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Flashcards in Regulating neuronal excitability Deck (51):
1

Describe the difference between local and general anaesthetics?

Local anaesthetics produce regionalised inhibition of pain/sensory pathways, with no loss of consciousness

General anaesthetics depress cortical processing of pain/sensory signals, and result in loss of consciousness

2

What is the site of action for analgesics?

Peripheral nerves, spinal cord and brain cortex

3

What is the site of action for local anaesthetics?

Peripheral nerves and spinal cord

4

What is the site of action for general anaesthetics?

Brain cortex

5

What the first local anaesthetic?

Cocaine

6

Describe the broad action of local anaesthetics?

Drugs that reversibly block conduction of nerve impulses at the axonal membrane Interfere with influx of Na

7

Are local anaesthetics acidic or basic? Are they strong or weak?

Weak bases

8

How do the various local anaesthetic agents differ?

Differ in onset, duration and toxicity

9

List three classes of local anaesthetics?

Aminoesters Aminoamides Benzocaine

10

What is the difference in duration and metabolism between aminoesters and aminoamides?

Aminoesters are shorter acting and are hydrolysed by esterases Aminoamides are longer acting and undergo hepatic metabolism

11

What sorts of tissue can local anaesthetics affect?

Will affect all nerves and excitable tissue

12

What do local anaesthetics selectively bind to?

Na channels

13

How can systemic distribution of local anaesthetics be limited? Why is this important?

Local application Limits toxicity and makes them safer

14

Describe the difference in sensitivity to local anaesthetics between motor and sensory nerves?

Sensory nerves more sensitive (require less drug for same effect)

15

How can the level of nerve blockade achieved with local anaesthetics be altered?

Alter dose of drug

16

Which part of the Na channel do local anaesthetics interact with?

Transmembrane domain

17

Which part of the Na channel do toxins interact with?

Bind extracellular domain

18

What are the two mechanisms of action of local anaesthetics?

Hydrophobic Hydrophilic

19

What is the difference between the hydrophobic and hydrophilic mechanisms of local anaesthetics, in terms of speed and use dependence?

Hydrophobic: fast, non use dependent Hydrophilic: slow, use dependent

20

What limits the rate of onset/offset of local anaesthetics?

Diffusion across membranes (hydrophobic fast vs hydrophilic slow)

21

How does the size of nerves affect the rate of onset/offset?

Small nerves > smaller membranes > quicker access

22

Are sensory nerves or motor nerves larger?

Motor nerves are larger

23

What is the extracellular gate of the Na channel called?

m-gate

24

What is the intracellular gate of the Na channel called?

h-gate

25

Describe the hydrophobic mechanism for local anaesthetics?

A image thumb
26

Describe the hydrophilic mechanism for local anaesthetics?

A image thumb
27

Why are local anaesthetics that use the hydrophobic mechanism not use-dependent?

Hydrophobic > can cross membrane > doesn't matter whether gates are open or closed

28

Why are local anaesthetics that use the hydrophilic mechanism use dependent?

Hydrophilic> cannot cross membrane > requires gates to be open

29

What is the effect of local anaesthetics on axon membrane potential?

Stabilises axon membrane 

No change in resting membrane potential 

30

When is the effect of local anaesthetics more pronounced?

In a basic medium

31

Describe the effect of a basic medium on local anaesthetics?

Have a more pronounced effect

32

What determines the toxicity of local anaesthetics?

Proprtional to blood level

Dose determines effect

33

Describe some of the toxic cardiovascular effects of local anaesthetics?

Direct myocardial depression

Depression of vasomotor centre

Hypotension

34

Describe of the toxic CNS effects of local anaestheitcs?

Excitation

Tremor

Convulsion

Respiratory arrest

35

How can we tell if a local anaesthetic is acting in the wrong location?

Begin to see toxic side effects

36

Which side effects of local anaesthetics are not proportional to blood level?

Hypersensitivity reactions

37

Which side effect is particularly common with local anaesthetics?

Hypersensitivity reactions

38

Which forms of local anaesthetics are available over the counter?

Lozenge

Gels

39

Which forms of local anaesthetics are for professional use only?

Eye drops

Injection

40

Describe the four stages of general anaesthesia?

Stage 1: amnesia, euphoria

Stage 2: excitement, delirium, resistance to handling

Stage 3: unconsciousness, regular respiration, decreasing eye movement

Stage 4: respiratory arrest, cardiac depression and arrest

41

At which stage of general anaesthesia is surgery commenced?

Stage 3

42

How long does it take to progress from Stage 1 to Stage 3 once general anaesthetics are administered?

Seconds

43

What are the main methods of administration for general anaesthetics?

Inhalation

Intravenous injection 

44

What are some of the respiratory side effects of general anaesthetics?

Impaired ventilation

Depression of respiratory centre

Obstruction of airways

45

How can retention of secretions due to obstruction of airways be combatted under general anaesthesia?

Administer ant-MuscR

46

List the cardiovascular side effects of general anaesthetics?

Decreased vasomotor centre function

Depress contracility

Peripheral vasodilation

Cardiac arrythmias

Inadequate response to fall in BP or CO

47

When can the side effect of inadequate response to fall in BP under general anaesthesia become a problem?

If the patient must be moved upright for surgery

48

What are the theories of mechanism of action of general anaesthetics?

Lipid theory

Receptor interaction theory

49

Describe the the lipid theory of general anaesthetics?

Act by dissolving in the fatty fraction of brain cells and removing fatty constituents from them, thus changing activity of brain cells and inducing anaesthesia.

50

Describe the receptor interaction theory of general anaesthetics?

Inhibit excitatory receptors (glutamate, NMDA)

Enhance effects on inhibitory receptors (GABA, glycine)

51