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Autonomic Nervous System. Dr Dileep Verma Associate Professor Deptt of Physiology KGMU. Lecture-4 :Topics. Parasympathetic division- Preganglionic parasympathetic fibre Autonomic Ganglia Postganglionic parasympathetic fibre.
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Autonomic Nervous System Dr DileepVerma Associate Professor Deptt of Physiology KGMU
Lecture-4 :Topics Parasympathetic division- Preganglionic parasympathetic fibre Autonomic Ganglia Postganglionic parasympathetic fibre
Learning Objectives • Details organization and distribution Parasympathetic nervous system
Parasympathetic division • Preganglionic neurons in the brainstem and sacral segments of spinal cord • Ganglionic neurons in peripheral ganglia located within or near target organs
Contd…. Parasympathetic Nervous System • Parasympathetic Preganglionic neurons -Cranial parasympathetic outflow Midbrain outflow Bulbar outflow -Sacral parasympathetic outflow Preganglionic fibers Postganglionic fibers
CONTD.. • Preganglionic fibers leave the brain as cranial nerves III, VII, IX, X • Sacral neurons form the pelvic nerves • Almost 75% of all parasympathetic outflow travels along the vagus nerve (cranial nerve X) • Pre ganglionic fiber are- Large & Myelinated
CONTD.. Parasympathetic postganglionic fibres – • Innervate the target tissue • Very small fiber • Nonmyelinated • Conduction velocity low
Receptors • The parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter. • Receptor-Cholinergic • The ACh acts on two types of receptors – Muscarinic Nicotinic
Contd… • Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of the postganglionic nerve. • The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.
Anatomical Differences between the Sympathetic and Parasympathetic Divisions
1-Parasympathetic stimulation causes-- Constriction of pyloric sphincter Positive inotropic effect Negative inotropic effect Increased gastric secretion
2-What percentage of all parasympathetic nerve fibers are in the vagus nerve ? 25 50 75 100
3-Which cranial nerve have parasympathetic fibers? 3rd 4th 5th 6th
4-The maximum parasympathetic fibers are contained in the: III nerve VII nerve IX nerve X nerve
5-Stimulation of postganglionic parasympathetic neurons causes-- Dilatation of pupil Secretion of saliva Release of epinephrine from adrenal medulla Sweating