Autonomic nervous system

By

Dr Manah Chandra Changmai

The autonomic nervous system represents the visceral component of the nervous system.

It consists of neurones located within both the central nervous system (CNS) and the peripheral nervous system (PNS) and which are concerned with the control of the internal environment, through innervation of secretory glands, and both cardiac and smooth muscle.

'Autonomic' is a convenient rather than appropriate title, since the functional autonomy of this part of the nervous system is illusory.

The autonomic activities is expressed by regulationofbodytemperature,bloodpressure,cardiorespirato ry rate gastro-intestinal motility and glandular secretion

The autonomic nervous system

Plan of autonomic nervous system

Autonomic afferent pathways resemble somatic afferent pathways.

The cell bodies of autonomic afferent origin are unipolar neurones located in cranial and dorsal root ganglia. Their peripheral processes are distributed through autonomic ganglia or plexuses, or possibly through somatic nerves, without interruption.

Autonomic afferent

Autonomic afferent

Autonomic efferent pathways differ from their somatic equivalents in that the former are interrupted by peripheral synapses, there being a sequence of at least two neurones between the CNS and the target structure

These are referred to as preganglionic and postganglionic neurones.

Autonomic nervous system

Sympathetic system Parasympathetic system

Visceral efferent

Autonomic efferent

somatic efferents Autonomic efferents

1.Motor fibres consists of single set of neurons and reach effectorCell directly

1.Motor fibres consists of two successive sets,preganglionic and postganglionic,before reaching effector cell

2.Target cells belong to one type-striated or skeletal muscle

2.Target cells consists of three types-cardiac muscle,smooth muscle and glandular cell.

3.Stimulation of target cell cause excitation only

3.Stimulation of target cells cause either excitation or inhibition.

4.Activity of target cell completely dependent on intact motor supply

4.Activity of target cells not completely on nerve supply;i e postdenervational hypersensitivity of smooth muscle

5.Form plexuses close to CNS 5.Form plexuses close to target .

Difference between somatic and autonomic motor neuron

Sympathetic system

The preganglionic motor neurons of sympathetic system are located in lateral horn cells of all thoracic and upper two lumbar vertebrae

Also known as thoraco-lumbar outflow.

The postganglionic sympathetic neurons consists of lateral ,collateral and terminal ganglia.

-The lateral ganglia are the two sympathetic trunks-The collateral ganglia are prevertebral in position and represented by coeliac,superior mesentric,inferior mesentric superior hypogastric ganglia.

The terminal ganglia of sympathetic system is found only in suprarenal medulla.

Lateral horn of spinal cord(T1 – L2 or L3)

Thoraco-lumbar outflow

Sympathetic/Parasympathetic

Sympathetic system

Sympathetic system is also called adrenergic systembecause post ganglionic sympathetic fibres liberateadrenaline.But sympathetic fibres to sweat glands ofhairy skin are cholinergic.

The entire function of sympathetic is a nerve of emergencyand during stress and strain to ‘Fight,Fright or Flight’.It is acatabolic nerve and works for today.

In sympathetic system,the preganglionic fibres areshort and post ganglionic fibres are long.One preganglionic fibre make synaptic connections withtwenty or more postganglionic neurons

Preganglionic sympathetic fibres

Postganglionic sympathetic fibres

Sympathetic system

Autonomic motor neurons

Anatomy of sympathetic system

It presents definite anatomical entity

Consists of a pair of ganglionated trunk,theirrami of communications,branches,plexusesand subsidiary ganglia

Ganglionated trunk-Paravertebral in position,extends from base of the skull to the first coccygeal vertebrae.-The trunk presents Three ganglia in cervical part:Superior Middle Inferior Eleven ganglia in thoracic part Four lumbar Four sacral ganglia.

Thoracic and upper two lumbar sympathetic ganglionis connected to corresponding spinal nerve by bothwhite and grey rami communicans.

Above the 1st thoracic and below 2nd and 3rd lumbarare connected to corresponding spinal nerves onlyby grey rami communicans.

Grey rami convey post-ganglionic sympathetic fibresfrom lateral ganglia through 31 pairs of spinal nerve.

Plexuses form by this nerves supply sudomotor,pilomotor and vasoconstrictor fibres.

