Phys. II Test One: Smooth Muscle Flashcards
Nerves to smooth muscle are derived from what NS?
Autonomic
What anchors actin to the cells plasma membrane and is analogous to Z discs in skeletal muscle?
Dense Bodies
Describe Single unit/visceral muscle.
Entire group of muscle fibers responds to stimulation as a single unit due to gap junctions
What happens to muscle fibers in a single unit that have pacemaker activity?
They spontaneously generate AP’s that can spread to other cells through gap junctions
What affects the contractile activity of cells?
Nerves
Hormones
Local factors
How can the entire single unit muscle be regulated?
By controlling the frequency that the pacemaker fires
Describe multi-unit muscle.
Few to no gap junctions so each cell within the muscle responds independently of each other. Depends on the number of fibers that are activated and frequency of nerve stimulation
Which muscle unit can respond to stretch?
Single Unit
What regulates cross bridge binding and movement?
Calcium activating the enzyme myosin light chain kinase
How is MLCK activated?
Concentration of Ca in cytoplasm is increased through opening of membrane calcium channels allowing extracellular calcium in, or through stimulation of SR to release intracellular calcium. Calcium then binds with Calmodulin to activate/bind with MLCK.
What does calcium bind to since troponin is not in smooth muscle?
Calmodulin
What does MLCK use ATP for?
To phosphorylate one of the light chains of each myosin head
How does smooth muscle relax?
Myosin needs to be dephosphorylated. First the slow acting ATP requiring pump movews calcium back into the SR so MLCK is no longer activated. Then the dephosphorylating enzyme myosin light chain phosphatase, which is always active, outpaces MLCK and relaxation occurs.
Which muscle type has faster rates of ATP splitting and cross bridge cycling during contraction?
Skeletal
What is the “latch state”?
Smooth muscle develops a full contraction and tension generated is high and can be maintained nearly full level even with a decline in energy.
What inputs can increase a cells cytosolic Ca concentration?
- Transmitters from ANS
- Hormones
- Local factors, acididty, osmolarity, O2 or CO2 and paracrines
- Stretch of fibers
- spontaneous electrical activity in fibers PM
How can a smooth muscle cell contract in the absence of a membrane potential change?
An internal second messenger molecule such as IP3 is generated in response to external chemical messenger binding which will trigger the release of calcium from the SR.
What cation causes action potentials in smooth muscle?
calcium not Na
Where are slow waves typically found?
Single unit smooth muscle. When the AP is produced the AP will spread over the entire unit.
What does smooth muscle have instead of a motor end plate region?
Axons of post ganglionic auto.neurons have swollen regions called varicosities which contain NT and when the AP reaches the varicosity it releases it NT.
What happens if a Norepinephrine binds to alpha adrenergic receptors?
Most blood vessel smooth muscle contraction is enhanced.
What happens if Norepinephrine binds to beta2 adrenergic receptors?
It relaxes bronchiole smooth muscles
