Nerve Cells & Neural Signaling pt 2

Question 1

which types of membranes have the ability to make action potentials

Answer 1

excitable (those associated with nerves and muscle cells)

Question 2

when do action potentials occur

Answer 2

in response to graded potentials that reach threshold

Question 3

what structure transfers action potentials, describe its path briefly

Answer 3

• along axons from cell body to axon terminal
• if afferent neuron: receptor to terminal

Question 4

what are the stages of action potentials

Answer 4

• depolarization (more positive)
• repolarization (negative towards resting pot)
• post-hyperpolarization (more negative than resting)

Question 5

describe rapid depolarization in action potentials

Answer 5

• Vm changes from -70mV to +30mV
• sudden increase in permeability to Na+ (Na+ channels open which leads to more Na+ channels opening)

Question 6

describe repolarization in action potentials

Answer 6

• Vm returns to -70mV (resting)
• rapid decrease in Na+ permeability
• K+ permeability increases (K channels open which leads to more K channels opening)

Question 7

describe post-hyperpolarization in action potentials

Answer 7

• Vm even more negative than at rest
• K+ permeability remains elevated for 5-15msec

Question 8

generation of action potentials is due to

Answer 8

• selective permeability of plasma membrane
• electrochemical gradients of Na+ and K+

Question 9

where are voltage-gated ion channels located

Answer 9

mostly in axon hillock and axon

Question 10

what are myelinated axons

Answer 10

• axons covered in myelin sheath (multilayer of proteins and lipids)
• ion channels more concentrated at nodes of Ranvier b/c it doesn’t have sheath covering

Question 11

what are unmyelinated axons

Answer 11

• axons unprotected with myelin sheath
• ion channels evenly distributed along length of axon

Question 12

what are the two gates associated with the voltage-gated Na+ channel model

Answer 12

activation and inactivation gate

Question 13

a sodium channel can exist in three conformations. what are they?

Answer 13

• closed but capable of opening
• open
• closed and incapable of opening

Question 14

for the sodium channel to be open, which gate(s) need to be open

Answer 14

both activation and inactivation

Question 15

the opening of sodium activation gates is ____________

Answer 15

regenerative

Question 16

describe voltage-gated potassium channels

Answer 16

• one gate
• depends on voltage and time
• negative feedback

Question 17

what does threshold for generating action potential mean

Answer 17

minimum depolarization necessary to induce sodium positive feedback loop

Question 18

what is subthreshold stimulus

Answer 18

opens some Na+ channels but not enough to produce inflow of Na+ to counterbalance outflow of K+ through leak channels

Question 19

what is suprathreshold stimulus

Answer 19

makes action potential but is not stronger or larger than action potential produced by threshold stimulus because APs have the “all-or-none” property

Question 20

what is the all-or-none principle

Answer 20

whether a membrane is depolarized to threshold or greater, the amplitude of the resulting action potential is the same; if the membrane is not depolarized to threshold –> no action potential occurs

Question 21

what does the level of depolarization at the peak of the action potential depend on

Answer 21

• relative strengths of electrochemical gradients for Na+ and K+
• relative permeabilities of membrane to Na+ and K+
• does not depend on the strength of the stimulus

Question 22

define the refractory period

Answer 22

period of time following an action potential is marked by decreased excitability

Question 23

what are the two types of refractory periods

Answer 23

absolute and relative

Question 24

refractory periods establish some properties of action potentials, what are they?

Answer 24

• all-or-none property (compare to graded potentials)
• frequency coding (info about intensity of stimulus, like how loud a sound is)
• unidirectional propagation of action potentials

Question 25

define frequency (in reference to potentials)

Answer 25

number of action potentials that occur in given period of time

Question 26

graded potentials last _________ and are ________ than action potentials, they may generate a burst of action potentials

Answer 26

longer; stronger

Question 27

what does the mechanism of propagation of action potentials depend on

Answer 27

presence or absence of myelin

Question 28

what factors affect propagation (how quick the signal spreads)

Answer 28

• refractory period (unidirectional)
• axon diameter (larger: less resistance, faster and opposite for smaller)
• myelination (saltatory conduction = faster propagation)