Week 2 Review

Question 1

which ions carry the early inward & late outward currents during AP?

Answer 1

during early part of AP, influx of Na ions across membrane briefly depolarizes membrane. brief inward sodium current is consequence of opening voltage-gated potassium channels after delay of 1msec.

Question 2

why is AP referred to as all or none?

Answer 2

bc no partial AP exists. physical or electrical event opens Na permeable channels, but resulting influx if Na ions & resulting depolarization (generator potential) must reach threshold before axon generates AP. after threshold depolarization cell fires AP.

Question 3

why do AP travel in only one direction?

Answer 3

membrane just behind AP is refractory due to inactivated sodium channels

Question 4

there is higher potassium K+ concentration inside cell than outside. why, then is the resting membrane potential negative?

Answer 4

bc neuron is filled with negatively charged molecules, i.e. proteins, that don’t transverse cell membrane thru channels the way ions do

Question 5

when brain is deprived of oxygen, mitochondria within neurons stop producing ATP. what effect would this have on membrane potential & why?

Answer 5

sodium-potassium pump, which requires ATP, will not function so resting potential membrane won’t exist & brain won’t function

Question 6

why is excitatory synapse on soma more effective in evoking AP in postsynaptic neuron than an excitatory synapse on tip of a dendrite?

Answer 6

current entering sites of synaptic contact must spread to spike initiation zone & zone must be depolarized beyond threshold to generate AP. also, depolarization decreases as function of distance along dendrite. as a result effectiveness of excitatory synapse for triggering AP depends on how far synapse is from spike initiation zone (SIZ).
bc soma is closer to SIZ, excitatory synapse on soma is more effective in firing APs than synapse on dendrite

Question 7

what is resting membrane potential?

Answer 7

difference in electrical charge across membrane at rest

Question 8

which of the following is major charge carriers involved in conduction of electricity in neurons?

Answer 8

ions

Question 9

how do the lipids of neuronal membrane contribute to neuronal membrane potential?

Answer 9

forms barrier to water-soluble ions & water

Question 10

how do APs differ from passively conducted electrical signals?

Answer 10

APs are signals of fixed size & duration; passively conducted signals are not signals of fixed size & duration

Question 11

which if the following is true of ion channels?

Answer 11

a) permit passage of ions thru cell membrane

b) composed of proteins that form pores in cell membrane

c) responsible for passive transport of ions thru cell membrane

answer is all of the above

Question 12

which of the following might cause neuron to fire?

Answer 12

a) EPSPs triggered by activity @ five synapses @ same time

b) EPSPs triggered by activity @ five nearby synapses

c) multiple EPSPs @ same synapse triggered in rapid succession

answer is all of the above

Question 13

golgi stain

Answer 13

labels only small fraction of all granules & processes in brain to see stained structures against clear background

Question 14

neuron doctrine

Answer 14

developed by Cajal, idea that neurons are cells that transmit info across tiny gaps called synapses

Question 15

resting membrane potential

Answer 15

voltage difference of -70mV between inside & outside of neuron

Question 16

action potential

Answer 16

brief reversals of polarity (becoming positively charged) that neurons use to transmit info along axons

Question 17

Na+/K+ -ATPases (sodium potassium pump) move

Answer 17

2 potassium ions in for every 3 sodium ions they move out of

Question 18

resting potential of typical neuron

Answer 18

-70mV

Question 19

what is major cause of neuronal resting potential?

Answer 19

push & pull of potassium ions across neuronal membrane

Question 20

ion channels

Answer 20

pore-forming proteins

Question 21

in the process of generating AP

Answer 21

electrical potential across membrane reverses polarity & briefly surges from -70mV to +40mV

Question 22

depolarization

Answer 22

positively charged sodium ions generate inward current that causes inside of axon to become more positive

Question 23

action potential threshold

Answer 23

membrane potential at which positive feedback between membrane depolarization & sodium influx kicks in (typically 10-20mV more positive than resting potential of -70mv)

Question 24

equilibrium potential for potassium

Answer 24

-80mV

Question 25

axon potentials initiated in

Answer 25

axon hillock

Question 26

refractory period

Answer 26

voltage gated sodium channels that open during AP rising phase close automatically shortly after & voltage gated potassium channels open slowly on depolarization & stay open for a while; as long as potassium channels are open and sodium channels closed, membrane cannot generate another AP (this is known as refractory period)

Question 27

how does myelination boost conduction velocity?

Answer 27

1) by increasing an axon’s length constant

2) decreasing axon’s membrane capacitance

Question 28

synaptic vesicles

Answer 28

~50 nanometers in diameter & filled with thousands of NT molecules each

Question 29

Neurotransmitters (NT)

Answer 29

for most excitatory neurons in the CNS, the NT is L-glutamate (ionic form of glutamate acid) generally referred to as glutamate

Question 30

synaptic cleft

Answer 30

tiny gap about 20-25nm wide between pre & post synaptic cells

Question 31

voltage gated calcium channels

Answer 31

AP comes into axon terminal, calcium channels open, calcium ions rush down concentration gradient, raising calcium levels in terminal causing some synaptic vessels to fuse w cell membrane & thru exocytosis release NT in synaptic cleft

Question 32

Excitatory Post Synaptic Potential (EPSP)

Answer 32

when glutamate binds to AMPA receptors of neuron at rest, neuron experiences net influx of positive ions (mainly sodium) & is consequently depolarized

Question 33

Inhibitory Post Synaptic Potentials (IPSP) caused by

Answer 33

15-40% neurons use NT GABA (gamma-aminobutyric acid)

Question 34

EPSP vs IPSP

Answer 34

ipsp’s often located close to axon hillock of post synaptic cell, epsp’s mainly found on dendrites, making ipsp’s frequently more powerful in their effect than epsp’s

Question 35

ionotropic receptors

Answer 35

class of receptors that contain central pore thru which ions flow, effects can be excitatory or inhibitory, depending on ions that come thru, but effects usually fast & brief

Question 36

metabotropic receptors

Answer 36

class of receptors that don’t have central pore for ions to pass, but can open other close nearby ion channels indirectly by modulating intracellular signaling cascades that ultimately affect ion channels. most belong to fam of G-protein-coupled receptors & affect neuronal activity by activating enzymes that control production of secondary messengers. post synaptic effects of metabotropic receptors significantly slower but longer lasting than ionotropic receptors