ANS-SoNS anatomy and physiology Flashcards
Origin of parasympathetic neurons
cranial nerve nuclei and sacral segments of spinal cord (S2-S4)
Origin of sympathetic neurons
Thoracic (T1-T12) and lumbar (L1-L5) segments of spinal cord
Location of parasympathetic ganglia
innervated organs
Location of sympathetic ganglia
2 paravertebral chains along spinal cord (most) or in prevertebral ganglia in the abdomen (some)
cholinergic receptor subtypes
nicotinic (N) and muscarinic (M)
somatic nervous system neurotransmitter and receptor
acetylcholine (ACh), nicotinic cholinergic receptors
PNS neurotransmitters, pre and postganglionic
preganglionic neurons release ACh, which interacts with nicotinic cholinergic receptors. Postganglionic neurons release ACh, which interacts with muscarinic cholinergic receptors.
SNS neurotransmitters, pre and postganglionic
pre release ACh, which interacts nicotinic cholinergic receptors. Postganglionic neurons release: norepinephrine at effect organs (alpha adrenergic in blood vessels, eye, GI tract) and beta-adrenergic (beta 1 in heart and smooth muscle but low affinity). acetylcholine at sweat glands (muscarinic cholinergic receptors) and dopamine (at the renal vascular smooth muscle, dopamine receptors).
Neurotransmitter(s) released by adrenal medulla
epinephrine (EPI) and some NE that interact with adrenergic synapses with alpha1, beta1, beta2 receptors.
ratio of pre- to post-ganglionic neurons in the PNS versus SNS
PNS = ratio is 1:1, which functions in a discrete/localized fashion. SNS = ratio is 1:20-50, which allows SNS to function in a diffuse or widespread manner.
Action and regulation of the adrenal medulla
The adrenal medulla is basically a modified sympathetic ganglion. It secretes epinephrine into the circulation.
Effects mediated by nicotinic neuronal receptors at autonomic ganglia
cardiovascular: chiefly sympathetic effects (vasoconstriction, tachycardia, elevated Bp). GI/urinary tract: parasympathetic effects (nausea, vomiting, diarrhea, urination).
Effect of B1 receptors on heart
chronotropy, positive inotropy, increase in conduction velocity.
How is renin released from the kidney?
NE acts on beta1 receptors on juxtoglomerular cells.
mechanism for pupillary constriction
alpha1 agonism causes constriction of radial pupillary dilator muscle, causing mydriasis/dilation.
aqueous humor mechanism
beta2 receptor agonism causes increased production, which increases IOP. alpha1 receptor agonism causes vasoconstriction, leading to decreased IOP.
GI tract regulation
smooth muscle is relaxed via presynaptic alpha2 receptor agonism, which inhibits release of ACh and ACh-mediated muscle contraction. Direct relaxiation is mediated by beta2 receptors on smooth muscle.
Uterine smooth muscle control
relaxation via B2 receptors
uretal sphincter, bladder base, prostate control
contraction via alpha1 receptors promotes continence
bladder wall musculature regulation
relaxation via beta3 receptors promotes continence
ejaculation control
alpha1 receptor activation in vas deferens, seminal vesicles, and prostate.
tremor, shakiness mechanism
b2 receptor action on contractile proteins
glycogenolysis mechanism
beta2 receptor agonism
lipolysis in adipose cells mechanism
beta3 receptor agonism
insulin control
alpha2 receptor agonism decreases insulin secretion (major effect). beta2 receptor agonism increases insulin release.
Effect of different receptor subtypes on blood pressure
alpha1: vasoconstriction (by increasing TPR and BP). beta1: chronotrpy and inotropy increase CO and BP. beta2: vasodilation (decreases TPR and BP). **alpha2: decrease in SNS outflow decreases BP.
Outline the baroreceptor reflex arc
stretch receptors in the carotid sinus or aortic sense increased arterial pressure –> synapse with baroreceptor neurons in the spinal cord –> inhibit sympathetic discharge from the medulla resulting in vasodilation and decreased HR (reflex bradycardia) –> decreased arterial pressure. *This reflex also increases vagus (PNS) nerve activity.
relaxation of baroreceptor
decrease in arterial pressure disinhibits tonic sympathetic discharge –> NE released in heart -> NE agonism at beta1 receptors causes reflex tachycardia + NE alpha1 agonism at blood vessels causes vasoconstriction –> increaase in arterial BP. *Also decreases vagus nerve action.
respiratory tract control
bronchial smooth muscles are relaxed and bronchodilation occurs via beta2 receptors. Upper respiratory tract mucosal blood vessels are constricted via alpha1 receptors.
Location of muscarinic receptors
heart, lungs, GI/GU tract, eye
what is cycloplegia?
block of accomodation.
