Muscle 14 Flashcards
What is the variation in the action potentials of smooth muscle?
Some exhibit prolonged action potentials and some exhibit action potentials similar to skeletal muscle and some cannot generate action potentials at all
What causes smooth muscle cells to undergo changes in membrane potential?
Neuro, hormonal or mechanical stimulation. They can also initiate spontaneous electrical activity
What does the spontaneous electrical activity of smooth muscle cells result from?
Pacemaker currents
What does the spontaneous electrical activity in smooth muscle result in?
Regular repetitive oscillations in the membrane potential
What are Slow Waves?
The membrane oscillations of smooth muscle due to spontaneous electrical activity
What starts the process of slow waves?
•Voltage gated calcium channels that are active at rest depolarize the cell enough to activate more voltage gated calcium channels causing a calcium influx
What happens in a slow wave once there is a calcium influx?
The amount of calcium became enough to depolarize the cell to threshold causing an action potential leading to further calcium influx and contraction of the smooth muscle
What happens after the action potential occurs in smooth muscle slow wave?
There is continued calcium influx from the action potential and a rise in the internal calcium concentration which opens calcium dependant potassium channels
What happens after calcium dependent potassium channels open in a slow wave?
Potassium leaves the cell and slow hyperpolarization occurs and the membrane becomes more negative
In a smooth muscle slow waves, what happens after potassium leaves the cell and the cell becomes hyperpolarized?
Voltage gated calcium channels close and the internal calcium concentration decreases and the cell is hyperpolarized allowing the potassium channels to close
What happens after the calcium gated potassium channels close in slow wave smooth muscle?
Potassium will no longer leave the cell, the cell becomes less hyperpolarized and voltage gated calcium channels open and start the process over
What is different about what causes the action potential in smooth muscle?
We do not have an external stimulus causing action potentials in the smooth muscle cells, it is due to changes in calcium conductance
What do the thin filaments lack in smooth muscle?
Troponin
What are smooth muscle cells turned on by?
Calcium dependent phosphorylation of myosin
What are attached to the proteins of myosin heads in smooth muscle?
Lightweight chains
