ANS1 Flashcards
ANS
- 2 divisions- SNS and PNS
- SNS is thoracolumbar
- PNS is craniosacral
- enteric is sometimes in
- SNS and PNS innervate smooth and cardiac muscle, secretory epithelia, glands
- arterial pressure, GI motility and secretions, bladder, sweating, temp
- SNS is fight or flight, PNS is rest and digest
- survival possible but function compromised without
SNS activation
- stimulation of heart rate at SA node- pos chronotropic effect
- stimulation of AV nodal conduction- pos dromotropic effect
- stimulation of myocardial contractility- pos inotropic effect
PNS activation
- inhibition of HR at SA node- neg chronotropic
- inhibition of AV nodal conduction- neg dromotropic
- inhibition of atrial contractility- mild, neg inotropic effect
- both systems always on, one just wins out
2 synapse pathway
- preganglionic neuron in CNS and postganglionic neuron either in paravertebral or near organ and then target cell
- pre is short in SNS, long in PNS
- post is long in SNS, short in PNS
- pre are small slow myelineated type B
- post are small slow unmyelinated type C
divergence
-SNS pre neurons make multiple contacts to post- about 100
PNS only 10-15
en passant synapses
-single axon has broad actions in target tissues
somatic neurons
- pathway is monosynaptic
- Ach binds to N1 nicotinic cholinergic receptors on post synaptic membrane of skeletal muscle
N1 receptor antagonist
-d-tubocurarine
Nicotinic agonist
nicotine
SNS and PNS pre ganglionic neuron
- releases Ach
- binds to N2 nicotinic cholinergic receptors on postsynaptic membrane of the postganglionic neuron
N2 receptor antagonist
-hexamethonium
post ganglionic PNS
- Ach
- receptor is muscarinic cholinergic (type 1-5)
post ganglionic SNS
- norepi
- receptor is adrenergic receptor a or B
- some can also still release Ach and go to muscarinic receptors
SNS and adrenal
- directly innervates chromaffin cells of adrenal medulla
- releases epi and some norepi
- hormones in blood now, affect multiple tissues
- 5-10 times longer, and reach tissues without their own sympathetic innervation
- secretes enough epir and norepi to maintain near normal BP if sympathetic innervation to heart is disrupted
SNS target tissues
- express distinct andrenergic receptor subtypes with different affinities for epi and norepi
- sometimes use muscarinic cholinergic receptors-eccrine sweat glands
- are broadly activated by epi/norepi from medulla
PNS target tissues
-express various combinations of 5 muscarinic cholinergic receptors
alpha 1
BV
- norepi binds, activates G protein
- alpha/GTP subunit activates phospholipase C
- cleaves PIP2 to DAG and IP3 (releases Ca from ER/SR)
- Ca and DAG activate protein kinase C
beta1
heart
beta2
bronchi
mechanism of B receptors
- norepi binds, activates G protein
- alpha/ATP subunit activates adenylyl cyclase
- cAMP activates physiologic actions
mechanism of nicotinic cholinergic receptors
- somatic muscle cells and post synaptic receptors for 1 synapse for SNS and PNS (somatic N1, ANS N2)
- Ach binds
- conformational change
- depolarization and Na in makes EPSP
muscarinic cholinergic receptors
- exert action through G proteins linked to:
1. PLC leading to generation of IP3 and DAG (M1,3,5)- like a1
2. inhibition of andenylate cyclase leading to decreased cAMP (m2,4)
d-tubocurarine
N1 nicotinic Ach receptor antagonist
hexamethonium
N2 nicotinic Acg receptor antagonist
atropine
M1,3,5 muscarinic Ach receptor antagonist
propanolol
-B1 andrenergic (which is more sensitive to epi than norepi) receptor antagonist
beta vs alpha
- alpha more sensitive to norepi
- beta to epi
- reflected by adrenal medullary contribution
- epi affects heart, lungs, liver
- norepi affects vasculature
Massive SNS discharge results in
- mydriasis and eyelid retraction (a1)
- increased HR and force of contraction (b1)
- bronchial dilation (B2)
- vasoconstriction (a1)*
- sweating- muscarinic
- increased cellular met, epi from adrenal medulla (a and B)
- decreased GI motility, smooth muscle walls (a and B) and increased contraction of sphincters (a1)
*there is increased blood flow to active muscles (vasodilation via B-andrenergic receptors of skeletal and coronary muscle) but adenosine causes most of the vasodilation
pheochromocytoma
- neoplasm of the adrenal medulla (sometimes extra medullary
- secrete excessive amounts of norepi, epi, or both resulting in sustained hypertension, cold hands and feet, sweating, feeling hot
- increased dopamine secretion rare
- occur in less than 0.1% of hypertensive patients
- observed at all ages males and females but esp during 4th-5th decade
- tumors are well circumscribed with weights ranging from 1g to several kg
- treatment is excise the tumor
- can treat a1 abd b1 antagonists can be used
horners syndrome
- anhidrosis, ptosis, miosis
- injuries to SNS produce deficits ipsilateral to the lesions
