Medicine Notes Neurology Notes
These notes helped me achieve a mark of 76% in my neurology exam, which is the equivalent of a 1st. The notes are based on a series of 49 lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the nervous system (e.g. physiology o...
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Lecture 13
General anaesthetics
Examples
Injection/Intravenous Anaesthetics
Thipentone
Propofol (better than above)
Etomidate
Midazolam (sedative)
Ketamine (dissociative anaesthetic)
Inhalation anesthetics
Nitrous oxide
Isoflurane, desflurane, sevoflurane (halothane)
Effects
Loss of consciousness (not asleep)
Analgesia (many, but not all, produce pain relief)
Muscle relaxation (important in surgery)
Associated with loss of reflexes
Stages of anaesthesia (occur with increasing drug in brain)
STAGE 1- ANALGESIA
Drowsiness (not yet unconscious)
STAGE 2- EXCITEMENT
Loss of consciousness
Respiration is irregular, patient is thrashing (unwanted)
Need to get through this stage as quickly as possible
STAGE 3- SURGICAL ANAESTHESIA
Regular respiration
Decline in muscle tone
Loss of reflexes (planes
STAGE 4- MEDULLARY PARALYSIS
Too much general anaesthetic
Stop breathing=death
Drug combinations
Premedication- sedative
Rapid induction- propofol, thiopental (anaesthesia induced)
Maintenance of anaesthesia- isoflurane, nitrous oxide
Analgesic supplement- opiate (give during anaesthesia to stop pain going to spinal cord that causes adaptation which would cause pain after surgery)
Muscle relaxant- NMJ blocking agent e.g. atracurium
Muscarinic antagonist- Atropine (operations could increase secretion as PSNS stimulate, so atropine)
(Anticholinesterase)
Mechanisms of action (not certain)
No structure activity relationship
No obvious receptor they would all bind to
Unitary theory
Lipid theories
Membrane expansion
GA dissolves into lipid membrane and expands lipid
Membrane fluidity
GA goes into membrane and make more fluid
Problem as active ingredient in cannabis is highly lipid soluble but does not give GA effect, so theory wrong
Protein theory
Binding to hydrophobic regions
GA lipid soluble to get into membrane, then bind to proteins in lipid and disrupt function
Effects on ion channels
General
Not all GAs do all of these
Antagonists
Mechanisms
Enhance GABA(A) receptor function
Volatile anaesthetics- bind at interface between a & B subunits
IV anaesthetics- bind to B subunits (some donβt bind at all)
Activate K channels
(Two pore K channels- TREK, TASK)
Volatile and gaseous anaesthetics only
Block NMDA receptors
NO, xenon and ketamine (only on this receptor)
Other channels
Inhibit voltage-sensitive Ca channels
Inhibit voltage-sensitive Na channels
Glycine, nicotinic and 5-HT ligand gated ion channels
Effects on nervous system
Inhibit excitatory synaptic transmission
Decrease NT release (presynaptic)
Decrease action of NT (postsynaptic)
Decrease excitability (opening of K channels) of postsynaptic neurone
Enhance or inhibit inhibitory synaptic transmission
Injectable anaesthetics
Types
General
Barbiturates (thiopental)
Propofol
Imidazole derivatives (etomidate)
Steroids (veterinary)
Dissociative
Ketamine
Benzodiazepine
Midazolam (also used in endoscopy + analgesic (e.g. fentanyl) where full anaesthesia not required)
Advantages and disadvantages
Advantages
Easy too administered
Rapid/instant induction
Disadvantages
Complex pharmokinetics
Slow elimination
Side effects
Barbiturate anaesthetics (thiopental)
Distribution of blood (and therefore drug)
Brain (majority of CO; brain will equilibrate with drug)
Heart, lungs, liver, kidneys
Muscle and fat (if not exercising, get small amount)
Liver metabolism (for thiopentone=smallest)
Distribution of thiopentone following IV injection
Blood and brain equilibrate fairly quickly
Problem as stores are finite and so can get full (in fat etc.)
After 2 hours, lots of drug in body but barely any in blood, so little in brain
Repeated doses...
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These notes helped me achieve a mark of 76% in my neurology exam, which is the equivalent of a 1st. The notes are based on a series of 49 lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the nervous system (e.g. physiology o...
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