Transcript nervous3

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 class
1. Membranes of neuronal dendrites and cell bodies
a)
b)
c)
d)
e)
Have voltage-gated ion channels
Conduct electrical signals decrementally
Are myelinated
Receive synapses from other neurons
Have a resting membrane potential near -70 mV.
2. Dorsal root ganglia
a)
b)
c)
d)
e)
Have astrocytes
Have oligodendrocytes
House the cell bodies of sensory neurons
House the cell bodies of autonomic neurons
are part of the efferent pathway to muscle cells.
1QQ # 11 for 9:30 class
1. Membranes of neuronal dendrites and cell bodies
a)
b)
c)
d)
e)
Have ligand-gated ion channels
Conduct electrical signals non-decrementally
Are myelinated
Have graded potentials
Have a resting membrane potential near -70 mV.
2. Ventral roots
a)
b)
c)
d)
e)
Have astrocytes
Have oligodendrocytes
House the cell bodies of sensory neurons
House the cell bodies of autonomic neurons
are part of the efferent pathway to muscle cells.
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+
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?
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]
Now consider a
situation in which
only Na+ is
permeable.
Fig. 06.11
S3
Fig. 06.11a
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
Predict the
change in
membrane
potential if Na+
were added to the
extracellular fluid.
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.
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?
The Goldman 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+
Increase
PK+
Can the membrane
potential go more
negative than -90 mV?
S 15
Leak Channels
Gated Channels
….. Ligand-gated
….. Mechanically-gated
….. Voltage-gated
Electrogenic SodiumPotassium ATP-ase maintains
concentrations across
membrane
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.
3 Na+
2K+
S 16
Open Na+ channels,
Na+ goes _____
Open K+ channels,
K+ goes _____
S 17
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 18
Types and locations of Ion Channels
Sensory neuron
Leak Channels
Gated Channels
….. Ligand-gated
….. Mechanically-gated
….. Voltage-gated
Interneurons & Motoneurons
Intracellular
Recording
Electrode
End of Material For Test # 1
Begin Material For Test # 2
S 19
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.
How is the intensity of a
stimulus encoded by action
potential if all action potentials
have the same size (amplitude)?
S 20
S 21
Rising
Phase
Falling
Phase
Relative permeabilities
Duration of AP
Refractory periods
absolute RP
relative RP
Why does the
peak of the
action potential
not reach ENa?
Properties of V-gated
Na and K channels
account for the shape
of the action potential
and the refractory
periods.
S 22
To reset from inactivated state
to closed state, membrane must
repolarize.
Open at -55 mV
Membrane must repolarize to
“reset” Na+ Channels to be
capable of opening again.
Compare and contrast voltagegated Na and K channels based on
time to open and duration of
open time.
S 23
What accounts for the
afterhyperpolarization?
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.)
S 24
S 25
Who
Cares?
Novacaine, lydocaine, xylocaine,
All block voltage-gated Na+ channels
Prevent 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!