ANS Flashcards
What is the ANS? What does it do? What does it consist of
- Located in CNS and PNS
- Coordinates and maintains steady state among the visceral organs
- Neurons
- preganglionic (myelinated)
- postganglionic (unmyelinated)
- 2 division classified anatomically
- sympathetic
- parasympathetic
Characteristics of SNS innervation?
- Preganglionic neurons cell bodies located in T1-L2/3
- INTERMEDIOLATERAL HORN OF GREY MATTER
- Post ganglionic neuron cell bodies in ganglia
- paravertebral chain
- prevertebral ganglia (celiac, superior, inferior, mesenteric)
- Short pre, long post
What is characteristics of PSNS?
- Pre-ganglionic neurons arise from
- cranio (medullary CN 3,7, 9. 10)
- Sacral (spinal cord S2-S4) regions
- Post ganglionic neuron cell bodies in
- target organs
- descrete ganglia in head/neck
- LONG pre, short post
What is main role SNS?
- Self preservation;: mst important function is maintenance of vasomotor tone
What is main function PSNS?
Rest for organism but excitatory visceral functions such as digestion
Many organs have innervation by SNS and PSNS. WHat are exceptions to the rule?
- Only innervated by SNS
- sweat glands
- Blood vessels (however muscarinic are present at blood vessels)
- Only innervated by PSNS
- Ciliary muscle of the eye (accomodate eye for near vision)
- bronchial smooth muscle (B2 receptors present though)
Receptros can be present in a tissue and NOT be innervated. In this case, receptor will only respond when something is circulating in blood
What is major role of SNS?
- Amplicfication resposne with diffuse innervation
- controls:
- postural changes
- excercie (world class marathon runner won’t want to take beta blocker)
- Emergency massive response
- controls:
PSNS exhibits ___ and ____ targeted resposnes
discrete; narrolwy targeted
Which baseline tones do both systems (SNS, PSNS) exhbiit at rest?
HR- Vagal predominance
Blood vessels- SNS tone
What is NT released/receptor at skeletal muscle?
ACh at nicotinic receptor (Nm)
Pre/post NT/receptor for blood vessels?
- Pre ACh at Nic (Nn)
- Post Norepinephrine @ adrenergic
Pre/post NT/receptor for sweat glands?
- Pre: Ach at Nicotinic (Nn)
- Post Ach at Muscarinic (exception to rule)
What is preganglionic for adrenal medulla?
Ach on nicotinic, adrenal medulla acts like post ganglionic
What is pre/post NT/receptor for parasympathetic system
- Pre Ach at nicotinic
- Post ach at muscarinic (salivary glands, etc)
What are receptors on cholinergic receptors?
- Nicotinic Ach receptors
- Nm and Nn<– selective drugs
- Muscarinic Ach receptors
- M1-M5 <– not as selective, more of a sledgehammer
What are adrenergic receptors?
- alpha 1,2
- Beta 1,2,3
What does adrenal medulla release?
Norepi 20%
Epi 80%
What are 3 major anomalies to SNS?
- Adrenal medulla acts like ganglia but releases NE and Epi in 20/80 ratio
- Sweat glands
- sympathetic cholinergic fibers
- Post ganglionic Ach onto muscarinic Ach receptor
- Blood vessels
- no innervation PSNS
- there are muscarinic Ach on blood vessels, activate NO with eventual vasodilation if you had circulating Ach
M1?
Receptor, signal, 2nd messenger, physio response?
- Receptor: Gαq
- Signal: excitatory CNS, modulatory at ganglia
- 2nd messenger:
- PLC activated
- IPC & DAG increase
- PKC and increased free Ca, decreased K conductance= contraction!
- Physiologic response
- CNS activity, modulation at ganglia
- located CNS and stomach
M2
Receptor? Signal? 2nd messenger? Physiologic response?
- Receptor Gαi
- Signal: inhibitory cardiac
- 2nd messenger:
- inhibit adenylate cyclase
- decrease cAMP
- increase K conductance
- Physiologic effect
- decreased cAMP slows HR and decreases contractility
M3?
Receptor, signal, 2nd messenger, physiologic?
- Receptor: Gαq
- Signal: excitatory smooth muscle, glands
- 2nd messenger
- PLC activated
- IP3 and DAG increase
- PKC and increased free Ca
- Physiologic response: smooth muscle contraction
Nn receptor?
