Neurophysiology
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10 terms
Terms | Definitions |
|---|---|
 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 -1.2msec 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 incisors more The mental wears for first, then core |
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