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61 Cards in this Set
- Front
- Back
Three divisions of the ANS
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Parasympathetic → rest and digest
Sympathetic → fight or flight Enteric → brain of the gut |
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Sympathetic and Parasympathetic Autonomic Ganglia
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Relay stations between CNS and organs
- Sympathetic: paravertebral chain of ganglia parallels spinal cord, but there are a few more distal prevertebral ganglia (celiac, splanchic, mesenteric) - Parasympathetic ganglia are at the organ of innervation |
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The Sympatho-Adrenal System
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Adrenal Gland located above kidneys has an outer cortex (secretes steroid hormones) and an inner medulla (secretes Epi and NE in response to sympathetic stimulation) – different functions, different embryonic origins. The adrenal medulla is like a sympathetic ganglion and its cells are unique neuroendocrine cells → permits global sympathetic stimulation of all cells in the body via the bloodstream
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Sympathetic: Spinal origin, Fiber types, Activation
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Origin: thoracolumbar spine (C8-L12)
Fibers: short pre-ganglionic, long post-ganglionic Activation: discharges as a unit (mass activation) |
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Parasympathetic: Spinal origin, Fiber types, Activation
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Origin: craniosacral (CN III, VII, IX, X=vagus nerve), (S2-S4)
Fibers: long pre-ganglionic, short post-ganglionic Activation: discreet activation of specific targets |
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Sympathetic systemic effects and response
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"Catabolic → mediates release of Epi and NE from adrenal medulla, which can affect entire organism. Mediates the fight or flight response.
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Parasympathetic systemic effects and response
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"Anabolic → modulates sympathetic neurotransmission through muscarinic cholinergic receptors on sympathetic post-gang. neurons, no mass activation (can ↓ HR without affecting bladder activity, for example). Systems are in opposition and continuously adjust in response to the changing environment.
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Enteric nervous system
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Controls GI motility and secretion and is comprised of submucosal, myenteric, and subserosal plexuses. Its activity is modulated by the sympathetic (inhibits) and parasympathetic (activates) systems, but denervation studies have shown the enteric NS can maintain function independent of any other autonomic innervation.
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Autonomic nerve baseline firing rate
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Refers to the level of activity (frequency of depolarization) of an autonomic nerve → helps maintain a "resting tone" or basal level of stimulation in a tissue or organ.
The baseline rate is ↑ or ↓ in response to stimuli in order to maintain homeostatic balance. |
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ANS innervation of organs
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Most tissues receive innervation from both the SNS and PNS
Some receive innervation ONLY from the SNS Control of BP is primarily sympathetic |
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Organs that receive innervation from the SNS only
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Adrenal medulla
Kidney Pilomotor muscles Sweat glands |
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Parasympathetic stimulation effects - "DUMBBELSS + Abd cramping"
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Diarrhea
Urination Miosis Bradycardia Bronchoconstriction Lacrimation Erection Salivation Sweating Abdominal cramping |
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Baroreceptor reflex responses
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Drugs that ↑ BP produce reflex bradycardia
Drugs that ↓ BP produce reflex tachycardia |
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Baroreceptor reflex mechanims
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↑ arterial pressure activates stretch receptors in aortic arch and carotid sinus → initiates afferent impulses to brain stem vasomotor center (VMC). Via solitary tract fibers, the VMC activates the vagal motor nucleus, which ↑ vagal (parasympathetic) outlfow and slows heart. At the same time, the VMC ↓ stim of spinal intermediolateral neurons that activate SNS pregang fibers, and this ↓ SNS stim of heart and blood vessels. So, drugs that ↑ BP produce reflex bradycardia and those that ↓ BP attenuate this response causing reflex tachycardia.
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Sympathetic (adrenergic) response and primary receptors:
Heart |
Rate: ↑, β1
Force: ↑, β1 |
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Sympathetic (adrenergic) response and primary receptors:
Blood vessels |
Arteries: vasoconstriction, α1
Skeletal muscles: vasodilation, α1/β2 |
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Sympathetic (adrenergic) response and primary receptors:
Bronchial |
Bronchodilation, β2
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Sympathetic (adrenergic) response and primary receptors:
Uterus |
Contraction, α1
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Sympathetic (adrenergic) response and primary receptors:
Vas deferens |
Contraction, α1
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Sympathetic (adrenergic) response and primary receptors:
GI tract |
Relaxation α2
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Sympathetic (adrenergic) response and primary receptors:
Eye |
Rad. muscle (iris): contraction, α1
Circ. Muscle (iris): none Ciliary muscle: relaxation, β2 Net effect: mydriasis |
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Sympathetic (adrenergic) response and primary receptors:
Kidney |
Renin secretion, β1
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Sympathetic (adrenergic) response and primary receptors:
Pancreas |
↓ insulin secretion, α2
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Sympathetic (adrenergic) response and primary receptors:
Urinary bladder |
Detrusor: relaxation, β2
Trigone/Sphincter: contraction, α1 |
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Sympathetic (adrenergic) response and primary receptors:
Ureter |
Relaxation, M3
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Sympathetic (adrenergic) response and primary receptors:
Fat cells |
Lipolysis, β3
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Sympathetic (adrenergic) response and primary receptors:
Liver |
↑ glycogenolysis, α1/β2
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Sympathetic (adrenergic) response and primary receptors:
Nasal secretions |
Decreased, α1
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Sympathetic (adrenergic) response and primary receptors:
Salivary secretions |
Decreased, α1
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Sympathetic (adrenergic) response and primary receptors:
Sweat glands |
Decreased, α1
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Parasympathetic (cholinergic) response and primary receptors:
Heart |
Rate: ↓, M2
Force: ↓, M2 |
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Parasympathetic (cholinergic) response and primary receptors:
