Graded and Action Potentials

Question 1

what is neural communication?

Answer 1

based on rapid changes in membrane permeability to ion

Question 2

why do you use ion permeability changes and not 2nd messenger systems or hormones for cell-to-cell signaling in the brain?

Answer 2

because the change in membrane potential is VERY fast –> a lot faster than hormone signaling

Question 3

what ion channels are involved in gated and action potentials?

Answer 3

ligand-gated and voltage-gated channels

Question 4

what does depolarization cause?

Answer 4

decrease in potential –> membrane becomes less negative

Question 5

what does repolarization cause?

Answer 5

return to resting potential after depolarization

Question 6

what does hyperpolarization cause?

Answer 6

increase in potential –> membrane becomes more negative

Question 7

what do graded potentials depend on?

Answer 7

the permeability changes induced by the neurotransmitter in the postsynaptic neuron

Question 8

what is EPSP?

Answer 8

excitatory postsynaptic potentials —> makes the membrane less negative

Question 9

what is IPSP?

Answer 9

inhibitory postsynaptic potentials –> makes the membrane become more negative

Question 10

how many postsynaptic potentials are needed to create an action potential?

Answer 10

if threshold is reached, then it creates an action potential

ie: depends on how many it takes to reach the threshold

Question 11

what is a typical EPSP voltage and how long does it last?

Answer 11

0.5 mV

20 ms

Question 12

what is temporal summation?

Answer 12

occurs when single synapse receives many EPSPs in a short period of time

Question 13

what is spatial summation?

Answer 13

occurs when single synapse receives many EPSPs from many presynaptic cells

Question 14

what is action potential and how does it propagate?

Answer 14

one-way propagation/all or none contraction

signal propagates non-decrementally –> the impulse propagates along an axon (the amplitude of the impulse is maintained as it progresses)

Question 15

what type of gates do voltage-gated Na+ channels have?

Answer 15

activation gate AND inactivation gate

Question 16

what type of gates do voltage-gated K+ channels have?

Answer 16

ONLY HAS ONE GATE that can be open or closed

Question 17

describe the resting potential conformation of voltage-gated sodium channels

Answer 17

closed but is capable of opening

at resting potential –> -70 mV

Question 18

describe the activated conformation of voltage-gated sodium channels

Answer 18

open (activated)

from threshold to peak potential (-50 mV to +30 mV)

Question 19

describe the inactivated conformation of voltage-gated sodium channels

Answer 19

closed and not capable of opening (inactivated)

from peak to resting potential (+30 mV to -70 mV)

Question 20

describe the resting conformation of voltage-gated K+ channels

Answer 20

closed

at resting potential, delayed opening triggered at threshold

remains closed to peak potential (-70 mV to +30mV)

Question 21

describe activated conformation of voltage-gated potassium channels

Answer 21

open

from peak potential through after hyperpolarization phase (+30 mV to -80 mV)

Question 22

what is the absolute refractory period?

Answer 22

interval during which no stimulus can elicit an action potential

most voltage-gated Na+ channels are inactivated

Question 23

what is the relative refractory period?

Answer 23

interval when a supranormal stimulus is required to elicit an action potential

due to elevated gK coupled with the residual inactivation of voltage-gated Na+ channels

Question 24

why is there a refractory period?

Answer 24

ensures a one-way propagation of the action potential

limits the frequency of action potentials (energy conservation; prevent seizures)

Question 25

what determines the speed of conduction?

Answer 25

diameter of the fiber: the larger the diameter of the fiber, the lower the internal resistance for current flow and the faster it conducts
-rapid fibers: motorneurons
-slow fibers: internal organs

myelination: lipid insulator of nerve fibers that greatly increases the conduction velocity by decreasing the capacitance of the axon and restricting the AP generation to the nodes of ranvier

Question 26

what is contiguous conduction?

Answer 26

conduction in unmyelinated fibers

AP spreads along every portion of the membrane