Action Potentials

Question 1

membrane potential

Answer 1

potential to do work

Question 2

polarized

Answer 2

difference in charge on either side of membrane

Question 3

voltage

Answer 3

measurement of AP

Question 4

excitable cells

Answer 4

cells that can rapidly change MP

Question 5

is the membrane more permeable to K+ or Na+?

Answer 5

K+, 100x more

Question 6

hyperpolarization

Answer 6

become more negative inside cell; MP decrease below RP -> inhibitory

Question 7

inhibitory

Answer 7

lowers the ability to generate a signal

Question 8

depolarization

Answer 8

becomes less negative inside cell (may become positive); still negative, but less positive; MP increases above RP -> excitatory

Question 9

excitatory

Answer 9

increases ability to generate a signal

Question 10

action potential

Answer 10

electrical signal w/in a neuron

• all or none
• either happens or doesn’t
• always the same voltage change

Question 11

within action potentials, what does the intensity of the message depend on

Answer 11

• # neurons stimulated
• frequency of stimulus
• NOT strength of AP

Question 12

voltage-gated (VG) ion channels

Answer 12

• aka “gates”
• ONLY open at certain voltages/MPs
• opened by a stimulus (facilitated diffusion of that ion down concentration gradient)

Question 13

magnitude of depolarization (small stimulus)

Answer 13

• FEW Na+ gates open
• weak depolarization
• MP does NOT reach -55 mV
• no AP

Question 14

magnitude of depolarization (strong stimulus)

Answer 14

• MANY VG Na+ channels open
• Strong depolarization
• if MP reaches -55 mV -> AP

Question 15

conductions of AP

Answer 15

• signal propagates as series of APs along axon
• axon hillock -> synaptic terminal
• voltage shift in one region -> opens Na+ gates further down
• area behind now in refractory period (Na+ gates resetting)
• unidirectional signal

Question 16

continuous conduction

Answer 16

• occurs in unmyelinated axons

- every spot on axon depolarizes and repolarizes

Question 17

saltatory conduction

Answer 17

• occurs in myelinated axons

- insulation surrounding vertebrate axons, made by olgiodendrocytes (CNS) and Schwann Cells (PNS)

Question 18

internodes

Answer 18

regions covered myelin - no depolarization

Question 19

nodes of ranvier

Answer 19

no myelin - lots of Na+, K+ VG channels; depolarization only occurs at nodes
-“saltatory” - signal “jumps” from node to node

Question 20

which is better: saltatory or continuous?

Answer 20

saltatory. its >50 x faster and more E efficient

Question 21

multiple sclerosis

Answer 21

• immune system attacks myelin sheath and oligodendrocytes in the CNS
• slows AP conduction, exposes nerve fibers to damage
• weakness, impaired vision, numbness … depending on sites of damage