Membrane Electrophys: Action Potentials

Question 1

Define action potential.

Answer 1

rapid change in membrane potential away from the normal, negative resting voltage to a positive voltage (followed by return back to negative potential)

Question 2

What allows nerve and muscles to have excitability?

Answer 2

have specialized function allowing ability to deviate membrane potential from RMP through altering permeability of key ions

Question 3

what is polarization?

Answer 3

positive or negative charge of membrane (what it sits at) other than OmV

Question 4

what happens when membrane potential becomes less polar (less negative) than resting?

Answer 4

hypopolarization

Question 5

what happens when membrane loses negative polarity or RMP (become less negative-0-positive)?

Answer 5

depolarization

Question 6

what is it called when the membrane returns to RMP after depolarization?

Answer 6

repolarization

Question 7

what is it called when the membrane become more polarized that RMP (even more negative)?

Answer 7

hyperpolarization

Question 8

what is threshold?

Answer 8

potential where, when hypopolarized membrane potential reaches it, causes sudden increased of Na+ into the cell and depolarization

Question 9

what voltage gates open and close quickly?

Answer 9

Na+

Question 10

what voltage gates open and close slowly?

Answer 10

K+

Question 11

what does the flow of Na+ ions into the cell do?

Answer 11

reverses the membrane potential and drives it to the Na equilibrium potential (depolarization)

Question 12

what does the flow of K+ out of the cell do?

Answer 12

restores the membrane potential to resting (depolarization)

Question 13

what are the stages of depolarization?

Answer 13

1. initial depolarization
2. Na+ channels open
3. Na+ influx
4. Peak Na+ conductance

Question 14

what are the stages of depolarization?

Answer 14

1. early depolarization
2. K+ efflux
3. peak K+ conductance

Question 15

what helps to reestablish the RMP?

Answer 15

Na+/K+ pump - gradually helps restore original resting ion distribution

Question 16

why can numerous APs occur even in absence of Na+K+ pump keeping pace?

Answer 16

because only a small fraction of ions contribute to AP (1 of 100,00 K+ ions exit the cell during AP)

Question 17

time period after AP when a subsequent AP either cannot or likely will not be generated?

Answer 17

refractory period

Question 18

what is the point of a refractory period?

Answer 18

ensure unidirectional propagation of APs

Question 19

period when no AP regardless of stimulus intensity can occur due to “locking” of Na+ channels.

Answer 19

absolute refractory period

Question 20

period when AP can only be produced if the stimulus is large enough due to hyperpoloarization of the membrane potential?

Answer 20

relative refractory period

Question 21

what are the two factors that cause presence of refractory period?

Answer 21

• inactivation of Na+ channels

- membrane hyperpolarization

Question 22

what the main characteristics of action potentials?

Answer 22

• undiminished propagation/”regeneration” of AP along the plasma membrane
• “all-or-none” law: AP is either generated or not, same size every time

Question 23

local sub-threshold changes in membrane potential?

Answer 23

graded potentials

Question 24

what are the main characteristics of graded potentials?

Answer 24

• sub-threshold
• duration and strength directly proportional to duration and strength of stimulus
• decremental
• can be summated

Question 25

what will happen to a graded potential if it reaches threshold?

Answer 25

will become an action potential.

Question 26

what part of the neuron has the lowest threshold for AP initiation?

Answer 26

axon hillock (initial segment)

Question 27

what are the two ways a signal can be conducted down the axon?

Answer 27

1. contiguous - locally propagated down each adjacent portion of the membrane
2. saltatory - ‘jumping’ along nodes of ranvier (holes in myelinated axon)

Question 28

what two things increase conduction down an axon?

Answer 28

• large axon diameter

- myelination

Question 29

what does myelin do?

Answer 29

• forces current to travel node to node where there is lower resistance
• minimizes loss of current across otherwise leaky membrane

Question 30

what is the specialized junction between the opposing membranes of two excitable cells?

Answer 30

synapse

Question 31

what are the 2 categories of synaptic communication

Answer 31

electrical synapses

chemical synapses

Question 32

what is used to carry a signal across synapses to postsynaptic receptors in chemical synapse?

Answer 32

neurotransmitters

Question 33

influence of thousand of presynaptic cells on a single cell?

Answer 33

convergence

Question 34

influence of one presynaptic cell on many cells via branching axon terminals

Answer 34

divergance

Question 35

what are the two kinds of ‘signals’ a cell can receive?

Answer 35

excitatory synapse - always excitatory, depolarizes/hypopolarizes membrane (EPSP)

inhibitory synapse - always inhibitory, hyperpolarizes the membrane (IPSP

Question 36

how can graded potentials summate from dendrites to generate AP at axon?

Answer 36

• temporal summation: arrive at rapid enough frequency to be summed and reach threshold
• spatial summation: from multiple inputs combine and are summed to reach threshold
• cancellation: EPSP and IPSP combine to cancel each other –> no AP