Module B-03

Question 1

Receptor potential

Answer 1

occur in the primary afferent sensory neuron that experiences the stimulus

Question 2

Synaptic potential

Answer 2

occur in postsynaptic neurons after the primary afferent neuron

Question 3

Graded potential

Answer 3

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

Question 4

how do graded potentials spread?

Answer 4

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

Question 5

Length constant

Answer 5

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

Question 6

Length constant increases with ___________ and decreases with ________

Answer 6

electrical resistance of the membrane ; electrical resistance of cytoplasm

Question 7

Larger diameter axons have _______ length constants

Answer 7

Greater

Question 8

The larger the area of axon the _________ the cytoplasmic resistance

Answer 8

smaller

Question 9

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

Answer 9

slower; lower ; greater

Question 10

Depolarizations that are all or none and show no decrement

Answer 10

Action potentials

Question 11

Trigger zone aka

Answer 11

impulse initiation zone (IIZ)

Question 12

describe IIZ

Answer 12

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

Question 13

IIZ or trigger zone in Multipolar neurons

Answer 13

Axon hillock ( btw cell body and first myelinating cell)

Question 14

IIZ or trigger zone in pseudounipolar and bipolar neurons

Answer 14

near sensory nerve ending

Question 15

What occurs during rising phase of Action potential

Answer 15

• 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

Question 16

What occurs during falling phase

Answer 16

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

Question 17

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

Answer 17

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

Question 18

What confers ion specificity to the voltage gated ion channel

Answer 18

Pore loop

Question 19

Absolute refractory period

Answer 19

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

Question 20

Relative refractory period

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

1) Paranodal
2) Juxtaparanodal
3) Terminal

Question 23

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

Answer 23

Terminal

Question 24

Where do impulses occur in myelinated axons

Answer 24

at nodes of Ranvier

Question 25

What is the effect of demyelination on impulse conduction

Answer 25

large uninsulated internodes diminish the axonal length constant

Question 26

Electrotonic conduction

Answer 26

passive flow of charge within the cell

Question 27

How is impulse conducted along unmyelinated axon?

Answer 27

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

Question 28

Continuous conduction occurs in

Answer 28

Unmyelinated axons

Question 29

Saltatory conduction occurs in

Answer 29

Myelinated axons

Question 30

How is impulse conducted along myelinated axon?

Answer 30

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

Question 31

Why are conduction velocities in unmyelinated axons slower?

Answer 31

1) they have smaller diameters (smaller length constants)

2) requires sequential driving of ALL axonal segments

Question 32

Why are conduction velocities in myelinated axons faster?

Answer 32

1) They have larger diameters (larger length constant)

2) only need to drive current at the nodes

Question 33

What effect do Lidocaine and Procaine have on membrane channels?

Answer 33

Block Voltage gated Na+ channels

Question 34

What effect does lidocaine have on sensory neurons

Answer 34

Suppresses action potentials