Graded Potentials And Action Potentials

Question 1

Signal transmission types

Answer 1

. Graded potentials

. Action potentials

Question 2

Depolarization

Answer 2

. Membrane potential becomes less negative (inside of cell more positive)

Question 3

Hyperpolarization

Answer 3

. Membrane potential becomes more negative (inside of cell more negative)

Question 4

Repolarization

Answer 4

. Membrane potential returns toward resting membrane potential after a depolarization of hyperpolarization

Question 5

Overshoot

Answer 5

. Reversal of polarity of membrane potential (inside of cell becomes positive compared to outside)

Question 6

Voltage-gated channels

Answer 6

. Voltage sensor that causes channel to undergo conformational change when membrane potential is changed over specific range
. Opening of these initiates action potential (NOT graded)

Question 7

Ligand-gated channels

Answer 7

. Chemically-gated
. Respond to binding of extracellular neurotransmitters to their receptors (receptor-operated channels) OR respond to intracellular second messengers
. Opening these generates graded potentials

Question 8

Mechanosensitive channels

Answer 8

. Stretch-activated (respond to membrane deformation)
. Mediate pressure of touch and sensory inputs
. Stimulates graded potentials

Question 9

Background channels

Answer 9

. Spontaneously open and close in absence of external stimulus
. Generate resting membrane potential

Question 10

Postsynaptic potentials

Answer 10

. Occur at postsynaptic membrane of neuron-neuron synapse
. Stimulus is neurotransmitter released from presynaptic neuron
. Either excitatory or inhibitory

Question 11

Excitatory postsynaptic potentials (EPSPs)

Answer 11

. Postsynaptic response to excitatory neurotransmitter opens mixed cation channels that carry Na and K
. Results in depolarization
. Brings membrane closer to hers hold for firing action potentials

Question 12

Inhibitory postsynaptic potentials (IPSPs)

Answer 12

. Postsynaptic response to inhibitory neurotransmitter
. Opens K (or Cl) channels
. Causes hyperpolarization
. Takes cell further away from threshold for firing action potential

Question 13

T/F Opening of K or Cl channels stabilize the cell at resting membrane potential without changing the resting membrane potential

Answer 13

T

Question 14

End-plate potentials (EPPs)

Answer 14

. graded potentials
. Occur at motor end plate of neuromuscular junction
. Stimulus is neurotransmitter (Ach) released from motor nerve
. Caused by opening of mixed cation channel that allows Na and K to pass through

Question 15

Receptor Potentials

Answer 15

. Graded potentials
. Occur at receptor of afferent (sensory) nerve
. Stimulus is physical (stretch, pressure)

Question 16

The changes from resting membrane potential that don’t cause AP, the repolarization after removal of stimulus depends on _____

Answer 16

Changes in driving force that were set up by stimulus

Question 17

When cell is hyperpolarized from resting potential, the driving force for K is ____

Answer 17

Reduced (membrane potential becomes nearer to Ek, driving force for Na influx inc.)

Question 18

After removal of a stimulus, the return to resting potential is ____

Answer 18

Passive, based solely on driving forces and permeability for specific ions

Question 19

In response to a depolarization from resting potential, the driving force for K ____ and driving force for Na ______

Answer 19

. K efflux increases

. Na influx decreases

Question 20

Graded potentials can be depolarizing or ____

Answer 20

. Hyperpolarizing

. Depends on currents involved

Question 21

Graded amplitude

Answer 21

. Magnitude of response (mV) varies w/ magnitude of stimulus

Question 22

Decrement also conduction

Answer 22

. Magnitude of potential change declines the further away from the stimulus site you get

Question 23

Action potentials

Answer 23

. Rapid, large changes in membrane potential

Question 24

Graded potentials have what relationship to action potentials?

