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53 Cards in this Set

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  • Back
What are the two types of smooth muscles and which one is predominant?
1. Multiunit Smooth muscle
2. Unitary Smooth muscle (predominant)
Describe the composition of multiunit smooth muscles.
Discrete smooth muscle fibers
Describe the composition of unitary smooth muscles.
Large conglomerate of smooth muscle fibers.
Describe the innervation of multiunit smooth muscle.
Each muscle fiber is individually innervated, thus FINE control.
Describe the innervation of unitary smooth muscle.
A single neuromuscular junction serves the entire bundle/sheet of smooth muscles. The (outer) cells that receive stimulus will transmit it to other cells via gap junction.
Unitary smooth muscle is also known as what?
Syncitial smooth muscle.
Examples of where you might find multiunit smooth muscle.
Ciliary muscle of eye
Iris of eye
Examples of where you might find unitary smooth muscle.
Blood vessels
GI tract
Uterine wall
What is the ratio of actin to myosin in smooth muscles?
15 actin to 1 myosin
Describe the organizational structure of actin and myosin in smooth muscles.
Irregular structure
In smooth muscle, what is analogous to the Z disc in skeletal muscle?
Dense bodies
Describe the sarcoplasmic reticulum in smooth muscle in comparison to skeletal muscles.
Much reduced in smooth muscles
Where does the calcium predominantly come from in smooth muscles?
Outside the cell (ECF)
Upon depolarization of smooth muscle cell membrane, the calcium comes in (from outside) and does what?
Binds to calmodulin
What activates the light chain kinase to phosphorylate myosin?
Calcium / calmodulin complex
What needs to happen to myosin so that contraction can occur?
Needs to be phosphorylated by light chain kinase and needs the presence of actin.
Why does smooth muscle stay contracted involuntarily?
Because an enzyme is needed for relaxation to occur.
Describe the four steps of contraction termination in smooth muscles.
1. Calcium channels close
2. Cytosolic Ca levels fall below "critical level"
3. Myosin light chain is dephosphorylated by myosin phosphatase.
4. Cross-bridge cycling stops.
Compare speed of cross-bridge cycling in smooth muscle to skeletal muscle.
Slower in smooth muscle
Compare onset of contraction and relaxation after stimulus in smooth muscle vs. skeletal muscle
Slower in smooth muscle
Compare energy of sustained contraction in smooth muscle vs. skeletal muscle.
Less energy required in smooth muscle.
Compare maximum force of contraction in smooth muscle vs. skeletal muscle.
Greater in smooth muscle.
Compare degree of shortening in smooth muscle vs. skeletal muscle.
Greater degree in smooth muscle.
Compare the quantitative energy of sustained contraction between smooth muscle and skeletal muscle.
Smooth muscle uses 1/300th the energy of skeletal muscle to sustain a contraction
Describe the "Latch" mechanism.
Once smooth muscle in fully contracted, it will sustain it at 1/300 the energy of skeletal muscle.
What occurs slower in smooth muscle than in skeletal muscle?
1. Cycling of cross bridges
2. Relaxation
3. Contraction
What are the two mechanisms of control in smooth muscle contraction?
Neural and hormonal mechanism.
Describe the receptors of muscle contraction in smooth muscles in comparison to skeletal muscles.
1. Smooth muscle membrane has many different receptor types (rather than just Na+/K+).
2. Smooth muscles also have receptors that can inhibit contraction (not seen in skeletal muscles)
Do smooth muscles have discrete neuromuscular junctions?
No. Nerves terminate over muscle fibers, not in them.
Describe the actions of diffuse junction in smooth muscles.
Secretes transmitters into fluid surrounding muscle fibers.
What are the transmitting substances of autonomic nerves?
Acetylcholine and Norepinepherine
T/F - Acetylcholine and norepinephrine are released by the same nerve.
False - released by different nerves, where one is stimulatory and the other is inhibitory.
What is the general rule of ACh/NE effects on organs.
Action varies with organ type, but in general: if ACh excites, NE inhibits. and vise versa.
What is the resting potential in smooth muscles?
-50 mV.
Action potentials are seen in what type of smooth muscles?
In unitary smooth muscles, but not much in multiunit smooth muscles.
What are the two types of action potential seen in unitary smooth muscles?
1. Spike potential
2. Action potential with plateaus
Describe the duration of spike potentials
10 - 50 milliseconds
Describe the polarization character of spike potentials with plateaus.
Very slow repolarization.
Where would you find spike potentials?
Places of peristalsis (approx. 8 contractions per minute)
Where would you find action potentials with plateaus.
In muscles requiring extended period of contraction usch as ureter, uterus, and vascular smooth muscle.
Describe the number of calcium channels in smooth muscle cells.
Calcium channels far exceed sodium channels in smooth muscle cells.
The flow of what is responsible for Action potential in smooth muscles.
Describe the opening of calcium channels.
Opening is much slower.
What are the characters of these slow waves? X 3
1. Self excitatory
2. No extrinsic stimulus needed
3. Source of slow waves unknown
What are the possible reasons for explaining slow waves?
1. Changes in Na pumping
2. Ion conductance changes
3. Leak of ions (either Na or Ca)
Action potential is directly COUPLED with what in smooth muscles?
What causes excitation by stretch in smooth muscles? X 2
1. Normal slow waves
2. Increase in membrane potential (less negative)
Half of smooth muscle contraction is caused by what two factors?
1. Local tissue factors
2. Hormones
What are the five local tissue factors?
1. Lactic acid
2. Acidity
3. Carbon Dioxide
4. Oxygen
5. Prostanoids
How does hormones effect smooth muscle contraction?
Alters the ion conductance
T/F - Troponin - Tropomyosin complex seen in smooth muscles.
What are three major factors of contraction stimulation in smooth muscles.
1. Stretch
2. Hormones
3. Local factors
What exhibits intrinsic contraction without external stimuli?
Slow waves