HI

1. INTRODUTION TO A.N.S
BY: DR VARUN GUPTA
JR-2 DEPT.OF PHARMAOLOGY
RMCH BLY

2. CONTENTS
• CLASSIFICATION OF NERVOUS SYSTEM(N.S)
• NOMENCLATURE
• SOMATIC N.S
• AUTONOMIC N.S
• ENTERIC N.S
. SUMMARY

3. INTRODUCTION
ENTERIC
SYSTEM
3
Central nervous system
(brain & spinal cord)
Peripheral nervous system
(P.N.S)
Somatic or
Voluntary
Autonomic or
Involuntary
Sympathetic
system
Parasympathetic
system
13/07/2010

4. PERIPHERAL NERVOUS SYSTEM(P.N.S)
• The PNS (Somatic + A.N.S) consists of all
 Afferent (sensory) neurons- which carry nerve
impulses from sensory end organs in peripheral
tissues into the CNS.
 Efferent (motor) neurons- which carry nerve impulses
from the CNS to effector cells in peripheral tissues.
 The fibers that control voluntary movements are
somatic nerves.

5. NOMENLATURE
• Synapse is the junction across which a nerve
impulse passes from axon of a neuron to
dendrite of another neuron.
• Nerve fibers carrying the signal into a Synapse
are: presynaptic.
• Nerve fibers carrying the signal out of a
Synapse are: postsynaptic.

7. Contd..
• Ganglion is a group of nerve cells forming a
nerve center, especially one located outside
the brain or spinal cord.
• Nerve fibers carrying the signal into a
ganglion are: Preganglionic.
• Nerve fibers carrying the signal out of a
ganglion are: Postganglionic.

9. SOMATIC NERVOUS SYSTEM
• It consist of two types of neurons
1. Afferent(Sensory) neurons - carry information from
cutaneous & special sensory receptors in the peripheral
organs to the C.N.S.
2. Efferent(motor) neurons- conduct impulses from the C.N.S
to skeletal muscle only.
since the effect of motor neurons can be consciously
controlled, the motor part of somatic nervous system is
primarily concerned with the voluntary functions like
locomotion, respiration, posture and deep tendon reflexes.

10. Contd.
• Axons of somatic motor neurons extend from the CNS are
myelinated, they run uninterrupted without any ganglia or synapse
straight up to neuromuscular junction (NMJ).
• Neurotransmitter released by somatic nerves at NMJ is Ach.
• Stimulation of Nm (neuromuscular nicotinic receptors) by Ach
produces contraction of the skeletal muscle.

11. Contd..
• Cholinergic crisis- excessive stimulation of Nm receptors by Ach,
leads to initial fasciculations or jerks( due to persistant
depolarisation) followed by flaccid paralysis due to desensitization
of Nm receptors.
• Blockade of Nm receptors by drugs like d-tubocurarine leads to
progressive flaccid paralysis.
• Somatic nerve degeneration leads to paralysis or atrophy of
skeletal muscle.

12. Autonomic Nervous System
Afferent neurons – convey information from receptors located in the
viscera to the CNS.
 Efferent neurons – conduct impulses from the CNS to the effector
organs.
 Efferent responses of ANS are autoregulatory or involuntary in
nature.
 ANS regulates - contraction & relaxation of smooth muscles
- exocrine & some endocrine secretions
- heart rate
- blood pressure
- metabolic functions
 Section of the autonomic nerve or its complete degeneration leads
to denervation supersensitivity of autonomic receptors of the
organ supplied by that nerve.

13. Contd..
 Two neurons are required to connect the CNS and a visceral
effector cell of the ANS.
 All autonomic nerves have a relay center in between called
ganglion, which lies outside CNS.
• The first neuron in this sequence is called the preganglionic
neuron.
• The second neuron, whose cell body is within the ganglion,
travels to the visceral effector cell; it is called the
postganglionic neuron.

