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ANS consists of motor neurons that
- innervate smooth and cardiac muscle and glands
- make adjustments to ensure optimal support for body activities
- operate via subconscious control
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what are other names for the autonomic nervous system
- involuntary nervous system
- general visceral motor system
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what is a similarity between somatic versus autonomic nervous systems
both have motor fibers
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what is a difference between somatic verses autonomic nervous system
- they have different
- effectors
- efferent pathways and ganglia
- target organ responses to neurotransmitters
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what are the effectors of the ANS
- cardiac muscle
- smooth muscle
- glands
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what are the effectors of the somatic nervous system
skeletal muscles
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efferent pathways of the ANS
- ANS pathway uses two nueron chain
- preganglionic neuron (CNS): has a thin, lightly myelinated preganglionic axon
- postganglionic neuron in autonomic ganglion outside CNS: nonmyelinated postganglionic axon that extends to effector organ
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neurotransmitter effects of the ANS
- preganglionic fibers release ACh
- postganglionic fibers releases norepinephrine or ACh at effectors
- effect is either stimulatory or inhibitory, depending on type of receptors
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neurotransmitter effects of the somatic nervous system
- all somatic motor neurons releases ACh
- effects always stimulatory
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what is epinephrine
adrenaline
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overlap of somatic and autonomic function
- most spinal and many cranial nerves contain both somatic and autonomic fibers
- adaptations usually involve both skeletal muscles and visceral organs
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what are the divisions of the ANS
- sympathetic division
- parasympathetic division
- dual innervation: all visceral organs served by both divisions but cause opposite effects
- dynamic antagonism between two divisions maintains homeostasis
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role of the parasympathetic division
- promotes maintenance activities and conserves body energy: directs digestion, diuresis, defecation
- as in person relaxing and reading after a meal: blood pressure/hreat rate/respiratory rate are low, gastrointestinal tract activity is high, iris constricted
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role of sympathetic division
- mobilizes body during activity'"fight or flight"
- exercise, excitement, emergency, embarrassment: increased heart rate, dry mouth, cold, sweaty skin, dilated iris
- during vigorous physical activity: shunts blood to skeletal muscles and heart, dilates bronchioles, causes liver to release glucose
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parasympathetic cranioscaral division
- long preganglionic fibers from brain stem and sacrum:
- extend form CNS almost to target organs
- synapse with postganglionic neurons in terminal ganglia close to/within target organs
- short postganglionic fibers synapse with effectors
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cranial part of parasympathetic division
- cell bodies in brain stem
- preganglionic fibers in ocuomotor, facial, glossopharyngeal, and vagus nerves
- oculomotor nerves: smooth muscle of the eye
- facial nerves: stimulate large glands in head
- glossopharyngeal nerves: parotid salivary glands
- vagus nerves: neck and nerve plexuses for all thoracic and abdominal viscera
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sacral part of parasympathetic division
- serves pelvis organs and distal half of large intestine
- from neurons in lateral gray matter of S2-S4
- axons travel in ventral root of spinal nerves
- synapse with ganglia in pelvic floor, intramural ganglia in walls of distal half of large intestine, urinary bladder, ureters, and reproductive organs
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sympathetic division
- preganglionic neurons are in spinal cord segments T1-L2 (form lateral horns of spinal cord)
- preganglionic bers pass through white rami communicantes and enter sympathetic trunk ganglia
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sympathetic trunks and pathways
- paraertebral ganglia vary in size, position, and number
- there are 23 paravertebral ganglia in sympathetic trunk: 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, 1 coccygeal
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upon entering sympathetic trunk ganglion short preganglionic fiber may
- synapse with ganglionic neuron in same trunk ganglion
- ascend or descend sympathetic trunk to synapse in another trunk ganglion
- pass through trunk ganglion and emerge without synapsing (only in abdomen and pelvis)
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how do postganglionic axons enter ventral rami
via gray rami communicantes
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what does the postanglionic axons innervate
- sweat glands
- arrector pili muscles
- vascular smooth msucle
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pathways to the head
- fibers emerge from T1-T4 and synapse in the superior cervical ganglion
- these fibers:
- innervate skin and blood vessels of the head
- stimulate dilator muscles of the iris
- inhibit nasal and salivary glands
- innervate smooth muscle of upper eyelid
- branch to the heart
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pathways to the thorax
- preganglionic fibers emerge from T1-T6 and synapse in cervical trunk ganglia
- postganglionic fibers emerge from middle and inferior cervical ganglia and enter nerves C4-C8
- these fibers innervate the heart via cardiac plexus, thyroid gland and the skin, lungs and esophagus
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pathways with synapses in collateral ganglia
- most fibers from T5-L2 synapse in collateral ganglia
- they form thoracic, lumbar, and sacral splanchnic nerves
- their ganglia include the celiac and the superior and inferior mesenteric
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pathways to the abdomen
- sympathetic
- preganglionic fibers from T6-L2 travel through thoracic splanchnic nerves
- synapses occur in celiac and superior mesenteric ganglia
- postganglionic fibers serve the stomach, intestines, liver, spleen, and kidneys
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pathways to the pelvis
- preganglionic fibers from T10-L2 travel via lumbar and sacral splanchnic nerves
- synapses occur in the inferior mesenteric and hypogastric ganglia
- postganglionic fibers serve the distal half of the large intestine, the urinary bladder, and the reproductive organs
- primarily inhibit activity of muscles and glands in abdominopelvic visceral organs
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adrenal medulla i misplaced...
