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5 Cards in this Set
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NERVOUS SYSTEM The nervous system is divided into: (I) Central nervous system (CNS) comprising of brain and spinal cord (II) Peripheral nervous system (PNS) composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Autonomic Nervous System The essential function of the autonomic nervous system is to maintain homeostasis by controlling the organs and structures involved in the processes of digestion, circulation, respiration, excretion, reproduction and maintenance of normal body temperature. •Innervates smooth and cardiac muscle and exocrine and someendocrine glands The organs and structures carrying out the list of functions above are NOT UNDER CONSCIOUS CONTROL, i.e. they are involuntary. The three divisions of the ANS are: sympathetic nervous system, parasympathetic nervous system and enteric nervous system. - Receptors for the ANS include chemoreceptors, baroreceptors and osmoreceptors. - All interneurons of the ANS use dopamine. |
Comparison of Autonomic NS with Somatic Nervous System.
- Autonomic nervous system involuntarily controls organs and other structures. - The SNS has one peripheral efferent neuron to striated muscle. - The ANS has two efferent peripheral neurons which synapse in ganglia of the brain to the spinal cord to the target organs. - In the SNS, motor axon is myelinated - In the ANS the pre-ganglionic axon is myelinated, the post-ganglionic axon is unmyelinated. |
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CENTRAL CONTROL OF THE ANS The hypothalamus is the controlling and integrating centre for the autonomic nervous system. Activity in the hypothalamus itself is influenced by many other areas of the central nervous system. For example, ascending pathways from the spinal cord and brainstem bring information originating in the viscera. The anterior part of the hypothalamus controls parasympathetic nervous system and the posterior part controls the sympathetic nervous system. (I) Anterior (preoptic nuclei) stimulates parasympathetic NS where it: - Lowers blood pressure - Reduces heart rate - Contracts bladder - Increases GIT motility - Pupillary constriction (II) Posterior and lateral nuclei stimulate sympathetic NS where it: - Increases blood pressure - Increases heart rate - Reduces GIT motility& secretions - Pupillary dilation |
PARASYMPATHETIC NERVOUS SYSTEM. It is “rest and digest” part of the autonomic nervous system. It is composed of two nerves, a preganglionic neuron and a postganglionic neuron. All parasympathetic ganglia are found close to their specific target like organ smooth muscle and glands. This is the opposite to the sympathetic nervous system. It does not innervate blood vessels or the sweat glands unlike the sympathetic nervous system. Preganglionic neuron cell bodies are located in the brainstem where the oculomotor, facial, glossopharyngeal and vagus nerves are. Preganglionic nerves are cholinergic, myelinated. The postganglionic cell bodies are situated away from the CNS near the structure/organ they innervate so they are shorter than sympathetic postganglionic fibres and cholinergic (using acetylcholine as the neurotransmitter). The Preganglionic fibres of the parasympathetic system originate from the grey matter in the nuclei of the brainstem (cranial) and from the lateral horn of the spinal grey matter of three of the sacral segments of the spinal cord, i.e. S2-S4 (CRANIOSACRAL OUTFLOW) - Cranial part is distributed in 4 peripheral ganglia: ciliary, pterygopalatine, submandibular and otic. Sacral part is from S2-S4 spinal nerves. - All preganglionic and postglaglionic fibres of the parasysmpathetic nervous system uses acetylcholine. |
