Action Potentials and Graded Potentials

Question 1

Graded potentials

Answer 1

Small-scale local changes that degrade over a dfistance

Within a neuron
Magnitude can change

Can be depolarising or hyper (synaptic are either but receptor are depolarizing)

Question 2

Action potentials

Answer 2

Large all or none changes that propogate long distances

Between neurons

Question 3

initiation of graded potential

Answer 3

Chemical signal
Gated ion channel opens
Current at cell membrane, charge carried by ions
Local depolariszation or hyperpolarization
Depolarization spreads

Question 4

Graded potential variable amplitude

Answer 4

Size is porportional to stimulus intensity

Question 5

Graded potentials decremental

Answer 5

Decary of distance because of leakage of K+

Question 6

RC circuit of a nerve cell

Answer 6

Ion channel acts as a resistor…more ion channels decreases resistance

PLasma membrane capacitor that separates charge…larger membrane surface area means greater capacitance

Question 7

membrane time constant

Answer 7

Time to get to 63% of steady state value

More channels means less resistance so shorter time
Increased membrane SA means more capacitance so greater

Question 8

Space (length) constant

Answer 8

Distance over whic ha potnetial can change

INcrease in membrane resistance (from decrease in resistors) means lengthen

Increased axial resistace - shorten

Question 9

All or none of action potentials

Answer 9

Weak stimuli are termed subthreshold potentials
Strong will hit the threshold potnetial

A single AP cannot convey stimulus intensity BUT multiple APs together can

Question 10

Voltage gated Na and K channels

Answer 10

Will open at a certain voltage

Inactivation gate blocks Na gate quickly

K open and close slower

Question 11

Permeability at resting potential

Answer 11

K = 1 
Na = .04
Cl = .45

Question 12

K vs Na voltage gated

Answer 12

Na = faster opening and closing and inactivate spontaneously 
K = slower and only inactivate once repolarization occurs

Question 13

Absolute refreacto yperiod

Answer 13

Second AP CANNOT occur during this time (Na in the open or inactivated state)

1) Allows re-establishment of membrant potential
2) Limits # of APs
3) Directs towasrd terminal
4) Separates APs

Question 14

Relative refractory

Answer 14

Can occur during hyperpolarization but only if strong enough

Cotrol over frequency of APs

Question 15

Na channel structure

Answer 15

6 TM segments with 4 subunits
Voltage sensor
Inactivation particle that blocks the gate

Question 16

K+ channel structure

Answer 16

A gene encodes 1 of 4 subunits whcih form a functional channel

Question 17

Procaine/lidocain and tetrodoxin

Answer 17

Block voltage gated Na channels and prevent AP

Question 18

Ca channel family

Answer 18

Happens after each AP…as more calcium accumulates, opens K channels and causes hyperpolarization….prevents formation of AP over and over again

Longer lasting AHP

Question 19

Propogation

Answer 19

Initated at axon hillock…once it moves to 2, then 1 is refractory and 2 is depolarizing toward the threshold potentia l

Question 20

Saltatory conduction

Answer 20

Myelin increases speed and fidelity of AP

Path of least resistance at next node
Na+ channel concentration higher at nodes of ranvier