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Introduction to

AUTONOMIC NERVOUS SYSTEM

Nervous system---------------Anatomical classificationNervous system---------------Anatomical classificationCNS……….Brain……Forebrain………...Cerebrum (Telencephalon) (Prosencephalon) Diencephalon……….Thalamus (Interbrain) Epithalamus Metathalamus Hypothalamus Subthalamus Midbrain (Mesencephalon) Hindbrain………..Metencephalon……...Pons (Rhombencephalon) Cerebellum Mylencephalon……...Medulla oblongata Spinal cord

PNS……….Cranial nerve Spinal nerve

Nervous system---------------Functional classificationNervous system---------------Functional classificationSomatic nervous systemAutonomic nervous system………. Sympathetic nervous system Parasympathetic nervous system Enteric nervous system

• Somatic nervous system-

The part of nervous system which controls somatic/voluntary structures of the body. Its target structures are skeletal muscle and skin.

• Autonomic nervous system-

The part of nervous system which controls involuntary structures of the body. Its target structures are smooth muscle, cardiac muscle, glands (exocrine) and mucus membrane of viscera.

Autonomic vs. Somatic NS

• Somatic nervous system– excitation of skeletal muscle– consciously perceived sensations– one neuron connects CNS to organ

• Autonomic nervous system– involuntary inhibition or excitation of smooth muscle,

cardiac muscle or glandular secretion – unconsciously perceived visceral sensations – two neurons needed to connect CNS to organ

CharacteristicSomatic Nervous

SystemAutonomic Nervous System

EffectorsVoluntary(skeletal) muscle

Smooth muscle, Cardiac Muscle, Glands

General functionAdjustment to

external environment.

Adjustment within the internal environment (homeostasis)

Number of neurons fromCNS to effector

1 2

Ganglia outside the CNS 0 Chain ganglia, collateral ganglia or terminal ganglia

Neurotransmitter Acetylcholine Acetylcholine, adrenaline, noradrenaline

Effect of nerve damage onthe effector

Paralysis and muscle wastage (atrophy)

Effector remains functional but not able to quickly respond to the changing needs of the body.

Autonomic vs. Somatic• Somatic NS motor pathway only contains one neuron.• Autonomic NS motor pathway is a 2 neuron pathway

• Endocrine system and autonomic nervous system control internal environment of the body. They bring about fine internal adjustments necessary for the optimal internal environment (milieu interior of Claude Bernard/homeostasis of Canon) of the body.

• These control effect is extremely rapid, widespread and occurs at subconscious level.

• Distribution of autonomic nervous system occurs through somatic nervous system.

• ANS is controlled by hypothalamus and it receives input from limbic system.

Autonomic nervous system has 3 subdivisions-1. Sympathetic nervous system

2. Parasympathetic nervous system

3. Enteric nervous system Sympathetic and parasympathetic division of ANS produce opposite effects in most organs, thus considered as physiological antagonists. However they operate in conjunction with one another and it is the balance in activities that maintains a stable internal environment.

Exception: Both sympathetic and parasympathetic increase salivation.

Enteric nervous systemEnteric neurons form plexuses that surround and extend along the length of the gut, including stomach, small and large intestines.

Enteric system activate coordinated contraction of smooth muscles to cause peristaltic constriction of the gut.

Most of enteric nervous system functions independently of higher CNS control.

ANS has motor/efferent component and

sensory/afferent components.

Motor componentsThey represent GVE functional components.2 sets of neuron which synapse at ganglion.

