ANS and PNS Flashcards
SNS
- Thoracolumbar
- Fight or flight
PNS
- Craniosacral
- Rest and digest
SNS effects on the heart
- Stimulation of HR at SA node: + chronotropic effect
- Stimulation of AV nodal conduction: + dromotropic effect
- Stimulation of myocardial contractility: + inotropic effect
- Primarily through activation of B1 adrenergic receptors (epi is the NT)
PNS effects on the heart
- Inhibition of HR at SA node: - chronotropic effect
- Inhibition of AV nodal conduction: - dromotopic effect
- Inhibition of atrial contractility (mild): - inotropic effect
- All via action of muscarinic cholinergic receptors
Propanolol
- B1-adrenergic antagonist
- Used to treat hypertension and tachycardias
Characteristics of SNS 2-synapse pathway
- Short preganglionic fibers
- Long postganglionic fibers
- Divergence of preganglionic fivers
Characteristics of PNS 2-synapse pathway
- Long preganglionic fibers
- Short postganglionic fibers
- Less divergence of preganglionic fibers
Preganglionic fibers
- Small diameter, slower conducting myelinated B-fibers
- Release ACh that binds to N2 nicotinic cholinergic receptors
Postganglionic fibers
- Small diameter, slower conduction myelinated C-fibers
- Parasympathetic: ACh binds a muscarinic cholinergic receptors
- Sympathetic: most use norepi that binds an adrenergic receptor (A or B)
Chromaffin cells
- Of adrenal medulla
- Directly innervated by SNS
- Primarily releases Epi, but also some Norepi
- Hormones carried by the blood to affect other tissues
- Helps in maintaining blood pressure
Mechanism of A1 adrenoreceptors
- Inactive: aq subunit of Gq protein bound to GDP
- Active: Norepi bound to A1 receptor, aq subunit bound to GTP
- aq-GTP then activates PLC–PIP2–DAG + IP3
- DAG increases PKC, IP3 causes Ca2+ release
Mechanism of B adrenoreceptors
- Inactive: as subunit of Gs protein bound to GDP
- Active: Norepi bound to B receptor, as subunit bound to GTP
- as-GTP then activates adenylyl cyclase which then converts ATP to cAMP
Mechanism of nicotinic cholinergic receptors
- ACh opens an ion channel for Na+ and K+
- Receptor has 5 subunits
Mechanism of muscarinic cholinergic receptors
- GPCRs linked to PLC
- PLC leads to generation of IP3 and DAG
- Inhibition of adenylate cyclase leading to decreased cAMP
d-Tubocurarine
-Antagonist of N1 Nicotinic ACh receptors
Hexamethonium
-Antagonist of N2 nicotinic ACh receptors
Atropine
-Antagonist of M1, M2, M3, M4, M5 muscarinic ACh receptors
Pheochromocytoma
- Tumor of adrenal medulla
- Excessive amounts of norepi (epi too though, rarely dopa)
- Hypertension
- Sweating
- Cold hands and feet
- Anxiety
- Palpitations
- Epigastric pain
- Tremor
- Headache
- Test with assay evaluating metanephrine and free catecholamines
Postsynaptic effects of M1, M3, M5 muscarinic cholinergic receptors
- PLC activation
- Increased intracellular Ca2+
- Increased DAG
Postsynaptic effects of M2, M4 muscarinic cholinergic receptors
- Inhibition of adenylyl cyclase
- Decreased cAMP generation
Nuclei of origin for vagus nerve
- Dorsal motor nucleus of vagal nerve
- Medulla
Edinger-Westphal nucleus
- Cell bodies of preganglionic fibers traveling with CN3
- Pupillary light reflex
Superior salivatory nucleus
-Cell bodies of preganglionic fibers traveling with CN7 to pterygopalatine and submandibular ganglia
Inferior salivatory nucleus
-Cell bodies of preganglionic fibers traveling with CN9 to the otic ganglion
Myenteric plexus
- In the gut
- Regulates motility–PNS activation is depolarizing and stimulates APs to cause contractions
- PNS regulation (SNS inactivation)
- Excessive activation: diarrhea
- ACh released by PNS nerve terminals
- Norepi released by SNS nerve terminals–hyperpolarizes and relaxes muscles, sphincter constriction
Submucosal plexus
- Controls GI secretions
- PNS regulation (SNS inactivation)
Micturition-Bladder Filling
- SNS dominates
- Relaxation of detrusor–B2
- Contraction of internal sphincter–A1
- L1-L3 contributions
Micturition-Bladder Emptying
- PNS dominates
- Contraction of detrusor–M
- Relaxation of internal sphincter-M
- S2-S4 contributions
