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HUMAN ANATOMY LECTURE THIRTEEN AUTONOMIC NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM • Contains both motor and sensory neurons • Motor neurons - some are somatic and innervate skeletal muscles - some are autonomic and innervate smooth and cardiac muscle and glands • Sensory neurons are not divided into somatic and autonomic since there is an overlap in function ie/ pain receptors can stimulate both somatic and autonomic reflexes SOMATIC AND AUTONOMIC SYSTEMS Somatic Autonomic • Skeletal muscle • Conscious and unconscious movement • One synapse • Acetycholine (neurotransmitter) • Smooth and cardiac muscle, glands • Unconscious regulation • Target tissues stimulated or inhibited • Two synapses • Acetycholine by preganglionic neurons and Ach or norepinephrine by postganglionic neurons AUTONOMIC NERVOUS SYSTEM • Two axons - 1st is preganglionic, 2nd is postganglionic • Divided into sympathetic and parasympathetic divisions, also the enteric system • Sympathetic and parasympathetic divisions often supply the same organs but differ in responses ENTERIC SYSTEM • Consists of nerve plexuses within wall of digestive tract • Contributions from: sensory neurons between digestive tract and CNS, ANS motor neurons between CNS and digestive tract, and enteric neurons confined within the plexuses • Functions: - stimulate/inhibit smooth muscle contraction - stimulate/inhibit gland secretions - detect changes in content of lumen SYMPATHETIC SYSTEM Prepares body for physical activity “fight or flight” - heightened mental awareness - increased metabolic rate - reduced digestive and urinary functions - activation of energy reserves - increased respiratory rate and dilation of respiratory passageways - increased heart rate and BP - activation of sweat glands Axons reach organs through T1-L2 • Innervate - sweat glands, smooth muscles of blood vessels, skeletal muscles, skin, arrector pili - cardiac and pulmonary organs - organs of abdominopelvic cavity Ganglions • 1st (preganglionic) fibres are very short with cell bodies located in lateral grey horns and axons entering ventral roots • 2nd (postganglionic) fibres are long Neurotransmitters (excitatory) • • preganglionic secrete acetylcholine (Ach) postganglionic secrete mainly norepinphrine (NE) PARASYMPATHETIC SYSTEM Stimulates “vegetative” state: - decreased metabolic rate - decreased heart rate and BP - increased secretion by salivary and digestive glands - increased motility and blood flow in the digestive tract - stimulation of urination and defecation Reach organs through: • Cranial nerves - oculomotor (III), facial (VII), glossopharyngeal (IX) • Vagus nerve and thoracic nerves - heart, lungs, esophagus • Abdominopelvic nerve plexuses - stomach • Pelvic nerve plexuses - colon, urinary bladder, reproductive organs Ganglions • 1st (preganglionic) fibres are long synapsing near the effector • 2nd (postganglionic) fibres are short Neurotransmitter • preganglionic secrete Ach • postganglionic secrete Ach Sympathetic and parasympathetic systems work in opposition - one stimulates while one inhibits (using different neurotramsitters) Distribution of Autonomic Nerve Fibers
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