Intro to PNS Flashcards
Describe pathway of somatic nerves
Single neuron efferent pathway
Directly innervates skeletal muscle
Describe pathway of sympathetic nerves
Two neuron efferent pathway (preganglionic and postganglionic)
Preganglionic neuron - short
Postganglionic neuron - long
Ganglia are paravertebral (sympathetic chain) or prevertebral (celiac, s. & i. mesenteric)
Describe pathway of parasympathetic nerves
Two neuron efferent pathway (preganglionic and postganglionic)
Preganglionic neuron - long
Postganglionic neuron - short
Ganglia are in/near the structures innervated
Where does the sympathetic division originate?
T1-L2 (thoraco-lumbar division)
Where does the parasympathetic division originate?
Cranial nerves 3, 7, 9, 10 and sacral (cranio-sacral division)
What is the neurotransmitter of somatic nervous system?
ACh
What is the preganglionic neurotransmitter of parasympathetic nervous system?
ACh
What is the postganglionic neurotransmitter of parasympathetic nervous system?
ACh
What is the preganglionic neurotransmitter of sympathetic nervous system?
ACh
What is the postganglionic neurotransmitter of sympathetic nervous system?
NE
What are the exceptions to postganglionic neurotransmitter of sympathetic nervous system?
Normally NE
ACh - sweat glands
Dopamine - renal vascular smooth muscle
Describe synthesis and packaging of ACh
ACh synthesized from choline and acetyl-CoA by choline acetyltransferase (ChAT) ACh transported into vesicles by H+-coupled countertransporter (VAT) ACh released (with ATP and cotransmitters) in Calcium dependent process
Describe termination of ACh action
ACh rapidly degraded into choline and acetate by AChE
Choline is taken back up and recycled by Na-coupled choline cotransporter
Describe synthesis and packaging of NE
Tyrosine transported into nerve terminal by Na-coupled cotransporter Tyr converted to DOPA by tyrosine hydroxylase (rate limiting step) DOPA converted to dopamine Dopamine transported into vesicles by H+-coupled countertransporter (VMAT) Dopamine converted to NE by dopamine-beta-hydroxylase (DBH) NE released (with ATP, DBH, and cotransmitters) in Calcium dependent process
Describe termination of NE action
NE reuptake into nerve terminal by NET
NE diffuses from the site of action
How is epinephrine formed?
NE converted to EPI by phenylethanolamine-N-methyltransferase in the adrenal medulla
What are metabolic products of catecholamines?
Normetanephrine and metanephrine
MHPG (MOPEG)
VMA
What are the general categories of cholinergic receptors?
Nicotinic
Muscarinic
What are the general categories of adrenergic receptors?
Alpha
Beta
What type of receptor are nicotinic receptors?
Ionotropic
What type of receptor are muscarinic receptors?
G protein coupled receptors
What are the types of nicotinic receptors and where are they located?
Nm (neuromuscular junction)
Nn (autonomic ganglia, adrenal medulla)
What are the types of muscarinic receptors, where are they located, and which G protein is used?
M1 - autonomic ganglia, Gq
M2 - heart, Gi
M3 - smooth muscle, glands, endothelium, Gq
What is the response of M1 activation?
Late EPSP in ganglia
What is the response of M2 activation?
Decreased heart rate and contractility, slows spontaneous depolarization
What is the response of M3 activation?
Contraction of smooth muscle
Secretion
What type of receptor are adrenergic receptors?
G protein coupled receptors
What are the types of alpha receptors, where are they located, and which G protein is used?
Alpha1 - smooth muscle in vasculature, Gi and Go
Alpha2 - pancreatic beta cells, platelets, nerve endings, Gi and Go
What are the types of beta receptors, where are they located, and which G protein is used?
Beta1 - cardiac muscle, Gs
Beta2 - smooth muscle pulmonary, liver, skeletal muscle, Gs
Beta3 - adipose cells, Gs
What is the response of Alpha1 activation?
Vasoconstriction
GU relaxation
Glycogenolysis and gluconeogenesis
What is the response of Alpha2 activation?
Decreased transmitter release, causes contraction
What is the response of Beta1 activation?
Increased heart rate, force of contraction, and renin release
What is the response of Beta2 activation?
Relax smooth muscle
Increase glycogenolysis and K uptake
What is the response of Beta3 activation?
Increased lipolysis
What is the response of dopaminergic receptor activation by NE?
Relaxation of renal vascular smooth muscle
What is the predominant tone of bronchiole smooth muscle?
Parasympathetic (no sympathetic innervation)
M3 receptors - constriction
No sympathetic but B2 receptors can be activated by circulating epinephrine, causing dilation
What is the predominant tone of arterioles?
Sympathetic
Alpha receptors - constriction
What is the predominant tone of veins?
Sympathetic
Alpha receptors - constriction
What is the predominant tone of the iris?
Parasympathetic
M2 receptors - constriction
What are the two negative feedback loops involved in regulation of MAP?
Hormonal loops (renin/angiotensin) ANS loop (Baroreceptor reflex)
What are the 4 variables that the sympathetic system directly influences that controls blood pressure?
Increased TPR
Heart rate
Contractile force
Increased venous tone
What variable does the parasympathetic system influence that controls blood pressure?
Decreased heart rate
Describe the autonomic functions in the eye
Sympathetic - Alpha1 receptor, mydriasis (dilation)
Parasympathetic - M3 receptor, miosis (constriction)
What are the symptoms of Horner’s syndrome?
Anhydrosis
Miosis (constriction)
Ptosis
Describe test for Horner’s syndrome and the rationale of each step
Cocaine - inhibits NE reuptake, should cause mydriasis (dilation)
- If no dilation, indicates a problem at either pre or postganglionic neuron
Hydroxyamphetamine - causes release of NE from presynaptic vesicles, should cause mydriasis (dilation) and requires intact postganglionic nerve with some NE in vesicles.
- If no dilation, indicates a problem with the postganglionic neuron
What drug inhibits uptake of choline by Na+-coupled cotransporter?
Hemicholinium
Reduced uptake of choline = neuromuscular dysfunction
What drug activates alpha 2 receptors, thereby inhibiting NE release?
Clonidine