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SIUE Smooth Muscle
Kyles Lecture Physiology Smooth Muscle
| Question | Answer |
|---|---|
| contraction is activated by | Calcium |
| Smooth muscle contains actin & myosin, but NO | troponin |
| Smooth muscle can contract up to ___ % | 80% (or 2/3) it's size |
| Multi unit smooth muscle are (name examples) | Iris, cilla, and piloerector muscles |
| Single Unit Smooth muscle are (name examples | Hollow organs (visceral) GI gut, ureters, urethra, blood vessels, uterus, bile ducts |
| Calcium pump in smooth muscle | is slower than in skeletal |
| Sarcoplasm Reticulum | less extensive than skeletal muscle |
| Calcium source for smooth contraction | diffusion through ECF |
| Positive feedback mechanism | Ca++ influx, very few Na+ gates |
| Resting potential | 50-60 |
| Neurotransmitters | ACh & NE |
| Regulatory protein | Calmodulin |
| Nerve Junction | diffuse junctions that secrete their transsmitter substance into the matrix of smooth muscle |
| Varocosities | found on terminal axons, similar to vesicles on skeltal muscle, contain neurotransmitter ACh and NE; multiple sites of neurotransmitter release |
| Diffuse Junctions | branch diffusely on top of a sheet of muscle, not a specialized NMJ. inner layers are excited by upper layers. |
| Gap junctions | site of direct eletrical connection, synytical smooth muscle (if one nerve fires, the rest fire) |
| Stimuli | Nervous stimuli (multi unit), vasodilation, hormonal stimuli, ions, lactic acid, angiotensin, ADH, oxytosin |
| Force of conraction in smooth muscle | Very strong compared to smooth muscle (think the uterus) |
| Spread of contraction/relaxion is? | Slower in the smooth, 30 x slower than skeletal |
| Energy requirements | 10-300 x Less than needed in skeletal |
| Myosin actin interation is | Longer in smooth than skeletal |
| Cross bridge cycling is | Slower in smooth (compared to skeletal) |
| Actin to Myosin Ratio | 15:1 |
| Smooth muscle sustantained contraction can occur from | latch mechanism |
| Depolarization of the multi-unit smooth musclce can occur without | and action potential. Most of these muscle fibers can be stimulated by neurotransmitter release alone. There muscle fibers are too small to generate ap |
| Calamodulin & activation of A/M | Calamodulin binds with Ca++, C/C complex activates myosin kinase which then phosphorolates the myosin head and allows for myosin/actin interaction. |
| Multiunit smooth muscle characteristics | separate, descrete fibers that are innervated separately & controlled by a single nerve (nervous stim onlY) ending. contracts independantly, sledom contract spontaneously |
| Singleunit smooth muscle characteristics | large number of fibers that act (contrat) together as a single unit, usually controlled by non-nervous stimuli, have many gap junctions |
| Dense bodies | actin is bound together, act as intracellular bridges that transmit the forces of contraction |
| Action potentials occur in | single units, not multiunits |
| Actions potentials in Single Unit | have spike potentials, action potentials with plateau, calcium involvement has voltage gated calcium channels. |
| Slower and longer Action potential is due to | calcium channels staying open longer and are slower than the Na+ channels in skeletal muscle |
| Action potentials with a plateau | results from delayed repolarization, causes a prolonged contraction which is typically seen in vascular, uterus, and ureters. |
| Slow wave potential | causes spontaneous AP in some smooth muscle which cause a slow wave rhythm (pacemaker waves) seen in the gut |
| Local tissue factors that are responsible for vasodilation that stimulates multiunit smooth muscle | ions - lack of O2, excess CO2, excess H+ excess K+, decrease in Ca+ adenosine, and mild to moderate temp decrease |
| Hormonal factors that affect contraction | ACh, NE, Epinephrine, angiotensin, vasopressin, ADH, oxytosin, histamine, serotonin |
| Hormones have | gated receptors that are excitatory (contraction) or inhibitory (relaxation) important in heart and uterus. |
| Contact Junction | prevalent in multiunit. has short latency signals which act quickly, varicosities with neurotransmitters sit directly on the muscle which is how eye muscles work so fast. |
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