TEST 2: Membrane Potentials

Question 1

Resting Membrane Potential (RMP)

Answer 1

-70 mV

Question 2

RMP created/ maintained by

Answer 2

• 50-75x greater membrane permeability to K+ than to Na+

- Na+/K+ pump

Question 3

Polar

Answer 3

carries a charge

Question 4

Graded Potentials

Answer 4

• Localized changes in membrane potentials
• May be strong at area of initiation on dendrites, but only 1-2 mV in strength by the time they reach the axon hillock- decremental spread because of leak channels over surface of cell body
• caused by opening of neurotransmitter (NT)- gated ion channels

Can be two types

• depolarizations or EPSPs, membrane becomes less negative
• hyperpolarizations or IPSPs, membrane becomes more negative

Question 5

Why do we have IPSPs?

Answer 5

provides a way for one set of signals to offset another. often involved in protecting body from injury

Question 6

+ ion with high concentration on outside of cell

Answer 6

open a channel for it 
\+ ion moves down concentration gradient into cell
positives going in
inside becomes less negative
creates a DEPOLARIZATION (EPSP)

Question 7

+ ion with high concentration on inside of cell

Answer 7

open a channel for it
\+ ion moves down concentration gradient out of cell
positives going out
inside becomes more negative
creates a HYPERPOLARIZATION (IPSP)

Question 8

• ion with high concentration outside of cell

Answer 8

open a channel for it
-ion moves down concentration gradient into cell
negatives going in
inside becomes more negative
creates a HYPERPOLARIZATION (IPSP)

Question 9

-ion with high concentration inside of cell

Answer 9

open a channel for it
-ion moves down concentration gradient outside of cell
negatives going out
inside becomes more positive
creates DEPOLARIZATION (EPSP)

Question 10

Most sum of all GPs at axon hillock

Answer 10

if you reach or exceed threshold potential then action potential sent out axon

• temporal summation
• spatial summation

Question 11

temporal summation

Answer 11

one presynaptic neuron in rapid fire

Question 12

spatial summation

Answer 12

many presynaptic neurons firing simultaneously

Question 13

What happens if summation result in hitting or exceeding Threshold Potential?

Answer 13

Action Potential is sent down axon

Question 14

Why is Summation Important?

Answer 14

So that we have discrimination as to what info we act upon and what we don;t

Question 15

Why have IPSPs in addition to EPSPs?

Answer 15

Finer degree of decision making capability provides a war for one set of signals to offset another set

Question 16

Threshold Potential

Answer 16

-55mV

Question 17

All ion channels involved in Action Potential are :

Answer 17

voltage gated and all triggered at Threshold Potential

Question 18

Depolarization

Answer 18

opening of Na+ activation gates. Na+ rushes into cell, changing membrane potential to +30 mV

Question 19

Repolarization

Answer 19

Na+ inactivation gates close- stops the influx of Na+. K+ gates open: K+ flows out of cell —-> inside more negative again

Question 20

Refractory Period

Answer 20

• AP is self-generating, unlike GP
• Absolute Refractory Period
• Relative Refractory Period

Question 21

Absolute Refractory Period

Answer 21

impossible to restimulate membrane because Na+ gates have not yet reset- occurs from the pout where TP reached until Na+ gates reset

Question 22

Relative Refractory Period

Answer 22

possible, but harder to restimulate membrane because K+ gates haven’t closed yet- somewhat hyper polarized at this time, so stimulus has to be greater to reach TP
-occurs after absolute refractory until back to -70 mV as K= gates all close

Question 23

Major significance of refractory periods

Answer 23

-keeps impulse going in 1 direction because area upstream of area that is currently depolarizing is an absolute refractory, so signal can only spread forward and not backward

Question 24

Restoration of Normal Resting Concentrations of K+ and Na+

Answer 24

During AP, some K+ moved outside and some Na+ moved inside, so we need to get concentrations back to normal. This is accomplished via the Na+/K+ pump

Question 25

Does AP increase or decrease in intensity as it spreads?

Answer 25

AP does not decrease in intensity as it spreads (self-generating, no decremental spread) due to myelin. Myelin insulates the axon from loss of charge as the signal passes down axon. Other major function of myelin is to speed the conduction of the AP. Remember, APs only occur at axon hillock and nodes in myelinated neurons-myelination allows for saltatory conduction