Terminal cisternae (singular: terminal cisterna) are enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules.

Function

Terminal cisternae are discrete regions within the muscle cell. They store

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

(increasing the capacity of the sarcoplasmic reticulum to release calcium) and release it when an

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

courses down the transverse tubules, eliciting

muscle contraction Muscle contraction is the activation of Tension (physics), tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in musc ...

. Because terminal cisternae ensure rapid calcium delivery, they are well developed in muscles that contract quickly, such as fast twitch

skeletal muscle Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

. Terminal cisternae then go on to release calcium, which binds to

troponin Troponin, or the troponin complex, is a complex of three regulatory proteins (troponin C, troponin I, and troponin T) that are integral to muscle contraction in skeletal muscle and cardiac muscle, but not smooth muscle. Measurements of cardiac-spe ...

. This releases

tropomyosin Tropomyosin is a two-stranded alpha-helical, coiled coil protein found in many animal and fungal cells. In animals, it is an important component of the muscular system which works in conjunction with troponin to regulate muscle contraction. It ...

, exposing active sites of the thin filament,

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...

. There are several mechanisms directly linked to the terminal cisternae which facilitate excitation-contraction coupling. When excitation of the membrane arrives at the

T-tubule T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells. With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permi ...

nearest the

muscle fiber A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadl ...

, a dihydropyridine channel ( DHP channel) is activated. This is similar to a

voltage-gated calcium channel Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (''e.g.'' muscle, glial cells, neurons) with a permeability to ...

, but is not actually an ionotropic channel. Instead, it serves to activate ryanodine, which will let

calcium ions Calcium ions (Ca2+) contribute to the physiology and biochemistry of organisms' cells. They play an important role in signal transduction pathways, where they act as a second messenger, in neurotransmitter release from neurons, in contraction ...

pass into the sarcoplasmic reticulum, and triggers calcium release to the muscle fiber itself. A T-tubule surrounded by two terminal cisternae is called a triad. The terminal cisternae, along with the transverse tubules, are the mechanisms of transduction from a nervous impulse to an actual

References

Anatomy articles needing expert attention Anatomy {{cell-biology-stub

Function

See also

References