AUTONOMIC NERVOUS SYSTEM

Second year MBBS2013 - 14

• The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body.

• In most situations, we are unaware of the workings of the ANS because it functions in an involuntary, reflexive manner.

The ANS is most important in two situations:

1- In emergencies that cause stress and require us to "fight" or take "flight" (run away).

2- In no emergencies that allow us to "rest" and "digest".

• The autonomic nervous system provides an involuntary control of internal environment and the viscera.

• The two systems are anatomically separated form each other, but functionally they cannot perform their work independently, and they work with each other in an integrated manner

Peripheral Nervous System

• Somatic NSConsists of nerves

connected to sensory receptors and skeletal muscles

Permits voluntary action (writing your name)

• Autonomic NSPermits theInvoluntary functionsof blood vessels,Glands and internal organs e.g.:-

the bladder stomach heart

Characteristic Somatic nervous system

Autonomic N. system

Effectors Voluntary muscle Cardiac muscle glands, s. muscle

General functions Adjustment to external environment

Adjustment within internal environment

Numbers of neurons 1 2

Ganglia outside the CNS

------------ Chain ganglia, collateral ganglia or terminal ganglia

Neurotransmitter acetylcholine Acetylcholine, adrenaline, noradrenaline

Center Anterior Horn cells Lateral Horn cells

Comparison of Autonomic and Somatic Motor Systems

• Autonomic nervous system– Chain of two motor neurons

• Preganglionic neuron• Postganglionic neuron

– Conduction is slower due to thinly or unmyelinated axons

Pre-ganglionic

Ganglion

Post-ganglionic

Sympathetic N.S. Parasympathetic N.S.

Like the accelerator of your car

Like the brakes in your carSlows the body down to keep its rhythm

Mobilized the body for action

Enables the body to conserve and store energy

Preganglionic: short, synapse within the lateral & collateral ganglia

Preganglionic: long, synapse within the terminal ganglia

Postganglionic: long Postganglionic: short

Has a wide distributions Has a restricted distributions

Autonomic Nervous System• Often work in

opposition• Cooperate to fine-

tune homeostasis• Regulated by the

brain; hypothalamus, pons and medulla

• Can also be regulated by spinal reflexes; no higher order input

• Pathways both consist of a two neuron system

Preganglionic neuron autonomic ganglion postganglionic neuron target from CNS outside CNS

Fig. 45.34(TE Art)Hypothalamus activatessympathetic division ofnervous system

Heart rate, blood pressure,and respiration increase

Blood flow toskeletal musclesincreases

Stomachcontractions are inhibited

Adrenal medulla secretes epinephrine and norepinephrine

Sympathetic division

Fight or Flight, Dealing with stress

thoracolumber, intermediolateral column, T1 -L2

Parasympathetic division

Rest and Digest Craniosacral

S2-S4

Sympathetic nerve endings also activate the release of NE and E from the adrenal medulla

Enhances effects of NE from sympathetic nerve endings

Adds the effects of E to the overall arousal (“fight or flight”) pattern

The Autonomic System

Sympathetic

• Sometimes called the “thoracolumbar” division

• Short preganglionic neurons; long postganglionic neurons; ganglia are called the chain ganglia

• Preganglionic neurons secrete Ach onto nicotinic receptors

• Postganglionic neurons secrete NE on to a or b receptors

• Target tissues are smooth muscle, cardiac muscle, endocrine glands, brown fat

Parasympathetic•Sometimes called the “cranio-sacral division

•Long preganglionic neurons;

• short postganglionic neurons (often in the target organ)

•Preganglionic neurons secrete Ach on to nicotinic receptors

•Postganglionic neurons secrete Ach on to muscarinic receptors

•Target tissues are smooth muscle, cardiac muscle, exocrine glands, brown fat

Anatomical Differences in Sympatheticand Parasympathetic Divisions

Anatomical Differences in Sympatheticand Parasympathetic Divisions

Similarities between Sympathetic & Parasympathetic

• Both are efferent (motor) systems: “visceromotor”• Both involve regulation of the “internal” environment generally outside of our conscious control: “autonomous”• Both involve 2 neurons that synapse in a peripheral ganglion and Innervate glands, smooth muscle, cardiac muscle

