Drugs and Somatic Motor Activity

Question 1

Identify the neurotransmitter released by somatic neurons at the neuromuscular junction

Answer 1

Acetylcholine is released

It binds to specific receptors on the muscle fibre membrane (sarcolemma), triggering a cascade of events that lead to muscle contraction

Question 2

Identify the receptor type expressed at the somatic neuromuscular junction:

Answer 2

Nicotinic acetylcholine receptors (nAChRs) are expressed at the neuromuscular junction

These ligand-gated ion channels (Nm subtype) open upon ACh binding, allowing Na⁺ influx and muscle depolarisation

Known as Nm (muscle-type nicotinic receptor)

Question 3

Explain why nicotinic agonists act as muscle relaxants and give an example of this type of drug:

Answer 3

Nicotinic agonists overstimulate nAChRs, causing persistent depolarisation.

This leads to depolarisation blockade, preventing further muscle contraction.

Example: suxamethonium – used for temporary paralysis during intubation or surgery

Question 4

Explain why nicotinic antagonists also act as muscle relaxants and give an example of this type of drug:

Answer 4

Nicotinic antagonists block ACh from binding to nAChRs,

Prevent depolarisation of the muscle fibre membrane, which means the muscle cannot contract.

The antagonists effectively paralyse the muscle, making them muscle relaxants

antagonists block the receptor from being activated

As a result, nicotinic antagonists such as tubocurarine and pancuronium prevent Ach mediated muscle contraction

Question 5

Explain the rationale behind the use of anticholinesterase drugs as an adjunct to surgery

Answer 5

Drugs which inhibit cholinesterase enzyme and reduce acetylcholine breakdown

Reversible anticholinesterases bind to the enzyme and are hydrolysed by it, but at a very slow rate compared to Ach

Clinical benefits:
- speeds up recovery as patient regains muscle function more quickly
- prevents respiratory complications

Question 6

Describe the role of neuromuscular blocking agents during surgery:

Answer 6

During surgery, neuromuscular blocking agents (NMBAs) are used to induce muscle relaxation

Depolarising blockers:

• suxamethonium
• initially produce a prolonged depolarisation, followed by relaxation

Non-depolarising blockers:

• pancuronium
• Competitively block nicotinic receptors at the neuromuscular junction (NMJ), preventing acetylcholine (Ach) from activating skeletal muscles

Question 7

What are the 3 possible channel states ?

Answer 7

Resting, open, and inactivate