|Neurophysiology||Dendritic Zone- free nerve endings ,most distal portion|
Axon- synapses with the CNS to transmit input to the brain
Cell Body- provides metabolic support for the entire neuron
The anesthetic alter the cell membrane to allow things to enter and exit the axolema
Nerve cell- -75 angstroms thick
Proteins primary element of membrane
Myelin wraps around the axon- created by Schwann cells
Nodes of Ranvier form gaps b/t adjoining Schwann cells- faster rate of conductivity because they hope from one to the next
|Nerve Conduction||nerve resting potential = -70 mV |
internal is negative and outer is positive before stimulus accures.
Slow depolarization - outside become more negative and the inside become more positive.
Threshold Potential- extremely rapid depolarization
Rapid depolarization- interior +40 and outside -70
Repolarization- electric potential become more negative inside and outside becomes more positive restoring to -70mv
depolarization: excitation leads to increased permeability to Na+ ions.and the transient widen to allow Na+ to pass through the channel.
This goes from resting to firing threshold -50 to -60mv (around 15mv)
Exposure to a nerve with local anesthetic raises the firing threshold
Depolarization lasts= .3 msec.
|Repolarization||takes longer because in need ATP energy to happen|
requires= .7 msec
during this time the action potential is terminated
absolute refractory period: the nerve is unable to respond to any stimulus regardless of the strangth.
Relative refractory period: a new impulse can be initiated at this time butonly by a stronger than normal stimulus , following the absolute refractory.
|Membrane channel|| Sodium pass easier then potassium |
Na+ is thinner when depolarization accurs
Na+ is fat and can't pass when nerve is at rest
So during depolarization sodium passes and during rest the potassium passes
|Impulse Propagation|| when needle enters it disrupts the resting potential|
internal goes from negative to postive -70(+40)
-Waves of depolarization can move in only one direction due to the absolute and relative refractory period.
|Impulse Spread||- unmyelinated nerve-creeping spread of impulses|
myelinated nerve-current leads from node to node- saltatoryconduction
-.3 msec 4 times faster
Test Question: myelinated nerve has saltatory conduction.
8-10 mm of nerve must be covered by anesthetic to insure block
to keep local anesthetic working we want decrease depolization and increase in repolarization
|Modes and Site||permeability to sodium ions eliminated no conduction when anesthetic is working|
BQ: displacement of calcium ions from the sodium channel resceptor site
binding of the LA molecule to this receptor site
blockade of the sodium channel
decrease in sodium conductivity
depression of the rate of electrical depolarization
|Active Forms of Local anesthetics||Most anesthetics are teritary amines except for Prilocaine which is an ester|
Lipophilic part isthe LA is the largest- aromatic ring
Hydrophilic part of LA is an amino derivative of ethyl alcohol or acetic acid
LA are aromatic in structure derived from benzoic acid/amine
intermediate chain- esters and amides
Local anesthetic used for injection are dispensed as salts, most commonly thehydrochloride salt, dissolved in either sterile water or saline in carpules they are salts! When being prepared in a lab they are basic
|Ph Variation||pH of normal tissue = 7.4 |
pH of inflammed tissue= 5.5
lower the pH more burning of tissue/ slow onset of anesthetic
You don't want to increase the pH od the solution because the local anesthetic base is unstable, it would percipitate out of alkalinized solution
Free base- neutral
cation- extra hydrogen
Free base allows the Na to move throughthe channel
You need free base to form the local anesthetic is responsible for diffusion through the nerve sheath.
The free base move into the axon the cation blocks the nerve, so you need both for anesthetic to work.
|Clinical Omplication of pH and local Anesthetic activity|| Sodium bisulfite- antioxidant|
Mental Bundle= (outside) fasciculi further away from nerve, first one reached, molar from IANB)
Core Bundle= fasciculi found closer to the center of the nerve, pulp not anesthetized first, intervates
The mental wears for first, then core