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 regulation ofbodytemperature,bloodpressure,cardiorespirato ry rate gastro-intestinal motility and glandular secretion The 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 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
somatic efferents Autonomic efferents 1.Motor fibres consists of single set of neurons and reach effector Cell 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)
Sympathetic system is also called adrenergic system because post ganglionic sympathetic fibres liberate adrenaline.But sympathetic fibres to sweat glands of hairy skin are cholinergic. The entire function of sympathetic is a nerve of emergency and during stress and strain to ‘ Fight,Fright or Flight’ .It is a catabolic nerve and works for today. In sympathetic system,the preganglionic fibres are short and post ganglionic fibres are long.One preganglionic fibre make synaptic connections with twenty or more postganglionic neurons Preganglionic sympathetic fibres Postganglionic sympathetic fibres Sympathetic system
Anatomy of sympathetic system It presents definite anatomical entity Consists of a pair of ganglionated trunk,their rami of communications,branches,plexuses and 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 ganglion is connected to corresponding spinal nerve by both white and grey rami communicans. Above the 1 st thoracic and below 2 nd and 3 rd lumbar are connected to corresponding spinal nerves only by grey rami communicans. Grey rami convey post-ganglionic sympathetic fibres from lateral ganglia through 31 pairs of spinal nerve. Plexuses form by this nerves supply sudomotor,pilo motor 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 motor And 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 supply Sudomotor,Pilomotor and vasoconstrictor fibres of the body wall.
The parasympathetic system The preganglionic motor neurons are partly Located in the brainstem in connection with -3 rd cranial nerve(oculomotor) -7 th cranial nerve(facial) -9 th cranial nerve(glossopharyngeal) -10 th cranial nerve(vagus) Partly in the lateral horn cells of 2 nd to 4 th sacral segments of the spinal cord. It is also known as cranio-sacral outflow Postganglionic para-sympathetic neurons consists of collateral and terminal ganglia.
Postganglionic parasympathetic fibres liberate Acetyl-choline on effector cell,also known as Cholinergic 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 2 nd to4th sacral nerves. Preganglionic nerve fibre Postganglionic nerve fibres
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 tommorow because constriction of the pupil after parasympat- thetic stimulation permits distant vision which sym bolises activities of the future. The parasympathetic system is essential to 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 1 st 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 nucleu s 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
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
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