test 3: lecture 3

Question 1

Electrical signals necessary for neural function are
mediated by the flow ___ through aqueous pores
in the nerve cell membrane

Answer 1

of ions (electrical activity)

Question 2

Vm

Answer 2

membrane potential

Question 3

charge difference across the plasma membrane

Answer 3

membrane potential

Question 4

resting Vm is ___

Answer 4

-70 mV

Question 5

Any positive change in the membrane potential

Answer 5

depolarization (inside of cell becomes more positive)

Question 6

Any negative change in the membrane potential

Answer 6

hyperpolarization

(inside of the cell becomes more negative)

Question 7

Na moving in or out would cause depolarization

Answer 7

Na moving in, the inside of the cell would become more positive

(depolarization = more + )

Question 8

K moving in or out would cause hyperpolarization

Answer 8

K moving out

hyperpolarization= more negative

Question 9

V= Current x resistance

Answer 9

ohms law

driving force is by membrane potential

Question 10

the amount of ___(ion flux/flow through an open channel) is directly proportional to the voltage across the membrane, i.e. the electrical “gradient” or electrical driving force

Answer 10

current

Question 11

___ dictates the amplitude of ion flux

Answer 11

membrane potential

Question 12

electrochemical gradient is a combo of ___

Answer 12

electrical (membrane potential)

chemical (concentration gradient) forces

Question 13

Equilibrium is achieved when the tendency of an ion to move down its ___ gradient is exactly counter-balanced by an opposing ___ gradient, resulting in no net ion flux.

Answer 13

concentration

electrical

Question 14

primary intracellular cation is ___

Answer 14

potassium (positive charge K+)

Question 15

primary extracellular cation

Answer 15

sodium (Na+)

Question 16

primary intracellular anion

Answer 16

proteins (negative charge)

Question 17

primary extracellular anion

Answer 17

Cl-

Question 18

how is resting membrane potential maintained

Answer 18

• Na⁺/K⁺ ATPase - Contributes only a small amount (~8-10mV) of the resting membrane potential
• K⁺ “leak” channels - Relatively selective permeability of the plasma membrane to K⁺ (via “leak” channels) contributes MOST of the resting membrane potential (K+ will leave the cell)

Question 19

E_ion

Answer 19

equlibrium(reversal) potential

Question 20

equilibrium potential

Answer 20

•Defined as the Membrane Potential** at which the direction of ion flow through a particular channel reverses direction. **Enables one to predict which direction ions will flow

• Determined primarily by the intracellular and extracellular concentration of each ion.
• Unique for each ion
• Nernst Equation

Question 21

Na/K pump

Answer 21

3 Na out

2 K in

(uses ATP)

helps maintain resting Vm at -70 → small amount 8-10 mV

Question 22

How does Na/K pumps work to set up K leak channels

Answer 22

Na/K will pump 3 Na out, 2 K in (net loss of +1)

K channels will open- there is more K inside cell than out. K will move down concentration gradient and will move out of cell. inside of cell becomes more negative

Question 23

most of resting Vm is from ___

Answer 23

the loss of K from the cell

(potassium leaves cell through channels due to concentration gradient set up by Na/K pumps)

Question 24

what happens to K at -120 mV?

at -70?

at +70?

Answer 24

will flow into the cell

out of cell slowly (small current)

out of cell quickly (large current)

Question 25

what does the chart tell you

Answer 25

what an ion will do at specific membrane potentials wether it will go in or out of the cell and how fast it will leave or enter

Question 26

Very ___ cell interior is needed to pull K⁺ into the cell against outward concentration gradient

Answer 26

negative

Question 27

Very ___ cell interior is needed to push Na⁺ out of the cell against inward concentration gradient

Answer 27

positive

Question 28

\_\_\_\_ is determined by ion distribution (concentration differences) across the plasma membrane and the permeability of the membrane to each ion at a given time.

Answer 28

**Actual membrane potential**

Question 29

•Direction of flow for a particular ion is determined by the relationship of its ___ to the actual membrane potential.

Answer 29

equilibrium potential

Question 30

•Ion current (flow) amplitude is also determined by Vm; the electrical driving force (\_\_\_).

Answer 30

Ohm’s law

Question 31

\_\_\_\_ is a very rapid change in membrane potential. It occurs when a "stimulation" of the nerve cell membrane depolarizes the membrane enough to allow voltage gated Na⁺ channels to open

Answer 31

An action potential

Question 32

what is the threshold for action potential?

