# Ion Channels are responsible for the membrane potential

Document Sample

```					  Ion Channels are responsible
for the membrane potential.
When the
ion channel
is closed,
there is no
potential
difference
across the
cell
membrane
Ion Channels are responsible
for the membrane potential.
When the
cation-
selective ion
channel opens,
cations will
diffuse
through,
whereas
anions will not
Ion Channels are responsible
for the membrane potential.

The crossing-
over of cations
will create a
potential
difference
(voltage) across
the cell
membrane.
Simulation of membrane:
The Nernst Potential.
These qualitative demonstrations can be
put in more quantitative terms using the
Nernst Equation, which relates the
voltage V across the membrane which is
in equilibrium with the concentration
concentrations Co, outside, and Ci,
inside.
potentials:

Characterization of mechanisms of disease.
In This case:
- Learning more about a new ion channel that
causes neurons to die during anoxia.
reversal potentials
Characterization of a cation
current in anoxic neurons
Control (n=4)     NaCN 2 hr (n=6)
Back to the Axon & How it works

1. Ion Channels
2. Concepts of Diffusion
3. Basic Concepts of Electricity
4. How to Put 1-3 Together
Equivalent circuit of the
membrane

Cm = membrane capacitance (in pF)
Rm = membrane resistance
Em = Vm = Trans-membrane potential difference
Rm = 1/Gm      Gm = membrane conductance
Generation of the AP

The action potential is produced through the
sequential activation and inactivation of sodium
and potassium channels in the axon.

As the membrane depolarizes, Na channels
open, allowing an inward Na current to occur.
Then, K Channels open, to repolarize the cell
while Na Channels inactivate.
Generation of the AP
Generation of the AP
Generation of the AP
Generation of the AP
Generation of the AP
Generation of the AP
Propagation of the AP

Must now
take into
account the
3D geometry
of the Axon.
Propagation of the AP

Simplified
into an
equivalent
circuit that
can be
mathe-
matically
analyzed
Simulation:
AP Propagation
We have covered:
1. Ion Channels
2. Concepts of Diffusion
3. Basic Concepts of Electricity
4. How to Put 1-3 Together to get propagation of
nerve imulses

Now: Back to our patient…..
The Arterial Line is in …
Now we have to put the patient
to sleep: General Anesthesia
Now we have to put the patient
to sleep: General Anesthesia
Now we have to put the patient
to sleep: General Anesthesia
Now we have to put the patient
to sleep: General Anesthesia
How General Anesthesia is done:

1. Give patient something to make them sleep
(Anesthetic)
2. Give patient something to relax (muscle
relaxant)
3. Intubate / Ventilate
4. Monitor them throughout the surgery
General Anesthetics:
Are compounds that depress excitatory brain
activity, accentuate inhibitory brain activity, or both.
• Inhalational compounds
(Halothane, Isoflurane, Enflurane)

• IV compounds (Barbiturates,
Propofol, Ketamine, Opiates).
Mechanisms of action:
Inhalational Anesthetics
Textbook Explanation:                                         Halothane

“The exact mechanism by which inhalational anesthetics function is
not known. There appears to be a correlation between anesthetic
potency and lipid solubility (Meyer-Overton theory), suggesting that
these anesthetics likely affect the lipid matrix of nerve cell
membranes in the brain. Furthermore, NMR and electron spin
resonance studies indicate that anesthetics cause a local
disordering of the lipid membrane matrix, possibly decreasing the
number of molecules that alternate simultaneously between the gel
and crystalline states, and thereby altering membrane function”.
Mechanisms of action:
Intravenous Anesthetics

Diverse mechanisms of action, depending on the
drug (Benzodiazepines, Opiates, Propofol, etc…)
Diazepam       Fentanyl       Ketamine   Propofol
However, they all affect

Synaptic Activity.

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 157 posted: 5/27/2010 language: English pages: 32
How are you planning on using Docstoc?