sympathetic ganglion
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pathways with synapses in the adrenal medulla
- some preganglionic fibers pass directly to adrenal medulla without synapsing
- upon stimulation, medullary cells secrete norepinephrine and epinephrine into blood
- sympathetic ganglia and adrenal medulla arise from same tissue
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visceral reflexes
- visceral reflex arcs have same components as somatic reflex arcs, but visceral reflex arc has two neurons in motor pathway
- visceral pain afferents travel along same pathways as somatic pain fibers, contributing to phenomenon of referred pain
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visceral reflex pathway (steps)
- receptor in viscera:
- visceral sensory neuron:
- integration center: may be preganglionic neuron, may be dorsal horn interneuron, may be within walls of gastrointestinal tract
- motor neuron (2 neuron chain): preganglionic neuron, post ganglionic neuron
- visceral effector: response
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cholinergic fibers releases
- neurotransmitter ACh;
- all ANS preganglionic axons
- All parasympathetic postganglionic axons at effector synapse
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adrenergic fibers release
- neurotransmitter NE;
- most sympathetic postganglionic axons
- exception: sympathetic postganglionic fibers secrete ACh at sweat glands
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what two types of receptors bind to ACh
- nicotinic
- muscarinic
- (named after drugs that bidn to them and mimic ACh effects)
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nicotinic receptors
- found on sarcolemma of skeletal muscle cells
- all postganglionic neurons (sympathetic and parasympathetic)
- hormone-producing cells of adrenal medulla
- effect of ACh at nicotinic receptors is always stimulatory: opens ion channels, depolarizing postsynaptic cell
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muscarinic receptors
- found on all effector cells stimulated by postganglionic cholinergic fibers
- effect of ACh at muscarinic receptors can be either inhibitory or excitatory, depending on receptor type of target organ
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what are the two major classes of adrenergic receptors
- alpha
- beta
- (effects of NE depend on which subclass of receptor predominates on target organ)
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atropine
- anticholinergic; blocks muscarinic ACh receptors
- used to prevent salivation during surgery, and to dilate iris for examination
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neostigmine
- inhibits acetylcholinesterase that breaks down ACh
- used to treat myasthenia gravis
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what do over the counter drugs for colds, allergies, and nasal congestion do
stimulate adrenergic receptors
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what do beta blockers do
drugs that attach to B2 receptors to dilate lung bronchioles in asthmatics
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interaction of the autonomic divisions
- most visceral organs have dual innervation
- dynamic antagonism allows for precise control of visceral activity: sympathetic division increases heart and respiratory rates and inhibits digestion and elimination; parasympathetic division decreases heart and respiratory rates, and allows for digestion and discarding of wastes
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sympathetic tone
- sympathetic division controls blood pressure, even at rest
- vascular system-entirely innervated by sympathetic fibers
- sympathetic tone (vasomotor tone) keeps blood vessels in continual state of partial constriction
- sympathetic fibers fire more rapidly to constrict blood vessels and cause blood pressure to rise
- sympathetic fibers fire less rapidly to prompt vessels to dilate to decreases blood pressure
- alpha blocker drugs interfere with vasomotor fibers (used to treat hypertension)
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parasympathetic tone
- parasympathetic division normally dominates heart, smooth muscle of digestive and urinary tract organs, activate most glands except for adrenal and sweat glands (slows heart, dictates normal activity levels of digestive and urinary tracts)
- the sympathetic division can override these effects during times of stress
- drugs that block parasympathetic responses increase heart rate and cause fecal and urinary retention
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cooperative effects
- best seen in control of external genitalia
- parasympathetic fibers cause vasodilation; are responsible for erection of penis or clitoris
- sympathetic fibers cause ejaculation of semen in males and reflex contraction of a female's vagina
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unique roles of the sympathetic division
adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels receive only sympathetic fibers
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sympathetic division controls
- thermoregulatory responses to heat
- release of renin from kidneys
- metabolic effects: increases in metabolic rates of cells, raises blood glucose levels, mobilizes fats for use as fuels
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localized versus diffuse effects
- parasympathetic division: short-lived, highly localized control over effectors (ACh quickly destroyed by acetylcholinesterase)
- sympathetic division: longer lasting, bodywide effects (NE inactivated more slowly than ACh, NE and epinephrine hormones from adrenal medulla prolong effects)
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control of ANS function
- hypothalamus: main integrative center of ANS activity
- subconscious cerebral input via limbic system structures on hypothalamic centers
- other controls come from cerebral cortex, reticular formation, and spinal cord
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hypothalamic controls
- control may be direct or indirect (through reticular system)
- centers on hypothalamus control: heart activity and blood pressure, body temp, water balance and endocrine activity, emotional stages (rage, pleasure) and biological drives (sex, thirst, hunger), reactions to fear and fight or flight system
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cortical controls
- connections of hypothalamus to limbic love allow cortical influence on ANS
- voluntary cortical control of visceral activities is possible; e.g. biofeedback
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biofeedback
- awareness of physiological conditions with goal of consciously influencing them
- biofeedback training allows some to control migraines and manage stress
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