Answer 24

Graded potentials have stimulus (trigger) for generation (firing) of AP

Question 25

Threshold potential

Answer 25

. Point when stimulus is just adequate to initiate AP 50% of the time . Due to voltage-dependence of activation (opening) of Na channels responsible for initiating AP

Question 26

T/F Graded potentials and action potentials have a threshold potential

Answer 26

F, only AP has it

Question 27

AP relationship to distance

Answer 27

. AP does not decrease in amplitude over distance | . Propagated

Question 28

Absolute refractory period

Answer 28

. Period where AP can’t be elicited no matter how strong the stimulus

Question 29

Relative refractory period

Answer 29

. Period where another AP can be elicited only by greater than normal stimulus

Question 30

How is the shape of an AP determined?

Answer 30

. time-dependent changes in Na and K currents

Question 31

Voltage clamp technique

Answer 31

. Voltage can be set and help by investigator . Clamping membrane potential above threshold for AP causes current to flow w/o change in membrane potential . Allows investigation of current flowing at any membrane potential . Looked at current in Na-containing, Na free, K-containing, and K free to see contributions of each ion

Question 32

Upstroke (depolarizing phase) of AP is caused by what kind of mechanism?

Answer 32

Positive feedback | . Opening of some Na channels causes depolarization which causes more Na channels to open

Question 33

Na vs K channel behavior during voltage clamp pulse

Answer 33

. Na does not remain high, but spontaneously decays (inactivated) . K turns on more slowly but maintains during voltage pulse, do not exhibit inactivation

Question 34

Na channels exert what kind of feedback onto voltage-gated channels?

Answer 34

Positive feedback

Question 35

K channels exert what kind of feedback on voltage-gated ion channels?

Answer 35

Negative feedback

Question 36

Why doesn’t membrane potential ever reach Ena?

Answer 36

. Driving force for Na dec. as membrane potential approaches Ena . Na decreases due to inactivation of Na channels . K slowly starting to build

Question 37

What causes repolarization?

Answer 37

. Inactivation of Na (dec. inward positive current) | . Activation of K (inc. outward positive current)

Question 38

Afterhyperpolarization

Answer 38

. Mechanisms responsible for repolarization cause transient hyperpolarization . Na channels don’t immediately recover from inactivation and K channels are slow to close upon repolarization .

Question 39

Role of Na-K-ATPase

Answer 39

. Maintains resting membrane potential by maintaining concentration gradients needed for resorting membrane potential and AP

Question 40

Conduction of AP by local current flow

Answer 40

. Depolarization causes inside of cell to be positive in that region of axon . In areas adjacent, the cell is still at rest w/ negative inside . Current flow locally since opposite charges attract

Question 41

Saltatory conduction

Answer 41

. Axon covered w/ myelin sheath . Gaps btw myelin (nodes of Ranvier) have fast Na channels and are the only areas that can generate AP . AP in one node depolarizers the next node to threshold . Areas in between don’t generate APs

Question 42

Saltatory conduction is a good mechanism because of what reasons?

Answer 42

. Faster conduction: process of depolarizing a node further away is faster than depolarizing adjacent areas (less intermediate steps) . Energy efficient: process fo cintuinally generating APs require less energy in myelinated nn.

Question 43

What determines speed of conduction?

Answer 43

. Diameter of the fiber (larger fiber conducts faster) | . Presence of myelin (myelinated faster than unmyelinated

Question 44

Tubocurarine

Answer 44

. Neuromuscular blocking agent found in arrow poison . Dec. EPP amplitude so it is insufficient to reach threshold for skeletal muscle APs . Assists w/ intubation, setting fractures and dislocation . Used to diagnose Myasthenia Gravis

Question 45

tetrodotoxin (TTX)

Answer 45

. found in puffer fish . Voltage-gated Na channel inhibitor to inhibit upstroke of AP . Causes loss of sensory and motor function

Question 46

Multiple sclerosis

Answer 46

. Attacks myelin of myelinated axons . As myelin sheath degrades, scarring occurs giving symptoms . AP conduction is adversely affected by demyelination