8. Synthesis of Acetylcholine
Synthesized in terminal endings of cholinergic
fibers.
Most of the synthesis occurs in axoplasm
outside the vesicles.
10. Synthesis of Norepinephrine
Synthesis begins in axoplasm of terminal nerve
endings of adrenergic nerve fibers
But its completed in vesicles
In adrenal medulla 80 % of norepinephrine is
transformed in epinephrine
12. Continued…
After secretion of NE, it is removed from
the site by three ways:
1. Reuptake into adrenergic nerve endings by
active transport process (50 to 80 % of NE)
2. Diffusion away from the nerve endings into
the body fluids and then to the blood (remaining
NE)
13. Continued…
3. Destruction of small amount by tissue
enzyme:
Monoamine oxidase
Catechol-O-methyl transferase (occurs
mainly in liver)
14. Receptors on Effector Organs
To stimulate effector organ, neurotransmitters
must bind with receptors on the effector cells
Receptors are present outside the cell
membrane that penetrates cell membrane
Binding causes conformational change in the
protein
In turn, altered protein molecule excites or
inhibits the cell, most often by 2 means :
15. Continued…
1.Causing a change in the cell
membrane permeability to one or more
ions
2. Activating or inactivating an enzyme
attached to the other end of the receptor
protein
16. Types of Acetylcholine Receptors
Mainly 2 types
1.Muscarinic
Origin- Muscarine means poison from
toadstool
Activates only muscarinic receptors
Found on all effector cells stimulated by
parasympathetic nervous system
And also stimulated by cholinergic
neurons of sympathetic system
17. Continued…
2.Nicotinic
Found at synapses between the pre and
postganglionic neurons of both sympathetic and
parasympathetic system
Also present at nonautonomic nerve endings e.g.
neuromuscular junction in skeletal muscle
Activated by nicotine , not muscarine
NOTE: Acetylcholine can activate both of the
receptors.
