ANS overview Flashcards
sympathetic nervous system
SNS
fight or flight response
Parasympathetic nervous system
PSNS
rest and digest response
regulation of ANS
-regulation of the activity of smooth and cardiac muscle, glands, lymphoid and some adipose tissue
Parasympathetic vs sympathetic actions
often opposing but not always
autonomic tone of ANS
involuntary, meaning that these pathways tend to be active to some degree at rest
somatic nervous system
controls skeletal muscles and mostly voluntary
what is the anatomy of the ANS
-2 neuron path
ganglia
group of cell bodies outside of CNS
First neuron
-CNS
-preganglionic neuron
-located in CNS
-projects to the autonomic ganglia
second neuron
-peripheral
-postganglionic neuron
-located outside of the CNS in the autonomic ganglia
-projects to the target organ
primary transmitter of all preganglionic neurons
acetylcholine
transmitter in all ___________ neurons is acetylcholine
PSNS postganglionic
transmitter in most SNS postganglionic neuron is
norepinephrine
other places we have ACh, epinephrine, and dopamine
ACh- sweat glands
-epinephrine- adrenal medulla
-dopamine- renal vasculature
PSNS postganglionic neurons
-short
-synapse on the target cell
-release ACh to activate muscarinic receptor on the target organ
PSNS preganglionic neurons
-long
-synapse with postganglionic neurons at or near organ
-release ACh to activate nicotinic receptors on postganglionic neurons
SNS preganglionic neuron
-short
-synapse with postganglionic neuron near spinal cord
-release ACh to activate nicotinic receptors on postganglionic neurons
spinal cord is also called
paraverterbral sympathetic ganglion
SNS postganglionic neuron
-long
-synapse on the target organ
-release norepinephrine to activate adrenergic receptors on target organs
exceptions in the SNS sweat glands
-postganglionic neurons involved with stress-related excretion release norepinephrine (sweaty palms)
-postganglionic neurons involved with thermoregulation release ACh
exceptions in the SNS adrenal glands
-preganglionic neurons do not synapse in the paraverterbral sympathetic ganglion
-preganglionic neurons synapse directly on the adrenal gland, release ACh, and activate nicotinic receptors on the adrenal gland
-adrenal glands release epinephrine into systemic circulation
exceptions in SNS kidneys
-affected by dopamine (mainly synthesized locally, not ANS)
most postganglionic SNS release with neurotransmitter?
Norepinephrine
neuron types of the PSNS
cholinergic
-Acetylcholine (endogenous)
-muscarine (exogenous)
-nicotine (exogenous)
neuron types in SNS
adrenergic
-norepinephrine (noradrenaline, endogenous)
-epinephrine (adrenaline, endogenous)
influence of drugs on ANS
-mimic or block the effects of the two primary neurotransmitters (acetylcholine and norepinephrine/ epinephrine)
drugs that mimic neurotransmitters are referred to as
-receptor agonists
-these drugs activate receptors
drugs that block neurotransmitters are referred to as
-receptor antagonist
-these drugs block the endogenous neurotransmitters from activating receptors
classification of drugs that PSNS mimic acetylcholine
-cholinergic
-muscarinic agonist
-parasympathmimetic
classification of drugs that PSNS block acetylcholine
-anticholinergic
-muscarinic antagonist
-parasympatholytic
classification of drugs that SNS mimic norepinephrine
-adrenergic
-adrenergic agonist
-sympathomimetic
classification of drugs that SNS block norepinephrine
-antiadrenergic
-adrenergic antagonist
-sympatholytic
cholinoceptors
nicotinic - Nw,Nn
muscarinic - M1, M2, M3
adrenoceptors
alpha - a1, a2
beta - B1, B2, B3
nicotinic receptors
-ganglionic, skeletal muscles, neuronal CNS
-Na+ Ion Channel
-5 subunits ionotropic ligand-gated Na+ channels
-Opening leads to depolarization of membrane
-Lead to opening of voltage-gated sodium channels to produce action potential
-Selectively activated by nicotine (exogenous)
muscarinic receptors
-M1,M3, M5 (signal via Gq pathway– IP3–>mobilize Ca++ from intracellular stores. DAG, activate protein kinase C)
-M2, M4 (signal via G1 pathway)
alpha 1 receptors
-signal via Gq pathway
-mediates vasoconstriction
-IP3—-> mobilize Ca++ from intracellular stores
-DAG –> activates protein kinase C
-tissue distribution (vascular smooth muscle, genitourinary smooth muscle, intestinal smooth muscle, heart, liver)
alpha 2 receptor
-signal through Gi
-inhibit adenylyl cyclase
-reduced cAMP- dependent protein kinase activity
-activate certain K+ channels
-found pre-synaptically and function as autoreceptors to inhibit sympathetic output: results in decreased transmitter release
beta receptos
-signal through Gs
-activate adenylyl cyclase
-increase cAMP leading to protein kinase activation
-results in phosphorylation of ion channels and other proteins
pupilary constriction
(miosis)
circular muscle is constricted by activation of parasympathetic nerves (M3)
pupillary dilation
(mydriasis)
radial muscle is constricted by activation of sympathetic nerves (a1)
iris
ring of muscles oriented in two different ways whose activity determines the amount of light entering the eye through the pupil
glaucoma
increased intraocular pressure:
decreased outflow through trabecular network
increased secretion from ciliary body epithelium
ciliary muscle
-M3 agonist, pilocarpine
-contraction facilitates outflow of aqueous humor
-decreases intraocular pressure
ciliary body
-alpha 2 agonist, brimonidine
-inhibit production and increase outflow of aqueous humor
-decrease intraocular pressure
ciliary epithelium
-NE-beta
-secretion of aqueous humor
-beta antagonist (timolol)
-decrease intraocular pressure
