2. Intro to ANS Flashcards
Where do the pre-ganglionic fibers of the Parasympathetic Nervous System arise from?
- CN nuclei III, VII, X
- Sacral region (S2-S4) of the spinal cord
Where do the pre-ganglionic fibers of the PNS synapse?
Ganglia close to the effector organ
In the PNS are the pre-ganglionic fibers long or short?
long
In the PNS are the post-ganglionic fibers long or short?
short
Where do the pre-ganglionic fibers of the Sympathetic Nervous System arise from?
- Thoracic (T1-T2) region of the spinal cord
- Lumbar (L1-L5) region of the spinal cord
Where do the pre-ganglionic fibers of the SNS synapse?
- Paravertebral ganglia close and parallel to the vertebral column
- Post-ganglionic axons lead to an effector organ
How is the role of the SNS illustrated by a person who is threatened? (4)
- HR increases
- Breathing is rapid and deep
- Skin is cold and sweaty
- Pupils dilate
How is the role of the PNS illustrated by a person who relaxes after a meal? (4)
- BP, HR, RR are low
- GI tract activity is high
- Skin is warm
- Pupils are constricted
What do sympathetic and parasympathetic pre-ganglionic fibers release?
Acetylcholine (ACh)
What are the two types of receptors for ACh?
- Muscarinic
- Nicotinic
What receptors do post-ganglionic nerves have?
Nicotinic
What do post-ganglionic sympathetic nerves release?
NE
What do post-ganglionic parasympathetic nerves release?
ACh
What receptors do NE from post-ganglionic sympathetic nerves bind to?
Adrenergic
What receptors do ACh from post-ganglionic parasympathetic nerves bind to?
Muscarinic
What is the SNS exception for sweat glands?
Post-ganglionic nerves release ACh, which binds to muscarinic receptors
Normally NE to adrenergic receptors
What is the SNS exception for the adrenal gland?
Adrenal gland is both post-ganglionic and effector organ, releasing NE
How does adrenergic transmission begin?
Tyrosine is transported actively into the noradrenergic nerve ending
What occures after tyrosine enters the nerve terminal?
Tyrosine is converted to DOPA by tyrosine hydroxylase and then to dopamine
What occurs in adrenergic transmission once dopamine is synthesized?
Dopamine is transported into the vesicles and then converted to NE by dopamine-beta-hydroxylase
Where is NE further converted to Epinephrine?
Adrenal Medulla
What is the agonist action for the α1 adrenergic receptor?
- Smooth muscle contraction
- Glycogenolysis
- Lipolysis
What is the agonist action for the α2 adrenergic receptor?
- Post-junctional: smooth muscle contraction
- Pre-junctional: inhibit NT release
What is the agonist action for the β1 adrenergic receptor?
- Contraction
- Increase cardiac rate and force
What is the agonist action for the β2 adrenergic receptor?
Relaxation of visceral smooth muscle
What is the agonist action for the β3 adrenergic receptor?
- Lipolysis in fat cells
- Detrusor muscle relaxation
What is the fate of catecholamines?
-
NE in the synaptic space is actively re-uptaken into the nerve and the storage vesicles (U1)
- It is the most important mechanism for termination of the action
- NE penetrates into smooth cells (U2) and diffuses away from the receptor site.
What is the fate of NE after it penetrates into smooth cells (U2)?
Inactivated by the COMT enzyme to normetanephrine (NMN)
How is ACh synthesized?
From Ac-CoA + choline through the catalytic action of choline acetyl transferase (CHAT)
What terminates the action of ACh?
Acetylcholine-esterase (ACHE) hydrolyzes ACh, terminating the action of the transmitter
Where are muscarinic receptors (mAChR) primarily located?
- On effector cells that are innervated by postganglionic parasympathetic nerves:
- Smooth muscle
- Heart
- Secretory glands
What receptors are G protein-coupled?
