Smooth Muscle Contraction Flashcards
Why is there no banding pattern in smooth muscle ?
Not organised into myofibrils, and there are NO sarcomeres
What is the name of the contraction mechanism used in smooth muscle ?
Sliding-filament mechanism
Where is smooth muscle found ?
Smooth muscle surrounds hollow structures and organs that undergo changes in volume with accompanying changes in the lengths of the smooth muscle fibers in their walls
What is the shape of smooth muscle cells ?
Spindle-shaped
What is the average height and length of smooth muscle cells ?
Height: 2-20 μ
Length: 20-200 μ
What is the amount of myosin and actin smooth muscle contains, relative to the amount of myosin and actin found in striated muscle ?
10%
What is the actin:myosin ratio in smooth muscle cells ?
15:1
What are the steps of smooth muscle contraction ?
- Initiated by calcium from Extracellular Fluid or SR.
- Calcium binds to calmodulin (instead of troponin as in skeletal muscle)
- Ca-calmodulin-MLCK (Myosin light chain kinase) complex leads to phosphorylation of MLC (requires 1 ATP)
- MLC (Myosin light chain) is part of myosin head
- Phosphorylated myosin head binds to actin and power stroke occurs automatically
- A second ATP is required to release myosin head from ac/n
MLC = Myosin light chain
MLCK = Myosin light chain kinase
Why is myosin phosphorylated as part of smooth muscle contraction ?
Because only the phosphorylated form of smooth muscle myosin can bind to actin and undergo cross-bridge cycling.
What are the steps of smooth muscle relaxation ?
- Calcium concentration dips below a critical level due to being pumped out of the cell or into the SR
- Calcium is released from calmodulin
- MLCP (Myosin light chain phosphatase) removes phosphate from the MLC, causing detachment of the myosin head from the ac/n filament, causing relaxation.
What are the sources of Calcium contributing to the rise in systolic concentration of calcium in smooth muscle, thus initiating smooth muscle contraction ?
-SR Ca2+
-Extracellular Ca2+ entering the cell through plasma-
membrane Ca2+ channels
When smooth muscle relaxes, where does the Calcium go (to reduce cystolic Calcium concentrations) ?
To the SR or to the Extracellular fluid (ECF)
What are some inputs which influence smooth muscle contractile activity ?
- Spontaneous electrical activity in the plasma membrane of the muscle cell.
- Neurotransmitter released by the autonomic neurons.
- Hormones.
- Locally induced changes in the chemical composition (paracrine factors, acidity, oxygen, osmolarity, ion concentrations) of the extracellular fluid surrounding the cell.
- Stretch
What is the membrane potential change occurring during the spontaneous depolarization to threshold ?
Pacemaker Potential
What are the main types of spontaneous electrical activity found in smooth muscle cells ?
- Some types of smooth muscle cells generate action potentials spontaneously in the absence of any neural or hormonal input (membrane potential change occurring during the spontaneous depolarisation to threshold is known as a pacemaker potential.)
- Other smooth muscle pacemaker cells have a slightly different pattern of activity. The membrane potential drifts up and down due to regular variation in ion flux across the membrane. These periodic fluctuations are called slow waves.