CNS ganglion

preganglionicneuron

postganglionicneuron

glands

smoothmuscle

cardiacmuscle

Differences between Sympathetic & Parasympathetic

Location of Preganglionic Cell Bodies

ThoracolumbarT1 – L2/L3 levels of the spinal cord

CraniosacralBrain: CN III, VII, IX, XSpinal cord: S2 – S4

Sympathetic Parasympathetic

SympatheticCNS ganglion

short preganglionicneuron

long postganglionicneuron

target

ParasympatheticCNS ganglion

long preganglionicneuron

target

short postganglionicneuron

Differences between Sympathetic & Parasympathetic

Relative Lengths of Neurons

Parasympathetic

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Neurotransmitters

ACh, +

NE (ACh at sweat glands),+ / -, α & ß receptors

ACh, + / -muscarinic receptors

• All preganglionics release acetylcholine (ACh) & are excitatory (+)• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)

• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)

Sympathetic

• Excitation or inhibition is a receptor-dependent & receptor-mediated response

ACh, +

Overview of the Autonomic Nervous SystemDifferences between Sympathetic & Parasympathetic

Target TissuesParasympatheticSympathetic

• Organs of head, neck, trunk, & external genitalia

• Organs of head, neck, trunk, & external genitalia

• Adrenal medulla• Sweat glands in skin• Arrector muscles of hair• ALL vascular smooth muscle

» Sympathetic system is distributed to essentially all tissues (because of vascular smooth muscle)

» Parasympathetic system never reaches limbs or body wall (except for external genitalia)

Overview of ANSFunctional Differences

Sympathetic• “Fight or flight”• Catabolic (expend energy)

Parasympathetic• “Feed & breed”, “rest & digest”• Homeostasis

» Dual innervation of many organs — having a brake and an accelerator provides more control

The reflex arc

The autonomic reflex arc

The somatic reflex arc

Origin Lateral horn cells Anterior horn cells

Efferent Relay in autonomic ganglia outside the CNS.

Supply the effector organ directly.

Interneuron

------------------------ present

Effector organs

Smooth , cardiac muscles,glands

skeletal

Visceral Reflex Arc

Fig. 45.32(TE Art)

Viscera

Autonomicganglion

Postganglionic neuron

Autonomic motor reflex

Interneuron Dorsal rootganglion

Preganglionicneuron

Sensoryneuron

Spinalcord

Autonomic and Somatic Motor Systems

spinalnerve

dorsalramus

ventralramus

gray ramuscommunicans white ramus

communicans

sympatheticganglion

intermediolateralgray column

Structure of spinal nerves: Sympathetic pathways

Sympathetic Division of the ANS

somatic tissues(body wall, limbs)

visceral tissues(organs)

Sympathetic System: Preganglionic Cell Bodies• Preganglionic cell bodies in

intermediolateral gray• T1 — L2/L3• Somatotopic organization

intermediolateralgray columns

lateralhorn

T1 –L2/L3

Clinical Relevance» dysfunction due to cord injury» spinal nerve impingement & OMM» referred pain

Sympathetic System: Postganglionic Cell Bodies

Paravertebralganglia

Prevertebral ganglia• celiac ganglion• sup. mesent. g.• inf. mesent. g.

aorta

sympathetictrunk (chain)

1. Paravertebral ganglia• Located along sides of vertebrae• United by preganglionics into Sympathetic Trunk• Preganglionic neurons are thoracolumbar (T1–L2/L3)

but postganglionic neurons are cervical to coccyx• Some preganglionics ascend or descend in trunk

synapse atsame level

ascend tosynapse athigher level

descend tosynapse atlower level

Sympathetic System: Postganglionic Cell Bodies

Paravertebralganglia

Prevertebral ganglia• celiac ganglion• sup. mesent. g.• inf. mesent. g.

