Pharmacology of the neuromuscular system

what is the motor unit

motor nerve + muscle fibres it controls

how big is the gap between the nerve and the muscle?

60nm

what cell forms 'lids' over the junctional cleft?

Schwarnn cells

what are the 5 things drugs can interfere to modify synaptic transmission?

synthesis, storage, release, receptors, removal mechanism of NTs

what is the role of Ca2+ in neurotransmission?

Triggers release of synaptic vesicles (acetylcholine)

what causes calcium channels to open?

action potentials

what is CAT?

Choline Acetyl Transferase

what is the function of CAT?

synthesises acetylcholine (ACh)

what 2 compounds is ACh synthesised from?

choline + acetylchoenzyme A (AcCoA)

What does hemicholinium inhibit?

blocks uptake of choline (stops synthesis)

what does AH5183 (vesamicol) do?

blocks uptake of Ach into vesicles (prevents storage)

how can Mg2+ stop neuromuscular transmission?

they block voltage gated calcium ions

how does Botox (botulinum toxin) work?

blocks the process of exocytosis (prevents release)

Clostridium botulinum gives what drug?

botulinum toxin

if botox is ingested it can cause death, how?

stops contraction of diaphragm and intercostal muscles- breathing stops

What is blepharospasm? how is it treated?

involuntary tight closure of the eyelids- treated with small amounts pf botox

what is hyperhidrosis?

excessive sweating

what type of receptors to ACh activate after they diffuse across the junctional gap?

NAChR- nicotinic ACh receptors

Acetylcholine is the only NT in neuromuscular transmission, true or false?

true

in the synapse, an enzyme hydrolyses ACh, what is it called?

AChE- acetylcholinesterase

how long is an action potential?

2ms (0.02sec)

nicotinic receptors are what type of receptors?

ionotropic/ ion channel

Describe nicotinic receptors (3)

-5 subunits
-non-selective cation channel
-permeable to Na+ and K+

what is epp?

end plate potential- depolarisation of muscle membrane after NAChR activation

reversible competitive antagonist can act on NAChR to stop ACh binding and activating, T or F

true

what is tubocurarine?

competitive antagonist at NAChR

what is the clinical use of reversible competitive antagonists?

muscle relaxants

What does neostigmine do?

reverses the effect of general anaesthesia

why must patients be artificially ventilated when administered muscle relaxants?

they cannot breathe- diaphragm and intercostal muscle contraction is inhibited by muscle relaxant

Suxamethonium (succinylcholine) is an ______________ at NAChR

agonist

describe the structure of suxamethonium

2 molecules of ACh joined

How does suxamethonium prolong transmission?

it cannot be hydrolysed by AChE

how quick does suxamethonium take effect?

few sec

how does suxamethonium relax skeletal muscle?

refractory/recovery period is not allowed to occur- only one action potential goes through then no more