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1QQ#11 for 10:30
Revise two of the following misleading statements.
Your revision cannot consist of a “not” statement.
1. Retrograde axonal transport limits the rate of
axonal regeneration to 1-2 mm/day.
2. The cell body of an afferent neuron is located in
the ventral root.
3. Microglia are a component of the blood-brain
barrier.
4. The neural crest consists of cells, some of
which will become somatic motoneurons.
1QQ#11 for 11:30
Revise two of the following misleading statements.
Your revision cannot consist of a “not” statement.
1. Anterograde axonal transport limits the rate of
axonal regeneration to 200 mm/day.
2. The cell body of an interneuron is located in the
dorsal root ganglion.
3. Microglia adjust the concentration of ions and
neurotransmitters in the interstitial fluid
surrounding neurons of the CNS.
4. The neural crest consists of cells, some of
which will become interneurons.
Topics covered with board
drawings
Axonal regeneration
• Peripheral vs central
• Role of growth cones
• Timecourse of recovery
• Wallerian degeneration
• Schwann cells and
Schwann tubes
• CNS and spreading
necrosis
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
Squid
Giant
Axon
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.
Equilibrium potential = Nernst potential = diffusion potential
Fig. 06.10e
E ion+ = 61/Z log ([conc outside]/ [conc inside])
E K+
E K+
= 61/1 log (5/150)
= -90 mV
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?
S2
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]
S1
Equilibrium potential = Nernst potential = diffusion potential
Fig. 06.10e
Predict the change
in membrane
potential if K+ were
added to the
extracellular fluid.
E ion+ = 61/Z log ([conc outside]/ [conc inside])
E K+
E K+
5 mM
= 61/1 log (5/150)
= -90 mV
150 mM
50 mM
K+
What hormone regulates the levels of Na+ and K+ in extracellular fluid?
S3
Fig. 06.11a
Now consider a
situation in which
only Na+ is
permeable.
S4
Fig. 06.11b
S5
Fig. 06.11c
S6
Fig. 06.11d
S7
Equilibrium potential for Na+
Fig. 06.11e
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.
1QQ#12 for 10:30
Revise two of the following misleading statements.
Your revision cannot consist of a “not” statement.
1. Ligand-gated ion channels are found
exclusively in the axonal membrane.
2. Leak channels are found only at the distal tips
of sensory neurons.
3. Trigger zones and axons hillocks are the sites
which convert action potentials to graded
potentials.
4. Graded potentials are conducted nondecrementally and are well suited for longdistance signalling.
1QQ#12 for 11:30
Revise two of the following misleading statements.
Your revision cannot consist of a “not” statement.
1. Ligand-gated ion channels are found
exclusively in the membrane of dendrites.
2. Leak channels are found only at the distal tips
of efferent neurons.
3. Trigger zones and axons hillocks are the sites
where action potentials are converted to graded
potentials.
4. Action potentials are conducted nondecrementally and are well suited for longdistance signaling.
Test 1 Monday
• Thermoregulation
• Glucose homeostasis
• Negative feedback, positive feedback,
feedforward
• Endocrine System and endocrine
disorders
• Reflexes. Neurons and glial cells
• Equilibrium potentials and Resting
Membrane potential.
Comprehensive list of topics at http://webs.wofford.davisgr/bio342/test1study2012.htm
S8
Electrical and
concentration gradient
driving forces for
Sodium and Potassium
Size and
Direction
of Arrows
show
driving
forces!
What would
happen to
membrane
potential if
suddenly PNa
became very
great?
How can the
membrane
become
suddenly more
permeable to
Na+?
The G-H-K Equation!
Why is resting
membrane
potential closer
to EK than ENa?
How does the membrane potential
change if
1) permeability to sodium increases
2) Permeability to potassium increases
S9
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 10
At RMP, some Na+ leaks in, some K+ leaks out.
S 11
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 12
Animations of the
Origin of Resting Membrane Potential
Animation of Resting Membrane Potential (single ion)
Origin of Resting Membrane Potential and intracellular recording
YouTube animation of Na-K-ATPase, Sodium Co-transporter, and K Leak channels
S 13
S 14
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?
Increase
PNa+
Can the membrane
potential go more
negative than -90 mV?
Increase
PK+
Increase
PK+
How do ions get across the membrane? Ion channels!