aorta

sympathetictrunk (chain)

2. Prevertebral (preaortic) ganglia• Located anterior to abdominal aorta, in plexuses surrounding its major branches• Preganglionics reach prevertebral ganglia via abdominopelvic splanchnic nerves

abdominopelvicsplanchnicnerve

Sympathetic Trunk Ganglia

Sympathetic System: Summary

T1

L2

4- somatic tissues(body wall, limbs)

visceral tissues(organs)

postganglionicsvia 31 spinal nervesto somatic tissues of neck, body wall, and limbs

sympathetictrunk

prevertebralganglia

2- Cardiopulmonary Splanchnics: postganglionic fibers to thoracic viscera

3- Abdominopelvic Splanchnics: preganglionic fibers to prevertebral ganglia, postganglionic fibers to abdominopelvic viscera

1- Cervical division

1- Cervical divisionOrigin: T1-2Course: preganglionic fibres reach the sympathetic

chain and then ascend upwards to relay in the superior cervical ganglion.

Postganglionic neuron: pass from ganglion to the following organs:-

• EYE: pupil dilatation, widening of palpebral fissure, exophthalmos, Vasoconstriction of eye b.v. and Relaxation of ciliary muscle.

• Salivary gland : trophic secretion, Vasoconstriction of its blood vessels and Squeezing of salivary secretion.

• Lacrimal gland: Trophic secretion and Vasoconstriction.• Face skin blood vessel: Vasoconstriction of (Pale color).• Sweet secretion: copious secretion.• Hair: erection due to contraction of erector pilae muscles..• Cerebral vessels: Weak vasoconstriction

Sympathetic Pathways to the Head

(2) Cardiopulmonary division

Origin: Lateral horn cells of upper 4-5 thoracic segments.Course: Preganglionic neurons reach the sympathetic chain to relay in

the three cervical ganglion and upper four thoracic ganglion. The postganglionic arise from these ganglia supply the following structures:-

• Heart: Increase all properties of cardiac muscle (contraction, rhythmicity, excitability, conductivity.

• Coronary vessels, its sympathetic supply. At first it causes vasoconstriction, and then it causes vasodilatation due to accumulation of metabolites.

• Bronchi: Broncho dilation, decrease bronchial secretions and vasoconstriction of pulmonary blood vessels.

Sympathetic Pathways to Thoracic Organs

3- Splanchnic division

Origin: lateral horn cells of the lower six thoracic and upper four lumber segments.Course: Preganglionic neurons originate from these segments reach the sympathetic chain

where they pass without relay, and then they divided into two branches:(1) Greater splanchnic nerve (2) Lesser splanchnic nerve.

Greater splanchnic nerve:• Origin: Preganglionic nerves fibers emerge from lateral horn cells of lower six thoracic

segments and then relay in the collateral ganglion in the abdomen.• Course: Postganglionic nerve fibers arise from these ganglia (celiac, superior mesenteric and

inferior mesenteric ganglia) and supply the abdominal organs causing the following effects:• Vasoconstriction: of most arteries of stomach, small intestine, proximal part of large

intestine, kidney, pancreas and liver.• Relaxation of the musculature of: stomach, small intestine and proximal part of large

intestine.• Contraction of sphincters: of the stomach and intestine leading to (food retention).• Contraction of the capsule: of the spleen leading to evacuation of about 200 ml of blood. • Breakdown of the glucose in the liver: (glycogenolysis) leading to increase of blood glucose

level.• Stimulation of adrenal medulla: Secrete adrenaline and noradrenalin.

Sympathetic Pathways to the Abdominal Organs

Sympathetic Pathways to the Pelvic Organs

(4) Somatic divisionOrigin: Preganglionic nerve fibers arise from all lateral horn

cells of all sympathetic segments, and then relay in the cervical and sympathetic chain ganglia.

