The voltage-dependent sodium channel, which mediates the muscle action potential, is also time dependent: prolonged depolarization inactivates the action potential. This can be reversed only by a repolarization of the…
The membrane of the nerve terminal has a different assortment of ion channels: fewer sodium channels, several types of potassium channels, and, most important, voltage-dependent calcium channels. When an action…
In mammalian skeletal muscle, each muscle fiber is innervated by only one motor neuron. The combination of a single motor neuron and all the muscle fibers it innervates is called…
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…
However, for the action potential to affect the sarcoplasmic reticulum deep within the muscle fiber, it must be propagated inward as well as along the surface. This is accomplished through…
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…
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…
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…
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…
