Week 1 Neuroanatomy 2 of 4 Flashcards
What is the spread of depolarization?
Opening of Na+ channels generates local current circuit that depolarizes adjacent membrane, opening more Na+ channels
Picture:
at rest
stimulated (depolarization)
spread of depolarization
spread of depolarization

Saltatory conduction: node to node jumping of depolarization

Un-ionizes form enter and ionized form blocks


Explain the action potential of local anesthetics.

Local anesthetics slow the rate of depolarization of the nerve action potential such that the threshold potential is not reached. As a result, an action potential cannot be propagated in the presence of local anesthetic and conduction blockade results.
Examples of Local Anesthetics.
A.Procaine, cocaine, lidocaine, bupivacaine
Mechanism of Action of local anesthetics.
- Local anesthetics are weak bases present in un-ionized form (LA) and ionized form (LAH+)
- Un-ionized form (LA) penetrates the cell membrane.
- The pH is slightly acidic inside the cells -> more ionized form (LAH+) produces.
- Ionized form (LAH+) blocks the Na+ channels (from inside)
- Inhibit conduction of pain impulses from periphery to CNS (afferent fibers)
When using local anesthetics how many nodes of Ranvier be blocked to stop nerve conduction?
A.For myelinated axon, 2-3 nodes of Ranvier must be blocked to stop the nerve conduction.
______ the frequency of action potential, the _____ the nerve is blocked by LA
D.Greater the frequency of action potential, the faster the nerve is blocked by LA
LA must attach to the ____________ when it is in the inactivated state
D.LA must attach to the sodium channel when it is in the inactivated state
____________ fibers are more sensitive to LA.
D.Small diameter fibers are more sensitive to LA.
_________ are relatively resistant to LA
D.C-fibers are relatively resistant to LA
What are LA normally used in?
D.Uses: minor surgical procedures, spinal anesthesia
Height of Sensory Versus Motor Block After Subarachnoid (spinal) injection of Local Anesthetic
A.Sympathetic block is 2-6 dermatomes higher than sensory block
B.Motor block is 2 dermatomes lower than sensory block
What pH are agents with lower pKa are more un-ionized?
A.Agents with lower pKa are more un-ionized at pH=7.4
A.Un-ionized form is lipid soluble and can easily penetrate axon cell membrane –> faster conduction block
Look at slide 28 on Regional ANesthesia Neuroanatomy (couldnot copy and paste table)
What blocks sodium channels which will inturn block nerve conduction?
A.LA blocks sodium channels –> block nerve conduction
More lipid solubility means what?
B.More lipid solubility –> more easier to cross cell membrane
When local anesthetics are highly protein bound they will have what kind of duration?
C.LA that are highly protein bound will have prolong duration of action
What does pKa of a local anesthetic determine?
D.pKa of a LA determines the speed of onset
1.Lower pKa = faster onset
In regards to potency of local anesthetics, the greater the oil: water coeffcient __________________
A.Greater the oil : water coefficient, the greater the lipid solubility
The more lipid solubility of the LA; the greater its _______
B.The more lipid solubility of the LA; the greater its potency
Potency depends on what 5 things?
C.Potency also depends on
- Fiber size
- Myelination
- pH (acidic pH antagonizes block)
- Frequency of nerve stimulation
- Electrolyte balance ( hypokalemia and hypercalcemia antagonize block)
Potency of LA
look at slide 31 in Regional Anesthesia under Neuroanatomy (unable to paste chart)