passive membrane properties Flashcards
What does Cm represent in the electrical model of the membrane?
Capacitance: the ability to store charge
What does Rm represent in the electrical model of the membrane?
Membrane Resistance: depends on the number of open ion channels
How does membrane resistance (Rm) affect ion channels?
The lower the resistance, the more ion channels open, leading to a leakier cell
What are graded potentials?
Changes in membrane potential that lose strength as they move through the cell
What does a longer length constant (λ) indicate?
Graded potentials can travel longer distances
What factors influence the length constant (λ)?
Proportional to d (distance) and Rm (membrane resistance); inversely proportional to Ri (internal resistance)
What does a larger time constant indicate?
A slower change in potential in response to a stimulus
What is temporal summation?
Summation of graded potentials in regards to how long/short the time constant is
What is spatial summation?
How close/far the action potentials (APs) are located to each other
How does membrane capacitance affect propagation velocity?
Membrane capacitance has a negative effect on propagation velocity
What factors influence the propagation of current?
Resistance of the membrane to current leak and the diameter of the axon
How does the diameter of an axon affect current conduction?
Large diameter axons provide low resistance to current flow, speeding conduction
What happens to Rm when it increases?
More ions stay inside the cell, increasing depolarization potential
What happens to Ri when it decreases?
Ions/current propagate more freely
What effect does a decrease in Cm have on depolarization?
More ions enter, available to depolarize the cell, leading to faster voltage changes
How does an increased length constant (λ) affect conduction velocity?
Current travels further, leading to faster conduction velocity
How does a decreased time constant (τ) affect response speed?
Faster response of voltage to current, higher propagation speed
What initiates action potential propagation?
Graded potentials trigger action potentials by opening voltage-gated Na+ channels
How do Na+ ions contribute to action potential propagation?
Na+ spreads in all directions, attracting negative ions in adjacent regions
What is the role of myelin sheath?
Wraps around axons, preventing current leak and acting as an insulator
What are the Nodes of Ranvier?
Portions of axons lacking myelin sheath with high concentrations of Na+ channels
What is saltatory conduction?
The apparent leapfrogging of action potentials from node to node along the axon
What is demyelination?
Slows down or stops conduction of the action potential by allowing electrical current to leak
Name two pathologies affecting conduction of action potentials in the central nervous system.
- Multiple sclerosis (MS)
- Devic’s disease
Name two pathologies affecting conduction of action potentials in the peripheral nervous system.
- Guillain-Barre syndrome
- Charcot-Marie-Tooth disease
What is remyelination?
Pathological nerve overgrowth, potentially treatable by activating or transplanting glial stem cells