Blood vessels |
Arteries: little effect
Skeletal muscles: little effect |
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Parasympathetic (cholinergic) response and primary receptors:
Bronchial |
Bronchoconstriction, M3
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Parasympathetic (cholinergic) response and primary receptors:
Uterus |
Variable response
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Parasympathetic (cholinergic) response and primary receptors:
Vas deferens |
None
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Parasympathetic (cholinergic) response and primary receptors:
GI tract |
Contraction, M3
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Parasympathetic (cholinergic) response and primary receptors:
Eye |
Rad. muscle (iris): none
Circ. Muscle (iris): contraction, M3 Ciliary muscle: contracion, M3 Net effect: miosis |
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Parasympathetic (cholinergic) response and primary receptors:
Kidney |
None
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Parasympathetic (cholinergic) response and primary receptors:
Pancreas |
None
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Parasympathetic (cholinergic) response and primary receptors:
Urinary bladder |
Detrusor: contraction, M3
Trigone/Sphincter: relaxation, M3 |
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Parasympathetic (cholinergic) response and primary receptors:
Ureter |
Relaxation, M3
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Parasympathetic (cholinergic) response and primary receptors:
Fat cells |
Little effect
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Parasympathetic (cholinergic) response and primary receptors:
Liver |
Little effect
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Parasympathetic (cholinergic) response and primary receptors:
Nasal secretions |
Increased, M3
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Parasympathetic (cholinergic) response and primary receptors:
Salivary secretions |
Increased, M3
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Parasympathetic (cholinergic) response and primary receptors:
Sweat glands |
Increased, M3
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Organs with a dominant cholinergic response
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Heart
Lungs GI tract Ciliary and Circ. Muscles of the eye Detrusor of the urinary bladder Secretory glands (nasal, salivary, sweat) |
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Organs with a dominant adrenergic response
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Blood vessels
Uterus Vas deferens Radial muscles of the eye Kidney Pancreas Ureter Adipocytes Liver |
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Locations of cholinergic neurotransmission
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All preganglionic neurons of the entire ANS are cholinergic (nicotinic), and all parasympathetic postganglionic neurons are cholinergic (muscarinic)
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Metabolism of acetylcholine
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Choline acetyltransferase is synthesized in the cell body & transported to axon terminals which are high in mito →abundance of AcetylCoA substrate. Choline is taken up by active transport from the extracellular fluid. Uptake of choline is rate-limiting step in ACh synthesis. ACh is synthesized in cytoplasm. High and low affinity transporters for choline in axon terminal. High affinity transporter is unique to cholinergic neurons and is dependent on extracellular Na+. The transporter recycles choline from the synapse. ACh is stored in vesicles of the axon terminals. Concentration of ACh in vesicles is ATP dependent. Note that the ACh is RECYCLED by cholinesterase
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Acetylcholinesterase (AChE)
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Removes ACh from the synapse by degradation to choline + acetate → terminates neurotransmission at cholinergic synapses
Time required is less than 1 millisecond |
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Sympathetic/Parasympathetic cross-reactivity
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Some cholinergic systems have M1 autoreceptors on the presynaptic neuron, for negative feedback regulation of firing. These receptors can also be involved in drug reactions and rarely, one branch (para or symp) can affect the other branch via these receptors.
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Muscarinic ACh receptors
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Locations: autonomic ganglia, sympathetic effector neurons (pre-synaptic, inhibitory), pre-synaptic autoreceptors, parasympathetic neuroeffector junctions and CNS
High affinity for muscarine Second messenger-operated (G protein coupled) Able to regulate (inhibit) sympathetic system |
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Nicotinic ACh receptors
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Locations: sympathetic and parasympathetic ganglia, skeletal muscle, CNS
High affinity for nicotine Ligand gated ion channels (Na+) Does not regulate parasympathetic system |
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Muscarinic ACh receptors: Gq coupled subtypes
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M1: sympathetic presynaptic neuroeffectors
M3: bladder, eye, lungs, vasculature M5: locations, pathways, and effects not well known Note: M3 receptors are present in vasculature despite the fact that there is no parasympathetic innervation of vasculature, reason is unknown. |
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Muscarinic ACh receptors: Gi coupled subtypes
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M2: heart
M4: locations, pathways, and effects not well known |
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Properties of Muscarinic Cholinergic Receptors: M1 -"neural"
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Principal location: Parasympathetic, pre-synaptic autoreceptors, CNS (note that all 5 subtypes on neurons of CNS)
Signal transduction: Increased IP3 and DAG Effects: Modulation of neurotransmissioncognition in CNS |
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Properties of Muscarinic Cholinergic Receptors: M2 - "cardiac"
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Principal location: Cardiac tissue (sinoatrial & AV nodes) & smooth muscle, some in CNS
Signal transduction: Increased K+ efflux or decreased cAMP, Hyperpolarization Effects: Slowing of heart rate and conduction |
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Properties of Muscarinic Cholinergic Receptors: M3 - "glandular"
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Principal location: Smooth muscle & glands, some in CNS
Signal transduction: Increased cGMP due to NO stimulation Effects: Vasodilation |
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Properties of Nicotinic Cholinergic Receptors: Nn - "neuronal"
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"Principal location: Autonomic Ganglia, Adrenal medulla
Signal transduction: Increased Na+ Influx – Depolarization (excitatory) Effects: Excitation of postganglionic neurons, increased release of NE in sympathetic system, ACh in parasympathetic. Release of Epi and NE at adrenal medulla |
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Properties of Nicotinic Cholinergic Receptors: Nm - "muscular"
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"Principal location: Somatic Neuromuscular Junctions
Signal transduction: Increased Na+ Influx – Depolarization (excitatory) Effects: Contraction of muscles |