SNS Flashcards
how is autonomic outflow to target tissue organized? describe pathway of SNS. name any exceptions. DRAW it
- mediated through 2-neuron pathway
- pregang synapse on postgang in a GANGLION
- pregang is SHORT comes from CNS (thoracic/lumbar) and releases ACh
- postgang is LONG comes from ganglion releases NE - exception is SWEAT GLANDS
Name the 3 main targets that pregang symp fibers project to
- sympathetic chain
- adrenal medulla
- collateral gang
describe sympathetic chain ganglion paths
- spinal nerve route - same level
- sympathetic chain route - travel up or down the SCR before synapsing
describe the myelination of these pre vs postgang fibers
pre = myelinated; post = unmyelinated
=> white ramus and grey ramus
what allows for the widespread activation of sympathetic nervous system.
- connection between ganglia through the sympathetic chain. one pregang neuron can synapse on up to 20 postgang.
- direct innervation of postgang neurons
- indirect effects mediated by adrenal (NE released into bloodstream)
- bead-like varicosities
describe collateral ganglia route
innervates abdominal viscera
describe the adrenal medulla route
AM acts as a modified postgang fiber and release NE into the bloodstream
describe the difference between directly innervated tissue NE action and adrenal catecholamines
- directly innervated tissue NE action is terminated by uptake into presynaptic terminal (FAST ie millisec)
- action of adrenal catecholamine in general circulation requires degradation in liver (LONGER ie mins.)
how is specificity of function achieved in target tissue if NE will bin to ALL types of adrenergic RECEPTORS?
expression of adrenergic receptor is specific to tissue type and determines the response of each tissue.
list all of the adrenergic receptors and their GPCR
a1-2
b1-3
a1 couples to Gq
a2 couples to Gi
b1-3 couples to Gs
what GPCR pathway is alpha 1 receptors coupled to and where are they expressed?
a1 couples to Gq >PLC >IP3 > CA2+ > calmodulin > ca2+:calmodulin >MLCK > phos- MLC > contraction of smooth muscles
(excitatory in nature)
expressed in:
- SM of vasculature (vasoconstriction)
- Visceral organ sphincters
- Radial muscle of the eye (causes dilation)
- Alpha cell of pancreas to release glucagon
list the clinical uses of a1 agonist
- oral administration (OTC decongestants)
- topical administration (nasal spray, eye drops)
- intravenous administration (victims in shock)
what are some examples of oral a1 agonist. describe mechanisms and draw backs
oral decongestant
sudafed and sudafed PE
- activates adrenergic receptors express on blood vessels of nasal mucosa > vasoconstriction > shrinkage of NM
draw back:
can affect all body tissue ie. vasoconstriction of vasculature > increase BP
contraction of internal sphincter > decrease ability to urinate
what are some examples of topical administration of a1 agonist? describe mecs and draw backs?
topical decongestants: fewer side effects (possible rebound)
can also be used to decrease redness in the eye (visine). vasocon of BV in conjunctiva
how does a1 agonist treat shock?
shock = inadequate perfusion (from decrease blood supply)
phenylephrine raise BP
