Lec 5

Question 1

Why are action potentials needed

Answer 1

Graded potentials decay over space and time

Action potentials propagate over long distances

Propagation is slow

Question 2

Why do graded potentials decay

Answer 2

there is resistance to current flow across the membrane and through the cytoplasm

The current is leaking out through potassium channels

Question 3

Decay is given by what constant

Answer 3

Lambda-length constant

Question 4

When lambda is large

Answer 4

The change in the membrane potential degrades less with distance

Question 5

When lambda is small

Answer 5

The change in membrane potential degrades rapidly with distance

Question 6

Length constant in relation to axon radius

Answer 6

Larger radius decreases resistance of neuron membrane in proportion to circumference (increases length constant)

Question 7

Myelin effect on length constant

Answer 7

Increased myelin increases length constant

Question 8

Nodes of ranvier

Answer 8

Small surface area nodes resulting in about 1000x less active membrane and about 100-fold fewer Na+ ions entering the cell per impulse

Question 9

Saltatory conduction of action potential between nodes of ranvier

Answer 9

Height of potential in internode

But not as much as myelin increases length constant

Just has to stay above threshold at the next node

Question 10

Non-spiking neurons

Answer 10

Graded potentials travel down the axon but not action potentials

Useful when axons are very short

Because axon is short, there is no need for action potentials