Transmission in ANS (Acetylcholine)
Dr Asma Jabeen
Assistant professor
Learning Objectives
At the end of this session, the student should be able to:
•List the sites of release of acetylcholine as a chemical
transmitter
•Diagram the steps of acetylcholine synthesis
•Describe the actions of acetylcholine and classify the
cholinergic receptors according to these actions.
•Discuss the mechanism of actions of acetylcholine.
•Describe the removal of acetylcholine and the role of
cholinesterase enzyme.
Transmitters of ANS
Acetylcholine -- parasympathetic
transmitter.
 Nor epinephrine – sympathetic
transmitter.

Acetylcholine
Otto Loewi (1903-1961)
 Born in Germany, American Citizen
 1920 - Discovered 1st NT
 “Dreamed” the experiment
 Acetylcholine  “vagus substance”
 1936 - Nobel Prize
ACh
ACh
ACh
ANS neurotransmitters
SOMATIC NERVOUS SYSTEM
ACh
Striated
muscle
AUTONOMIC NERVOUS SYSTEM
Sympathetic
ACh
NE
ACh
ACh
Heart
Sm. mus.
Glands
Sweat,
PILOERECTOR
Glands,vasodilator
SK; MUS;
ACh
Parasympathetic
Ad. M.
ACh

E, NE

ACh
Heart
Sm. mus.
Glands
Cholinergic fibers:
 All preganglionic fibers are cholinergic in
both sympathetic and parasympathetic S.
 All or almost all postganglionic neurons
of parasympathetic system are cholinergic.
 Postganglionic sympathetic fibers to
sweat glands, piloerector muscle and
and few blood vessels are cholinergic.
Mechanism of transmitter secretion
Postganglionic autonomic nerve endings
are smaller than skeletal NMJ
 Mostly they end in connective tissue adjacent to the
effector cell.
 They have bulbous enlargements at the ends
called varicosities containing transmitter substance
and lots of mitochondria.
 AP →Calcium diffusion into cell →release
of transmitter from varicosities

Synthesis and removal of acetylcholine

Synthesized in terminal endings and
vericosities of cholinergic nerve fibers.
choline acetyltransferase
 Acetyl-CoA+ choline

Acetylcholine
Destruction:
After a few sec. split into acetate
ion and choline, catalyzed by acetylcholinesterase.
A cholinergic synapse
Choline
Na+, Cl-
Action
potential
Acetyl-CoA
Acetyl-Choline
Ca + +
Ca + +
Acetyl-Choline
Mechanism of action



The transmitter binds with specific
receptor on the effector cells
Receptor is on outside of a protein
molecule that penetrates the membrane.
This causes a conformational change
in protein molecule

Altered protein molecule excite or
inhibit the cell by:
Change of cell memb. permeability
 Activating or inactivating an enzyme
e.g. Adenyle cyclase → CAMP

Receptors in the parasympathetic system
Nicotinic receptor
Muscarinic receptor
Neuroscience, Sinauer Asssoc., Inc
Receptors of Autonomic nervous system
 General features
 Excitation and inhibition
Acetylcholine Receptors:
They are of two types:
1.
2.
Muscarinic receptors
Nicotinic receptors
Muscarinic receptors:
They are found on all effector cells
stimulated by postganglionic cholinergic
neurons of either parasympathetic or sympathetic
system.
Nicotinic receptors:
Found in autonomic ganglia at synapses
between pre and postganglionic neurons of both
sympathetic and parasympathetic NS.
Organs are
usually
innervated by
both systems
in opposing roles
Receptors on the effector ions
When the transmitter substance binds with the receptor,
this causes a confirmational change in structure of the
Protein molecule. In turn the alternate protein molecule
Excite or inhibit the cell most often by:
1. Causing a change in cell membrane permeability to
one or more ions
2. Activating or inactivating an enzyme attached to
the other end of the receptor protein( adenyl cyclase
- cAMP
Effects of Sympathetic and Parasympathetic
Systems
Parasympathetic Action
Organ
Heart
Action
heart rate
contractility
AV node conduction
Receptor
M
Gastrointestinal
Tract
motility
relaxes sphincters
M
Bronchioles
constricts
M
Male sex organs
erection
M
Bladder
contracts wall
relaxes sphincter
M
Pupil
constriction
M
Salivary glands
skin
secretion
blood flow
M
M
Autonomic Effects :

Eyes

Glands

Blood vessels

Heart

Lungs

Gut

Liver

Kidney

Bladder

Blood



Basal metabolism
Mental activity
Fat cells
Thank You