatomical and physiological reasons, the amount of structural lipids (phospholipids) varies between 0.3 and 0.5 per 100 g w/w of fish muscle and does not usually exceed 1% w/w. This is most likely the minimum level of phospholipids essential for the cell and organelle membranes, of which they are a major component. Phospholipids are the major lipid class in most Australian fish, and in mollusks and crustaceans, all of which are typically lean (Table 12.3). In contrast to finfish, which tend to store lipid as TAG, an increase in the lipid content of shellfish is usually due to an accumulation of polar lipids (Nichols et al., 1998). This is similar to the case in Antarctic krill Euphausia superba D.), the phospholipids of which serve as storage lipids along with TAG. 

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