14. Differences between somatic and
autonomic nervous system
Somatic
• Skeletal muscles
• All Myelinated
• Ganglia Absent
• Neurotransmitter-
Acetylcholine
• On sectioning –
Paralysis and atrophy
Autonomic
• All other organs (visceral, etc)
• Preganglionic fiber Myelinated
• Ganglia Present
• Neurotransmitter –
Acetylcholine, Nor adrenaline
• On sectioning –
Activity maintained, no atrophy

16. A.N.S
• ANS consists of three main anatomical
divisions:-
 Parasympathetic Nervous System
 Sympathetic Nervous System
 Enteric Nervous System

17. Parasympathetic Nervous System
• cranio-sacral outputs
 The cranial part of the parasympathetic nervous
system innervates structures in the head, neck,
thorax, and abdomen (e.g., the stomach, part of the
intestines, and pancreas).
 The cranial parasympathetic fibers leave the CNS in
the oculomotor, facial, glossopharyngeal, and vagal
cranial nerves.
The sacral division (S2 to S4) of the parasympathetic
nervous system innervates the remainder of the
intestines and the pelvic viscera

19. CONTD..
• Parasympathetic preganglionic fibers are usually myelinated & long
• Parasympathetic postganglionic fibers are shorter in length & non
myelinated.
• Parasympathetic preganglionic fibers tend to synapse with only a very
little number of postganglionic parasympathetic fibers.
• Ramification of postganglionic parasympathetic fibers at the
neuroeffector junction is least diffused.
• Neurotransmitter – Ach

20. CONTD..
Ach releasing sites
1. Autonomic ganglia
2. Postganglionic Parasympathetic fibers
3. Postganglionic sympathetic fibers to sweat
glands
4. Skeletal muscles (NMJ)
5. Adrenal medulla
6. Brain

21. Sympathetic Nervous System (SNS)
 The preganglionic neurons of the sympathetic nervous system have
their cell bodies in the thoracic (T1-T12) and lumbar regions (L1 to
L2) of the spinal cord.
 Termed the thoraco-lumbar division.
 Just outside the spinal cord, preganglionic fibers communicate with
paravertebral chain of 22 sympathetic ganglia.
 These ganglia lie bilaterally on either side of the spinal cord, each
ganglia is connected with each other by the nerve trunk.
 Preganglionic fibers terminate in ganglia (paravertebral chains)
 Postganglionic sympathetic fibers innervate peripheral tissues

22. Contd..
• sympathetic ganglia lie close to the vertebral column.
• preganglionic fibers are generally short in length & are myelinated.
• Post ganglionic fibers are long & non-myelinated
• Preganglionic sympathetic fibers tend to synapse with a large
number of postganglionic fibers which in turn have a more diffused
ramification at neuroeffector junction.
• Neurotransmitter at sympathetic ganglia is Ach.
• All postganglionic sympathetic fibers release norepinephrine at
the neuroeffector junction.
• A few sympathetic ganglia lie near the organs innervated (e.g.,
(urinary bladder and rectum); thus these preganglionic fibers are
long and postganglionic fibers are short

23. CONTD..
• Not all sympathetic postganglionic neurons are
noradrenergic.
• Some are cholinergic; that is, they release acetylcholine
rather than norepinephrine, even though anatomically they
are sympathetic neurons.
• Exceptions:
• sweat glands
• some smooth muscles and vascular beds (piloerector
muscles & some blood vessels of skeletal musculature)

25. Differences Sympathetic Parasympathetic
Origin Dorsolumbar (T1 – L2 or
L3)
Craniosacral (3,7,9,10,S2-S4)
Distribution Wide Limited to head, neck, trunk
Ganglia Away from organs On or close to the organ
Postganglionic fibre Long Short
Fibre ratio
Pre:Post
1:20 to 1:100 1:1 to1:2 except enteric plexus
Neurotransmitter Noradrenaline (major)
Acetylcholine (minor)
Acetylcholine
Duration and
actions
NA stable, diffuses for
wider actions
Rapidly destroyed locally by AChE

26. Major Autonomic Receptor Types
Cholinoceptors
• Muscarinic M1
• Muscarinic M2
• Muscarinic M3
• Muscarinic M4
• Muscarinic M5
• Nicotinic NN
• Nicotinic NM
. Central nicotinic receptor
• Adrenoceptors
• Alpha1
• Alpha2
• Beta1
• Beta2
• Beta3

27. Major Autonomic Receptor Types
Dopamine receptors
D1
D 2
D3
D4
D5

28. Enteric Nervous System (ENS)
Organized collection of different neurons located in the wall of git.
 ENS function independently of CNS.
 Controls motility, exocrine and endocrine secretions and microcirculation of GI
tract.
 It is modulated by both the parasympathetic and sympathetic nervous system(dual
innervation)
 Parasympathetic cholinergic activity generally increases the motility of intestine (
while relaxing the sphincters).
 Sympathetic noradrenergic activity usually decreases the motility of the gut (
while contracting the sphincters).
 The preganglionic fibers make contact at the ENS ganglia in the myenteric and
submucosal plexus.

