that is greater than skeletal muscle Can develop considerable tension even when stretched up to 2.5 times its resting length (urinary bladder, small intestine); connective tissue within restricts how much stress can occur
o Resting length is less than that for skeletal muscle o Thin filaments in smooth muscle overlap the thick filaments even when stretched out Stress relaxation response: smooth muscle is stretched and increases in tension, but quickly adjusts to this new length and relaxes to the initial tension level – thus enabling smooth muscle to exist at a variety of lengths with little change in tension SR is poorly developed on smooth muscle- contract the Ca 2+ by pumping it out of the cell not sequestering it Length that gives you the most tension- I o resting length is ready to exert the most power it can Stretched and maintain then revert back as if they weren’t stretched ° ° Comparisons of Muscle Types : Memorize the table and predict it Hormones don’t effect alpha motor neurons Autonomic is modified by hormones
° ° ° Figure 8.30: Comparison of the role of calcium in bringing about contraction in smooth muscle and skeletal muscle. ° Smooth is biochemical event
Skeletal is physical event ° Figure 8.6: Role of calcium in turning on cross bridges. ° ° Calcium activation of myosin cross-bridge in smooth muscle Depolarization of smooth muscle cells activates membrane Ca 2+ channels and releases Ca 2+ from underdeveloped sarcoplasmic reticulum Myosin light chains require phosphorylation to allow for actin-myosin interaction à BIG difference between skeletal and smooth muscle Rise in Ca 2+ induces chemical change in myosin whereas in skeletal muscle Ca 2+ causes a physical change (movement of tropomyosin away from the actin binding site on the myosin head)
° ° Figure 8.29: Calcium activation of myosin cross bridge in smooth muscle. Light chain- gets phosphorylated ° ° °
Cardiac Physiology Chapter 9 ° Cardiac Muscle Only found in the heart Striated Under involuntary control Acted on by the ANS ° ° Cardiac Muscle Striated o Thin filaments contain troponin and tropomyosin o Clear length-tension relationship o T-tubules and moderately well-developed sarcoplasmic reticulum. Like oxidative skeletal muscle: possess lots of mitochondria and myoglobin As in smooth muscle, Ca 2+ enters extracellular and through voltage-gated DHP receptors (in T-tubule membrane). As in single-unit smooth muscle, cardiac muscle displays pacemaker (but not slow- wave) activity interconnected by gap junctions. Cardiac fibers exist in a branching network and action potentials last a relatively long time. 99% contractile cells; 1% pacemaker (autorhythmic) cells that do not contract o See Fig. 9-7 Pacemaker activity of cardiac autorhythmic cells. o Single Unit: Both will contract when heart beats right atrial activate those atrial fibers that are interconnected through gap junctions with the fibers on the left side
° ° Blood flow through the heart: 1. Superior and Inferior Vena Cava 2. Right Atrium 3.
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- Fall '08