1 October 2010• Test # 1 Monday

• See Test 1 Study topics on website

• See supplemental powerpoint on EPI and NE posted to powerpoint folder.

• Today in class– Ionic basis of resting membrane potential– Role of sodium potassium ATPase– Ionic basis of action potential– Action potential conduction

• Lab next week: Measuring AP CV

1QQ # 11 for 8:30 class1. Membranes of neuronal dendrites and cell bodies

a) Have voltage-gated ion channels

b) Conduct electrical signals decrementally

c) Are myelinated

d) Receive synapses from other neurons

e) Have a resting membrane potential near -70 mV.

2. Dorsal root gangliaa) Have astrocytes

b) Have oligodendrocytes

c) House the cell bodies of sensory neurons

d) House the cell bodies of autonomic neurons

e) are part of the efferent pathway to muscle cells.

1QQ # 11 for 9:30 class1. Membranes of neuronal dendrites and cell bodies

a) Have ligand-gated ion channels

b) Conduct electrical signals non-decrementally

c) Are myelinated

d) Have graded potentials

e) Have a resting membrane potential near -70 mV.

2. Ventral rootsa) Have astrocytes

b) Have oligodendrocytes

c) House the cell bodies of sensory neurons

d) House the cell bodies of autonomic neurons

e) are part of the efferent pathway to muscle cells.

Fig. 06.10eEquilibrium potential = Nernst potential = diffusion potential

When the electrostatic force that impedes diffusion of K+ is exactly equal to the driving force favoring diffusion based on a concentration gradient. the membrane potential reaches an equilibrium at which the voltage is called Nernst Potential or Equilibrium Potential.

So which compartment corresponds to intracellular fluid?

E ion+ = 61/Z log ([conc outside]/ [conc inside])

E K+ = 61/1 log (5/150)E K+ = -90 mV

150 mM5 mM

K+50 mM

Predict the change in membrane potential if K+ were added to the extracellular fluid.

S 1

The Nernst Equation

• If the membrane is permeable to ONLY ONE ion species and you know the concentrations on both sides of the membrane, use the Nernst Equation to calculate the membrane potential.

Nernst potential for X = 61/Z log [Outside ] / [Inside]

S 2

Fig. 06.11Now consider a situation in which only Na+ is permeable.

Fig. 06.11aS 3

Fig. 06.11bS 4

Fig. 06.11cS 5

Fig. 06.11dS 6

Fig. 06.11eEquilibrium potential for Na+

E Na+ = 61/1 log (145/15)

E Na + = +60 mV

145 mM 15 mM

Extracellular Intracellular

So, given these concentrations of Na+ and a membrane permeable only to Na+, use Nernst equation to calculate what the membrane potential would be.

At the equilibrium potential, no net movement of Na+ because driving forces (concentration and electrical) are exactly equal and opposite.

Predict the change in membrane potential if Na+ were added to the extracellular fluid.

S 7

Electrical and concentration gradient driving forces for Sodium and Potassium

How does the membrane potential change if 1) permeability to sodium increases2) Permeability to potassium increases

Why is resting membrane potential closer to EK than ENa?

What would happen to membrane potential if suddenly PNa

became very great?

Size and Direction of Arrows show driving forces!

The Goldman Equation!S 8

The Goldman Hodgkin Katz Equation

• If you know the concentrations of ALL permeable ions and their relative permeabilities, you can calculate the membrane potential using the GHK Equation.

S 9

At RMP, some Na+ leaks in, some K+ leaks out.

S 10

Na+ K+ ATPase maintains the concentration gradients across

cell membranes

Animation of the Pump

What would happen to membane potentials and concentrations of Na+ and K+ if cells didn’t have this pump?

S 11

Animations of the Origin of Resting Membrane Potential

Animation of Resting Membrane Potential (single ion)

YouTube animation of Na-K-ATPase, Sodium Co-transporter, and K Leak channels

Origin of Resting Membrane Potential and intracellular recording

S 12

S 13

Which ion moving in which direction (into or out of cell) is responsible for depolarization and overshoot? Which ion moving in

which direction (into or out of cell) is responsible for repolarization and hyperpolarization?

Can the membrane potential go more negative than -90 mV?

Increase PK+

Increase PNa+

S 14

Graded potentials are conducted decrementally for only a few millimeters, die out over distance and time, and are proportional to the size of the stimulus.

Leak ChannelsGated Channels….. Ligand-gated….. Mechanically-gated….. Voltage-gated

Electrogenic Sodium-Potassium ATP-ase maintains concentrations across membrane

2K+

3 Na+

S 15

Open Na+ channels, Na+ goes _____

Open K+ channels, K+ goes _____

S 16

Graded potentials are conducted no more than 2mm

Insect bites foot (stimulus).Sensory neuron produces graded potential in proportion to intensity of the stimulus.How is signal conducted to the brain?

S 17

Leak ChannelsGated Channels….. Ligand-gated….. Mechanically-gated….. Voltage-gated

Interneurons & Motoneurons

Sensory neuronTypes and locations of Ion Channels

Intracellular RecordingElectrode

S 18

End of Material For Test # 1

Begin Material For Test # 2

How is the intensity of a stimulus encoded by action potential if all action potentials have the same size (amplitude)?

What happens when the membrane is depolarized by more than about 15 mV?

Action potentials are all or nothing.Analogy of shutter release pressure on a camera, either trips shutter or not.

S 19

S 20

Relative permeabilitiesDuration of APRefractory periods

absolute RPrelative RP

Properties of V-gated Na and K channels account for the shape of the action potential and the refractory periods.

Why does the peak of the action potential not reach ENa?

RisingPhase

FallingPhase

S 21

To reset from inactivated state to closed state, membrane must repolarize.

Compare and contrast voltage-gated Na and K channels based on time to open and duration of open time.

Open at -55 mV

Membrane must repolarize to “reset” Na+ Channels to be capable of opening again.

S 22

Explain the shape of the action potential based on the properties of Voltage-gated sodium and potassium channels (when and how long each type opens and closes.)

What accounts for the afterhyperpolarization?

S 23

S 24

Who Cares?

Novacaine, lydocaine, xylocaine, All block voltage-gated Na+ channelsPrevent action potentials, so stimulus does not result in an action potential in sensory neurons which would convey that information to the brain where person would be conscious of the stimulus!

S 25