INTRODUTION TO A.N.S

BY: DR VARUN GUPTAJR-2 DEPT.OF PHARMAOLOGY

RMCH BLY

CONTENTS

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

INTRODUCTION

M

ENTERICSYSTEM

Nervous 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

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.

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.

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.

SOMATIC NERVOUS SYSTEM• It consist of two types of neurons1. 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.

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.

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.

Autonomic Nervous SystemAfferent 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.

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.

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

A.N.S

• ANS consists of three main anatomical divisions:-

Parasympathetic Nervous System

Sympathetic Nervous System

Enteric Nervous System

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

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

CONTD..

Ach releasing sites 1. Autonomic ganglia2. Postganglionic Parasympathetic fibers3. Postganglionic sympathetic fibers to sweat

glands4. Skeletal muscles (NMJ)5. Adrenal medulla6. Brain

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

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

CONTD..• Not all sympathetic post ganglionic 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)

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

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

Major Autonomic Receptor Types

Dopamine receptors D 1

D2

D3

D4

D5

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.

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.

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.

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.

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.

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.

Contd..

• Presynaptic alpha2 receptor activation – decreases NE release.

• Presynaptic beta 1&2 receptor activation – increases NE release

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.

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)”.

•THANK YOU

Smooth muscle of vessels residing in skeletal muscle