Lecture 3 - Neuronal Excitability

Question 1

what are the two types of cells in the CNS?

Answer 1

neurons and glia

Question 2

true or false: there are 10-50x more glia cells than neurons in the CNS but both cell types take up to 50% of the space

Answer 2

true

Question 3

cells that provide structure/support, isolating neurons from one another

Answer 3

oligodendrocytes/satellite cells

Question 4

cells that produce myelin

Answer 4

oligodendrocytes (CNS) and Schwann cells (PNS)

Question 5

cells that guide migrating neurons and direct axonal outgrowth during development

Answer 5

radial glia

Question 6

cells that form the blood brain barrier, and play a role in neurotransmitter clean up after synaptic transmission

Answer 6

astrocytes

Question 7

cells which act as scavengers, removing debris after injury or cell death

Answer 7

microglia

Question 8

the word “glia” means:

Answer 8

glue

Question 9

what are the three main categories of neurons?

Answer 9

• afferent neurons
• efferent neurons
• interneurons

Question 10

neurons that carry information from the periphery to the CNS and are excitatory

Answer 10

afferent neurons

Question 11

neurons that carry information from the CNS to the periphery and are excitatory

Answer 11

efferent neurons

Question 12

neurons that carry information between neurons within the CNS and can be excitatory or inhibitory

Answer 12

interneurons

Question 13

the anatomy of a neuron is determined by its:

Answer 13

function

Question 14

what are the three main shapes of neurons?

Answer 14

biopolar, pseudo-unipolar, and multipolar

Question 15

what is the purpose of protein pumps and channels in the cell membrane? (in the context of membrane potential)

Answer 15

controls movement of ions through the membrane

Question 16

pumps in the cell membrane are _____, and help generate _____

Answer 16

active transporters, resting membrane potential

Question 17

ion channels in the cell membrane can be ______ or ______, and they disrupt the membrane potential to ______

Answer 17

passive, gated, trigger action potentials

Question 18

a measure of the electrical potential difference between the intracellular environment and extracellular environment

Answer 18

resting membrane potential (Em)

Question 19

what is the resting membrane potential of a cell?

Answer 19

-70mV (negative inside)

Question 20

which ions are primarily involved in setting resting membrane potential?

Answer 20

K+ and Na+

Question 21

which pumps/channels are involved in setting resting membrane potential?

Answer 21

Na+/K+ exchanger, Na+ leak channels, and K+ leak channels

Question 22

at rest, the concentration of K+ inside the cell is _____ than the concentration of K+ outside the cell

Answer 22

greater

Question 23

at rest, the concentration of Na+ inside the cell is _____ than the concentration of Na+ outside the cell

Answer 23

less

Question 24

at rest, the concentration of Cl- inside the cell is _____ than the concentration of Cl- ouside the cell

Answer 24

less

Question 25

why doesn't Cl- affect the resting membrane potential (Em)?

Answer 25

the equilibrium potential of Cl- is -70mV

Question 26

the Na+/K+ pump is _______ as it moves charges across the membrane

Answer 26

electrogenic

Question 27

where does the Na+/K+ pump get its energy from?

Answer 27

the hydrolysis of ATP to ADP and Pi

Question 28

how many Na+ and K+ molecules are moved across the cell membrane by the Na+/K+ pump per molecule of ATP?

Answer 28

3Na+, 2K+

Question 29

the Na+/K+ pump creates:

Answer 29

an electrochemical gradient

Question 30

what are the chemical gradients created by the Na+/K+ pump?

Answer 30

- [K+]in > [K+]out (K+ wants to diffuse out of the cell) - [Na+]in < [Na+]out (Na+ wants to diffuse into the cell)

Question 31

what is the electrical gradient created by the Na+/K+ pump?

Answer 31

the intracellular environment is negative (and wants to become more positive)

Question 32

Em is set by the:

Answer 32

relative number of leak channels

Question 33

true or false: leak channels are always open

Answer 33

true

Question 34

what is the function of leak channels?

Answer 34

they allow passive flow of ions into/out of the neuron

Question 35

are leak channels selective?

Answer 35

yes - each ion has its own leak channels through which only they can pass

Question 36

the membrane potential at which the chemical concentration gradient is balanced

Answer 36

equilibrium potential

Question 37

what is the equilibrium potential for K+?

Answer 37

-90mV (alone, K+ would force Em to -90mV)

Question 38

what is the equilibrium potential for Na+?

Answer 38

+60mV (alone, Na+ would force Em to +60mV)

Question 39

the more permeable the membrane is to a given ion, the closer Em is to:

Answer 39

the equilibrium potential for that ion

Question 40

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

Answer 40

K+ (why the equilibrium potential for K+ is closer to the equilibrium potential for Na+)

Question 41

what is the effect of increasing the number of K+ leak channels on Em?

Answer 41

Em is decreased

Question 42

what is the effect of increasing the number of Na+ leak channels on Em?

Answer 42

Em is increased

Question 43

why is the resting membrane potential -70mV?

Answer 43

due to Na+/K+ pump and leak channels

Question 44

what is the Nerst equation?

Answer 44

Eion = (RT/ZF)(ln([ion]out/[ion]in))

Question 45

at 20C, (RT/ZF) =

Answer 45

25mV

Question 46

go review slide 38

Answer 46

ewwwww Nerst equation calculations

Question 47

how are afferents activated?

Answer 47

stimuli results in opening of specialized, physically-gated Na+ receptors, Na+ enters afferent terminals, and depolarization occurs

Question 48

if Na+ entry into the afferent terminals is sufficient to depolarize the neuron to its threshold, the result is:

Answer 48

the opening of voltage gated Na+ channels and an action potential

Question 49

what is the threshold potential of a neuron?

Answer 49

~-50mV

Question 50

what are the 6 major stages of an action potential?

Answer 50

1) rest 2) depolarizing input 3) start of action potential (depolarization) 4) repolarization 5) end of action potential (hyperpolarization) 6) return to rest

Question 51

what is the reason for the change in membrane permeability during depolarization?

Answer 51

the voltage gated Na+ channels open

Question 52

what is the reason for the change in membrane permeability during repolarization?

Answer 52

voltage gated K+ channels open and Na+ channels inactivate

Question 53

what is the reason for the change in membrane permeability during hyperpolarization?

Answer 53

voltage gated Na+ channels are at rest and voltage gated K+ channels are still open

Question 54

what is the relative membrane permeability to K+ and Na+ at rest?

Answer 54

K+ > Na+

Question 55

what is the relative membrane permeability to K+ and Na+ at the start of an action potential?

Answer 55

slight increase in Na+ permeability, but still more permeable to K+

Question 56

what is the relative membrane permeability to K+ and Na+ during depolarization?

Answer 56

Na+ > K+

Question 57

what is the relative membrane permeability to K+ and Na+ during repolarization?

Answer 57

K+ > Na+

Question 58

what is the relative membrane permeability to K+ and Na+ during hyperpolarization?

Answer 58

K+ > Na+

Question 59

dictates the phases of the action potential

Answer 59

relative membrane permeability