Nerve Cells and Neuron Potentials 2

Question 1

Electrical signals in neurons result in …

Answer 1

membrane potential changes

Question 2

Electrical signals are due to …

Answer 2

gated channels (voltage, ligand, mechanically gated)

Question 3

Describe gated channels.

Answer 3

• open or close in response to stimuli
• affect movement of ions
• ion movement = electrical signal

Question 4

What are the 2 types of electrical signals?

Answer 4

• graded potentials

- action potentials

Question 5

Graded potentials are (small/large) and communicate over (short/long) distances.

Answer 5

• small

- short

Question 6

Action potentials are (small/large) and communicate over (short/long) distances.

Answer 6

• large

- long

Question 7

Describe graded potentials.

Answer 7

• initiated by a stimulus
• small change in membrane potential
• magnitude varies (graded)
• spread by electronic conduction
• are decremental (magnitude decays as it spreads)
• communicate over short distances

Question 8

What is the purpose of graded potentials?

Answer 8

determine whether an action potential will occur

Question 9

What is the threshold?

Answer 9

level of depolarization necessary to elicit action potential

Question 10

Excitatory is …

Answer 10

depolarization

Question 11

Inhibitory is …

Answer 11

hyperpolarization

Question 12

What is temporal summation?

Answer 12

same stimulus repeated close together in time

Question 13

What is spatial summation?

Answer 13

different stimuli that overlap in time

Question 14

Describe action potentials?

Answer 14

• rapid, large depolarization of membrane
• used for communication
• travel from cell body –> axons –> axon terminal

Question 15

What can generate action potentials?

Answer 15

excitable membranes

Question 16

What are the phases of an action potential?

Answer 16

• depolarization
• repolarization
• hyperpolarization

Question 17

What happens to trigger depolarization?

Answer 17

Na+ channels open

Question 18

What happens to trigger repolarization?

Answer 18

K+ channels open

Question 19

Name 2 threshold triggers (depolarization).

Answer 19

• graded potentials bring membrane to threshold

- rapid opening of Na+ channels

Question 20

What parts of the neuron are responsible for graded potentials?

Answer 20

• dendrites
• cell body
• receptors

Question 21

Rapid opening of Na+ channels means …

Answer 21

• slow closing of Na+ channels

- slow opening of K+ channels

Question 22

Why does the action potential not reach the equilibrium potential of sodium?

Answer 22

• K+ channels opening

- Na+ channels closing

Question 23

What happens during repolarization?

Answer 23

• Na+ channels closed

- K+ channels opened

Question 24

What happens during hyperpolarization?

Answer 24

• K+ channels remain beyond -70 mV

- membrane potential gets close to the equilibrium potential of potassium

Question 25

What restores resting potential?

Answer 25

Na+/K+ pump

Question 26

What are the 2 gates associated with voltage-gated sodium channels?

Answer 26

- activation gate | - inactivation gate

Question 27

Describe the activation gate.

Answer 27

- voltage dependent - opens at threshold and depolarization - positive feedback

Question 28

Describe the inactivation gate.

Answer 28

- voltage and time dependent - opens during depolarization - closes during repolarization

Question 29

Describe voltage-gated potassium channels.

Answer 29

- one gate - voltage/time dependent - negative feedback: restores resting membrane potential, prepares the neuron for another AP

Question 30

What is the refractory period? What are the 2 categories?

Answer 30

- follows an action potential - decreased excitability - absolute and relative

Question 31

Describe the absolute refractory period.

Answer 31

- all of depolarization + most repolarization phase - second action potential cannot be generated - Na+ gates are inactivated

Question 32

Describe the relative refractory period.

Answer 32

- spans the last part of the repolarization phase and hyperpolarization - second action potential can be generated with a stronger stimulus - some Na+ gates are closed; some are inactivated

Question 33

What kind of stimulus can generate an AP during the absolute refractory period?

Answer 33

no stimulus of any strength can

Question 34

What kind of stimulus can generate an AP during the early parts of relative refractory period?

Answer 34

a much stronger stimulus than normal

Question 35

What kind of stimulus can generate an AP during the late parts of relative refractory period?

Answer 35

a stimulus a little stronger than normal

Question 36

What is the all or none principle in reference to threshold stimulus?

Answer 36

- threshold depolarization = AP - sub threshold depolarization = no AP - suprathreshold depolarization = AP

Question 37

What are 3 consequences of refractory periods?

Answer 37

- all or none principle - frequency: greater frequency of AP for greater stimuli - unidirectional propagation of action potentials

Question 38

What 3 factors affect propagation?

Answer 38

- refractory period (unidirectional) - axon diameter - myelination

Question 39

Describe how axon diameter affects propagation.

Answer 39

- larger: less resistance, faster | - smaller: more resistance, slower

Question 40

Describe how myelination affects propagation?

Answer 40

- saltatory conduction | - faster propagation

Question 41

Mechanisms of action potential conduction depends on the presence or absence of _______.

Answer 41

myelin

Question 42

What are the 2 effects of graded potentials/APs?

Answer 42

- dissipate Na+ and K+ concentration gradients | - the Na+/K+ pump prevents dissipation