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

Learning Objectives Details organization and distribution Parasympathetic nervous system

Organization: Parasympathetic NS

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

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..

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.

Distribution of neurons

Parasympathetic Responses

Effects of stimulation of ANS

Anatomical Differences between the Sympathetic and Parasympathetic Divisions

1-Parasympathetic stimulation causes-- A. Constriction of pyloric sphincter B. Positive inotropic effect C. Negative inotropic effect D. Increased gastric secretion

2-What percentage of all parasympathetic nerve fibers are in the vagus nerve ? A.25 B.50 C.75 D.100

3-Which cranial nerve have parasympathetic fibers? A. 3 rd B. 4 th C. 5 th D. 6 th

4-The maximum parasympathetic fibers are contained in the: A. III nerve B. VII nerve C. IX nerve D. X nerve

5-Stimulation of postganglionic parasympathetic neurons causes-- A.Dilatation of pupil B.Secretion of saliva C.Release of epinephrine from adrenal medulla D.Sweating