Signal, 2nd messenger, physiologic response?
- Receptor: ligand gated ion channel
- Signal: excitatory ganglia CNS
- 2ND messenger: Na and K permeability
- Physiologic resposne: depolarization
Nm
Receptor? Signal? 2nd messenger? Phsyiologic response?
- Receptor: ligand gated ion channel
- Signal: excitatory @ NMJ
- 2nd messenger: increase Na and K permeability
- Physiologic: depolarization
α1?
Receptor, signal, 2nd messenger, physiologic resonse?
- Receptor: Gαq
- Signal: Excitatory blood vessels
- 2nd messenger:
- PLC acticated
- IP3 and DAG increased
- PKC and increased free Ca
- physiologic response: smooth muscle vasoconstriction
α2
Receptor, signal, 2nd messenger, pysiologic reponse?
- Receptor: Gαi
- Signal: inhibitory BV @ pre, CNS @post
- 2nd messenger:
- inhibit adenylate cyclase
- decrease cAMP
- Increase K conductance
- Physiologic
- decreased cAMP increases smooth muscle contraction (post)
- hyperpolarization with increase K
B 1,2,3
Receptor, signal, 2nd messenger, physiologic?
- Receptor: Gαs
- Signal: excitatory or inhibitory depends on cAMP actions
- 2nd messenger
- activate adnylate cyclase
- increase cAMP
- Physiologic
- increased cAMP causes smooth muscle relaxation
- stimulates cardiac contractility and increases rate
Where are α1 found? Actions?
- Most vascular smooth muscle (blood vessels, sphincters, bronchi)->>> causes contraction
- Iris–> contraction, dilates pupils
- pilomotor—> erects hair
- prostate and uterus–> contracts
- heart—> increases force of contraction (B1 more important though)
Remember, α1 causes activation PLC–> IP3 & DAG–> PKC and increased free Ca causing contraction!
Where are α2 receptors found? Actions?
- platelets–> aggregation
- adrenergic and cholincergic nerve terminals **presynaptic**–> inhibits transmitter release (decrease HR and BP)
- Vascular smooth muscle–> contraction (post synaptic) and dilation (pre-synaptic, CNS)
- GI tract–> relaxation (presynpatic)
- CNS—> sedationa nd analgesia via decrease CNS outflw from brain stem
Remember, alpha 2 causes inhibition of adenylate cyclase–> decrase cAMP–> increase K conductance
Where are beta 1 receptors found? Actions?
- Heart–> increase force and rate of contraction
- Kidney–> stimulate renin release
Remember Beta 1 (all betas) is Gαs causing increase adenylate cyclase, increase cAMP, and causing smooth muscle relaxation
Where are B2 receptors found, actions?
- Respriatory, uterine, vascular, GI, GU–> promotes smooth muscle relaxation
- Mast cells–> decrease histamine release
- Skeletal muscle–> potassium uptake, dilation of vascular beds, tremor, increase speed of contraction
- Liver–> glycogenolysis
- Pancrease–> increase insulin secretion
- adrenergic nerve terminals –> increase release NE
Remember Beta 2 is Gαs causing increase adenylate cyclae, increase cAMP, and causing smooth muscle relaxation, but also cAMP increase force/rate of contraction in cardiac muscle.
Where are beta 3 receptors found? Action?
Fat cells–> activate lipolysis, thermogenesis
Where are D1 receptors found, actions?
- Tissues- Post synaptic location: dilates renal, mesenteric, coronary, cerebral blood vessels
Where are D2 receptors found, actions?
- Nerve endings- presynpatic: modulates transmitter release; nausea and vomiting
What are endogenous catecholamines?
Epi, Norepi, Dopamine
What are synthetic catecholamines?
Isoproterenol,
Dobutamine
What are synthetic non-catecholamines?
- Indirect acting
- ephedrine
- mephentermine
- amphetamines
- Direct acting
- phenylephrine
- methoxamine
What are selective alpha-2 agonists
Clonidine
Dexmedetomidine
What are selective beta-2 adrenergic agonists?
Albuterol
Terbutaline
Ritodine
What are direct agonists?
