Autonomic Nervous System

Autonomic Nervous System Chapter 9 Organization of autonomic neurons: CNS  Preganglionic neurons  Autonomic ganglion  Postganglionic neurons  visceral organ Autonomic Nervous System Sympathetic Division = Thoracolumbar division Preganglionic neurons  paravertebral ganglion (sympathetic chain) / prevertebral ganglion  postganglionic neurons  visceral organ Cell bodies of Preganglionic neurons lie in lateral horns of gray matter in thoraco-lumbar part of spinal cord and enter paravertebral ganglia through white communicating ramus of spinal nerves. It travels through chain and may synapse and postganglionic nerve fiber comes out through gray ramus. Thoraco-lumbar - Sympathetic trunks (T1-T12 – L1-L2) Pre ganglionic fibers (before synapse) are shorter than postganlionic fibers Preganglionic neurons are Cholinergic and secrete Acetylcholine. Post ganglionic fibers are Adrenergic and secrete Norepinephrine formerly called noradrenalin. Mass Activation: all sympathetic neurons get simultaneously activated. fight or flight – response to unusual stimuli (emergency, excitement, exercise, embarrassment), increases activity ↑ heart rate, breathing rate, blood pressure, pupil size, bladder size Collateral Ganglia Preganglionic nerve fibers exit paravertebral ganglia below diaphragm enter prevertebral ganglia. These include: Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion Preganglionic nerve fibers do not synapse in paravertebral ganglia but synapse in prevertebral ganglia. Preganglionic nerve fibers above diaphragm synapse in paravertebral ganglion. Postganglionic nerve fibers innervate visceral organs. Sympathoadrenal System Adrenal Gland has outer cortex and inner medulla. Adrenal medulla is a modified sympathetic ganglion. Neurons in adrenal medulla are activated along with sympathetic division. Neurons in adrenal medulla are without axons and release mostly Epinephrine and smaller quantity of Norepinephrine into blood. Therefore, epinephrine and norepinephrine act as hormones. Somatic NS ANS

• Stimulates skeletal muscles • Stimulates visceral organ • Motor neurons • Preganglionic and postganglionic neurons • No ganglia in SNS between CNS and skeletal • Autonomic ganglion between CNS and visceral muscles. organ. • Axon terminals and motor end plates • Varicosities and normal cell membrane • Only cholinergic • Both cholinergic and adrenergic

Parasympathetic Division = Craniosacral division Preganglionic neurons lie in brain nuclei of cranial nerves and sacral part of spinal cord. Cranio-sacral – 3rd, 7th, 9th, 10th cranial nerves and spinal nerve cord through 2nd, 3rd, 4th sacral spinal nerves Pre ganglionic fibers are longer than post ganglionic fibers Preganglionic neurons and Post ganglionic fibers are Cholinergic and secrete Acetylcholine. Rest and Digest response: maintains house-keeping activities, conserves energy, promotes digestion, defecation and diuresis ANS - Complementary and Cooperative actions Sympathetic and Parasympathetic Divisions are mostly antagonistic in action. Complementary Action: when both divisions have similar effects on a visceral organ. For example, parasympathetic division stimulates salivary glands to secrete more saliva by stimulating more water to it and sympathetic division causes saliva to become thicker due to constriction of blood vessels. Cooperative Action: Parasympathetic and sympathetic divisions do separate acts of a bigger function. Male sexual action needs erection and ejaculation. Parasympathetic division stimulates erection by relaxing blood vessels in penis. But sympathetic division stimulates ejection to complete the function.