Autonomic Nervous System Flashcards
3 sympathetic nervous system activations
- chronotropic
- dromotropic
- inotropic
all positive effects via beta1-adrenergic receptors (usually norepinephrine)
- stimulate heart via SA node
- stimulate AV nodal condunction
- stimulate myocardial (ventricular) contractility
3 parasympathetic nervous system activations
- chronotropic
- dromotropic
- inotropic
all negative effects via muscarinic cholinergic receptors (usually ACh)
- inhibit heart rate at SA node
- inhibit AV nodal conduction
- inhibit atrial contractility (mild compared to sympathetic ventricular stimulation)
sympathetic VS parasympathetic in regards to preganglionic VS postganglionic fibers
symp: pre are short, post are long
para: pre are long, post are short and close to target tissues
locations of pre VS postganglionic fibers
pre: lie in CNS in columns in brain stem and spinal cord; exit to make synapses
post: in peripheral ganglia that project to target tissues
A, B, and C fibers
A: large-diameter, fast conducting myelinated motor neurons of skeletal muscle
B: small diameter, slow conducting myelinated preganglionic axons
C: small diameter, slow conducting unmyelinated postganglionic axons
divergence in SNS VS PNS
SNS: one preganglionic axon can contact ~100 postganglionic neurons by collateral branching
PNS: one preganglionic axon contacts 15-20 postganglionic
-enables widespread responses to numerous effectors when necessary
varicosities (in passing synapses)
characteristic of autonomic nervous system, with single axon having broad actions in target tissues
somatic nervous system origin, ganglia, and target organs
central nervous system, w/o ganglia, to skeletal muscle
-N1 nicotinic acetylcholine receptor on muscle
parasympathetic axon system origin, ganglia, and target organ
autonomic nervous system, w/ ganglia, to smooth muscle, cardiac muscle, or glands
- ganglion has N2 nicotinic cholinergic (ACh) receptor
- release ACh to muscarinic ACh receptor on organ (M1-5)
sympathetic axon system origin, ganglia, and target organ
autonomic nervous system, w/ ganglia, to smooth muscle, cardiac muscle, and glands, including adrenal glands
- ganglion has N2 nicotinic cholinergic (ACh) receptors
- all except adrenals and sweat have alpha/beta-adrenergic receptors (NE>E)
- adrenal “ganglion” Chromaffin cell has N2 receptor for ACh, and releases E to alpha/beta adrenergic receptors all over body
- sweat glands have mjuscarinic ACh receptors
Chromaffin cells
in adrenal medulla, and directly innervated by SNS
- release mostly epinephrine (80%), and carried in body to various tissues
- last 5-10 times longer b/c inactivated slowly, and reach tissues not innervated by sympathetic
mechanism of action of alpha1-adrenoreceptors (active VS inactive); GPCR metabotropic
inactive: alpha-q subunit of Gq is bound to GDP
active: NE bound to receptor, so alpha-q bound to GTP
- active to phospholipase C, which releases PIP2 that breaks into DAG and IP3
- IP3 releases Ca++, which acts on PRO kinase C with DAG
mechanism of action of beta-adrenoreceptors (active VS inactive); GPCR metabotropic
inactive: alpha-s subunit of Gs is bound to GDP
active: NE bound to receptor, so alpha-s bound to GTP
- active to adenylyl cyclase, which converts ATP to cAMP
mechanism of nicotonic cholinergic receptors; odds VS evens; GPCR metabotropic
M1, 3, 5: PLC leads to generation of IP3 and DAG (like alpha1 adrenergic receptors)
M2, 4: inhibition of adenylate cyclase causes decreased cAMP (opposite of B1/2)
antagonists of N1 (nicotinic ACh) N2 (nicotinic ACh) M1/3/5 (muscarinic ACh) M2/4 (muscarnic ACh) beta1 (adrenergic)
N1 - d-Tubocuraine
N2 - hexa-methonium
M1-5 - atropine (less selective for 2/4)
beta1 - propranolol
alpha 1 metabotropic adrenoreceptor effects in SNS
mydriasis (pupil dilation) and eyelid retraction
vasoconstriction
sphincter contraction
alpha+beta: epinephrine from adrenal medulla, smooth muscle wall contraction
beta metatropic adrenoreceptor effects in SNS
1: increased heart rate and force of contraction
2: bronchial dilation
alpha+beta: epinephrine from adrenal medulla, smooth muscle wall contraction
muscarinic cholinergic metatropic effects on SNS
sweating
epinephrine VS norepinephrine targets
E: beta-adrenergic receptors (CO, BMR, bronchiodilation, inhibit intestines)
NE: alpha-adrenergic receptors (BP elevation, urinary excretion)
pheochromocytoma cause, effect, treatment
tumor of the adrenal medulla (rarely extramedullary sites) secretes excessive amounts of NE, and less so E (since not enough cortisol); rarely increase dopamine
- sustained (rarely episodic) HTN
- in all ages/genders, esp. 40-50 yrs
- treat by excising well-circumscribed tumors (1 gram to kilograms)
- treat symptoms with alpha1 and beta1-adrenergic antagonists
Horner syndrome effects, types of lesions
injuries to SNS make ipsilateral lesions causing miosis (constricted pupil), ptosis (drooping eyelid), anhydrosis (lack of sweating)
- 1st order lesion: brainstem interrupting descending tracts (stroke)
- 2nd order lesion: preganglionic sympathetic cell bodies or fibers supplying eye synapse in superior cervical ganglion
- 3rd order lesion: postganglionic sympathetic cell bodies or fibers
pupillary constriction/miosis is controlled by?
CN III (pupillary light reflex); occulomotor
gland secretion is controlled by?
CN VII - nasal/lacrimal/submandibular
CN IX - parotid (glossopharyngeal)
CN X - gastric, pancreatic
GI peristalsis is controlled by?
CN X - increased motility and sphincter relaxation
