HLSC 1200U Lecture Notes - Lecture 13: Endoplasmic Reticulum, Intercalated Disc, Skeletal Muscle
Document Summary
Contains parallel myofibrils, t tubules and sr. Found only in the heart; forms the bulk of the wall of each chamber. Form a continuous, contractile band around the heart chambers that conducts a single impulse across a virtually continuous sarcolemma. T tubules are larger and form dyads with a rather sparse sarcoplasmic reticulum. Form syncytium (strong, electrically coupled junctions (intercalated disks) with other fibers) Longer: cannot come rapidly enough to produce tetanus. Rapidly depleted: leads to fatigue continuously produced: no fatigue. Contracts rhythmically and continuously to maintain constant blood flow. Looks smooth because thick and thin filaments are arranged differently than in skeletal or cardiac muscle fibers. No t tubules, no sarcomeres, loosely organized sarcoplasmic reticulum. Ca++ comes from outside the cell (not sr) and binds to calmodulin (not troponin) to trigger a contraction. Able to be stimulated and to respond to regulatory signals (nerves) Allows muscle to return to normal resting relaxed length.
