AUTONOMIC NERVOUS SYSTEM PART I: SPINAL CORD

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1 AUTONOMIC NERVOUS SYSTEM PART I: SPINAL CORD How is the organization of the autonomic nervous system different from that of the somatic nervous system? Peripheral Nervous System Divisions Somatic Nervous System operates under conscious control controls skeletal muscles Autonomic Nervous System operates without conscious instruction coordinates organ systems functions Hypothalamus Brain stem Limbic system Preganglionic neuron From brain or spinal cord Postganglionic neuron Outside central nervous system Synapse on to effector 2-Step Pathway Autonomic Nervous System Neural Pathway Preganglionic Neurons originate in hypothalamus goes through brain stem and spinal cord leaves central nervous system to synapse at ganglia Postganglionic Neurons originates in ganglia synapses on effector tissue cardiac or smooth muscle, glands, etc Autonomic Ganglia Synapse between pre- & post-ganglionic neurons: Synaptic terminals of preganglionic neurons Releasing the neurotransmitter ACETYLCHOLINE Dendrites & cell bodies of postganglionic neurons Contains NICOTINIC receptors

2 Divisions of the Autonomic Nervous System Sympathetic Nervous System Flight or Fight activated only during exertion, stress, emergency, or orgasm Parasympathetic Nervous System Feed and Breed Controls or maintains resting state Digestion, kidney function, etc Divisions of the Autonomic Nervous System 2 divisions may work independently: some structures innervated by only 1 division 2 divisions may work together: each controlling one stage of a complex process 8 Effects of Increased Sympathetic Activity 1. Heightened mental alertness 2. Increased metabolic rate 3. Reduced digestive and urinary functions 4. Energy reserves activated 5. Increased respiratory rate and respiratory passageways dilate 6. Increased heart rate and blood pressure 7. Sweat glands activated 8. Orgasm 8 Effects of Parasympathetic Activation Constriction of pupils: restricts light entering eyes Secretion by digestive glands: exocrine and endocrine 3. Increases smooth muscle activity: along digestive tract 4. Constriction of respiratory airways 5. Defecation: stimulation and coordination 6. Contraction of urinary bladder: during urination 7. Reduction in heart rate: and force of contraction 8. Sexual arousal: stimulation of sexual glands

3 KEY CONCEPT The autonomic nervous system: operates largely outside our awareness has 2 divisions: sympathetic division: increases alertness, metabolic rate, and muscular abilities parasympathetic division: reduces metabolic rate and promotes digestion Uses 2-step pathway to reach organs/tissues: Preganglionic neuron Postganglionic neuron Autonomic Nervous System Summary Activation & Reflexes Divisions & Innervation 2-Step Pathway Ganglia Differences Neurotransmitters and Receptors

4 AUTONOMIC NERVOUS SYSTEM PART II: SYMPATHETIC NERVOUS SYSTEM Structure of the Sympathetic Division Cell bodies of preganglionic neurons in lateral gray horns between T1 and L2 Axons exit via ventral roots Preganglionic fibers are short Postganglionic fibers are long Sympathetic Nervous System Chain Ganglia Thoracolumbar (T1-L2) 23 chain ganglia close to spinal cord (one set on each side): cervical, thoracic, lumbar, sacral, and coccygeal Sympathetic Synaptic Pathways 1. Preganglionic neuron synapses at chain ganglia onto postganglionic neuron, then to organ or tissue. 2. Preganglionic neuron goes through chain ganglia (no synapse) then to collateral ganglia to synapse onto postganglionic neuron, then to organ or tissue. 3. Preganglionic neuron goes through chain ganglia (no synapse) then through collateral ganglia (no synapse) to synapse onto adrenal gland. Adrenal gland releases neurotransmitter-like hormones into blood (norepinephrine & epinephrine). Collateral Ganglia 3 collateral ganglia: celiac ganglia Postganglionic fibers innervate: stomach, liver, gallbladder, pancreas, and spleen superior mesenteric ganglia Postganglionic fibers innervate: small intestine and proximal 2/3 of large intestine inferior mesenteric ganglia Postganglionic fibers innervate: parts of large intestine, kidney, urinary bladder, sex organs Adrenal Medulla center of each adrenal gland release hormones (neurotransmitters) into bloodstream hormones (norepinephrine & epinephrine) sympathetically stimulate target cells

