Musculoskeletal Key

The muscle fiber is surrounded by a connective tissue basement membrane that continues into the synaptic cleft, sending extensions into the junctional folds. The basement membrane contains a large amount…

The immediate trigger for muscular contraction is a sudden increase in the concentration of calcium ions in the cytoplasm of the muscle fiber, the sarcoplasm. To prevent the muscle from…

When the muscle fiber is electrically excited, calcium (Ca2+) ions released from the sarcoplasmic reticulum bind to the troponin C subunit of the troponin molecules on the actin filaments, with…

The contraction of a muscle fiber in response to a single nerve impulse is called a twitch. Under a given set of starting conditions, the force of a single fiber’s…

Most of the time, the sarcomere is in a state of relaxation. Because it is longer than a thick filament, there is a region at either end of the sarcomere…

During muscle contraction, the shortened muscle fibers bulge, squeezing against the surrounding connective tissue and one another. During very vigorous contraction, the blood vessels within the endomysium can be choked…

The structure of myosin has also been studied by breaking it down into smaller pieces with enzymatic digestion. For example, the enzyme papain splits off the head groups and a…

Each muscle fiber is invested by a thin layer of connective tissue called the basal lamina, or basement membrane. It is now believed that the basement membrane contains molecules important…

AMPHIOXUS The extant adult amphioxus, or lancelet, is considered to resemble an ancient ancestor of the vertebrates (see Plate 1-1). It is a fishlike animal, about 2 inches long, that…

The formation of muscles from the cervical hypaxial column of hypomeres, however, is quite different from what happens in the thorax; this is due to the development of the adjacent…