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30 Cards in this Set
- Front
- Back
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GENERAL PROPERTIES OF ANS
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* Motor nervous system that controls glands, cardiac and smooth muscle (also called visceral motor system)
* Regulates unconscious processes that maintain homeostasis (BP, body temperature, respiratory airflow) * ANS carries out its actions without our intent (automatically) -- biofeedback techniques (training that teaches some people to control hypertension, stress and migraine headaches) |
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VISCERAL REFLEXES
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* Unconscious, automatic responses to stimulation of glands, cardiac or smooth muscle
* Receptors detect internal stimuli (stretch, blood chemicals, body temperature, etc) * Afferent neurons connect to interneurons in the CNS * Efferent neurons carry motor signals to the effectors -- ANS is the efferent neurons of these reflex arcs -- glands, smooth or cardiac muscle is the effectors * ANS modifies effector activity rather than causing it -- high BP activates a visceral baroreflex |
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VISCERAL REFLEXES TO HIGH BLOOD PRESSURE (BP)
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* High BP detected by:
-- arterial stretch receptors -- signal transmitted to CNS -- efferent signals travel to heart -- heart slows reducing BP * Separate reflex arc for low BP exists |
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AUTONOMIC VS SOMATIC NERVOUS SYSTEM
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* Somatic nervous system
-- consciously perceived sensations -- excitation of skeletal muscle -- one neuron connects CNS to organ * Autonomic nervous system -- unconsciously perceived visceral sensations -- involuntary inhibition or excitation of smooth muscle, cardiac muscle / glandular secretion -- two neurons needed to connect CNS to organ are preganglionic and postganglionic neurons |
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AUTONOMIC VS SOMATIC PATHWAYS
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* ANS = 2 neurons span the distance from CNS to effectors
-- presynaptic neuron cell body in CNS (brain / spinal cord) -- postsynaptic neuron cell body in peripheral ganglion |
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BASIC ANATOMY OF THE ANS
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* Preganglionic neuron
-- cell body in brain or spinal cord -- axon is myelinated type B fiber that extends to autonomic ganglion * Postganglionic neuron -- cell body lies outside the CNS in an autonomic ganglion -- axon is unmyelinated type C fiber that terminates in a visceral effector |
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DIVISIONS OF ANS (PART I)
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* Two divisions that innervate the same target organs
* Two divisions may have cooperative or contrasting effects * Sympathetic division prepares body for physical activity (increases heart rate, BP, airflow, blood glucose levels, etc) * Parasympathetic division has calming affect on many body functions & assists in bodily maintenance (digestion and waste elimination) * Autonomic tone is the normal rate of activity that represents the balance of the two systems * Effects of each depend upon neurotransmitters released |
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DIVISIONS OF ANS (PART II)
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* 2 major divisions:
parasympathetic AND sympathetic * Dual innervation -- one speeds up organ -- one slows down organ * Sympathetic NS increases heart rate * Parasympathetic NS decreases heart rate |
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SOURCES OF DUAL INNERVATION
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* Sympathetic (thoracolumbar) division:
-- preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord * Parasympathetic (craniosacral) division -- preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord |
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LOCATION OF AUTONOMIC GANGLIA
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* Sympathetic Ganglia
-- trunk (chain) ganglia near vertebral bodies -- prevertebral ganglia near large blood vessel in gut (celiac, superior mesenteric and inferior mesenteric) * Parasympathetic Ganglia: -- terminal ganglia in wall of organ |
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SYMPATHETIC (THORACOLUMBAR) NERVOUS SYSTEM
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* Origin of presynaptic neurons
-- lateral horns of gray matter of thoracic to lumbar cord (T1-L2) * Sympathetic chain ganglia (paravertebral) -- 3 cervical, 11 thoracic, 4 lumbar, 4 sacral & 1 coccygeal ganglia -- white communicating rami (myelinated -preganglionic) -- gray communicating rami (unmyelinated -postganglionic) * Postganglionic cell bodies -- sympathetic chain ganglia along the spinal column -- prevertebral ganglia at a distance from spinal cord >>celiac ganglion >>superior mesenteric ganglion >>inferior mesenteric ganglion * Neuronal convergence= each postganglionic cell receives synapses from multiple preganglionic cells -- produces widespread effects on multiple organs |
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NEUROTRANSMITTERS AND RECEPTORS
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* Types of neurotransmitters released and types of receptors on target cells determines effects of ANS
* Sympathetic NS has longer lasting effect--reaches bloodstream before being broken down * Many other substances also released as neurotransmitters (enkephalin, substance P, neuropeptide Y, neurotensin, nitric oxide) |
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ANS NEUROTRANSMITTERS
