UWL BIO 312 - Smooth muscle (2 pages)

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Smooth muscle

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Smooth muscle


Remaining lecture notes on smooth muscle.

Lecture number:
Lecture Note
University of Wisconsin-La Crosse
Bio 312 - Human Anatomy and Physiology I
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Bio 312 Lecture 24 Lecture Outline 1 Smooth Muscle a Internal Structure b Excitation contraction coupling c Single unit vs multi unit Smooth Muscle Internal Structure much smaller than skeletal muscle o Poorly developed sarcoplasmic reticulum o No transverse tubules o No troponin on thin filaments o Contain tropomyosin but not in blocking position o No neuromuscular junction or motor end plate o Varicosities release NT over entire smooth muscle o Sliding filament mechanism thick and thin filaments interact to produce smooth muscle contraction Excitation contraction coupling relies on phosphorylation of cross bridge o As long as phosphate binds to cross bridge it will cycle and interact with thin filament o To stop contraction phosphate must be cleaved from cross bridge 1 Response to stimuli causes calcium to leak into cell 2 Calmodulin becomes active when extracellular calcium comes into cell 3 Activation of calcium calmodulin activates calcium colmodulin myosin light chain kinase which attaches phosphate cross bridge 4 Cycling and cross bridge activity occurs 5 Myosin light chain phosphatase cleaves phosphate from cross bridge and ends cross bridge cycling o Results in graded response depending on how much calcium made available in response to various stimuli not all or none response Influences on the entry or removal of Ca 2 from sarcoplasm o APs in sarcolemma some smooth muscle cells can spontaneously depolarize and fire APs Usually done rhythmically Caused by potassium leaking out faster than sodium and calcium leaking in o Neurotransmitters released by autonomic neurons o Hormones Oxytocin receptors on uterine smooth muscle Vasopressin receptors on vascular smooth muscle Epinephrine receptors in airway smooth muscle Gastrin receptors in stomach smooth muscle Release of NT will only effect smooth muscle where they have bindable receptors o Locally induced charges in the chemical composition of the extracellular fluid Oxygen CO2 H K o Passive stretch Done in blood and lymphatic vessels as a response to increased pressure Some smooth muscle receives dual innervation from the ANS Single unit smooth muscle Found in walls of hollow organs involved in peristaltic contractions Most smooth muscle falls under this category Spontaneous action potential induced by pacemaker rhythmic potential o Spread to non pacemaker cells through gap junctions o Individual AP stimulates multiple muscle cells Multi unit smooth muscle Found in skin eyes iris ciliary body Very dependent on ANS No pacemaker activity Can contract without action potential o Hormones or neurotransmitters can allow calcium into cell and allow cross bridge cycling without initiation from an action potential No gap junctions do not move in sync

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