BMS1052 Lecture Notes - Lecture 4: Resting Potential, Goldman Equation, Kurdistan Workers' Party

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5 May 2018

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WEEK 2 Lecture 4

Learning objectives

 Describe why passive ion diffusion is an unreliable way to transfer signals between

neurons

 Describe the components of an action potential, including what channels are

involved, and when.

 Explain the action potential in terms of changes in the membrane permeability and

ionic concentrations.

 Describe factors affecting the speed and nature of action potential conduction.

Revision – ionic equilibrium potential

Movement of a very small number of ions is sufficient to set up a large change in membrane

potential; thus ionic concentrations will not change significantly at equilibrium.

The ionic equilibrium potential defines the voltage across a membrane that will counteract

the difference in concentrations of a single ion on either side of the membrane. The

equilibrium potential is independent of whether the ions can actually move or not (i.e. if all

channels are closed, you can still calculate the equilibrium potential); Eion depends only on

the elatie ioi oetatios ad the io’s hage.

If a membrane is permeable to only one ion, then the membrane potential will move

toads that io’s ioi euiliiu potetial.

Note that very little ionic movement is required to change the membrane potential, thus

there is negligible change in ionic concentrations required to reach the equilibrium

potential.

In the case that the membrane is permeable to more than one ion, the Goldman equation is

required.

Revision – two important potassium channels

1. Two-pore-domain potassium channels (K2p)

- two pore loop domains, which are

- generally open => ongoing leak of K+

- help set the resting membrane potential

2. voltage gated potassium channels (KV)

- Open-state depends on the membrane potential

(normally closed at resting membrane potential)

- These ae also alled delayed-etifie haels.

delayed => they take soe tie to ope;

etifie => they etu the eae potetial to its estig leel

[ ]

out

ion

log

5.61

[ ] [ ]

out

NaPKP

log5.61

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Document Summary

Describe why passive ion diffusion is an unreliable way to transfer signals between neurons. Describe the components of an action potential, including what channels are involved, and when. Explain the action potential in terms of changes in the membrane permeability and ionic concentrations. Describe factors affecting the speed and nature of action potential conduction. Movement of a very small number of ions is sufficient to set up a large change in membrane potential; thus ionic concentrations will not change significantly at equilibrium. The ionic equilibrium potential defines the voltage across a membrane that will counteract the difference in concentrations of a single ion on either side of the membrane. The equilibrium potential is independent of whether the ions can actually move or not (i. e. if all channels are closed, you can still calculate the equilibrium potential); eion depends only on the (cid:396)elati(cid:448)e io(cid:374)i(cid:272) (cid:272)o(cid:374)(cid:272)e(cid:374)t(cid:396)atio(cid:374)s a(cid:374)d the io(cid:374)"s (cid:272)ha(cid:396)ge.

Related Questions

Santiago Ramon y Cajalâs theory of dynamic polarization refers to the:

(a)membrane potential of a neuron at rest.

(b)membrane potential of a neuron firing action potentials.

(c)opening and closing of gated channels in the membrane.

(d)one way flow of information in neurons from dendrites to axon terminals.

(e)one way flow of information in neurons from axon terminals to dendrites.

Over the course of scientific history, there are many examples of scientists reaching the right conclusion for the wrong reasons. When Schwann first proposed that the nervous system was made of individual cells, he based it on observations of:

(a)synapses.

(b)dendrites

(c)axon terminals.

(d)astrocytes.

(e)Nodes of Ranvier.

The synaptic cleft was finally seen in the 1950s. What prevented scientists from seeing it earlier?

(a)The resolution of the light microscope.

(b)They were looking in the wrong place.

(c)Their tissue was not appropriately stained.

(d)Myelination of the axons.

(e)all of the above

The resting membrane potential of a neuron is approximately:

(a) +65 V

(b) +65 mV

(d) -65 mV

What is largely responsible for the resting membrane potential in a neuron?

(a)Axonal insulation by myelin

(b)Voltage-Gated Sodium Channels

(c)The Action Potential

(d)Potassium Leak Channels

Which of the following would DECREASE the propagation velocity of an action potential down an axon?

(a)Increase in axon diameter

(b)Increase myelination between nodes of Ranvier

(c)Remove myelination between nodes of Ranvier

(d)Decrease density of voltage-gated Na+ channels except at the Nodes of Ranvier

The resting membrane potential of a neuron can be estimated using the:

(a)Nernst equation

(b)Goldman equation

(c)Hodgkin and Huxley equation

(d)Ohmâs law

18. What would happen to the resting membrane potential of a neuron if you added K+ to the extracellular fluid?

(a)Resting membrane potential would increase (become more positive)

(b)Resting membrane potential would decrease (become more negative)

(c)Resting membrane potential would not change

(d)Resting membrane potential would be abolished

. Which of the following statements is FALSE for Graded Potentials

(a)Magnitude changes with magnitude of triggering stimulus

(b)Magnitude decreases with distance from initial site

(c)Cannot be summed

(d)No refractory period

In the nervous system, the strength of the stimulus is coded into:

(a)The frequency of action potentials generated

(b)The amplitude of action potentials generated

(c)Both the frequency and amplitude of action potentials generated

(d)The duration of individual action potentials generated

Ion movement during both the depolarization and repolarization phases of an action potential are the result of:

(a)active transport pumps along the neuron membrane.

