Drugs and the Nervous System

Question 1

Actions of general anaesthetics and side effects

Answer 1

Act mainly on the CNS to promote insensitivity
Given by inhalation/intravenously
Promote:
> analgesia > unconsciousness > loss of reflexes
Usually fat soluble = cross blood/brain barrier
Act on membrane receptors to decreases excitability of neurones
May affect ion channels
Side effects:
- nausea/vomiting - confusion
-dizziness - feeling cold

Question 2

Phases of anaesthesia

Answer 2

Induction - usually intravenous so quick effects
Maintenance - usually inhaled so easy to control but takes longer
Stages:
1. Analgesia
2. Excitement
3. Surgical anaesthesia (skeletal muscle relaxation)
4. Medullary paralysis (loss of respiratory/motor control)

Question 3

What are the types of anaesthetics?

Answer 3

Barbiturates eg. Thiopental (intravenous), useful fir brief procedures, rapid awakening but causes sedation
Non-barbiturates eg. Propofol (intravenous), rapid action and recovery but may cause convulsions
Gases eg. nitrous oxide to maintain anaesthesia with O2, isoflurane, desflurane, sevoflurane
Volatile liquids

Question 4

Anxiolytics/hypnotics

Answer 4

BENZODIAZEPINES
Increase GABA (inhibitory neurotransmitter) in the brain to prevent action potential
eg. midazolam (used in children), temazepam, diazepam
Side effects:
- amnesia - hypotension
- no analgesic effect - constipation
-interact with alcohol - can cross the placenta

Question 5

Neuromuscular blocking drugs

Answer 5

Block transmission in motor nerves
Relax vocal chords allowing insertion of tracheal tube - require assisted respiration
Prolonged muscle paralysis
Causes histamine release = bronchospasm
> non-depolarising: compete with ACh for nicotinic receports at neuromuscular junction
eg. Atracurium (rapid, short acting), Pancuranium (longer acting)
>depolarising: mimic ACh causing sustained depolarisation of muscle = paralysis
eg. suxamethonium

Question 6

Narcotic (opioid) analgesics

Answer 6

Act on the CNS to relieve pain
Euphoric eg. fentanyl, alfentanil, morphine (post-op)
Side effects:
- nausea/vomiting and constipation
- decreased breathing rate
- small risk of addiction

Question 7

Local anaesthetics, how they work and how they are administered

Answer 7

Used for local pain in or after surgery
Act on specific nerve pathways so shirt acting
Block transmission of nerve impulses carrying pain signals fir the nociceptors to the brain
Inhibit sodium entry through voltage sensitive sodium channels so block transmission of nerve impulse = no action potential
Administered:
> epidural - injection into epidural space affecting nerve roots
>intradermal/topical - relieves minor irritation/superficial pain

Question 8

Commonly used local anaesthetics

Answer 8

Lidocaine
Prilocaine: mixed with lidocaine in cream (EMLA), surface anaesthetic
Side effects:
- abnormal heart beat
- restlessness
- convulsions

Question 9

Anti-depressants

Answer 9

Increase levels if excitatory neurotransmitters in the brain
3 main types:
> tricyclic’s:
- eg. Imipramine, Doxepin
- may cause dry mouth, blurred vision, constipation
> Selective serotonin re-uptake inhibitors:
- eg. Fluoxetine, Paroxetine
- may cause headaches, nausea, dizziness, convulsions
>Monoamine oxidase inhibitors:
- eg. Phenelzine
- may cause nausea, dizziness, insomnia
- interact with tyramine containing foods eg. cheese, red wine

Question 10

Antiparkinsonian and Anticonvulsant drugs

Answer 10

Antiparkinsonian drugs:
- increase levels of dopamine
Anticonvulsant drugs:
- treat epilepsy by decreasing conduction of excitatory nerve impulses and/or increase GABA activity