Neurons and Glia, Membrane Potential

Neurons

Communication cells in nervous system. Single cell

Glia

Support cells. Have more glia than neurons

Neurons

Communication cells in nervous system. Single cell

Glia

Support cells. Have more glia than neurons

Nerve fiber

Axon (+ myelin sheath, if present)

Nerve

A bundle of axons bound together by connective tissue in the PNS

Ganglia

Group of neuronal cell bodies in the PNS

Sensory receptors are found

by the dendrites of the afferent neuron

Afferent neuron

Sensory, unipolar, towards CNS

Interneuron

In the spinal cord, multipolar

Efferent neuron

Motor, multipolar, away CNS

Most numerous neurons

Interneurons

All of the following general statements are true about neurons EXCEPT:

A. An individual neuron can receive

information from multiple other neurons.

B. An individual neuron can transmit

information to multiple other neurons

C. A given neuron can be either a

presynaptic neuron or a postsynaptic

neuron.

D. A neuron can simultaneously release

more than one type of neurotransmitter.

E. A neuron receives information on its

axons and delivers it to other neurons

through its dendrites.

E. A neuron receives information on its

axons and delivers it to other neurons

through its dendrites.

An interneuron synapses with an afferent

neuron. In this 2 neuron sequence, the

interneuron would be considered a:

D. Postsynaptic neuron

E. Presynaptic neuron

D. Postsynaptic neuron

What is the function of oligodendrocytes and Schwann cells?

They form the myelin sheath for axons.

Current

Movement of electrical charge

Electrogenic

A process by which net charge is transferred to a different location

Potential difference (volts)

Difference in the amount of charge between 2 point

Membrane potential

Potential difference across the membrane

Resistance

Opposition to the movement of an electrical charge

If the resting membrane potential for a cell

is -70 mV (generally it is between -5 and -100 mV), what does that mean?

C. The inside is negative compared to the

outside

D. The outside is negative compared to

the inside

C. The inside is negative compared to the

outside

Membrane potentials in cells are determined primarily by three factors

1. The activity of pumps (e.g., Na-K ATPase and Ca++ transport pumps) that maintain the ion concentrations across the membrane

2. The concentration of ions on the inside and outside of the cell

3. The permeability of the cell membrane to those ions (i.e., ion conductance) through specific ion channels

What is the movement of ions in the Na-K ATPase

2K+ in and 3Na+ out

Is the Na-K ATPase electrically neutral or electrogenic?

Electrogenic

How much does the electrogenic nature of the Na-K ATPase contribute to the resting membrane potential (-70 mV)?

Only a small amount

What is the concentration of Na+ and K+ inside and outside the cell?

High Na+ outside and High K+ inside

What helps maintain these gradients for Na+ and K+?

Na-K ATPase

How can ions get across the plasma membrane?

1. Ligand-gated ion channels - Many

2. Voltage-gated ion channels - Many

3. Mechanical-gated ion channels - Not much

4. Leak channels

Closed when the membrane is at rest

At rest, the membrane is leaky, or somewhat permeable

K+

K+ leak channel, which is always

Open

Can K+ go in either direction through the leak channel?

Yes, but the net movement depends on the driving force

Electrical gradient and concentration gradient

First driving force when K+ Channels are open

Concentration gradient of K+

K+ moves out of the cell

Generates a potential difference

Second and opposite driving force when K+ Channels are open

Potential difference created by the efflux of K+

K+ moves back into the cell

The potential charges of K+ inside and out

Negative inside, positive outside

Equilibrium potential for K+ (EK)

-90 mV

How can we calculate the equilibrium potential for K+ (EK)?

Nernst equation

When the membrane is freely permeable to the ion

If the membrane is freely permeable to K+, at -90 mV, what happens to the movement of K+?

The amount of K+ exiting the cell due to the concentration gradient EQUALS The amount of K+ entering the cell due to the potential difference

If a neuron is permeable to K+ at rest, and the equilibrium potential for K+ is -90 mV, and the Na-K ATPase is electrogenic (makes the cell more negative), why is the resting membrane potential -70 mV instead of -90 mV, or even more negative?

The membrane is not freely permeable to K+ at rest

The membrane is very slightly permeable to Na+

Concentration gradient of Na+

Na+ moves inside of the cell

Potential difference of Na+

Na+ moves outside of the cell

The potential charges of Na+ inside and out

Positive inside, negative outside

Equilibrium potential for Na+

+60 mV

So the resting membrane potential takes into account the movement of other ions besides K+. How can we calculate the resting membrane potential?

Use the Goldman-Hodgkin-Katz (GHK) equation. Out/ In

This takes into account the equilibrium potential for K+,

Na+ and Cl- along with their relative permeabilities

Chlorine in the The Goldman-Hodgkin-Katz (GHK) equation

Flipped because chloride is negative charge. In/ Out

There are other ions inside and outside the cell besides K+, Na+ and Cl-. Why is their contribution to the membrane potential zero?

At rest the membrane is impermeable to these other ions

If you suddenly raised the extracellular concentration of K+, what would that do to its equilibrium potential, and hence the membrane potential?

A. EK would be less negative than -90 mV

B. EK would be more negative than -90 mV

C. EK would not change

A. EK would be less negative than -90 mV

If you suddenly raised the extracellular concentration of K+, what would that do to its equilibrium potential? (More or less negative)

Less negative then -90 mV

Depolarize

membrane potential becomes more positive than resting membrane potential (RMP)

Hyperpolarize

membrane potential becomes more negative than the RMP

Does raising the extracellular concentration of K+ cause the membrane to depolarize or hyperpolarize?

Depolarize

What happens to the membrane potential if a gated Na+ channel opens?

A. Depolarize

B. Hyperpolarize

A. Depolarize

What happens to the membrane potential if a gated K+ channel opens?

A. There is no change in the membrane potential from rest

B. Depolarize

C. Hyperpolarize

C. Hyperpolarize

The membrane if more permeable to K+

GO from -70mV to -90mV

Hyperpolarize

What maintains the concentration of Na and K in and out of the cell

The Na-K ATPase

If the cell membrane is permeable to Cl- (i.e there are some open Cl- channels), and there is no Cl- pump, what happens to the chloride concentrations inside and outside the cell?

They adjust until the equilibrium potential for chloride (ECl) equals the resting membrane potential

If Cl- was pumped out of the cell causing a large concentration gradient for Cl- influx thereby making ECl negative to the resting membrane potential, would opening a Cl- channel cause hyperpolarization or depolarization?

A. Hyperpolarization

B. Depolarization

A. Hyperpolarization

Concentration gradient of Cl-

Cl- moves inside the cell

Potential difference of Cl-

Cl- moves outside the cell

The potential charges of Cl- inside and out

Negative inside, positive outside

Is Cl- a depolarizing or hyperpolarizing current?

Hyperpolarizing

The [Ca++]o is 2 mM and [Ca++]i is 100 nM. The membrane at rest is impermeable to Ca++. If a Ca++ channel opens, does the membrane hyperpolarize or depolarize?

Depolarize

Concentration gradient of Ca++

Ca++ moves inside the cell

Potential difference of Ca++

Ca++ moves outside the cell

The potential charges of Ca++ inside and out

Positive inside, negative outside

Is Ca++ a depolarizing or hyperpolarizing current?

Depolarizing