Deck 19: Propagation of the Action Potential

Question 1

The delay between an action potential in a soma and its appearance 30 cm down the efferent axon is 5 m s. T he co nd uc tion ve loc ity is

A) 6 mm s-1
B) 6 cm s-1
C) 150 cm s-1
D) 15 m s-1
E) 60 m s-1

Answer 1

E

Question 2

The co nd uc tion ve loc ity is in cr ea se d b y

A) Sh orte nin g th e tim e at w hich a rem ote pat ch of m em bra ne is ex cited to th resh old
B) Increasing capacitance by insulating mem branes
C) Increasing axial resistance to current flow
D) Decreasing transmem brane resistances
E) None of the above

Answer 2

A

Question 3

We inje ct a slig htly d ep ola rizin g c ur re nt in to a n a xo n a t x = 0 c m co ntin uo us ly monitor the potential at x = 5 cm away. At steady state, the resting mem brane potential is -70 mV. At the point of injection, the p oten tial is -60 m V an d at x = 5 c m awa y it is -66 .3 m V. W hat is th e sp ace con stan t?

A) 2.5 cm
B) 5.0 cm
C) 10.0 cm
D) 15.0 cm
E) 20.0 cm

Answer 3

B

Question 4

To determine the length constant, o r space constant, you can inject current (without activating an action potential) and plot (Vr is the resting membr ane po tential; elec troton us is the s tead y-state voltage)

A) Ln (V - V r) vs x during conditions of electrotonus
B) Ln (V - V r) vs t during conditions of electrotonus
C) Ln (V - V r) vs t during the rise phase or decline phase of electrotonus
D) Ln (V - V r) vs t only during the decline phase of electrotonus
E) Ln (V - V r) vs t only during the rise phase of electrotonus

Question 5

An action potential begins at a special place, the axon hillock, adjacent to the soma of a motor neuron. You record an action potential 30 cm away on an efferent nerve. The action potential measured far away from the soma

A) Is much sm aller than the action potential near the soma because it decays with distance.
B) Is smaller, but not much, because the decay with distance is prevented by m ye lination
C) Is larger than the one at the soma because it is amplified at each new area of mem brane
D) Is the same size as the action potential near the soma because it is regenerated anew along the axon
E) Is the same size as the action potential near the soma because there is no decay of potentials in axons

Question 6

The specific capacitance of a bare mem brane is about

A) 1 pF cm -2
B) 1 nF cm -2
C) 1 µ F cm -2
D) 1 mF cm -2
E) 1 F cm -2

Question 7

The axial resistance

A) Depends inversely on the specific resistance of the cytoplasm
B) Depends inversely on the cross-sectional area of the cytoplasm
C) Depends directly on the electrolyte composition
D) Is decreased by myelination
E) Is Increased by myelination

Question 8

Mye lin increa ses con duc tion ve locity bec aus e it

A) Decreases Rm and Increases Cm
B) Increases Rm and Increases Cm
C) Increases R m and decreases Cm
D) Decreases Rm and decreases Cm
E) M yelin do es no t do this

Question 9

Increasing Rm by myelination

A) Decreases the time constant
B) Is pro po rtion al to the thic kn ess of th e m yelin
C) Is in ve rs ely p ro po rtio na l to th e th ick ne ss of t he m yelin
D) Increases proportionally with the cross-sectional area of the axon
E) Is inversely proportional to the cross-sectional area of the axon.

Question 10

Myelin does all of the following EXCEPT

A) It Increases the transmem brane resistance by insulating the axon interior from the exterior
B) It reduces the capacitance of the mem brane by Increasing its thickness
C) It reduces the time constant
D) It Increases the space or length constant
E) It increa ses con duc tion ve locity

Question 11

The co nd uc tion ve loc ity is f as tes t in

A) Sm all diameter myelinated axons
B) Sm all diameter unmyelinated axons
C) Sm all diameter axons with large internodal distances
D) Large diameter myelinated axons
E) Large diameter unmyelinated axons

Question 12

Decreasing the capacitance of the axon mem brane means

A) It takes few er charge s to effect a giv en ch ange in the m em brane poten tial difference across the membrane
B) For the same am ount of charges, the mem brane potential changes less
C) It ta ke s m or e a xia l cu rre nt to de po lar ize th e n ex t pa tch of m em br an e to thr es ho ld
D) It ta ke s m or e a xia l vo ltag e to de po lar ize th e n ex t pa tch of m em br an e to thr es ho ld
E) For the same voltage change, more current is required

Question 13

The time constant is given as

A) w = R C
B) w = q d / A
C) w = uc
D) w = 6 (R
E) w = Q /V

Question 14

The time constant describes

A) The tim e co urs e, when injecting a constant current, of changing from one steady-state voltage to another
B) The time it takes for the action potential to be regenerated
C) The time it takes for the action potential to propagate a characteristic distance
D) The delay of the action potential at the nodes of Ranvier
E) The decay of the action potential with time between the nodes of Ranvier

Question 15

The "specific capacitance" is the

A) Ca pac itance per u nit leng th
B) Capacitance per unit volume
C) C ap ac itan ce pe r un it tim e
D) Capacitance per unit area
E) Capacitance per unit charge

Question 16

M yelin

A) Decreases the capacitance of the axon membrane mainly by Increasing the separation between the inside and outside
B) Decreases the capacitance of the ax on m em br an e m ain ly by Increasing the dielectric constant within the mem brane
C) Decreases the capacitan ce of t he ax on m em br an e m ain ly by Decreas ing the die lec tric constant within the mem brane
D) Increases the capacitance of the axon mem brane mainly by Increasing the separation between the inside and the outside
E) Increases the capacitance of the axon mem brane mainly by Increasing the surface area

Question 17

Sa ltatory co ndu ction r efe rs to

A) Decreased resistance of internal solutions due to electrolytes
B) Jum ping of the action potentials from nerve to nerve
C) Jumping of the current from node to node
D) Rapid con duction in myelinated fibers
E) Both A and C are correct

Question 18

In a myelinated nerve, all of the following are true EXCEPT

A) Na+ enters the axon and K+ leaves the axon during the action potential
B) The Na,K-ATPase cont inually re-establishes the Na+ and K+ grad ients
C) Na+ influx occurs mainly at the nodes of Ranvier
D) The Na+ flux in a single action potential significantly changes axoplasmic [Na+] (> 5%)
E) None of the above

Question 19

The space constant or length constant is given as

A) h = R C
B) h = q d / A
C) h = uc
D) h = 6 (R
E) h = QN a /2q )