Module B-03 Flashcards Preview

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Flashcards in Module B-03 Deck (34):
1

Receptor potential

occur in the primary afferent sensory neuron that experiences the stimulus

2

Synaptic potential

occur in postsynaptic neurons after the primary afferent neuron

3

Graded potential

local change in potential due to stimulus which increases in amplitude with increase in amplitude of stimulus

4

how do graded potentials spread?

They depolarize adjacent regions without membrane receptors by decrementally spreading positive charge

5

Length constant

Distance over which grade potential declines to 37% or 1/e of the original

6

Length constant increases with ___________ and decreases with ________

electrical resistance of the membrane ; electrical resistance of cytoplasm

7

Larger diameter axons have _______ length constants

Greater

8

The larger the area of axon the _________ the cytoplasmic resistance

smaller

9

The greater the length constant the ________ the decrement, the _______ the intracellular resistance and the ________the membrane resistance

slower; lower ; greater

10

Depolarizations that are all or none and show no decrement

Action potentials

11

Trigger zone aka

impulse initiation zone (IIZ)

12

describe IIZ

dense population of voltage sensitive Na+ channels which open when sufficient depolarization has been reached

13

IIZ or trigger zone in Multipolar neurons

Axon hillock ( btw cell body and first myelinating cell)

14

IIZ or trigger zone in pseudounipolar and bipolar neurons

near sensory nerve ending

15

What occurs during rising phase of Action potential

- opening of enough Na+ channels that exceeds K+ efflux
- neuron depolarizes
- more Na+ channels open
-Na+ moves down its electrochemical gradient into the cell
- delayed rectifying K+ channels are also induced but are very slow

16

What occurs during falling phase

- efflux of K+ causes repolarization
- often hyperpolarizes
- depolarization induced Na channel inactivation

17

General structure of superfamily of voltage gated ion (K+,Na+, Ca2+) channels

- 4 identical subunits
- each subunit has 6 membrane spanning domains
- charged voltage sensor in segment 4
- pore loop

18

What confers ion specificity to the voltage gated ion channel

Pore loop

19

Absolute refractory period

- all Na+ channels are inactivated
- 1ms
- no impulse can be generated

20

Relative refractory period

incomplete return of inactivated Na+ channels to normal closed state plus residual K+ currents
- lasts longer (several ms)
- new impulse can be generated if stimulus is large enough

21

Where are voltage gated Na+ channels found in myelinated neurons of PNS and CNS?

1) Nodes
2) Trigger zone (IIZ)
3) terminal

22

Where are voltage gated K+ channels found in myelinated neurons of PNS and CNS?

1) Paranodal
2) Juxtaparanodal
3) Terminal

23

Where are voltage gated Ca2+ channels found in myelinated neurons of PNS and CNS?

Terminal

24

Where do impulses occur in myelinated axons

at nodes of Ranvier

25

What is the effect of demyelination on impulse conduction

large uninsulated internodes diminish the axonal length constant

26

Electrotonic conduction

passive flow of charge within the cell

27

How is impulse conducted along unmyelinated axon?

- electrotonic conduction depolarizes the adjacent Na+ channels beyond threshold and this continues along the axon length

28

Continuous conduction occurs in

Unmyelinated axons

29

Saltatory conduction occurs in

Myelinated axons

30

How is impulse conducted along myelinated axon?

- positive charge enters node of Ranvier then moves down its electric gradient to the next node which then reaches thershold

31

Why are conduction velocities in unmyelinated axons slower?

1) they have smaller diameters (smaller length constants)
2) requires sequential driving of ALL axonal segments

32

Why are conduction velocities in myelinated axons faster?

1)They have larger diameters (larger length constant)
2) only need to drive current at the nodes

33

What effect do Lidocaine and Procaine have on membrane channels?

Block Voltage gated Na+ channels

34

What effect does lidocaine have on sensory neurons

Suppresses action potentials