White ramus

Grey ramus

Post ganglionic neuron

Sympathetic ganglion

Spinal nerve

Planning of sympathetic nerve supply

white rami Grey rami

1.Lateral in position 1.Medial in position

2.Convey preganglionic motorAnd viscero sensory fibres

2.Convey postganglionic fibres only

3.Connected to lateral ganglia from T1 – L2 spinal nerves

3.Connected to all 31 pairs of spinal nerve

4.Inresegmental in distribution 4.Segmental in distribution and supplySudomotor,Pilomotor and vasoconstrictor fibres of the body wall.

The parasympathetic system

The preganglionic motor neurons are partlyLocated in the brainstem in connection with-3rd cranial nerve(oculomotor)-7th cranial nerve(facial)-9th cranial nerve(glossopharyngeal)-10th cranial nerve(vagus)

Partly in the lateral horn cells of 2nd to 4th sacralsegments of the spinal cord.

It is also known as cranio-sacral outflow

Postganglionic para-sympathetic neurons consistsof collateral and terminal ganglia.

Postganglionic parasympathetic fibres liberateAcetyl-choline on effector cell,also known asCholinergic system.

Both sympathetic and parasympathetic preganglionic fibres liberate acetylcholine.

The preganglionic fibres are longer than postganglionic fibres.One preganglionic neurons one or two post ganglionic neuron.

The action of parasympathetic is localise and accurate.

Afferent parasympathetic fibres convey general visceralsensationlikehunger,thirst or nausea,distension of bladderEtc.

The cell bodies are located in the ganglia IX and X cranial nerve and dorsal root ganglia of 2nd to4th sacral nerves. Preganglionic nerve fibre Postganglionic nerve fibres

Parasympathetic fibres

Fibres of autonomic nervous system

Actions of parasympathetic system

Actions are localised and accurate.

On stimulation,-the heart rate is diminished,-The blood pressure falls,-Pupil are constricted-The peristalsis and glandular secretion of alimentary tract are promoted.-The urinary bladder and rectum are evacuated.

It is anabolic in function and works for tommorowbecause constriction of the pupil after parasympat-thetic stimulation permits distant vision which symbolises activities of the future.

The parasympathetic system is essentialto our life.i.e;micturition is essentially a controlled by parasympathetic,both filling and evacuation.

Autonomic nervous supply of some important organ

The Eye ball-Sphincter pupillae by parasympathetic nerves Preganglionic neurons located in Edinger Westpal nucleus.-Dilator pupillae supplied by sympathetic nerves Preganglionic neurons located in lateral horn of 1st thoracic segment.

Horner’s syndrome-Interruption of sympathetic supply to head and neck results in horner syndrome a)Constriction of pupil b)Drooping of upper eyelids(ptosis) c) Reduced prominence of the eyeball(Enopthalmos) d)Absence of sweating on face and neck (anhydrosis) e) Flushing of the face.

The facial nerve contains preganglionic parasympathetic axons of neurones with their somata in the superior salivatory nucleus

Preganglionic fibres are conveyed to the submandibular ganglion, where they synapse on ganglionic neurones.

Postganglionic fibres innervate the submandibular and sublingual salivary glands and are said to travel in the lingual nerve.

Salivary gland

Submandibular and sublingual glands

The glossopharyngeal nerve contains preganglionic parasympathetic secretomotor fibres for the parotid gland.

Originate in the inferior salivatory nucleus and travel in the glossopharyngeal nerve and its tympanic branch.

Postganglionic fibres pass by communicating branches to the auriculotemporal nerve, which conveys them to the parotid gland.

Parotid gland

Nerve supply of Parotid gland

Autonomic nerve supplyOf heart

Cardiac plexus

The vagal nucleus (dorsal motor nucleus of the vagus) in the medulla is a major source of preganglionic parasympathetic fibres.

Efferent fibres travel in the vagus nerve and its pulmonary, cardiac, oesophageal, gastric, intestinal and other branches.

They synapse in minute ganglia in the visceral walls.

Gastrointestinal tract

Vagus nerve

Pelvic splanchnic nerves to the pelvic viscera travel in anterior rami of the second, third and fourth sacral spinal nerves.

The pelvic splanchnic nerves are motor to the muscle of the rectum and bladder wall but inhibitory to the vesical sphincter.

They supply vasodilator fibres to the erectile tissue of the penis and clitoris and are probably also vasodilator to the testes, ovaries, uterine tubes and uterus.

Pelvic sphlanic nerve

Pelvic splanchnic nerves

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