(b)diffusion of ions down their electrochemical concentration gradients.

(c)negative feedback loops.

(d)All of the above

At the peak of the action potential, the membrane potential is:

(a)Exactly at the Na+ equilibrium potential

(b)Greater (more positive) than the Na+ equilibrium potential

(c)Above 0 mV but less positive than the Na+ equilibrium potential

(d)0 mV

1. The plasma membrane of rod and cone cells are

a) At resting potential in the dark and deploarized in thelight

b) At resting pootential in the dark and hyperpolarized in thelight

c) Depolarized in the dark and hyperpolarized in the light

d) Hyperpolarized in the dark and at resting potential in thelight

e) Hyperpolarized in the dark and depolarized in the light

2. The equilibrium potential of K+ ions in nerve cells is about-90mV. The membrane potential of a typical nerve cells at rist is-70mV. Therfore

a) Increasing the permeability of a resting neuronal membrane toK+ ions will increase the membrane potential (that is, make it morenegative, inside with respcect to outside)

b) In nerve cells at rest, there is a net diffusion of K+ ionsout of the cell

c) Increasing the membrane potential of a nerve cell would slowthe diffusion of K+ ions out of it.

d) K+ is not the only ion that is permeable at rest

e) All of the above

3. Which of the following is responsible for the replarizingphase of the action potential?

a) Voltage-gated Na+ channels are opened.

b) The Na+-K+ pump restores the ions to theri original restingstate.

c) The permeability to Na+ increases greatly.

d) ATPase destroys the energy supply that was maintaining theaction potential at its peak.

e) The permeability to K+ increases greatly while that to Na+decreases

4. The Relative refractory period of an axonm conincides withthe period of

a) Activation and inactivatioin of voltage-gated Na+channels

b) Increased Na+ flux into the cell

c) Increased K+ flux into the cell

d) Increased K+ flux out of the cell

e) Increased Na+ flux out of the cell

5. The plasma membranes of rod and cone cells are

a) At resting potential in the dark and epolarized in thelight

b) At resting potential in the dark and hyperpolarized in thelight

c) Depolarized in the dark and hyperoplarized in the light

d) Hyperpolarized in the dark and tat resing potential in thelight

e) Hyperpolarized in the dark and depolarized in the light

1. The plasma membrane of liver cells contains a glucose uniportthat transports glucose by facilitated diffusion. When the[glucose] is higher inside the liver cell than the [glucose]outside the liver cell, the glucose uniport will

A. couple the transport of glucose out of the cell to thehydrolysis of ATP

B. couple the transport of glucose into the cell to thehydrolysis of ATP

C. switch to a closed conformation, allowing no transport ofglucose

D. transport glucose out of the cell by passive transport

E. transport glucose in of the cell by passive transport

2. Unlike the positive charged ion shown in the middle diagramof figure 11-4B, K+ is higher in concentration inside the cell. Howwill the membrane potential of a cell at rest (shown in both themiddle and right-hand diagrams of Figure 11-4B) affect theelectrochemical gradient for K+?

A. The membrane potential will increase the electrochemicalgradient

B. The membrane potential will decrease the electrochemicalgradient

C. The membrane potential will have no effect on theelectrochemical gradient

3. Which of the following proteins carries out activetransport?

A. gluclose symport

B. Bacteriorhodopsin

C. ABC transporter

D. NA K pump

E. All of the above

4. Aquaporin will not transport Na+ ions because

A. Two asparagine residues in the channel prevent the passage ofNa+ ions by binding the oxygen of each water molecule as it passesby

B. Na+ ions are repelled by the positive charges at the entranceto the channel

C. Na+ ions cannot make contact with the carbonyl (C=O) groupson all four sides of the channel

D. The passage of Na+ ions is energetically unfavorable becauseone side of the channel is hydrophobic in nature

5. The acetylcholine receptor is different from other channelproteins we have discussed, such as the K+ leak channel,because

A. The acetylcholine channel is composed of a single polypeptiderather than multiple subunits

B. The acetylcholine channel transports Na+ ions against theconcentration gradient for sodium

C. The acetylcholine channel has a much smaller diameter thanother channel proteins

D. The acetylcholine channel transports ions with theirassociated shell of water molecules

E. The acetylcholine channel is always open, and never switchesto a closed conformation

6. After opening briefly along the axon of a neuron,voltage-gated ion channels switch to an inactivated conformationthat slowly returns to the original closed conformation of theprotein. This slow change in conformation, requiring about amillisecond, is important because

A. all of the ions that were transported across the membranewhen the ion channels were open must be actively transported backto the other side of the membrane, restoring the originalconcentration gradient, before the ion channels can open again

B. ATP hydrolysis is necessary to drive this energeticallyunfavorable change in conformation

C. it prevents the action potential from reversing direction andtraveling back toward the cell body of the neuron

D. the channel protein must be dephosphorylated in order tocomplete the transport process and return to the originalnonphosphorylated conformation

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BMS1052 Lecture Notes - Lecture 4: Resting Potential, Goldman Equation, Kurdistan Workers' Party

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