passive membrane properties

Question 1

What does Cm represent in the electrical model of the membrane?

Answer 1

Capacitance: the ability to store charge

Question 2

What does Rm represent in the electrical model of the membrane?

Answer 2

Membrane Resistance: depends on the number of open ion channels

Question 3

How does membrane resistance (Rm) affect ion channels?

Answer 3

The lower the resistance, the more ion channels open, leading to a leakier cell

Question 4

What are graded potentials?

Answer 4

Changes in membrane potential that lose strength as they move through the cell

Question 5

What does a longer length constant (λ) indicate?

Answer 5

Graded potentials can travel longer distances

Question 6

What factors influence the length constant (λ)?

Answer 6

Proportional to d (distance) and Rm (membrane resistance); inversely proportional to Ri (internal resistance)

Question 7

What does a larger time constant indicate?

Answer 7

A slower change in potential in response to a stimulus

Question 8

What is temporal summation?

Answer 8

Summation of graded potentials in regards to how long/short the time constant is

Question 9

What is spatial summation?

Answer 9

How close/far the action potentials (APs) are located to each other

Question 10

How does membrane capacitance affect propagation velocity?

Answer 10

Membrane capacitance has a negative effect on propagation velocity

Question 11

What factors influence the propagation of current?

Answer 11

Resistance of the membrane to current leak and the diameter of the axon

Question 12

How does the diameter of an axon affect current conduction?

Answer 12

Large diameter axons provide low resistance to current flow, speeding conduction

Question 13

What happens to Rm when it increases?

Answer 13

More ions stay inside the cell, increasing depolarization potential

Question 14

What happens to Ri when it decreases?

Answer 14

Ions/current propagate more freely

Question 15

What effect does a decrease in Cm have on depolarization?

Answer 15

More ions enter, available to depolarize the cell, leading to faster voltage changes

Question 16

How does an increased length constant (λ) affect conduction velocity?

Answer 16

Current travels further, leading to faster conduction velocity

Question 17

How does a decreased time constant (τ) affect response speed?

Answer 17

Faster response of voltage to current, higher propagation speed

Question 18

What initiates action potential propagation?

Answer 18

Graded potentials trigger action potentials by opening voltage-gated Na+ channels

Question 19

How do Na+ ions contribute to action potential propagation?

Answer 19

Na+ spreads in all directions, attracting negative ions in adjacent regions

Question 20

What is the role of myelin sheath?

Answer 20

Wraps around axons, preventing current leak and acting as an insulator

Question 21

What are the Nodes of Ranvier?

Answer 21

Portions of axons lacking myelin sheath with high concentrations of Na+ channels

Question 22

What is saltatory conduction?

Answer 22

The apparent leapfrogging of action potentials from node to node along the axon

Question 23

What is demyelination?

Answer 23

Slows down or stops conduction of the action potential by allowing electrical current to leak

Question 24

Name two pathologies affecting conduction of action potentials in the central nervous system.

Answer 24

• Multiple sclerosis (MS)
• Devic’s disease

Question 25

Name two pathologies affecting conduction of action potentials in the peripheral nervous system.

Answer 25

• Guillain-Barre syndrome
• Charcot-Marie-Tooth disease

Question 26

What is remyelination?

Answer 26

Pathological nerve overgrowth, potentially treatable by activating or transplanting glial stem cells