Course: Postganglionic nerve fibers emerge from these ganglia proceeds outside the central nervous system to return back to spinal cord to join the spinal nerve when it comes out from the anterior horn cells, and supply the following structures:

Skin: • Vasoconstriction giving the pale color of the skin.• Stimulation of the sweet glands, the eccrine glands give copious secretion,

while the apocrine glands give thick odoriferous secretion.• Hair erection.

Skeletal muscle: • Its blood vessels show vasodilatation (V.D.) due to cholinergic effect or

vasoconstriction (V.C.) due to a adrenergic effect. • The type of stimulation depends upon the nature of stimulation.• Muscles: its stimulation causing delayed fatigue and early recovery.

4- somatic tissues(body wall, limbs)

postganglionicsvia 31 spinal nervesto somatic tissues of neck, body wall, and limbs

sympathetictrunk

Sympathetic Pathways to Periphery

Figure 15.9

The Role of the Adrenal Medulla in the Sympathetic Division

• Major organ of the sympathetic nervous system

• Secretes great quantities epinephrine (a little norepinephrine)

• Stimulated to secrete by preganglionic sympathetic fibers

The Adrenal Medulla

ParasympatheticPathways

Cranial outflow• CN III, VII, IX, X• Four ganglia in head• Vagus nerve (CN X) is major

preganglionic parasymp. supply to thorax & abdomen• Synapse in ganglia within wall of the target organs (e.g., enteric plexus of GI tract)

Sacral outflow• S2–S4 via pelvic splanchnics• Hindgut, pelvic viscera, and

external genitalia

Clinical Relevance» Surgery for colorectal cancer

puts pelvic splanchnics at risk» Damage causes bladder & sexual dysfunction

The Parasympathetic Division

• Cranial outflow – Comes from the brain– Innervates organs of the head, neck, thorax, and

abdomen• Sacral outflow

– Supplies remaining abdominal and pelvic organs

The Parasympathetic Division

Cranial Nerves

• Attach to the brain and pass through foramina of the skull

• Numbered from I–XII• Cranial nerves I and II attach to the forebrain

– All others attach to the brain stem• Primarily serve head and neck structures

– The vagus nerve (X) extends into the abdomen

The 12 Pairs of Cranial Nerves

CN III: Oculomotor Nerve• Innervates four of the extrinsic eye muscles

CN VII: Facial Nerve

• Innervates muscles of facial expression• Sensory innervation of face• Taste

CN IX: Glossopharyngeal Nerve• Sensory and motor innervation of structures of the

tongue and pharynx• Taste

CN X: Vagus Nerve• A mixed sensory and motor nerve • Main parasympathetic nerve

– “Wanders” into thorax and abdomen

Cranial Outflow

• Preganglionic fibers run via:– Oculomotor nerve (III)– Facial nerve (VII)– Glossopharyngeal nerve (IX)– Vagus nerve (X)

• Cell bodies located in cranial nerve nuclei in the brain stem

CN III: Oculomotor Nerve

Origin: Edinger-Westphal nucleus at midbrain.

Course: preganglionic from E-W nucleus to rely

in the ciliary ganglion.Postganglionic supply:

1- pupillconstrictor muscle 2- ciliary muscle.3- four of the extrinsic eye muscles.

Its stimulation leads to miosis, accommodation to neat vision and movements of the eye ball.

CN III: Oculomotor Nerve• Innervates four of the extrinsic eye muscles

CN VII: Facial Nerve

Origin: The superior salivary nucleus which is a part of facial nucleus in the lower part of pons.

Course: Preganglionic nerve fibers run in the chorda tympani nerve which is a part of facial nerve and relay in:-

- Submaxillary ganglion- Sphenopalatine ganglion.• Postganglionic nerve arises from Submaxillary ganglion

supply submandibular and sublingual salivary glands and anterior 2/3 of the tongue.

• Postganglionic nerve arises from Sphenopalatine ganglion supply the mucosa of the soft palate and nasopharynx and Lacrimal glands.

• Its stimulation causes vasodilatation and secretion at their effector organs.

