Transcript A Neurosurgical Operation

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
cationselective ion
channel opens,
cations will
diffuse
through,
whereas
anions will not
Ion Channels are responsible
for the membrane potential.
The crossingover 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
gradient established by the
concentrations Co, outside, and Ci,
inside.
Utility of learning about Nernst
potentials:
Characterization of mechanisms of disease.
In This case:
- Learning more about a new ion channel that
causes neurons to die during anoxia.
Utility of learning about
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
mathematically
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.
Can be administered as:
• 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.