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* Classified as either
1. Adrenergic or 2. Cholinergic neurons based upon the neurotransmitter released |
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CHOLINERGIC NEURONS AND RECEPTORS
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* Cholinergic neurons release ACh from preganglionic neurons & from para-sympathetic postganglionic neurons
* Excites / inhibits depending upon receptor type and organ involved |
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ORGANS INNERVATED BY SYMPATHETIC NERVOUS SYSTEM
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* Structures innervated by each spinal nerve
-- sweat glands, arrector pili mm., blood vessels to skin & skeletal mm. * Thoracic & cranial plexuses supply: -- heart, lungs,esophagus & thoracic blood vessels -- plexus around carotid artery to head structures * Splanchnic nerves to prevertebral ganglia supply: -- GI tract from stomach to rectum, urinary & reproductive organs |
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ADRENAL GLANDS
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* Paired glands sit on superior pole of each kidney
* Cortex: secretes steroid hormone * Medulla: modified sympathetic ganglion that secretes neurotransmitters (hormones) into blood and not onto other neurons -- catecholamines (85% epinephrine & 15% norepinephrine) * Sympathoadrenal system is the closely related functioning adrenal medulla and sympa-thetic NS |
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PARASYMPATHETIC (CRANIOSACRAL) NERVOUS SYSTEM
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* Origin of preganglionic fibers
-- pons and medulla oblongata for cranial nerve nuclei -- spinal cord segments S2-S4 * Pathways of preganglionic fibers: -- cranial nerves III, VII, IX and X (cardiac, pulmonary, esophageal, abdominal aortic plexus) -- arising from sacral spinal cord (pelvic splanchnic nerves & inferior hypogastric plexus) * Terminal ganglia in target organs due to long pre-ganglionic and short postganglionic fibers |
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CHOLINERGIC RECEPTORS FOR ACh
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* ACh binds to 2 classes of receptors:
1. Nicotinic receptors -- occur on all dendrites and cell bodies of ANS -- postganglionic neurons, in adrenal medulla, and at neuromuscular junctions (skeletal muscle) -- excitatory when ACh binding occurs 2. Muscarinic receptors: -- occur on all gland, smooth muscle & cardiac muscle cells that receives cholinergic innervation -- either excitatory/inhibitory when ACh binding occurs due to subclasses of muscarinic receptors |
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PARASYMPATHETIC FUNCTIONS OF CRANIAL NERVES
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* Oculomotor nerve (III)
-- narrows pupil & focuses lens * Facial nerve (VII) -- regulates secretion of tear, lacrimal & 2 salivary glands * Glossopharyngeal (IX) -- regulates parotid salivary gland * Vagus nerve (X) -- muscles and glands of the viscera as far inferiorly as the proximal half of colon |
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ENTERIC NERVOUS SYSTEM
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* Nervous system of the digestive tract
* Composed of 100 million neurons found in the walls of digestive tract (no components found in CNS) * Has its own reflex arcs * Regulates motility of viscera and secretion of digestive enzymes and acid in concert with the ANS |
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ADRENERGIC NEURONS AND RECEPTORS
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* Adrenergic neurons release norepinephrine (NE) )
-- from postganglionic sympathetic neurons only -- Excites or inhibits organs depending on receptors -- Alpha1 and Beta1 receptors produce excitation -- Alpha2 and Beta2 receptors cause inhibition -- Beta3 receptors(brown fat) increase thermogenesis * NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyl-transferase (COMT) * Function by means of 2nd messengers: --Beta receptors activate cAMP, alpha 2 inhibit it, and alpha 1 use calcium |
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PHYSIOLOGICAL EFFECTS OF THE ANS DUAL INNERVATION
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* Most of viscera receive nerve fibers from both parasympathetic & sympathetic divisions
-- antagonistic effects oppose each other 1. exerted through dual innervation of same effector cells (ie: heart slowed down or speeded up) 2. exerted because each division innervates different cells (ie: pupillary dilator muscle & constrictor pupillae change pupil size) -- cooperative effects seen when 2 divisions act on different effectors to produce a unified effect(salivation) >>parasympathetic NS increases salivary serous cell secretion >>sympathetic NS increases salivary mucous cell secretion * Both divisions do not normally innervate an organ equally |
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PHYSIOLOGICAL EFFECTS OF THE ANS CONTROL WITHOUT DUAL INNERVATION
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* Adrenal medulla, arrector pili muscles, sweat glands & many blood vessels receive only sympathetic fibers
* Sympathetic tone = a baseline firing frequency provides partial constriction (aka: vasomotor tone) -- increase in firing frequency (vasoconstriction) -- decrease in firing frequency (vasodilation) * Vasomotor tone can shift blood flow from one organ to another according to changing needs -- sympathetic stimulation increases blood to skeletal & cardiac muscles (reduced blood to skin) |
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SYMPATHETIC TONE
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* Sympathetic division prioritizes blood vessels to skeletal muscles & heart in times of emergency.
* Blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise. |
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SYMPATHETIC RESPONSES
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*Dominance by the sympathetic system is caused by physical or emotional stress (“E situations”--emergency, embarrassment, excitement, exercise )
* Alarm reaction = flight or fight response -- dilation of pupils -- increase of heart rate, force of contraction & BP -- decrease in blood flow to nonessential organs -- increase in blood flow to skeletal & cardiac muscle -- airways dilate & respiratory rate increases -- blood glucose level increase * Long lasting due to lingering of NE in synaptic gap and release of NE by the adrenal gland |
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PARASYMPATHETIC RESPONSES
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* Enhance “rest-and-digest” activities
* Mechanisms that help conserve and restore body energy during times of rest * Normally dominate over sympathetic impulses * SLUDD type responses (salivation, lacrimation, urination, digestion & defecation) and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil * Paradoxical fear when there is no escape route or no way to win -- causes massive activation of parasympathetic division -- loss of control over urination and defecation |
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CONTROL OF AUTONOMIC NERVUS SYSTEM
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* Not aware of autonomic responses because control center is in lower regions of the brain
* Hypothalamus is major control center -- input: emotions and visceral sensory information (smell, taste, temperature, osmolarity of blood, etc) -- output: to nuclei in brainstem and spinal cord -- posterior & lateral portions control sympathetic NS (increase heart rate, inhibition GI tract, increase temperature) -- anterior & medial portions control parasympathetic NS (decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility) |
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CENTRAL CONTROL OF AUTONOMIC FUNCTION
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ANS is regulated by several levels of the CNS
* limbic system connected to hypothalamus -- pathway through which emotions influence ANS * hypothalamus (major visceral motor control center) -- nuclei for primitive functions (hunger, thirst, sexuality) * reticular formation & brainstem nuclei -- can respond directly to sensory input from cardiac, vasomotor, & GI tract * spinal cord reflexes: -- defecation & micturition reflexes are integrated in the spinal cord -- brain can inhibit these responses consciously |
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DRUGS AND THE NERVOUS SYSTEM
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* Sympathomimetics enhance sympathetic activity
-- stimulate receptors / increase NE release * Sympatholytics suppress sympathetic activity -- inhibit NE release / block receptors * Parasympathomimetics enhance activity while Parasympatholytics suppress activity * Management of clinical depression -- Prozac blocks reuptake of serotonin to prolong its mood-elevating effect -- MAO inhibitors interfere with breakdown of monoamine neurotransmitters * Caffeine competes with adenosine (inhibitory causing sleepiness) by binding to its receptors |
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AUTONOMIC DYSREFLEXIA
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* Exaggerated response of sympathetic NS in cases of spinal cord injury above T6
* Certain sensory impulses trigger mass stimulation of sympathetic nerves below the injury * Results: -- vasoconstriction which elevates blood pressure -- parasympathetic NS tries to compensate by slowing heart rate & dilating blood vessels above the injury -- pounding headaches, sweating warm skin above the injury and cool dry skin below -- can cause seizures, strokes & heart attacks |