- Muscarinic receptors
- Dopamine receptors
Where are nicotinic receptors (nAChR) located?
- On postganglionic nerve cell bodies:
- __At all autonomic ganglia
- Adrenal medulla
- Motor end-plate of SKM at the NMJ in somatic NS
What receptors are ligand-gated ion channels?
Nicotinic receptors
What are nicotinic receptors permeable to?
Cations
What is the signal transduction mechanism of nicotinic receptors?
Open Na+ and K+ channels at:
- Autonomic ganglia
- Motor-end plate
What is the effect of dopamine on the heart?
-
Increases myocardial contractility and CO
- Without changing HR
- D4 receptors
What is the effect of dopamine on the kidney?
- Diuresis: excessive production of urine
- Natriuresis: Na excretion in urine, lowers [Na] in blood, which decreases BV
Receptors present along the nephron, with prox tubule epithelial cells showing the highest density
Where are purinergic nerves found? (5)
- GI Tract
- Vasculature
- Lungs
- Bladder
- CNS
What is stored in the vesicles of purinergic nerve endings?
When released, whic purinergic receptor does it directly activate?
ATP
P2 receptors
In purinergic transmission ATP can also be broken down to what?
What does it activate?
Adenosine
P1 receptors (adenosine receptors)
In purinergic transmission what is the function of Adenosine?
Regulate the release of NE through a feedback mechanism.
In purinergic transmission what is the function of ATP?
Can act as a co-transmitter with NE and ACh
Release of more than one neurotransmitter from the same nerve terminal may result in…
Synergistic = opposite actions
What is the function of the G protein-linked receptor Gαs?
- Activates effector enzymes such as adenylyl cyclase leading to the:
- Production of cAMP
- Activation of PKA
What is the function of the G protein-linked receptor GαI?
Inhibits adenylyl cyclase, which causes decreased cAMP production
What is the function of the G protein-linked receptor GαQ?
- Activates phospholipase C (PLC)
- Hydrolyzes PIP2
- Stimulating PKC
- Releasing Ca2+ from intracellular binding sites by IP3
What is the main integration center of ANS activity?
Hypothalamus
Whats effects may be superimposed on the effects exerted by the hypothalamus?
Limbic System
- Also plays an important role in:
- Pattern of sexual activity
- States of rage and fear
What also makes contributions to patterns of autonomic activity, but their importance is less than that of the hypothalamus?
- Cerebellum
- Cerebral Cortex
What drug enhances nor-adrenergic transmission (mechanism of action of SNS drugs), by facilitating release?
Amphetamine
What drug enhances nor-adrenergic transmission (mechanism of action of SNS drugs), by blocking reuptake?
Cocaine
What drug enhances nor-adrenergic transmission (mechanism of action of SNS drugs), acting as a receptor agonist?
Phenylephrine
What drug reduces nor-adrenergic transmission by inhibiting synthesis?
methyltrosine
What drug reduces nor-adrenergic transmission by disrupting vesicular transport and storage?
reserpine
What drug reduces nor-adrenergic transmission by inhibiting release?
guanethidine
What drug reduces nor-adrenergic transmission by acting as a receptor antagonists?
phentolamine
What drug is a nicotinic receptor agonists?
nicotine
What drug is a muscarinic receptor agonists?
bethanechol
What drug is a cholinesterase inhibitor?
physostigmine
What drug inhibits cholinergic transmission, via inhibitors of vesicular ACh transport?
vesamicol
What drug inhibits cholinergic transmission, via inhibitors of exocytotic release?
botulinum toxin
What drug inhibits cholinergic transmission, via nicotinic receptor antagonists?
mecamylamine
What drug inhibits cholinergic transmission, via muscarinic receptor antagonists?
atropine
What drug inhibits cholinergic transmission, via inhibitors of high-affinity choline transport?
hemicholinium
What drug inhibits cholinergic transmission, via inhibitors of pyruvate dehydrogenase?
bromopyruvate