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PRE-GANGLIONIC CELL BODIES IN THE BRAINSTEM OF THE PARASYMPATHETIC NERVOUS SYSTEM. Oculomotor nerve (3rd cranial nerve) Edinger-Westphal nucleus of the midbrain it travels to inferior oblique muscle to the ciliary ganglion. PG fibres run in the short ciliary nerves to ciliary muscles and sphincter pupillae. Function: Accommodation of near objects and pupillary constriction. Facial nerve (7th cranial nerve) - From superior salivatory nucleus (nervus intermedius), it leaves main trunk before stylomastoid to leave with chorda tympani, joins lingual nerve, to submandibular ganglion. - Postganglionic fibres go to submandibular and sublingual gland in the lingual nerve. - Lacrimal secretomotor fibres of the facial nerve via the greater petrosal branch and nerve of the pterygoid canal go to the pterygopalatine ganglion. - Postganglionic fibres of the facial nerve via the zygomatico-temporal nerve go to the lacrimal, nasal and palatine glands. Glossopharyngeal nerve (9th cranial nerve) From the inferior salivatory nucleus via tympanic branch of IX and at the tympanic plexus and lesser petrosal nerve to the otic ganglion, found in the infratemporal fossa close to foramen ovale. - Postganglionic fibres via the auriculotemporal n. to the parotid gland. Vagus - Dorsal motor nucleus of the vagus in the medulla to pulmonary, cardiac, oesophageal, gastric and intestinal branches. - Synapse in minute ganglia in the viscera. - Cardiac (atria, slow cycle), Pulmonary (bronchoconstrictors) |
POSITIONS OF GREY MATTER IN THE CRANIAL PART OF THE PRE-GANGLIONIC FIBRES OF THE PARASYMPATHETIC NERVOUS SYSTEM. Pterygopalatine ganglia • Suspended from the pterygopalatine nerves (br. Of CN V2) in the pterygopalantine fossa. • Parasympathetic fibres from facial nerve (gtr. Petrosal n.) joins deep petrosal nerve to form n. of the pterygoidcanal and exits (aka vidian canal). •Parasympathetic fibres synapse in the ganglion and pass to the lacrimal gland, palatine glands, mucosal glands of the nasal cavity and superior larynx. SUBMANDIBULAR GANGLION (facial nerve) • It situated lateral to hyoglossus muscle and below the lingual nerve. • Its parasympathetic fibres pass via the chorda tympani and lingual nerve, synapse in the ganglion and pass the submandibular, sublingual glands, mucous glands via the lingual nerve. |
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SYMPATHETIC NERVOUS SYSTEM - The Preganglionic fibres of the sympathetic system come from the lateral horn of the spinal grey matter T1-L3 (THORACOLUMBAR OUTFLOW). - It is called the intermediolateral cell column containing the cell bodies of the sympathetic neurons. - The neurons leave this region to form the white rami communicans. - The postganglionic fibres synapse at the chain and collateral ganglia. - All preganglionic neurons of the sympathetic nervous system use acetylcholine. - All postganglionic neurons of the sympathetic nervous system uses noradrenaline. |
Sympathetic innervation to the head and neck
- The superior cervical chain ganglia innervates the branches of the common, internal and external carotid artery; the submandibular, sublingual, parotid gland and ALL sympathetic activity to head and neck. - The routes of Sympathetic innervation of Head and Neck is routed to glands via external carotid, facial and lingual arteries. Sympathetic Autonomic innervation of Upper eyelids - Levator palpebrae superioris muscle (the smooth muscle is innervated by sympathetic fibres from the superior cervical ganglion) - Iris, the radial muscle dilator pupillae (via short and long ciliary nerves > carotid artery from Superior cervical ganglion) Lacrimal gland - SCG > Deep petrosal nerve > nerve of pterygoid canal > maxillary, V2 > lacrimal nerve V1 by communicating branch of zygomatic n. |
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AUTONOMIC NERVOUS SYSTEM DYSFUNCTION (NEUROPATHY) It affects both the sympathetic and parasympathetic nervous systems. It can affect multiple organs because many viscera are innervated by autonomic nerves. It causes postural hypotension, retention of urine, impotence, diarrhoea or occasionally constipation, diminished sweating, impaired pupillary responses and cardiac arrhythmia. - This condition occurs in diseases like diabetes mellitus, amyloidosis and Guillian-Barre syndrome. - Sweating over the site of a resected parotid gland (removal of the gland) can indicate Frey's syndrome. - Horner's syndrome as explained in the previous note (special senses). |
PARASYMPATHETIC AND SYMPATHETIC DIFFERENCES PARASYMPATHETIC: Parasympatheticafferents: Has dorsal horn (segments S2- S4 only) Parasympatheticefferents:lateralmass (nohorn;S2-S4 only) SYMPATHETIC: Sympatheticafferents: Has dorsal horn(segments T1- L2 only) Sympatheticefferents: Has lateral horn(segments T1- L2 only) |
