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The State Medical and Pharmaceutical University “Nicolae Testemitanu” Republic of Moldova Department of Human Anatomy The Anatomy of the Autonomic Nervous System Lecturer Globa Lilian Divisions of the NS • CNS Central Nervous System –Brain & spinal cord Divisions of the NS • PNS Peripheral Nervous System –Cranial nerves 12 pairs –Spinal nerves 31 pairs –Ganglia (sensitive and autonomic) –Nervous plexus Cranial and Spinal Nerves Somatic System • Somatic system includes nerves that take sensory information from external sensory receptors to the CNS and motor commands away from the CNS to the skeletal muscles. – Primarily voluntary – Reflexes are automatic, involuntary responses to a stimulus. Autonomic System • Autonomic system regulates the activity of cardiac and smooth muscles and glands. • Is involuntary • 2 component parts: – Sympathetic division brings about “fight or flight” responses. (norepinephrine) – Parasympathetic division brings about relaxed responses or “housekeeper system” (acetycholine) The autonomic divisions • Parasympathetic • Sympathetic • slow down the body activity when the body is not under stress • increase overall body activity during times of stress, excitement or danger • fight or flight response • Rest and digest • hormone epinephrine Sympathetic and Parasympathetic • Are Antagonistic • Work towards the automatic, subconscious maintenance of homeostasis. • The Peripheral Nervous System – The autonomic nervous system – Somatic nervous system • The part of the peripheral nervous system that controls the movement of skeletal muscles or transmits somatosensory information to the central nervous system. – Autonomic nervous system • The portion of the peripheral nervous system that controls the body’s vegetative functions. • The Peripheral Nervous System – The autonomic nervous system-sympathetic division – Sympathetic division • The portion of the autonomic nervous system that controls functions that accompany arousal and expenditure of energy. – Sympathetic ganglia • Nodules that contain synapses between preganglionic and postganglionic neurons of the sympathetic nervous system. • The Peripheral Nervous System – The autonomic nervous system-sympathetic division – Preganglionic neuron • The efferent neuron of the autonomic nervous system whose cell body is located in a cranial nerve nucleus or in the intermediate horn of the spinal gray matter and whose terminal buttons synapse upon postganglionic neurons in the autonomic nervous system. Postganglionic neuron • Neurons of the autonomic nervous system that form synapses directly with their target organ. • The Peripheral Nervous System – The autonomic nervous system-sympathetic division – Adrenal medulla • The inner portion of the adrenal gland, located atop the kidney, controlled by sympathetic nerve fibers; secretes epinephrine and norepinephrine. • The Peripheral Nervous System – The autonomic nervous systemparasympathetic division – Parasympathetic division • The portion of the autonomic nervous system that controls functions that occur during a relaxed state. • Supports activities involved with increases in the body’s supply of stored energy including salivation, gastric and intestinal motility, secretion of digestive juices, and increased blood flow to the gastrointestinal system. Autonomic nerve fibers • Motor pathways of somatic nervous system – SINGLE NEURON links CNS + skeletal muscle • Autonomic nervous system – motor pathway needs TWO NEURONS – PREGANGLIONIC FIBER – has cell body in CNS , axon synapses in autonomic ganglion; second neuron – POSTGANGLIONIC FIBER extends to visceral effector Efferent fibers of ANS • 1. Preganglionic fibers • 2. Postganglionic fibers 1 2 Simple Nerve Path Reflex Arc Sympathetic division • Thoracolumbar division C8-L2 • Preganglionic fibers in thorax & lumbar regions; leave spinal nerves thru white rami & enter sympathetic ganglia • Paravertebral ganglia – occur as chains along sides of vertebral column • Ganglia + fibers that connect them = sympathetic trunks • Collateral ganglia - within abdomen near large blood vessels • Preganglionic fibers that enter paravertebral ganglia can synapse within ganglia , can move up or down synaptic trunk & synapse; or may pass thru paravertebral ganglia & synapse in collateral ganglia • Axons of second neuron ( postganglionic fiber) leave paravertebral ganglia via gray rami & return to spinal nerve before going to effector • White rami – myelinated; gray ramiunmyelinated • Exception – • Preganglionic fibers pass thru sympathetic ganglia and extend to medulla of adrenal glands • Stimulation causes release of norepinephrine & epinephrine Parasympathetic division • Cranio-sacral division • Neurons of brainstem & sacral region • Preganglionic fibers – long, go to ganglion near or within various organs; myelin • Postganglionic fibers – short; unmyelinated • Cranial region – CN III, VII, IX, X • Sacral region – motor to viscera of pelvic cavity s2-s4 Divisions of the ganglia • Sympathetic Nervous System 1. Paravertebral ganglia 2. Prevertebral ganglia • Parasympathetic Nervous System 3. Paraorganic ganglia 4. Intraorganic ganglia Fight or Flight: parasympathetic and sympathetic are the 2 divisions of the Autonomic nervous system; which functions without conscious effort controls visceral activities regulates smooth muscle, cardiac muscle, and glands Autonomic neurotransmitters • Preganglionic fibers – S & P – acetylcholine – cholinergic fibers • Postganglionic fibers – P = acetylcholine • Postganglionic fibers – S – norepinephrine = adrenergic fibers • Exceptions post g fibers that stimulate sweat glands & vasodilation = ACh Actions of autonomic neurotransmitters • Ach - muscarine receptors & nicotinic receptors • Muscarine receptors – all postganglionic parasym. fibers & sympathetic cholinergic fibers – response excitatory & slow • Nicotinic receptors – pre & post ganglionic fibers of para & sym response rapid, excitatory • Adrenal gland releases epi & norepi as hormones but only norepi can be used as neurotransmitter by SNS • Adrenergic receptors – alpha & beta • Alpha – causes vasoconstriction • Beta – causes bronchiodilation • Acetylcholinesterase – decomposes Ach • Norepi removed by active transport back into nerve endings Referred pain