Topic 3 - NERVOUS SYSTEM I (Neuronal Physiology - AP Propagation)

Question 1

AP Propagation

to act as a communication mechanism, an AP must:

Answer 1

an AP must be propagated along the axon’s entire length

Question 2

AP Propagation

an AP must be propagated along the axons entire length to act as what?

Answer 2

to act as a communication mechanism

Question 3

AP Propagation

What are the steps of depolarization during AP (Na+ in)?

1. positive ions move towards where?
2. Adjacent membrane depolarizes to reach threshold (voltage-gated Na+ channels open)
3. get AP on adjacent membrane

Answer 3

1. Positive ions move toward more negative ions on adjacent membrane

Question 4

AP Propagation

What are the steps of depolarization during AP (Na+ in)?

1. Positive ions move toward more negative ions on adjacent membrane
2. adjacent membrane ______ to what?
3. get AP on adjacent membrane

Answer 4

Adjacent membrane depolarizes to reach threshold (voltage-gated Na+ channels open)

Question 5

AP Propagation

What are the steps of depolarization during AP (Na+ in)?

1. Positive ions move toward move negative ions on adjacent membrane
2. Adjacent membrane depolarizes to reach threshold (voltage-gated Na+ channels open)
   3.

Answer 5

get AP on adjacent membrane

Question 6

AP propagation

movement of charge occurs in what direction?

Answer 6

movement of charge occurs in both directions but action potentials move in 1 direction because preceding membrane is in the absolute refractory period

therefore, get sequence of action potentials along membrane, each one the same

Question 7

AP propagation

AP propagates along where?

Answer 7

along axons entire length to the axon terminal

Question 8

rate of propagation depends on:

Answer 8

• fibre (axon diameter)
• myelination

Question 9

rate of propagation depends on fibre (axon) diameter

Answer 9

• large diameter = faster propagation because less resistance to ion flow (=current)

Question 10

rate of propagation depends on myelination

what are the 2 types?

Answer 10

1. unmyelinated fibres
2. myelinated fibres

Question 11

rate of propagation depends on myelination

unmyelinated fibres

Answer 11

APs all along the fibre (Na+ channels are adjacent to each other) = continuous conduction = slower

Question 12

rate of propagation depends on myelination

myelinated fibres

Answer 12

action potential occurs at nodes of Ranvier (ion channels only present here) = saltatory (leaping) conduction ⇒ fast

Question 13

Fibre types range from:

Answer 13

Type A to Type C

Question 14

Fibre Type Range:

Type A

• size
• myelinated or unmyelinated
• propagate at what speed?
• found where?

Answer 14

• large diameter
• myelinated
• propagate action potentials at ~130m/sec
• most sensory neurons & motor neurons to skeletal muscles

Question 15

Fibre Type Range:

Type C

• size
• myelinated or unmyelinated
• propagate at what speed?
• found where?

Answer 15

• small diameter
• unmyelinated
• propagate action potentials at ~0.5m/sec
• found in ANS and some pain fibres

Question 16

Comparison GP and AP

location:

Answer 16

GP: Dendrites/Cell body

AP: axon hillock/axon

Question 17

Comparison GP and AP

strength of MP

Answer 17

GP: variable

AP: all-or-none (+30mV)

Question 18

Comparison GP and AP

summation:

Answer 18

GP: YES

AP: NO

Question 19

Comparison GP and AP

repolarization

Answer 19

GP: current dies away

AP: Na+ gates close

K+ gates open

Question 20

Comparison GP and AP

type of gates

Answer 20

GP: chemical, mechanical, thermal (NOT VOLTAGE)

AP: ONLY voltage

Question 21

Comparison GP and AP

distance travelled:

Answer 21

GP: short (1-2mm) and dies away

AP: produced AP on axon and propagates over long distances

Question 22

Comparison GP and AP

refractory period

Answer 22

GP: absent

AP: present