1QQ # 7: Answer one.1. For A-D list the four types of Glial Cells of the CNS and their

functions:A) B)C)D).E) Which type of neuron has its cell body in the PNS and an axon that enters the CNS?

2. These questions concern Menopause:A) Which hormones are found in excess in this condition?B) Which hormones are found deficient in this condition?C) If a woman elects to receive HRT, what hormone is being replaced?D) What are the risks associated with HRT?E) What are the risks of not replacing the hormone?

Fig. 06.03S 12

Orthograde =anterograde

retrograde

Axonal Transport

• Orthograde = Anterograde = from soma to terminals– slow……1-2 mm/day– fast …..200-400 mm/day (kinesin)

• Retrograde = from terminals to soma– fast….200-400 mm/day (dynein)

• What gets transported and why?• Axonal transport is too slow for rapid

signaling, so…

S 13

Who Cares?

Alayna Davis

October 1992 Age 5 October 31, 1992 October 1998

Regeneration in CNS?

So how can PNS axon regenerate and what prevents CNS axons from regenerating?

Bioelectricity is chemistry + physics

• Membrane potentials

• Ohm’s law

• Resting Membrane Potential

• The Nernst Equation

• The Goldman Equation

Who Cares?

Cortical vesicle exocytosis during fertilization leads to envelope elevationA, prior to fertilization (left), the proteinaceous vitelline coat of the sea urchin egg of Lytechinus pictus

is not visible in this differential interference contrast image.

Zimmerberg J et al. J Physiol 1999;520:15-21

©1999 by The Physiological Society

Virtues of SquidGiantAxon

Big questions:1)How do cells generate a resting membrane potential?2)What causes changes in the membrane potential?3)How do cells use these potentials? i.e. What is their purpose?

Fig. 06.09

Fig. 06.10a

There is a concentration gradient favoring the diffusion of Na+ and K+ through the selectively permeable membrane which has ion channels only for potassium.

At the start, is there an electrical driving force?

Fig. 06.10b

With K+ channels open, K+ diffuses down its concentraiton gradient, leaving behind CL- ions which are not permeable through the membrane. As more and more K+ move to the left, the compartment they leave becomes more and more negatively charged.

Is there an electrical driving force?

Fig. 06.10c

Fig. 06.10d

Soon, the accumulation of negative charges seriously impeded the diffusion of K+ as the electrostatic force builds up in opposition to the concentration driving force.

Fig. 06.10eEquilibrium potential = Nernst potential = diffusion potential

Eventually, the electrostatic force that impedes diffusion of K+ is exactly equal to the driving force favoring diffusion based on a concentration gradient. When these two driving forces are equal and opposite, the membrane potential reaches an equilibrium at which the voltage is called

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

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. 06.10eEquilibrium potential = Nernst potential = diffusion potential

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

What hormone regulates the levels of Na+ and K+ in extracellular fluid?

Fig. 06.11aS 3

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

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.

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 G-H-K Equation!S 8