29.  Besides Ach & NE many other substances have been identified in the ENS
 Neuropeptide (NP)
 Substance P
 Serotonin (5HT)
 Dopamine (DA)
 Cholecystokinin (CCK)
 Under the influence of these substances , the plexus perform their
peristaltic and other functions and also coordinate motor activity in the
total absence of CNS control.
 HETEROTROPIC RECEPTOR INTERACTION
 where one neuron control the neurotransmitter release of the other
neuron.

30. CONTD..
• In intestine, there is an anatomical proximity of the sympathetic and
parasympathetic postganglionic neuron.
• The alpha2 receptors are located presynaptically on the cholinergic
neurons.
• NE released from adrenergic neuron activates the alpha2 receptors
located presynaptically on cholinergic neurons.
• This would ultimately inhibit the release of Ach from cholinergic neurons.

32. AUTONOMI INNERVATION FEW
EXCEPTIONS
.ONLY SYMPATHETIC (NO PARASYMPATHETIC)
INNERVATION- Radial .muscle of iris, smooth
muscles of eyelids, nictitating membrane,
pilomotor muscle, ventriular myoardium,
bladder neck(trigone)., seminal vesicle & vas
defrens.
.Only parasympathetic (no sympathetic)
innervation- circular muscle of iris, ciliary musle.
Larimal gland, muous membrane of G.I.T and
bronhial tree, panreati exorine glands,detrussor
muscle of bladder and erretile tissue of penis.

33. Contd..
Only adrenergic receptors ( but no sympathetic
innervation)- adipoytes (lipolysis), liver
cell(gluconeogenesis), skeletal muscle cells (glycolysis) do
have beta reeptors but no sympatheti innervation.
Only holinergic receptor(but no parasympathetic
innervation)-
Blood vessels have musrainic receptors but no
parasympathetic innervation.hence they respond only to
exogenous given Ach.
At salivary gland effect of both the system is complementary
to each other.

34. AUTORECEPTORS
 These are the receptors located in presynaptic membrane and serves
as a part of a negative feedback loop in signal transduction.
 Neurotransmitter released from nerve terminal acts on its presynaptic
autoreceptors and inhibits or increase its own release.
 This is called Homotropic receptor activation.
 Cholinergic receptors-
 M2 receptor located presynaptically decrease the Ach release on
activation.
 Presynaptic nicotinic receptors increase the Ach release.

35. Contd..
• Presynaptic alpha2 receptor activation –
decreases NE release.
• Presynaptic beta 1&2 receptor activation –
increases NE release

36. summary
• Peripheral nervous system has two components…
– Somatic
– Autonomic … which has two divisions…
• Sympathetic
• Parasympathetic
• Preganglionic fibres of all the three divisions (sympathetic ,
parasympathetic and somatic nervous system) releases Ach.
• Ganglia of both (sympathetic and parasympathetic) system contains
nicotinic receptor.
• Somatic NS does not contain peripheral ganglia.
• Postganglionic SYMPATHETIC nerve endings in ADRENAL MEDULA releases
NA & ADR. (Adrenal medulla is the only site where Adrenalin is released
as neurotransmitter).
• Postganglionic SYMPATHETIC nerve endings in RENAL BLOOD VESSELS
releases DA.

37. CONTD..
• postganglionic sympathetic nerve endings in
sweat gland releases Ach. (remember even
though fibres are sympathetic , they release
Ach).
• Major neurotransmiter at most of the post
ganglionic “sympathetic nerve ending” is “NA”
• All post ganglionic “parasympathetic nerve
endings” releases acetyl choline “(Ach)”.

38. •THANK
YOU

47. Smooth muscle of vessels residing in
skeletal muscle