1. Preganglionic neuron/1st set/primary neuron2. Postganglionic neuron/2nd set/secondary neuron

Target structure-Target structure-•Smooth muscle•Cardiac muscle•Glands (exocrine)

GVEGVE

GVEGVE

Preganglionic neuron• Cell body in brain or spinal cord • Axon is myelinated type B fiber that extends to autonomic ganglion• Sympathetic preganglionic neurons are located in lateral horn of

T1-L2/L3 spinal segments------THORACOLUMBAR OUTFLOWTHORACOLUMBAR OUTFLOW• Parasympathetic preganglionic neurons are located partly in the

brain stem in connection 3rd, 7th, 9th and 10th cranial nerves and partly in S2, 3, 4 spinal segments---------------------CRANIOSACRAL CRANIOSACRAL OUTFLOWOUTFLOW

Postganglionic neuron• Cell body lies outside the CNS in an autonomic ganglion• Axon is unmyelinated type C fiber that terminates in a visceral

effector

Structure of autonomic ganglion

Connective tissue capsule

Cell bodies of post ganglionic neurons

Interneurons – SIF cells

Satellite/capsular cells

Nerve fibers-Pre- and postganglionic fibers

and fibers traversing the ganglion without synapse

Postganglionic neuron• Sympathetic postganglionic neuronsSympathetic postganglionic neurons

Lateral (paravertebral) ganglia- Ganglionated sympathetic trunk

Subsidiary ganglia

Collateral (prevertebral) ganglia Celiac ganglion

Superior mesenteric ganglion

Inferior mesenteric ganglion

Aorticorenal ganglion (renal)

Superior hypogastric ganglion

Terminal ganglia- Adrenal medulla

• Parasympathetic postganglionic neuronsParasympathetic postganglionic neurons

Collateral ganglia (cranial parasympathetic ganglia) Ciliary ganglion

Pterygopalatine ganglion

Submandibular ganglion

Otic ganglion

Terminal ganglia-close to or within wall of viscera

Cardiac plexusPulmonary plexusMyenteric plexusSubmucosal plexusInferior hypogastric (ganglion) plexus

Sensory componentsThey represent GVA functional components.

• Sympathetic sensory component- Their cell bodies are located within DRG of T1-L2/3 spinal nerves Conveys mainly visceral pain sensations from abdominal cavity

• Parasympathetic sensory component- Their cell bodies are located within- For cranial part -Sensory ganglia of facial, glossopharyngeal and vagus nerve

For sacral part -DRG of S2, 3, 4 spinal nerves

Convey- General visceral sensations- like nausea, hunger Sensations for normal visceral reflexes- like carotid sinus reflex, Hering Breuer’s reflex, micturition reflex and defecation reflex. Visceral pain sensations from some pelvic organs

Sympathetic nervous system(Adrenergic system, Thoracolumbar part of ANS/ Thoracolumbar outflow)

• It is the larger part of ANS• Presents definite anatomical entity• Widely distributed throughout body• Prepares body for emergency-nerve of emergency-works during stress and strain to fright,

fight or flight• A catabolic nervous system• Effect is widespread and produce a mass reaction• Works for today• Not essential for life

Components-• Efferent outflow from spinal cord• 2 Ganglionated sympathetic trunks (lateral ganglia)• Important branches• Plexuses• Subsidiary ganglia

Structures having only sympathetic supply- no parasympathetic supply:

Cutaneous viscera

JG cells of nephron

Pineal gland

Adrenal medulla

Follicular cells of thyroid gland

Efferent nerve fiber (sympathetic outflow)Efferent nerve fiber (sympathetic outflow)

Cell bodies of primary neuron in lateral gray horn of T1-L2/3 segment of spinal cord

Myelinated axon in anterior root………spinal nerve trunk……anterior ramus……..ganglionated sympathetic trunk through white rami communicantes (14/15 in number)

Fate of preganglionic fibers in the ganglion of sympathetic trunk-

• Some fibers make synapse with (cell bodies of postganglionic) neurons of corresponding ganglion. Post ganglionic fibers enter ventral ramus of spinal nerve through gray rami communicantes (31 in number). Distributed through spinal nerves to cutaneous viscera as vasomotor, pilomotor and sudomotor branches.

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

1

Subsidiary ganglia

deep seated viscera

• Some fibers leave the corresponding ganglion without making synapse as medial branch and synapse in subsidiary ganglia. These long preganglionic fibers are called splanchnic nerve. Postganglionic fibers from these subsidiary ganglia supply deep seated viscera.

