Autonomic Flashcards
What is the final common pathway linking the CNS to skeletal muscles?
Alpha motor neurons
What serves as the final common pathway from the CNS to visceral targets?
Sympathetic and parasympathetic neurons
Where is the myenteric (Auerbach’s) plexus?
Between external longitudinal and deeper circular smooth muscle layers of GI tract
What is the function of the myenteric (Auerbach’s) plexus?
GI motility
Where is the submucosal (Meissner’s) plexus?
Between circular muscularis mucosae
What is the function of the submucosal (Meissner’s) plexus?
Controls ion and fluid transport
Can the enteric nervous system function without input from the ANS?
Yes
What organs/tissues receive only sympathetic innervation?
- Hair follicles2. Sweat glands3. Liver4. Adrenal glands5. Kidneys6. Blood vessels (mostly)
All somatic nerves release what NT?
Ach
All preganglionic fibers in the ANS release what NT?
Ach
Sympathetic postganglionic fibers release what NTs?
- Adrenergic (Epi/NE) 2. Dopaminergic (renal vascular smooth muscle) 3. Exception - thermoregulatory sweat glands (muscarinic, Ach)
What are the steps of cholinergic transmission?
1 .Synthesis of NT at presynaptic terminals2. Storage of NT 3. Release of NT 4. Action at receptor sites5. Termination of transmitter action
What are the steps of Ach synthesis?
- Choline transport into neuron from extracellular fluid via sodium dependent choline transporter CHT 2. Acetyl CoA synthesized in mitochondria 3. Ach synthesized from choline and acetyl CoA via choline acetyltransferase (ChAT)
What drugs inhibit the choline transporter?
Hemicholiniums
What enzyme transports choline from the extracellular fluid into the neuron?
Choline transporter CHT (sodium dependent)
What enzyme synthesizes Ach?
Choline acetyltransferase (ChAT)
What are the steps of Ach storage?
- Ach transported into storage vesicle by vesicle associated transporter VAT 2. Vesicles held on inner surface of terminal via vesicle associated membrane proteins (VAMPs) and synaptosome associated proteins (SNAPs)
What drug inhibits VAT?
Vesamicol
What else is stored in the Ach storage vesicle?
- Peptides2. ATP 3. Proteoglycan
What are the steps of Ach release?
- Depolarization of nerve terminal2. Voltage dependent calcium entry3. Calcium binds calmodulin and activates VAMPs and SNAPs4. Vesicle fusion and NT release
What step in Ach release does Botox inhibit?
VAMP activity (removal of two amino acids)
What are the steps of NT termination of action?
- Rapid hydrolysis of Ach via acetylcholinesterase2. Choline reuptake into terminals
What are the three fates of Ach following release?
- Bind to receptors2. Degradation into choline and acetate3. Binds to presynaptic terminal
What drug inhibits AchE?
Neostigmine
What are the two categories of cholinergic receptors?
- Muscarinic2. Nicotinic
What are the properties of muscarinic receptors?
- G protein coupled 2. 5 subtypes (M1-M5)3. Signaling depends on type of G protein receptor associated with it
What are the M receptor - G protein couplings?
- M1 - Gq2. M2 - Gi/o3. M3 - Gq
What is the result of activation of Gq associated M receptors?
Increase in calcium concentration and activation of PKC
What is the result of activation of Gi/o associated M receptors?
Decrease in intracellular cAMP concentration and decreased PKA activity
What are the properties of nicotinic receptors?
- 5 subunit transmembrane ion channel 2. Channel is closed when no Ach is bound3. When Ach is bound to 2 alpha subunits a conformational change results in Na and K flowing down respective electrochemical gradients 4. Sodium influx produces an excitatory postsynaptic AP
What muscles in the eye use M3 receptors?
- Sphincter pupillae2. Ciliary muscle (also has B2)
The sphincter pupillae and ciliaries muscles have what type of receptor?
M3
The SA and AV nodes have what type of receptor?
M2
The bronchioles and lung glands have what type of receptor?
M3
The stomach and intestine have what type of receptors?
M3
The GI glands have what type of receptor?
M1
The bladder has what type of receptor?
M3
Sphincters have what type of receptor?
M3
Endothelial cells have what type of receptors?
M3
What is the effect of M3 activation in the eye?
- Constricted pupil / miosis 2. Accommodation for near vision
The radial (dilator) muscle of the eye is controlled by what type of nerve fibers?
Sympathetic a1 fibers
The ciliary epithelium has what type of receptors?
- B1 and B2 2. Activation increases aqueous humor production