Cholinergic Pharmacology 1

Question 1

What is the division of the peripheral nervous system?

Answer 1

Sensory <peripheral> Motor</peripheral>

Somatic (to skeletal muscles) <motor> Autonomic (to smooth muscle, cariac muscle, glands)</motor>

Sympathetic <autonomic> Parasympathetic</autonomic>

Question 2

What is the role of neurotransmitters?

Answer 2

Conversion of electrical signal to chemical signal and to electrical signal again

Question 3

What are the neurotransmitters of sympathetic division?

Answer 3

Preganglionic Neuron: ACh

Preganglionic Neuron: NA

Question 4

What are the neurotransmitters of parasympathetic division?

Answer 4

Preganglionic Neuron: ACh

Postganglionic Neuron: ACh

Question 5

What is a synapse?

Answer 5

Junction between 2 neurons

Question 6

What is a synaptic cleft?

Answer 6

• Narrow gap between neurones
  
  • action potential can’t cross the synaptic cleft
    
    • neurotransmitters carry nerve impulses

Question 7

What is the difference between presynaptic and postsynaptic nervous system?

Answer 7

• Pre-synaptic neurone: a neurone sending impulse
• Post-synaptic neurone: a neurone receiving impulse

Question 8

What is synaptic stage 1?

Answer 8

• Action potential arrives at presynaptic membrane
• Voltage gated Ca2+ channels in the presynaptic membrane open, Ca2+ enter

Question 9

What is synaptic stage 2?

Answer 9

• Ca2+ cause synaptic vesicles to fuse with the presynaptic membrane, releasing ACh into synaptic cleft

Question 10

What is synaptic stage 3?

Answer 10

• ACh diffuses across synaptic cleft and binds to receptors (nicotinic or muscarinic) in the postsynaptic membrane

Question 11

What is synaptic stage 4?

Answer 11

• Nicotinic receptors: Na+ channels open
  
  • Na+ diffuse into the postsynaptic membrane, causing depolarisation initiating an action potential
• Muscarinic receptors: signalling from GPCR activated
  
  • changes function of target tissue

Question 12

What is synaptic stages 5&6?

Answer 12

• ACh esterase breaks down ACh
• Products diffuse back into presynaptic neurone where ACh is resynthesised using ATP from the mitochondria

Question 13

What are the sequence of events at the neuromuscular junction?

Answer 13

1. Neuron depolarisation causes action potential
   
   • travels down nerve to neuromuscular junction
2. Depolarisation at terminal causes influx of Ca2+ which triggers fusion of synaptic vesicles
   
   • release ACh
3. ACh diffuses across the synaptic cleft and binds to postsynaptic nicotinic ACh receptor located on muscle
4. Binding of ACh to NAChRs opens channels causing influx of Na+, depolarisation of the muscle and ultimately causes the release of Ca2+ from intracellular vesicles
   
   • contraction
5. ACh in synaptic cleft is hydrolysed (inactivated) by ACh esterase (AChE) and signal is terminated

Question 14

What are cholinergic drugs?

Answer 14

• Drugs that stimulate the parasympathetic nervous system
  
  • cholinergic agonists or parasympathomimetics
• Mimic the effects of ACh

Question 15

What are the general effects of cholinergic drugs on organ systems?

Answer 15

• Salivation
• Lacrimation
• Urinary incontinence
• Diarrhoea
• GI cramps
• Emesis