Varied affinities for alpha 1, alpha 2, beta1, beta 2
What are indirect agonists?
Increase the release of neurotransmitters by stimulating nerve endings
Dnagerous to give long term, because you’re depleting nerve endings of neurotransmitters
How to choose right drug for right situation?
- All sympathomimetics are not created equal, have differing affinities for various types of adrenergic receptors
- need to consider all particular drug effects before giving it
- example phenylephrine vs ephedrine
- phenyl is direct
- ephedrine indirect
*
All sympathomimetics are ___
beta-phenylethylamine derivatives
What makes something a catecholamine?
- Amine group side chain
- hydroxyl group on 3,4 carbon of benzene ring–> called catechol (maximal alpha nad b receptor activity)
- thus names catechol-amines
What is doa of catecholamines vs non-catecholamines?
Catecholamines are very short DOA, more potent
Non- catecholamines are longer acting and may not be as potent as local agonists
What is pathway for creation of epinephrine?
What is mechanoism of action for sympathomimetics?
- Activation of g-protein coupled receptr (D, beta, alpha)
- indirect= drug increases endogenous NE release form post-ganglionic SNS nerves which then activates receptor
- direct= directly stilumates the receptor and activates G-protein itself
- G-protein will activate or inhibit an intracellular enzyme (adenylate cycale–> camp–> plc) or will open or close ion channel
- Usually g-protein cascade has an eventual positive or negative effect on amount on intracellular ca= physiologic effect we see clinically
What does specific effect of sympathomimetics depend on?
- Receptor stimulated
- receptor density in a given tissue
- what second messengers activate at a molecular level in the cell
Receptors will up or down regulate based upon plasma concentrations of sympathomimetic
How do we terminate effect of catecholamines?
- Reuptake
- uptake I- neuronal reuptake
- upatke II- extraneuronal uptake
- MAO
- COMT
- Lungs
Need infusion because it is short acting
How do we terminated effect of non-catecholamines?
- MAO
- Urinary excretion (unchanged)
What is it a bad idea to administer sympathomimetics to people taking MAOIs?
- MAO is in presynpatic terminal in order to break down norepinephrine
- If this is inhibited, then you aren’t metabolizing NE as much, and will have even more NE release with subsequent stimulation
What is selectivity of receptor for phenylephrine?
alpha 1> alpha 2>>>>> Beta
What is receptor selectivity of clinidine?
alpha 2> alpha 1>>>>>> B
What is receptor selectivity for norepinephrine?
alpha 1=alpha 2; B1>>>>>>>>>>> B2 (no clinical effect)
What is receptor selectivity for epinephrine?
alpha 1= alpha 2; b1=b2
Selectivity of B-agonist recpeotrs?
Dobutamine
Isoproteronol
Terbutaline/albuterol
Dobutamine B1>B2>>>>> alpha
Isoproterenol B1=B2>>>ALPHA
Terbutaline/albuteral B2>>B1>>>> ALPHA
What is receptor selectivity of dopamine agonists?
Dopamine D1=D2>>B>>ALPHA
Fenoldopam D1>>D2
Route, duration, dosages, indication for epinephrine?
- Route: SQ (onset 5-10 min), IV (1-2 min onset)
- Duration 5-10 min
- Dosages
- standard bolus dose 10 mcg/kg IV
- Start 2-8 mcg/kg
- 1-2 mcg/min IV- beta 2<<- low dose for anaphylaxis
- 4-5 mcg/min IV- beta 1
- 10-20 mcg/min IV- alpha and beta
- Indication
- bronchial asthma
- acute allergic reaction
- cardiac arrest, asystole
- electromechanical dissociation
- vfib unresponsive to intial defibriallation
- Poorly lipid soluble- little CNS effect
CV effects epinephrine?
- ALPHA 1:
- vasoconstriction- Increase BP, Increase CVP, Increase cardiac work
- skin, mucosa, hepatic, renal constriction
- alpha 2: negative feedback (decreaes BP) keeps sympathetic tone in check
- B1: Increased contractility, HR, CO, increae BP
- B2:
- peripheral vasodilation (decrease BP)
- Skeletal muscle dilation, increase K uptake, increase glucose
With moderate epi dose, SBP increases (B1, Alpha 1) DBP tends to decrease (B2), map stays same