Title: Human Physiology - Muscle
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Content: they pass completely through and open somewhere else on the sarcolemma (i.e., these tubules are not used to get things into and out of the muscle cell). The function of T-TUBULES is to conduct impulses from the surface of the cell (SARCOLEMMA) down into the cell and, specifically, to another structure in the cell called the SARCOPLASMIC RETICULUM. A muscle fiber is excited via a motor nerve that generates an action potential that spreads along the surface membrane (sarcolemma) and the transverse tubular system into the deeper parts of the muscle fiber. A receptor protein (DHP) senses the membrane depolarization, alters its conformation, and activates the ryanodine receptor (RyR) that releases Ca 2+ from the SR. Ca 2+ then bind to troponin and activates the contraction process (Jurkat-Rott and Lehmann-Horn 2005). Sarcoplasmic reticulum (SR) membranes in close proximity to a T-tubule. ' RyR' are proteins the aid in the release of calcium from the SR, 'SERCA2' are proteins that aid in the transport of calcium into the SR (Brette and Orchard 2007). The SARCOPLASMIC RETICULUM (SR) is a bit like the endoplasmic reticulum of other cells, e.g., it's hollow. But the primary function of the SARCOPLASMIC RETICULUM is to STORE CALCIUM IONS. Sarcoplasmic reticulum is very abundant in skeletal muscle cells and is closely associated with the MYOFIBRILS (and, therefore, the MYOFILAMENTS).