Peripheral and autonomic Nervous system

The objective of the lecture is to Discuss the organisation of somatic and autonomic nervous system Anatomical organisation of reflexes Their clinical importance.

Nervous System Has two divisions –Central Nervous System –Peripheral Nervous System Central Nervous System –It Consists of brain and spinal cord –They are center of integration and control Peripheral Nervous System –It is nervous system outside brain and spinal cord Consists of: –31 pairs of Spinal nerves –12 pairs of cranial nerves –They carry information to and from the spinal cord

Peripheral Nervous System 3 kinds of neurons connect CNS to the body –sensory –motor –interneurons Motor - connect CNS to muscles and organs Sensory - connect sensory receptors to CNS Interneurons: they are connections within CNS Spinal Cord Brain Nerves

Peripheral Nervous System Sensory -Conducts impulses from receptors to the CNS There are two divisions : –Somatic (from skin, skeletal muscles and joints) –Autonomic (from organs in body cavity) Motor Division –conducts impulses from CNS to effectors There are two divisions : –Muscles (Somatic ) –Smooth muscle,cardiac muscle Glands (Autonomic )

Peripheral nervous system SomaticAutonomic SympatheticParasympathetic

Somatic System It includes Nerves to and from spinal cord Controls muscle movements Sensory inputs from skin, skeletal muscles and joints Muscle Motor Neuron Interneuron Skin receptors Sensory Neuron Brain

Autonomic Nervous System Sympathetic nervous System “Fight or Flight” Parasympathetic Nervous System “Rest and Digest” These 2 systems are antagonistic Typically, we balance these two to keep ourselves in a state of dynamic balance.

Autonomic nervous system Once thought to be self governing But it is regulated by centers in the brain ANS operation follows reflex arc principal –At the spinal cord level –At brain stem level Higher centers of brain play modulatory role

ANS divisions Sympathetic and parasympathetic Sympathetic –Thoracolumbar outflow –From T1- L2 CENTRAL NERVOUS SYSTEM Brain Spinal cord SYMPATHETIC Dilates pupil Stimulates salivation Relaxes bronchi Accelerates heartbeat Inhibits activity Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Stimulates ejaculation in male Sympathetic ganglia Salivary glands Lungs Heart Stomach Pancre as Liver Adrenal gland Kidney

ANS divisions Parasympathetic –Craniosacral outflow –In III,VII, IX and X cranial nerves –And in Spinal S2-4 CENTRAL NERVOUS SYSTEM Brain PARASYMPATHETIC Spinal cord Stimulates salivation Constricts bronchi Slows heartbeat Stimulates activity Contracts bladder Stimulates erection of sex organs Stimulates gallbladder Gallbladder Contracts pupil

ANS Most viscera receive both Except sweat glands and arrector pili – supplied by sympathetic Normally their actions are opposite ANS efferent's have two neurons Preganglionic and postganglionic Preganglionic are in the CNS – relay on post ganglionic Postganglionic are in the ganglia – supply target organs

Autonomic nervous system Has a chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons Pre-ganglionic Ganglion Post-ganglionic

Autonomic and Somatic Motor Systems

Sympathetic nervous system Preganglionic neurons : Cell bodies in the lateral horn from T1-L2 Leave via the spinal nerve Enters ganglia of sympathetic trunk End at same level Or send branches above or below Or continue as splanchnic nerves to end collateral ganglion

Sympathetic nervous system Postganglionic neurons : Cell bodies are in the ganglia of the sympathetic chain Pre vertebral or collateral ganglia Adrenal medulla

Sympathetic trunks They are two cords on either side of vertebral column From base of skull to coccyx Contains cell bodies of postganglionic neurons There are 31 pairs Due to fusion number reduced to 22-23

Sympathetic pathway

Cervical portion & Superior cervical ganglion Has 3 ganglia Superior middle and inferior cervical ganglia Superior cervical ganglion is : Formed by fusion of upper 4 cervical ganglia Located in front of C2&3 vertebra Lies posterior to internal carotid artery Gives gray rami to C1-4 Forms plexus over internal and external carotid arteries Gives branches to pharynx and superior cardiac branches

Middle cervical ganglion Formed by fusion of 5 th and 6 th cervical ganglia Lies anterior to inferior thyroid artery Located at the level of C6 Communicates with inferior by ansa subclavia Gives gray rami to C5- 6 Middle cardiac nerves Thyroid gland pharynx larynx

Inferior cervical ganglion Formed by fusion of 7 th and 8 th cervical ganglia Lies anterior to transverse process of 7 th cervical vertebra The ganglion fuses with the T1 to from the Stellate ganglion Gives gray rami to C7 to 8 &T1 Inferior cardiac branches Tracheal and pulmonary branches Plexus around subclavian and vertebral arteries

Sympathetic Division of the ANS

White and gray rami White rami are –Myelinated preganglionic fibers –Enter ganglia of sympathetic trunk –Are limited from T1-L2 Gray rami are –Non myelinated post ganglionic fibers –Arise in the ganglia –Each spinal nerve has one gray rami

