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43 Cards in this Set

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