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

Subsidiary ganglia

deep seated viscera

• Some fibers travel upward to reach upper ganglia. Here they synapse. Some postganglionic fibers return back to corresponding spinal nerve through gray rami communicantes and distributed to skin viscera. Some postganglionic fibers are distributed along blood vessels to important structures of head-neck region.

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

3

Subsidiary ganglia

deep seated viscera

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

43

Subsidiary ganglia

deep seated viscera

• Some fibers travel downward to reach lower ganglia. Here they may synapse. Some postganglionic fibers return back to corresponding spinal nerve through gray rami communicantes and distributed to skin viscera. Some postganglionic fibers are distributed along splanchnic nerve. Some preganglionic fibers leave the ganglion as medial branch of the ganglion called lumber or sacral splanchnic nerve which synapse with subsidiary ganglia and distributed to viscera.

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

34

5

Subsidiary ganglia

deep seated viscera

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

34

6

5

Subsidiary ganglia

deep seated viscera

Splanchnic nerves-Splanchnic nerves-Sympathetic splanchnic nerve-

• Thoracic splanchnic nerve Greater splanchnic nerve-T5-9 ganglia

Lesser splanchnic nerve-T10-11ganglia

Lowest/least splanchnic nerve-T-12 ganglia

• Lumbar splanchnic nerve

• Sacral splanchnic nerve

Parasympathetic splanchnic nerve-Pelvic splanchnic nerve

(Nervi erigentes)

Ganglionated sympathetic trunk-Ganglionated sympathetic trunk-• Paravertebral in position

• Extends from base of the skull to 1st coccygeal vertebra---

where 2 trunks unite to form coccygeal ganglion/ganglion impar

• Initially number of ganglia of each sympathetic trunk corresponds with number of spinal nerve. (31 each)

• Later a number of fusion occurs. Ultimately the trunk presents- 3 ganglia in cervical region- Superior, Middle and Inferior 11/12 ganglia in thoracic region 4/5 ganglia in lumbar region 4/5 ganglia in sacral region

• Superior cervical ganglion is formed by fusion of upper 4 cervical ganglia

• Middle cervical ganglion is formed by fusion of 5th and 6th cervical ganglia

• Inferior cervical ganglion is formed by fusion of 7th and 8th cervical ganglia

• Sometimes inferior cervical and 1st thoracic ganglia fuse to form cervicothoracic/stellate ganglion

DCP

SCP

SupCervicalGanglion

MiddleCervicalGanglion

InfCervicalGanglion

EC Br

Pharyngeal Br

IC Br

Vertebral Artery Br

Subclavian Br

Thyroid Br

Tracheal Br

Esophageal Br

Ansa subclavia

G

R

C

Rami communicantes-Each of T1-L2/3 gangliaT1-L2/3 ganglia is connected to ventral ramus of corresponding spinal nerve

through 2 bundles of nerve fibers.

1. White rami communicantes: the lateral bundle containing myelinated preganglionic nerve fibers. 14/15 in number.

2. Gray rami communicantes: the medial bundle containing unmyelinated postganglionic nerve fibers. 31 in number.

Rest of the gangliaRest of the ganglia are connected to ventral ramus of corresponding spinal nerve only through gray rami communicantes.

Parasympathetic nervous systemParasympathetic nervous system(Cholinergic system, Craniosacral part of ANS/Craniosacral outflow)

• It is the smaller part of ANS• Presents no definite anatomical entity• Less widely distributed throughout body (pre-post ratio-1:3)• Conserves and restores energy -nerve of tranquillity• Anabolic nervous system• Effect is localized and produce isolated effects• Works for tomorrow• Essential for life

Efferent pathway

NUCLEUS CRANIAL NERVE GANGLION THROUGH TARGET

EDINGER WESTPHAL

NUCLEUS

C3:

OCCULOMOTOR NERVE

CILIARY

GANGLION

SHORT CILIARY NERVE •CONSTRICTOR PUPILLAE

•CILIARY MUSCLE

LACRIMATORY

NUCLEUS

C7:

