Neurophysiology L3: Action Potential- Long Distance Communication

Question 1

Action potential require special, ______ ion channels

Answer 1

voltage gated

Question 2

Dendrites have ______ potential

Answer 2

synaptic

Question 3

What are 2 things that local potentials are produced by?

Answer 3

1. Sensory stimulus
2. Synaptic contracts (dendritic field)

Question 4

What are synaptic contacts like?

Answer 4

• Most relatively silent- only some active (80% in reserve)
• Use stimulus to make others active

Question 5

All neurons have ______ segment

Answer 5

initial

Question 6

An AP can be triggered by a ________local potential reaching the ______segment (if large enough). This will have a (fast/slow) rise (fast/slow) drop (fast/slow) recovery

Answer 6

depolarizing; initial; fast; fast; slow

Question 7

During -70mV (resting potential), the Na2+ channel is _______(open/closed/inactivated). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).

Answer 7

closed; closed; open

Question 8

During -60mV, the Na 2+ channel is _______(open/closed). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).

Answer 8

open; open; open

Question 9

During +30mV (ideal Na2+ voltage), the Na 2+ channel is _______(open/closed/inactivated). This means that the activation gate is _______(open/closed) and the inactivation gate is _______(open/closed).

Answer 9

inactivated; open; closed

Question 10

Are local potentials graded or not graded?

Answer 10

Graded

Question 11

Are action potentials graded or not graded?

Answer 11

Not graded (all or none)

• Once gates are open –> all open

Question 12

Channels are either ____ or _____ (choose 2 out of the 3: opened/activated/inactivated)

Answer 12

open; inactivated (Can’t “activate” any gates)

Question 13

Sequence of events that underpin an AP: Step 1

Answer 13

• Na2+ activation gate opens
• K+ gate closed

Question 14

Sequence of events that underpin an AP: Step 2 (after Na2+ activation gate opens and K+ gate closed)

Answer 14

Na2+ flows in –> more positive (depolarization) –> towards +30mV

Question 15

Sequence of events that underpin an AP: Step 3 (after depolarisation towards +30mV)

Answer 15

Reaches +30mV –> Na2+ inactivation gate closes –> K+ gate opens –> Na+2 can’t come in –> K+ goes out –> more negative (hyperpolarization) –> drives potential back to equilibrium (overshoot)

Question 16

Sequence of events that underpin an AP: Step 4 (after hyperpolarisation towards equilbrium)

Answer 16

Back to equilibrium Na2+ inactivation gate open –> Na2+ activation gate closes –> less positive –> K+ gate opens –> more negative –> hyperpolarization to resting –> K+ gate closes

Question 17

Influx- all channels are ____. Efflux- coming ____ of cell. Summary- Sequence of events that underpin an AP

Answer 17

open; out

Question 18

What are the 2 AP refractory period(s)?

Answer 18

1. Absolute refractory period (ARP)
2. Relative refractory period (RRP):

Question 19

What is the absolute refractory period (ARP)?

Answer 19

• Impossible to trigger an AP
• Na+ channel inactivation

Question 20

What is the relative refractory period (RRP)?

Answer 20

• Larger than normal stimulus required
• Some residual Na channel inactivation
• High K+ permeability

Question 21

What are the 2 steps of action potential propagation of unmyelinated axons? Is it fast or slow conduction?

Answer 21

• Slower conduction 0.1-2m/s

1. AP at one point triggers AP in the next section
2. Due to the refractory period, APs cannot “change directions”

Question 22

What is step 1 of the action potential propagation of unmyelinated axons?

Answer 22

AP at one point triggers AP in the next section

Question 23

What is step 2 of the action potential propagation of unmyelinated axons?

Answer 23

Due to the refractory period, APs cannot “change directions”

Question 24

What are the 2 steps of action potential propagation of myelinated axons? Is it fast or slow conduction?

Answer 24

• Glial cells –> myelin sheaths to some axons –> duct tapes the channels = less leaky –> faster conduction 100m/s

1. AP only occurs at Nodes of Ranvier: salutatory conduction
   
   • Able to “jump”
2. Due to the refractory period, APs cannot “change directions”

Question 25

What is step 1 of the action potential propagation of myelinated axons?

Answer 25

AP only occurs at Nodes of Ranvier: salutatory conduction - Able to “jump”

Question 26

What is step 2 of the action potential propagation of myelinated axons?

Answer 26

Due to the refractory period, APs cannot “change directions”