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Flashcards in lecture 28 - transmission of AP Deck (31):
1

two types of axon and their features

- unmyelinated: small diameter, slow transmission of AP, continuous - myelinated: larger diameter, fast transmission of AP, saltatory

2

what are the 2 stages of action potential transmission, in both axon types?

- passive spread - generation of action potential

3

conventional current used in diagrams show

flow of cations (positive ions) from +ve to -ve terminals

4

3 stages in passive spread

1. subthreshold depolarisation at one region of the membrane 2. passive current flow (inside and outside the axon) 3. depolarisation of adjacent parts of the axon (both sides)

5

why is current only able to spread over a short distance? what is this distance

current dissipates quickly, restricting distance to less than 1mm

6

speed of unmyelinated axon AP transmission =

1m/sec

7

speed of myelinated axon AP transmission =

20-100m/sec

8

why is unmyelinated axon AP transmission so much slower

AP must be regenerated at every point in the membrane

9

is passive current flow between two points rapid or slow?

VERY rapid

10

5 steps to AP transmission in an unmyelinated axon

1. action potential 2. passive current flow 3. depolarisation on both adjacent parts of the membrane to THRESHOLD 4. voltage-gated Na+ channels open 5. new full sized AP generated

11

glia cells function

wrap axon in myelin

12

which cells form myelin sheath in CNS

oligodendrocytes

13

which cells form myelin sheath in PNS

Schwann cells

14

branch off axon called...

axon collateral

15

gaps in myelin =

Nodes of Ranvier

16

Myelination increases efficiency of passive spread of current because...

due to the insulating properties of myelin, there is less current dissipation (current can only leave via the nodes of Ranvier)

17

Passive transmission occurs in one direction TRUE/FALSE

FALSE. Passive transmission occurs in BOTH DIRECTIONS

18

Current flows ________ between nodes

current flows _passively_ between nodes

19

in myelinated axons, where does action potential potential regeneration occur?

at the nodes of Ranvier

20

Myelination increases AP transmission speed because

increasing efficiency of passive spread, so regeneration of AP only has to occur at the nodes, as opposed to every part of the membrane

21

why are axons not always myelinated?

too large. unmyelinated can fit more per volume - important in the human brain

22

AP at adjacent node will try to move passively to depolarise the 'previous' node, but why will it fail?

this node will still be in the absolute refractory period (for 1-2ms). By the time this period is over, AP has already moved on

23

Can action potentials moving in opposite directions pass each other?

NO, like the reasons for APs moving in one direction, this is due to the refractory period

24

antidromic direction =

towards cell body along axon

25

orthodromic direction =

from cell body along axon

26

collision =

process where antidromic and orthodromic APs will cancel each other out, due to their absolute refractory periods

27

where are axons of: sensory neurons, motor neurons, and 'autonomic nervous system' found?

PNS

28

where on the axon would a high-density of voltage-gated Na+ channels be found?

trigger zone of axon

29

In sensory neurons, do the receptors immediately evoke an action potential?

NO. A receptor potential is first evoked

30

receptor potential =

a graded depolarisation which is first evoked by sensory neurons (instead of an AP)

31

once generated the receptor potential spreads _________ to the more distally located _______ ____ where APs are generated. The action potential then spreads along the axon, towards the ___. Information about the strength of the stimulus is coded into the ________ of the receptor potential, then in the ________ of the action potential.

once generated the receptor potential spreads _passively_ to the more distally located _trigger_ _zone_ where APs are generated. The action potential then spreads along the axon, towards the _CNS_. Information about the strength of the stimulus is coded into the _amplitude_ of the receptor potential, then in the _frequency_ of the action potential.