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Introduction to AUTONOMIC NERVOUS SYSTEM

Nervous system---------------Anatomical classification CNS……….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 classification Somatic nervous system Autonomic 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

Effector remains functional but not able to quickly respond to the changing needs of the body. Paralysis and muscle wastage (atrophy) Effect of nerve damage on the effector Acetylcholine, adrenaline, noradrenaline Acetylcholine Neurotransmitter Chain ganglia, collateral ganglia or terminal ganglia 0 Ganglia outside the CNS 2 1 Number of neurons from CNS to effector Adjustment within the internal environment (homeostasis) Adjustment to external environment. General function Smooth muscle, Cardiac Muscle, Glands Voluntary (skeletal) muscle Effectors Autonomic Nervous System Somatic Nervous System Characteristic

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- Sympathetic nervous system Parasympathetic nervous system 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 system Enteric 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 components They represent GVE functional components. 2 sets of neuron which synapse at ganglion. Preganglionic neuron/1st set/primary neuron Postganglionic neuron/2nd set/secondary neuron Target structure- Smooth muscle Cardiac muscle Glands (exocrine) GVE GVE

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 OUTFLOW Parasympathetic preganglionic neurons are located partly in the brain stem in connection 3 rd , 7 th , 9 th and 10 th cranial nerves and partly in S2, 3, 4 spinal segments--------------------- CRANIOSACRAL OUTFLOW 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 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 neurons Collateral ganglia (cranial parasympathetic ganglia) Ciliary ganglion Pterygopalatine ganglion Submandibular ganglion Otic ganglion Terminal ganglia - close to or within wall of viscera Cardiac plexus Pulmonary plexus Myenteric plexus Submucosal plexus Inferior hypogastric (ganglion) plexus

Sensory components They 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) 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 L2/3 Spinal 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 L2/3 Spinal nerve 1 2 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 L2/3 Spinal nerve 1 2 3 Subsidiary ganglia deep seated viscera

T1-L2/3 spinal nerve Cervical Spinal nerve Below L2/3 Spinal nerve 1 2 4 3 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 L2/3 Spinal nerve 1 2 3 4 5 Subsidiary ganglia deep seated viscera

T1-L2/3 spinal nerve Cervical Spinal nerve Below L2/3 Spinal nerve 1 2 3 4 6 5 Subsidiary ganglia deep seated viscera

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- Paravertebral in position Extends from base of the skull to 1 st 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 5 th and 6 th cervical ganglia Inferior cervical ganglion is formed by fusion of 7 th and 8 th cervical ganglia Sometimes inferior cervical and 1 st thoracic ganglia fuse to form cervicothoracic/stellate ganglion

DCP SCP Sup Cervical Ganglion Middle Cervical Ganglion Inf Cervical Ganglion 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 ganglia is connected to ventral ramus of corresponding spinal nerve through 2 bundles of nerve fibers. White rami communicantes: the lateral bundle containing myelinated preganglionic nerve fibers. 14/15 in number. Gray rami communicantes: the medial bundle containing unmyelinated postganglionic nerve fibers. 31 in number. Rest of the ganglia are connected to ventral ramus of corresponding spinal nerve only through gray rami communicantes.

Parasympathetic 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

Cranial outflow SMOOTH MUSCLE CARDIAC MUSCLE GLANDS - ORGAN WALL (Intramural ganglion) C10: VAGUS NERVE DORSAL NUCLEUS PAROTID GLAND AURICULOTEMPORAL NERVE OTIC GANGLION C9: GLOSSOPHARYNGEAL NERVE INFERIOR SALIVATORY NUCLEUS SUBMANDIBULAR GLAND SUBLINGUAL GLAND LINGUAL NERVE SUBMANDIBULAR GANGLION C7: FACIAL NERVE SUPERIOR SALIVATORY NUCLEUS LACRIMAL GLAND Other glands LACRIMAL NERVE PTERYGOPALATINE GANGLION C7: FACIAL NERVE LACRIMATORY NUCLEUS CONSTRICTOR PUPILLAE CILIARY MUSCLE SHORT CILIARY NERVE CILIARY GANGLION C3: OCCULOMOTOR NERVE EDINGER WESTPHAL NUCLEUS TARGET THROUGH GANGLION CRANIAL NERVE NUCLEUS

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 Norepinephrine Neurotransmitters Everywhere Adrenal medulla Sweat gland Everywhere Sympathetic Parasympathetic 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- N M N N

Physiological Effects of the ANS 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 Hypothalamus

Parasympathetic nervous system

Difference between sympathetic and parasympathetic nervous system Central control Afferents Efferents Outflow Preganglionic neuron Ganglia Preganglionic fibers Pre-post ratio Action Anabolic/catabolic Works for Postganglionic transmitter Nerve of Necessity Anatomical entity Para Sym

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: Central Horner’s syndrome Preganglionic Horner’s syndrome 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 L2/3 Spinal nerve 1 2 3 4 5 6 Subsidiary ganglia deep seated viscera

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