Cholinergic Physiology

Question 1

Ach Funtcions

Answer 1

Somatic efferents at NMJ
Pre-synaptic neurons in parasympathetic and sympathetic ganglia
Post-ganglionic neurons in parasympathetic system to activate smooth muscle and glands

Question 2

Nicotinic Receptors

Answer 2

Fast acting & Ionotropic
Located at NMJ and autonomic ganglia to cause muscle contraction and post-synaptic firing respectively
Three types: Muscular, Ganglionic, CNS

Question 3

Muscarinic Receptors

Answer 3

Slow acting and metabotropic
Located on effector tissue
5 subtypes: M1-M5
Odd numbers act through Gq to activate Inositol Phosphate
Even numbers act through Gi to inhibit Adenylate Cyclase
All post-synaptic, evens are pre too

Question 4

Muscarinic Subtypes

Answer 4

M1(Neural): Excitatory in CNS and glandular tissue
M2(Cardiac): Inhibitory in cardiac muscle
M3(Glandular and Smooth Muscle): Excitatory of these
M4(CNS): Inhibitory in CNS
M5(CNS): Excitatory in CNS

Question 5

Ach Synthesis

Answer 5

Choline is taken into nerve terminal via Choline Transporter

Choline Acetyltransferase adds and Acetyl group from AcetylCoA to choline to form Ach

Question 6

Ach Storage

Answer 6

Synthesised Ach is pumped into vesicles for storage by vesicular Ach transporter

Question 7

Ach Release

Answer 7

Depolerisation of the nerve terminal causes Ca influx.

This causes fusion of storage vesicles to the membrane and release of Ach by exocytosis

Question 8

Ach Degradation

Answer 8

Cholinesterase enzymes break Ach into Choline and Acetate

Question 9

Ach Reuptake

Answer 9

Choline is recycled and taken into nerve terminal once again by Choline transporter where it is made into Ach again

Question 10

Pre-Synaptic Modulation

Answer 10

Inhibitory M2: Ach release stimulates these receptors which inhibit Ach release
Adrenergic Receptors: Sometimes present on pre-synaptic terminals. They are inhibitory and dampen parasympathetic transmission during sympathetic input