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Lecture5
1. Select the correct statement(s) regarding the membrane potential
a) If one disabled all Na/K ATPase pumps in a cellular membrane,
the membrane potential would gradually slip to zero.
b) At the equilibrium potential for Na, the inward driving force
on Na due to its concentration gradient exactly counterbalances
the outward driving force due the electrical gradient.
c) At the resting potential, the outward driving force on K due its
concentration gradient exactly counterbalances the inward
driving force due to the electrical gradient.
d) Both (a) and (b) are correct.
e) Both (a) and (c) are correct.
2. Lectures 5-6: Action Potential I and IILectures 5-6: Action Potential I and II
Reading: Ch 4: action potentials
3. Sir Alan Lloyd Hodgkin
1914 - 1998
Sir Andrew Fielding Huxley
1917 -
1963 Nobel Prize for their discovery of the physiochemical events
underlying conduction of nerve impulses along neuronal axon
4. Action Potential - Brief all-or-nothing reversal in membrane
potential (spike), lasting on the order of 1 millisecond, that is
brought about by rapid changes in membrane permeability to Na+
and K+
ions.
5. Action Potentials - Once the threshold potential is crossed, depolarization
occurs via a positive feedback loop.
6. Events underlying the rising phase of the action potential
Figure 4-9 in 5th
edition (no figure in later editions)
7. Events underlying the falling phase of the action potential
Figure 4-9 in 5th
edition (no figure in later editions)
9. Voltage-gated Na+
channel - opens quickly (< .5 ms) in response to
depolarization, allowing Na+
to flow down its electrochemical gradient
into the cell. Responsible for rising phase of AP.
10. Voltage-gated K+
channel - opens more slowly in response to
depolarization allowing K+
ions to flow out of the cell down their
electrochemical gradient. Responsible for falling phase of AP and for
the after hyperpolarization, or AHP.
11. Voltage-gated Na+
channel can exist in
three states
(1) Deactivated Closed but
capable of opening in
response to depolarization
(2) Activated Open
(3) Inactivated Closed and not
capable of opening.
Inactivation can only be
removed by repolarization
to about -70mV.
Voltage-gated K+
channel can exist in
two states
(1) Deactivated
(2) Activated
See also: Smartsite/Resources/DeBello/Animations/voltage_gated_ct.swf
12. - absolute refractory period - a brief period during a spike in which
a second spike cannot be generated.
- relative refractory period - a brief period following a spike during
which a higher intensity stimulus is
needed to generate a second spike.
Refractory Period:
13. Na+
/K+
ATPase - the concentration gradients of Na+
and K+
are
restored by this electrogenic pump.
14. Propagation - action potentials propagate when locally generated
depolarizing current spreads to adjacent regions of
membrane causing it to depolarize.
16. Contiguous conduction – propagation of action potentials in
unmyelinated fibers by spread of locally generated depolarizing
current to adjacent regions of membrane, causing it to depolarize.
17. Myelin - a multilayered sheath of plasma membrane, derived
from specialized glial cells, that wraps around axonal
fibers and acts as an insulator to the flow of current.
Nodes of Ranvier - gaps in myelin insulation containing high
densities of voltage-gated Na+
and K+
channels.
18. Schwann Cells - myelin-forming glial cells in the peripheral nervous
system.
Oligodendrocytes - myelin-forming glial cells in the central nervous
system.
19.
20. Saltatory conduction - propagation of action potentials in myelinated
axons by jumping from node to node.
Figure 4-16 in
5th
edition only
21. Saltatory conduction - propagation of action potentials in myelinated
axons by jumping from node to node.
Demyelinating Diseases - certain diseases, such as multiple
sclerosis, result from the degeneration
Figure 4-16 in
5th
edition only
22. SUMMARY- The Action Potential
- Does not decay with distance.
(conducts down the length of the axon)
- Relies on voltage-gated, time-variant ion channels.
- Brief transient depolarization of the membrane.
- Does not vary in size.
- Decay with distance.
- Rely on non-voltage gated ion channels.
- Can be depolarizing or hyperpolarizing.
- Can vary in size.
In contrast, Graded Potentials:
