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43 Cards in this Set
- Front
- Back
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What are the 2 main sites for control of excitation-contractraction coupling in smooth muscle?
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1. Sarcolemma (plasma membrane)
2. Sarcoplasmic reticulum |
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What feature of the cell membrane involves it in excitation contraction coupling?
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The presence of voltage-gated Calcium channels, where Ca influxes into the cell from ECF
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What feature of the sarcoplasmic reticulum involves it in excitation contraction coupling?
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It contains the calcium that is released by IP3 stimulation.
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What molecules are responsible for MODULATION of contractile force?
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cAMP and cGMP - second messenger systems.
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How do the 2nd msgr systems modulate contractile force?
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By increasing contractile filament calcium sensitivity
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So what are the 2 main sources of calcium for smooth muscle contraction?
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1. ECF
2. Membrane stores |
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What is the predominant way that Calcium gets in from the ECF?
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Via membrane potential-sensitive calcium channels controlled by voltage.
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How is the sarcoplasmic reticulum in smooth muscle predominantly different from that in skeletal muscle?
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It is much less extensive
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How is calcium released from the SR in smooth muscle? Skeletal?
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Smooth: Via PLC-IP3 mechanisms
Skeletal: Via Ryanodine sensitive mechanisms |
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What specific types of smooth muscle have:
-LOTS of SR -LITTLE SR |
Intestinal = LITTLE SR
Aorta = LOTS of SR |
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So the primary way that calcium enters smooth muscle from ECF:
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Via voltage-sensitive ion channels
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Are voltage-gated Ca channels the ONLY way that Calcium gets into smooth muscle from ECF?
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No; there are some receptor operated channels like stretch receptors that may do it too.
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Mechanism of Calcium release from SR:
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PLC/IP3
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What are the 3 mechanisms in smooth muscle for getting RID of calcium from the cell?
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1. SRCA - into SR
2. PMCA - into ECF 3. Na/Ca exchanger - 2ndary AT |
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What calcium removal mechanism is shared with both cardiac and skeletal muscle?
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SRCA
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In what type of muscle is the Ca/3Na exchanger most important?
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Cardiac
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What does the velocity and onset of smooth muscle contraction compare to skeletal?
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It has a VERY HIGHLY VARIABLE velocity of contraction, and the onset is much slower of both contraction and relaxation
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How does the force of contraction in smooth muscle compare to skeletal?
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Smooth muscle can generate forces that are equal to or greater than those in skeletal muscle per cross sectional area of fiber
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How is the length-tension curve different for smooth muscle compared to skeletal?
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Smooth muscle operates over a MUCH wider range of length - it can contract both when an organ is empty, and distended.
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So what type of muscle retains its ability to contract and generate force even at short lengths?
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Smooth
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How does the contraction time of smooth muscle compare to skeletal?
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Smooth muscle contractions have a much longer duration - because the onset of contraction and relaxation is much slower.
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What is a unique ability of smooth muscle that is seen when sudden changes in length occur at constant levels of tension?
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Stress relaxation (both fwd and reverse)
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What is an important example of where stress relaxation occurs?
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In the bladder - as it fills it stretches, but the force doesn't remain increased because of stress relaxation.
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What has a higher crossbridge cycling frequency; skeletal or smooth muscle?
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Skeletal - by far!
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What is the effect of skeletal muscle's crossbridge cycling frequency being higher than that for smooth muscle?
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Skeletal has a much higher energy consumption than smooth.
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What is responsible for neural innervation of smooth muscle?
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Autonomic innervation
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What is a type of smooth muscle in which there is not spontaneous contration, but it's dependent on autonomic innervation?
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Aorta
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What are the synapses of autonomic nerves on smooth muscle like?
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Sprinkler systems - adrenergic nerves dump NE on muscarinic receptors on the smooth muscle
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What structures on autonomic nerves release NT?
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Varicosities
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What are the 2 main types of autonomic neurotransmitters that act on smooth muscle?
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-Adrenergic
-Cholinergic |
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What are the receptors for Norepinephrine released from adrenergic neurons?
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Alpha (1/2)
Beta (1/2) |
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What happens when NE binds alpha 1 receptors in the aorta?
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It stimulates contraction
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What happens when NE binds alpha 2 receptors in the intestine?
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It causes relaxation
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What is the NT released from cholinergic neurons?
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Acetylcholine
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What are the ACh receptors on smooth muscle and endothelium that are activated by ACh?
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Muscarinic cholinergic receptors
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What are 3 other types of NTs that can affect smooth muscle?
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-Purinergic NTs
-Peptides -Gases (NO) |
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What is the cholinergic receptor in skeletal muscle?
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Nicotinic
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How does autonomic neural input on smooth muscle affect its tone?
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By causing changes in resting membrane potential that will either culminate in an AP (via depolarization) or inhibit it.
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What do NE and ACh do to uterine smooth muscle?
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ACh: stimulates contraction
NE: inhibits contraction, results in relaxation |
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What happens in a cerebral artery when MAP increases?
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The cerebral artery smooth muscle depolarizes which causes contraction.
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Why do cerebral arteries contract when MAP becomes high?
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To prevent transmission of the pulse pressure to the brain which could be damaging to it.
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What will hypoxia do to cerebral vessels?
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Cause hyperpolarization of cerebral vasculature smooth muscle so relaxation.
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Where does hypoxia NOT cause relaxation of blood vessels?
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In the lungs
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