5 AUTONOMIC NERVOUS SYSTEM PART III: PARASYMPATHETIC NERVOUS SYSTEM What are the structures and pathways of the parasympathetic nervous system? Parasympathetic NS Ganglia Craniosacral: Cranial Nerves (4) Pupil constriction Salivary glands Nasal & lacrimal glands *Vagus Nerve (75%) Sacral Nerves (S2-S4) Defecation/Urination Sexual Arousal Parasympathetic Division Preganglionic fibers originate in brain stem and sacral segments of spinal cord Synapse in ganglia close to (or within) target organs Preganglionic fibers are long Postganglionic fibers are short Parasympathetic Preganglionic Fibers Cranial nerves from the mesencephalon, pons, and medulla oblongata: III (oculomotor) VII (facial) IX (glossopharyngeal) X (vagus) 75% of parasympathetic activity Lateral gray horns of sacral spinal nerves S2 S4: kidneys urinary bladder portions of large intestine sex organs

6 AUTONOMIC NERVOUS SYSTEM PART IV: NEUROTRANSMITTERS & RECEPTORS What are the neurotransmitters utilized by the autonomic nervous system? Neurotransmitters of Autonomic Nervous System Cholinergic Acetylcholine Receptors activated by acetylcholine: nicotinic muscarinic Acetylcholine All neurons exiting central nervous system will release acetylcholine Sympathetic preganglionic neurons Parasympathetic preganglionic neurons Motor neurons and Parasympathetic postganglionic neurons Norepinephrine only Sympathetic postganglionic neurons (most of them) Sympathetic Pathway Central nervous system activation of preganglionic neuron Preganglionic neuron releases acetylcholine in ganglia In ganglia, nicotinic receptors on postganglionc neuron are activated Or adrenal medulla is activated Postganglionic neurons release norepinephrine to an alpha or beta receptor on effector organ or tissue Adrenal medulla releases norepinephrine into blood Neuroendocrine Cells of Adrenal Medullae Secretes two neurotransmitters that function as hormones: epinephrine: Also called adrenaline Is 75 80% of secretory output norepinephrine Hormone time duration is minutes to hours instead of milliseconds

7 Adrenergic Receptors Activated by norepinephrine & epinephrine Alpha (α) receptors Alpha-1 (α1) Alpha-2 (α2) Beta (β) receptors Beta-1 (β1) Beta-2 (β2) Parasympathetic Pathway Central nervous system activation of preganglionic neuron Preganglionic neuron releases acetylcholine in ganglia In ganglia, nicotinic receptors on postganglionc neuron are activated Postganglionic neurons release acetylcholine to a muscarinic receptor on effector organ or tissue Cholinergic Receptors Activated by acetylcholine Nicotinic receptors On dendrites of postganglionic neurons Sympathetic & parasympathetic Muscarinic receptors On effector cells Parasympathetic only KEY CONCEPT Preganglionic neurons of the sympathetic & parasympathetic nervous systems release ACh as a neurotransmitter to a nicotinic receptor Sympathetic postganglionic nerurons release norepinephrine to alpha or beta receptors Parasympathetic postganglionic nerurons release acetylcholine to muscarinic receptors Dual Innervation Most vital organs receive instructions from both sympathetic and parasympathetic divisions 2 divisions commonly have opposing effects

8 Autonomic Reflexes Cardiovascular Reflexes Baroreflex Gastrointestinal Reflexes smell good food full large intestine Pupil Reflexes light regulation into eye Brain Centers for Autonomic Reflexes Hypothalamus regulation Medulla Oblongata: salivation swallowing digestive secretions peristalsis urinary function