CN VII: Facial Nerve

• Innervates muscles of facial expression• Sensory innervation of face• Taste

CN IX: Glossopharyngeal Nerve

Origin: Glossopharyngeal nerve nucleus in the upper part of the medulla oblongata called inferior salivary nucleus, and then relay in the otic ganglion.

Course: Postganglionic nerve fibers arise from otic ganglion supply the parotid salivary gland and posterior 1/3 of the tongue

Its stimulation causes vasodilatation and secretion at their effector organs

CN IX: Glossopharyngeal Nerve

• Sensory and motor innervation of structures of the tongue and pharynx

• Taste

CN X: Vagus NerveOrigin: Dorsal vagus nucleus in medulla oblongata Course: Postganglionic nerve fibers from the terminal ganglia

which supplied from dorsal vagus nucleus and supply the following structures:

• HEART: The vagus nerve supplies the both auricles and don't supply the ventricles (and this called vagus escape phenomena).

• Its stimulation produces inhibition of all cardiac properties (decrease heart rate, decrease contractility and decrease conductivity).

• Its stimulation causes vasoconstriction of coronary vessels and reduction of O2 consumption by cardiac muscle.

• These responses lead to bradycardia.

• Lungs: Vagus stimulation causes:• Bronchoconstriction.• Increased bronchial secretion.• Vasodilatation of pulmonary blood vessels.• These responses lead to precipitation of asthma.

Gastrointestinal tract: Vagus stimulation causes:• Contraction of walls of esophagus, stomach, small intestine and proximal

part of large intestine.• Relaxation of their corresponding sphincter.• These responses promote deglutition, increased secretion of GIT and

evacuation of foods.

• Gall bladder: Vagus stimulation causes:• Contraction of the gall bladder wall.• Relaxation of its sphincter.• These responses lead to evacuation of the gall bladder.

CN X: Vagus Nerve

Sacral OutflowOrigin: Preganglionic nerve fibers arise from the lateral

horn cells of the 2nd, 3rd and 4th sacral segments.Course: These preganglionic passes without relay, then the

right and left branches unit together to form the pelvic nerve, the pelvic nerve relay in the terminal ganglia, where the postganglionic nerve fibers emerge and supply the following structures:- Urinary bladder: parasympathetic stimulation causes:- Contraction of the bladder wall - Relaxation of its sphincter.- These responses lead to micturition.

Rectum and descending colon: parasympathetic stimulation causes:

- Contraction of its wall.- Relaxation of internal anal sphincter.- These responses lead to defecation.

Seminal vesicles and prostate: parasympathetic stimulation -causes:

- Secretion of these glands.Erectile tissue: parasympathetic stimulation causes:

- Vasodilatation which lead to erection.

Neurotransmitter release sites

Acetylcholine receptors

• Two types of cholinergic receptors are well known: • Nicotinic receptors which are easily activated by agonist

molocule such as nicotine and • Muscarinic receptors: which are sensitive to muscarine.

Cholinergic receptors

Nicotinic receptors(Central)

Muscarinic receptors(peripheral )

Types Two types:- GanglionicNeruomuscular

M1, M2 (cardiac), M3 (glandular&smooth muscle) M4 (brain).M5,M6 and M7.

Stimulatedby

Nicotine in small doses, Ach, metacholine

Muscarine, Ach, carbarcholine

Blocked by Nicoitin in large doses- decameyhoniumd-tubourarine-

Atropinescopolamine

site Autonomic ganglia M.E.PAdrenal medullaPreganglionic neuron.

Parasympathetic(pre-postganglionic) Sympathetic postganglionic nerve endings (sweat glands & skeletal muscle).

Nicotinic Receptors

• Located in the ganglia of both the PSNS and SNS

• Named “nicotinic” because can be stimulated by the alkaloid nicotine

Muscarinic Receptors

• Located postsynaptically:– Smooth muscle– Cardiac muscle– Glands of parasympathetic fibers– Effector organs of cholinergic sympathetic fibers

• Named “muscarinic” because can be stimulated by the alkaloid muscarine

• Neurotransmitters• Receptors

Comparison of sympathetic and Parasympathetic Pathways