Chapter 4

Question 1

Cytosol relative to extracellular space

Answer 1

(-ve) charge

Question 2

Generating an action potential (cause)

Answer 2

caused by depolarization of membrane beyond threshold (-40mV)

Question 3

Chain reaction example

Answer 3

puncture foot-stretch membrane of nerve fibers-opens Na+permeable channels-Na+ influx-depolarized membrane-reaches threshold-Action potential

Question 4

Generation of multiple action potentials

Answer 4

Firing frequency reflects the magnitude of the depolarizing current

Question 5

Depolarization

Answer 5

influx of Na+

Question 6

repolarization

Answer 6

efflux of K+

Question 7

Membrane current

Answer 7

the net movement of K+ across membrane

Question 8

Potassium channel number

Answer 8

proportional to electrical conductances

Question 9

membrane potassium current

Answer 9

flow and driving force

Question 10

Rising phase

Answer 10

influx of Na+ (inward sodium current)

transient increase in g(Na)

Question 11

falling phase

Answer 11

efflux of K+ (outward potassium current)

transient increase in g(K)

Question 12

hodgekin and Huxley

Answer 12

Voltage clamp creators: clamped the membrane at a chosen potential value.

discovered existence of sodium “gates) in the axonal membrane

Question 13

Voltage-gated sodium channel

Answer 13

transmembrane, 6 subunits, one pore loop, a selectivity filter, voltage sensor and gate. selective to size of partially hydrated Na+ ion, as K+ is too big to fit. Opens at -40mV

Question 14

patch clamp method

Answer 14

(erwin Neher) for sodium gated channels

Question 15

functional properties of Voltage-gated sodium channel

Answer 15

1. open with little delay
2. Stay open for about 1ms
3. Cannot be opened again by depolarization

Question 16

Absolute refractory period

Answer 16

Channels are inactivated

Question 17

generalized epilepsy with febrile seizures

Answer 17

a channelopathic genetic disease

Question 18

tetrodotoxin

Answer 18

clogs Na+ permeable pore

Question 19

red tide (saxitoxin)

Answer 19

is a Na+ channel-blocking toxin

Question 20

Batrachotoxin

Answer 20

(frog) blocks inactivation so channels remain open

Question 21

Veratridine

Answer 21

(lillies) inactivates channels

Question 22

Aconitine

Answer 22

(buttercups) inactivates channels

Question 23

clues about 3D structure of channels

Answer 23

due to differential toxin binding sites and result it has on the Voltage-gated sodium channels

Question 24

Potassium vs Sodium gates similarities

Answer 24

both are open in response to depolarization

Question 25

Potassium vs Sodium gates dissimilarities

Answer 25

potassium gates open later than sodium gates.

Question 26

delayed rectifier

Answer 26

Potassium conductance (g(K)) serves to rectify/ reset membrane potential

Question 27

Voltage-gated potassium channels

Answer 27

four separate polypeptide subunits join to form a pore

Question 28

relative refractory period

Answer 28

the period after an action potential by which it takes more to depolarize and reach the threshold to create another action potential

Question 29

Orthodromic

Answer 29

action potential travels in one direction: down the acon terminal

Question 30

Antidromic

Answer 30

backwards propagation

Question 31

conduction velocity (typical)/length of action potential

Answer 31

10m/s

2ms

Question 32

factors influencing concudction velocity in an action potential

Answer 32

1. spread of action potential along membrane (dependent upon axon structure)
2. Path of +ve charge (inside of the axon=faster, across the axonal membrane=slower)
3. Axonal excitability (axonal diameter: bigger=faster, number of voltage-gated channels)
4. Myelin (layers of myelin sheath facilitate current flow)

Question 33

saltatory conduction

Answer 33

at nodes of ranvier (in myelinating cells), voltage gated sodium channels are concentrated at the nodes and travel to another node quicker

Question 34

spike initiation zone

Answer 34

membrane with high density of voltage-gated sodium channels, either at sensory nerve endings or the axon hillock

Question 35

Neuronal signal transmits

Answer 35

as the generation and regeneration of action potentials