Answer 32

(_threshold ~ -50mV_). cell must depolarize (become more + to -50) then it will launch the action potential down the axon

Question 33

explain action potential graph

Answer 33

stimulus opens some Na channels threshold at -50 voltage gated Na channels open (more + **depolarization)** voltage gated K channels slowly open (more negative but not enough to cancel out rapid influx of Na- cell will continue to depolarize until peak at +40) Na channels close (K channels still open cell becomes more negative and r**epolarization** starts) K channels close but slowly. Cell becomes too negative **(hyperpolarization)** resting potential is fixed by Na/K pumps to get to -70 **(refractory period)**

Question 34

Depolarization occurs when ligand-gated nonselective ___ channels at the post-synaptic membrane generate small excitatory depolarizing stimuli.

Answer 34

cation (+ go into the cell, make more +, depolarization)

Question 35

how is threshold reached?

Answer 35

* ligand-gated nonselective cation channels at the post-synaptic membrane generate small excitatory depolarizing stimuli. (cell becomes more +) * These signals allow Na⁺ to begin to pass into the cell, and the depolarization spreads to the **axon hillock and initial segment** where there are a large amount of voltage gated Na channels

Question 36

where does action potential start?

Answer 36

axon hillock and initial segment

Question 37

\_\_\_ contains a high conc. of voltage-gated sodium channels.

Answer 37

initial segment

Question 38

EPSP

Answer 38

**EPSP - Excitatory Post-Synaptic Potentials** (positive charges into the cell); graded potential **(depolarization)** **little + into the cell that try to get to threshold to trigger action potential**

Question 39

IPSP

Answer 39

**IPSP - Inhibitory Post-Synaptic Potentials** (negative charges into the cell); graded potential small negative into the cell causing **hyperpolarization** (more negative) → further away from threshold

Question 40

if IPSP + EPSP = 50 mV what will happen

Answer 40

summation inhibitory(hyperpolarization- more negative) + excitatory(depolarization more positive) **action potential**

Question 41

temporal summation of PSP

Answer 41

multiple stimulus from same place add on top of each other

Question 42

spacial summation

Answer 42

stimulus from different areas will add together

Question 43

compare graded and action potentials

Answer 43

Question 44

how do voltage gated sodium channels work?

Answer 44

open at threshold inactivation gate closes after specific time membrane returns to resting, gate closes and inactivation gate moves out of the way ready for next threshold

Question 45

absolute refractory period

Answer 45

Time immediately after action potential during which another AP cannot occur (due to Na⁺_v channel inactivation and delay in K⁺_v channel closing). **new action potential can not be triggered for specific time**

Question 46

relative refractory period

Answer 46

period of time during the refractory period that another action potential can be sent **if the stimulus was very big** ## Footnote **cell not back to normal but Na channels reset so technically they could go again if they had to**

Question 47

what can increase speed of action potential?

Answer 47

increase amount of voltage gated Na channels increase diameter of the axon (decrease in resistance will increase current flow) insulation (myelin)

Question 48

\_\_\_ is made by schwann cells and acts as insulation

Answer 48

myelin

Question 49

how does myelin increase speed of action potential

Answer 49

gaps in myelin (nodes of ranvier) will make action potential jump from node to node (saltatory conduction)

Question 50

\_\_\_ are regularly spaced gaps in the myelin sheath

Answer 50

nodes of ranvier

Question 51

jumping from node to node on an axon is called

Answer 51

saltatory conduction •Saltatory conduction is metabolically efficient – ion movements limited to nodal regions (including Na⁺/K⁺ ATPase and K⁺ “leak channels”) 100x faster conduction velocities, necessary for rapid reflex

Question 52

why does axon myelination do

Answer 52

**decreases cation leakage** (prevents + from leaving axon therefore keeping the strength of the AP all the way down the axon **(more downstream current)** myelin will also spread out the + and - charge → **lower capacitance** this will mean more + available down stream to continue AP

Question 53

how does myelin increase downstream current

Answer 53

prevent cation leakage

Question 54

what happens to capacitance with myelinated axon?

Answer 54

decreased capacitance because + and - farther apart lower capacitance= more downstream current

Question 55

AP jumping from node to node

Answer 55

saltatory conductance