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SIUE Smooth Muscle
| Question | Answer |
|---|---|
| Multi-unit smooth muscle | Each individual cell is innervated by its own nerve ending controlled mainly by nervous stimuli rarely contracts spontaneously ex.) iris, piloerector muscles, cilliary muscles |
| Single-unit smooth muscle | single whole mass, also called visceral represents a large # of fibers that contract together as a single unit (usually non-nervous stimuli) arranged in sheets/bundles w/ many adherences for effective force transfer many gap junctions |
| Gap Junction | Sites of direct electrical connections Allows for syncitial smooth muscle contraction allows ions to move freely from one cell to the next |
| Where are single unit smooth muscles typically found? | Hallow organs (uterus, vessels, gut, bladder, etc.) |
| Dense Bodies | found in smooth muscle and connect actin together Act as intracellular bridges |
| Chemical makeup of smooth muscle | Smooth muscle contains actin and myosin, but not troponin. Smooth muscle AP is regulated largely by Ca++, Calmodulin is present in smooth muscle |
| Myosin : Actin ratio of smooth muscle | 1:15 |
| Speed and force of smooth muscle contraction | smooth muscle contraction is slow compared to skeletal muscle, but it is much stronger |
| Crossbridge Cycling of Smooth Muscle | |
| Multi-unit smooth muscle | Each individual cell is innervated by its own nerve ending controlled mainly by nervous stimuli rarely contracts spontaneously ex.) iris, piloerector muscles, cilliary muscles |
| Single-unit smooth muscle | single whole mass, also called visceral represents a large # of fibers that contract together as a single unit (usually non-nervous stimuli) arranged in sheets/bundles w/ many adherences for effective force transfer many gap junctions |
| Gap Junction | Sites of direct electrical connections Allows for syncitial smooth muscle contraction allows ions to move freely from one cell to the next |
| Where are single unit smooth muscles typically found? | Hallow organs (uterus, vessels, gut, bladder, etc.) |
| Dense Bodies | found in smooth muscle and connect actin together Act as intracellular bridges |
| Chemical makeup of smooth muscle | Smooth muscle contains actin and myosin, but not troponin. Smooth muscle AP is regulated largely by Ca++, Calmodulin is present in smooth muscle |
| Myosin : Actin ratio of smooth muscle | 1:15 |
| Speed and force of smooth muscle contraction | smooth muscle contraction is slow compared to skeletal muscle, but it is much stronger |
| Crossbridge Cycling of Smooth Muscle | Slower frequency than skeletal muscle The interaction lasts longer between Actin and myosin because the fibers have less ATPase which yields less energy |
| Muscle shortening in smooth muscle | Smooth muscle does not shorten as much as skeletal muscle because of the random arrangement of the filaments. Smooth muscle shortens to 2/3 of its original length |
| Contraction sequence of smooth muscle | Ca++ channels open and Ca++ enters the cell Ca++ binds with calmodulin to create the C-CL complex C-Cl binds to and activates myosin light chain kinase to phosphorylate the myosin head and allow myosin to bind to actin |
| Relaxation sequence of smooth muscle | Ca++ levels decrease in the cell and myosin phosphotase removes phosphate from the head of the myosin, thus, stopping the contraction |
| What is a major determinant of the length of time of smooth muscle contraction? | The amount of myosin phosphotase in the cell |
| What are varicosities? | Small areas at the nerve ending that are not mylinated and they release neurotransmitters from their walls (ACh and NE) |
| Myosin Kinase | Enzyme that is activated by C-CL complex that phosphorylates the myosin head and allows for actin/myosin binding (contraction) |
| Myosin Phosphatase | Enzyme that dephosphorylizes the myosin head resulting in muscle relaxation |
| Diffuse Junction in Smooth Muscle | The nerves branch over sheets of muscle They are not specialized Inner layers of the myofibrils are excited by the upper layers |
| Contact Junction in Smooth Muscle | The axon endings are 20-30 nanometers from the cell, varicosities sit directly on the smooth muscle cells Cause muscles to act very quickly (fast focusing of the iris) |
| Smooth Muscle Neurotransmitters | ACh and NE If one is inhibitory the other is exitatory |
| Resting Membrane Potential of Smooth Muscle | -50 - -60 mV |
| How action potential is reached in single unit smooth muscle | Ca++ channels open and calcium enters the cells causeing depolarization. Na+ is responsible to lesser extent Depolarization takes longer because calcium channels are slow |
| Slow Wave Potential | Spontaneous AP that doesn't necessarily cause a contraction Not a full contraction rhythmic contractions are common (peristalsis) |
| Stretch activation of Smooth Muscle | The cells in single motor unit muscles depolarize in response being stretched ex.) gut moves food along when it is stretched |
| Non-nervous stimulation of Smooth Muscle | Ions, Adenosine, Temp change cause vessels to vasodilate Hormones/Neurotransmitters (ACh,NE, ADH, Oxytocin, Histamines, Seratonin) affect contraction Especially important in heart and uterus |
| Ca++ Sources for Smooth Muscle | ECF mostly, with some coming from the SR |
Created by:
SRNA84
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