Transmission in the sympathetic system

Cholinergic transmission at the presynaptic neurone

1. Uptake of choline via transporter (CHT – rate limiting)
2. Synthesis of ACh and AcCOA
3. ACh stored within a vesicle
4. Depolarisation of terminal by action potential
5. Ca2+ influx through voltage activated Ca2+ channels
6. Ca2+ induces exocytosis of ACh
7. Activation of ACh receptors (nicotinic or muscarinic) cellular response
8. Degradation of ACh to choline and acetate by AChE – terminates transmission
9. Reuptake and use of choline

Nicotinic ACh receptors

• Ligand-gated ion channel activated by ACh and other drugs such as nicotine
• Made of 5 glycoprotein subunits (wide range) that form a channel
• Dozens of distinct subtypes

Muscarinic cholinoceptors

• GDPRs activated by ACh
• 5 subtypes, M1-M3 are the most important in the ANS

Noradrenergic transmission at the postsynaptic neurone

1. NA synthesis and storage