Parasympathetic nervous system Cell bodies of preganglionic neurons are found in the brain stem nuclei Of III, VII, IX and X cranial nerves Lateral horns of S 2-4 Preganglionic are myelinated

Parasympathetic nervous system Postganglionic neurons : Cell bodies are in the peripheral ganglia They lie close to organ of innervation They send short postganglionic fiber They are not myelinated In the head region there are 4 ganglia –Ciliary –III CN –Pterygopalatine- VII CN –Submandibular _--VII CN –Otic - IX

The Parasympathetic Division Figure 15.5

Parasympathetic pathway

Ciliary ganglion Preganglionic nucleus : Edinger westphal nucleus Course :Occulomotor nerve IIICN Enters Ciliary ganglion Postganglionic : short ciliary nerves Supply : –Sphincter pupillae –Ciliary muscle

Pterygopalatine ganglion Preganglionic nucleus : lacrimatory nucleus Course : –VII CN –greater petrosal nerve + deep petrosal nerve –nerve of pterygoid canal –Enters Pterygopalatine ganglion Postganglionic fibers : –Maxillary nerve –zygomatic nerve –Lacrimal nerve Supply : –Lacrimal gland –Nasal palatal and pharyngeal glands

Submandibular ganglion Preganglionic nucleus : superior salivatory nucleus Course : VII CN –Chorda tympani nerve – Lingual nerve –Enters submandibular ganglion Postganglionic fibers : –Directly –Or branches of lingual nerve Supply : –Submandibular gland –Sublingual glands

Otic ganglion Preganglionic nucleus : Inferior salivatory nucleus Course : IX CN –Tympanic branch of IX CN – Lesser petrosal nerve –Enters otic ganglion Postganglionic fibers : –Auriculotemporal nerve Supply : –Parotid gland

Vagus nerve Preganglionic nucleus : Dorsal nucleus of vagus Course : vagal branches of –Pulmonary –Cardiac –Esophageal –Gastric Postganglionic nuclei : –Ganglia of pulmonary plexus –Ganglia of cardiac plexus –Aurbach’s and Meissners’ plexus –Ganglia in the wall of viscera Postganglionic fibers : –Direct branches Supply : –Smooth muscle and glands of respiratory system –Conducting system of heart –Esophagus –Stomach, small intestine, ascending colon and transverse colon

Sacral outflow Preganglionic nucleus : gray column of S2-4 Course : Pelvic splanchnic nerves Postganglionic nuclei : –Aurbach’s and Meissners’ plexus –Ganglia in the wall of viscera Postganglionic fibers : –Direct branches Supply : –Descending colon, sigmoid colon and rectum –All pelvic organs

Comparison of Peripheral& autonomic PeripheralAutonomic Type of controlVoluntaryInvoluntary Motor pathwayConsist of one neuron Consists of two neurons ActionAlways excitatoryMay be excitatory or inhibitory NeurotransmitterAcetylcholineAcetylcholine or norepinephrine

Comparison of Sympathetic and parsympathetic SympatheticParasympathetic OutflowThoracolumbar T1-L2Craniosacral III, VII, IX, XCN & S2-4 Postganglionic neuron – location Sympathetic trunk and pre vertebral ganglia – away from viscera Outside CNS Near to viscera Length of fibersPreganglionic fibers – short Postganglionic –long Preganglionic fibers – long Postganglionic – short Preganglionic fibers Synapse With many postganglionic neurons and supply many viscera With few postganglionic neurons that supply single viscous

Comparison of Sympathetic and parsympathetic SympatheticParasympathetic Neurotransmitter at preganglionic Acetylcholine Neurotransmitter at postganglionic Noradrenalin But sweat glands & blood vessels – acetylcholine Acetylcholine DistributionWhole bodyLimited to: Head & neck, thorax, abdomen and pelvis Type of systemFight or flight systemRest and repose system

Distribution Sympathetic : –Whole body Parasympathetic : –Limited to: –Head & neck –Thorax –Abdomen and pelvis

Applied anatomy Horner's syndrome consists of : Miosis – constriction of pupil Ptosis – drooping of upper eye lid Anhydrosis –loss of sweating Enopthalmos- sunken eyeball due to paralysis of orbitalis muscle Flushing of face Due to lesion of sympathetic supply to head and neck – e.g. cervical rib

Megacolon Hirschprung’s disease Congenital condition with failure of development of myentric plexus in the distal colon Extreme dilatation and hypertrophy of distal colon with retention of fecal mass

Thromboangitis obliterans It is an obliterative disease of arteries Particularly lower limbs Vascular spasm due to sympathetic over activity With reduced blood circulation Relieved by lumbar sympathectomy

Raynaud’s Disease Characterized by constriction of blood vessels Provoked by exposure to cold Or by emotional stress

Hypertension Can result from overactive sympathetic vasoconstriction

Achalasia of the Cardia Defect in the autonomic innervation of the esophagus

Learning outcomes At the end of the lecture, students should be able to: Outline the organization of the nervous system Describe the organization of spinal nerves. Enumerate the components of autonomic nervous system. Discuss the organisation of the sympathetic and parasymthathetic nervous system. Explain the clinical significance of reflexes.