FACIAL NERVE

PTERYGOPALATINE GANGLION

LACRIMAL NERVE •LACRIMAL GLAND

•Other glands

SUPERIOR SALIVATORY

NUCLEUS

C7:

FACIAL NERVE

SUBMANDIBULAR GANGLION

LINGUAL NERVE •SUBMANDIBULAR GLAND

•SUBLINGUAL GLAND

INFERIOR SALIVATORY

NUCLEUS

C9:

GLOSSOPHARYNGEAL NERVE

OTIC GANGLION AURICULOTEMPORAL NERVE

PAROTID GLAND

DORSAL NUCLEUS

C10:

VAGUS NERVE

ORGAN WALL

(Intramural ganglion) -

•SMOOTH MUSCLE

•CARDIAC MUSCLE

•GLANDS

Cranial outflow

For vagus nerve

Preganglionic myelinated fibers synapse in neurons of terminal ganglia lying close to or within organ wall.

Terminal ganglia are located in-

• Cardiac plexus

• Pulmonary plexus

• Myenteric plexus

• Submucosal plexus

Postganglionic unmyelinated fibers supply heart, lung, foregut and midgut portion of alimentary tract.

Sacral outflow

Cell bodies of preganglionic neurons lie in the gray matter of S2, 3, 4 spinal segments.

Myelinated preganglionic fibers….enter anterior root…sacral nerve trunk……leave sacral nerve and form pelvic splanchnic nerve (nervi erigentes).

Pelvic splanchnic nerve ultimately synapse in ganglia in the hypogastric plexuses (close to target structure). Post ganglionic unmyelinated fibers supplies pelvic viscera and hindgut part of alimentary tract.

Pre-post ratio-1:3

ANS Neurotransmitters

• Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released

• Adrenergic

• Cholinergic

Ach

Ach

Ach

Ach Ach

Ach

Epinephrine

NorepinephrineNeurotransmittersNeurotransmitters

Everywhere

Adrenal medulla

Sweat gland

Everywhere

M receptor

N receptor

N receptor

N receptor

A>B receptor

B>A receptor

M receptor

N receptor

Receptors•Adrenergic receptors- Alpha (A) receptor- A1-------for contraction A2 Beta (B) receptor- B1-------in heart B2-------for relaxation•Cholinergic receptors Muscarinic (M) receptor- M1 M2 M3 Nicotinic (N) receptor-

NM

NN

Functions of ANSFunctions of ANS

Physiological Effects of the ANS

Hypothalamus

• Some organs have only sympathetic innervation– sweat glands, adrenal

medulla, arrector pili mm & many blood vessels

– controlled by regulation of the “tone” of the sympathetic system

• Most body organs receive dual innervation– innervation by both

sympathetic & parasympathetic

• Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels

Sympathetic nervous system

Parasympathetic nervous system

Difference between sympathetic and parasympathetic nervous system

Sym Para

Anatomical entity

Efferents

•Outflow

•Preganglionic neuron

•Ganglia

•Preganglionic fibers

•Pre-post ratio

•Action

•Anabolic/catabolic

•Works for

•Postganglionic transmitter

•Nerve of

•Necessity

Afferents

Central control

Horner’s syndrome• Miosis• Ptosis (slight)• Enophthalmos• Anhydrosis• Vasodilatation of skin arteriole• Loss of ciliospinal/ pupillary skin reflex

Cause: due to interruption of sympathetic nerve supply to the head and neck region.

Types:1. Central Horner’s syndrome2. Preganglionic Horner’s syndrome3. Postganglionic Horner’s syndrome

• Argyll Robertson pupil

• Adie’s tonic pupil syndrome

• Frey’s syndrome

• Crocodile tear syndrome

• Hirschsprung’s disease (megacolon)

• Atonic, automatic and autonomous bladder

T1-L2/3 spinal nerve

Cervical Spinal nerve

Below L2/3Spinal nerve

12

34

5

6

Subsidiary ganglia

deep seated viscera